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Sestrins Activate Nrf2 by Promoting p62-Dependent Autophagic Degradation of Keap1 and Prevent Oxidative Liver Damage
Abstract
Sestrins (Sesns) protect cells from oxidative stress. The mechanism underlying the antioxidant effect of Sesns has remained unknown, however. The Nrf2-Keap1 pathway provides cellular defense against oxidative stress by controlling the expression of antioxidant enzymes. We now show that Sesn1 and Sesn2 interact with the Nrf2 suppressor Keap1, the autophagy substrate p62, and the ubiquitin ligase Rbx1 and that the antioxidant function of Sesns is mediated through activation of Nrf2 in a manner reliant on p62-dependent autophagic degradation of Keap1. Sesn2 was upregulated in the liver of mice subjected to fasting or subsequent refeeding with a high-carbohydrate, fat-free diet, whereas only refeeding promoted Keap1 degradation and Nrf2 activation, because only refeeding induced p62 expression. Ablation of Sesn2 blocked Keap1 degradation and Nrf2 activation induced by refeeding and thereby increased the susceptibility of the liver to oxidative damage resulting from the acute stimulation of lipogenesis associated with refeeding.
... Sestrins (SESNs) have important roles in regulating glucose and lipid metabolism, anti-tumor functions, and aging by inhibiting the reactive oxygen species (ROS) and mechanistic target of rapamycin complex 1 (mTORC1) pathways (Bae et al. 2013;Budanov and Karin 2008;Lee et al. 2010). SESN proteins exist widely in the animal kingdom, are highly conserved, and can be induced and activated under various stress environments, such as hypoxia, hyperlipidemia, DNA damage, and oxidative stress (Budanov et al. , 2002. ...
... One of the common functions of the SESN family is to activate the P62/sequestosome-1 (SQSTM1)dependent pathway to degrade Kelch-like epichlorohydrin-associated protein 1(KEAP1), enhance the transcription of Nrf2-dependent antioxidant genes to inhibit ROS, and then improve cell metabolism and maintain mitochondrial function (Bae et al. 2013). Another common function is to activate adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK) to inhibit the activity of mTORC1, thus protecting cells from age-related damage (Budanov and Karin 2008;Lee et al. 2010). ...
... NMDAR can upregulate PRX and then activate SESN2 through CCAAT/enhancer binding protein-β (c/EBPβ) and activator protein 1, respectively (Papadia et al. 2008). Recently, it has been found that oxidative stress can activate and promote Nrf2, and combine it with antioxidant response elements to induce expression of SESN2, which has an important role in cell protection under severe stress (Bae et al. 2013;Shin et al. 2012). In addition, sequence analysis showed that the binding site of C-Jun (TGA GCT CA) can be observed in SESN2 promoter, which also confirms that C-Jun participates in the regulation of SESN2 transcription. ...
Sestrins are a type of highly conserved stress-inducing protein that has antioxidant and mTORC1 inhibitory functions. Metabolic dysfunction and aging are the main risk factors for development of human diseases, such as diabetes, neurodegenerative diseases, and cancer. Sestrins have important roles in regulating glucose and lipid metabolism, anti-tumor functions, and aging by inhibiting the reactive oxygen species and mechanistic target of rapamycin complex 1 pathways. In this review, the structure and biological functions of sestrins are summarized, and how sestrins are activated and contribute to regulation of the downstream signal pathways of metabolic and aging-related diseases are discussed in detail with the goal of providing new ideas and therapeutic targets for the treatment of related diseases.
... The diverse set of physiological roles that SESN proteins perform is crucial for metabolic homeostasis. Once induced, SESNs regulate multiple signalling pathways, such as AMPdependent protein kinase (AMPK), mTORC1, nuclear factor erythroid 2-related factor 2 (Nrf2), mitogen-activated protein kinases (MAPKs) and transforming growth factor β (TGF-β) (Wempe et al. 2010;Bae et al. 2013;Lee et al. 2013;. SESN proteins received special attention in the field of regulation of the ROS level in the cell and its interplay with the systems determining energy and nutrient homeostasis. ...
... SESN1, 2 and 3 belong to conserved stress-responsive proteins whose expression is mostly regulated by p53 and the forkhead transcription factor (FoxO) (Budanov et al. 2010). However, depending on the cell's condition, other stress-inducible transcription factors regulate the expression of SESNs including Nrf2, the hypoxia inducible factor (HIF)-1α and JNK/c-Jun transcription factors (Bae et al. 2013;Zhang et al. 2013;Shi et al. 2016). SESN1 expression is under control of p53 tumour suppressor signalling pathway that is activated by excessive genotoxic damage . ...
... Ubiquitin-binding protein p62 enhances Keap1-Nrf2 dissociation and facilitates the degradation of Keap1 by p62-dependent autophagy, thus promoting Keap-1 degradation and Nrf2 activation. These interactions between p62, Keap-1 and Nrf2 lead to further stimulating the antioxidant response (Bae et al. 2013;Ornatowski et al. 2020;Kma and Baruah 2021). In addition, SESN proteins also promote p62-dependent autophagic degradation of Keap-1 by direct interaction with p62 and their activation (Bae et al. 2013;Ornatowski et al. 2020). ...
Since the beginning of SESN protein development, they have attracted highly progressive attention due to their regulatory role in multiple signalling pathways. Through their antioxidant activity and autophagy regulation implication, they can function as powerful antioxidants to reduce oxidative stress in cells. SESN proteins received special attention in the field of regulation of reactive oxygen species level in the cell and its interplay with signalling pathways determining energy and nutrient homeostasis. Since perturbations in these pathways are implicated in cancer onset and development, SESNs might constitute potential novel therapeutic targets of broad interest. In this review, we discuss the impact of SESN proteins on anti-cancer therapy based on naturally occurring compounds and conventionally used drugs that influence oxidative stress and autophagy-induced cellular signalling pathways. The significant changes in reactive oxygen species level and nutrient status in cancer cells generate subsequent biological effect through the regulation of SESN-dependent pathways. Thus, SESN may serve as the key molecule for regulating anti-cancer drugs’ induced cellular response.
... SESN2 belongs to the family of highly conserved proteins inducible by many different types of stress conditions, including oxidative stress, genotoxic stress, ER stress, hypoxia, and energetic and metabolic stress. Once induced, SESN2 fights back through an intrinsic antioxidant enzymatic activity [19], the activation of AMPK [6], the inhibition of mTORC1 [20,21], the activation of nuclear factor erythroid 2-related factor 2 (NRF2) [22], the activation of AKT [23] and autophagy [24]. Genetic deletion of SESN2 has been shown to worsen age-related pathologies and cardiac function in a variety of model organisms [9,10,25,26]. ...
... The antioxidant properties of SESN2 were initially credited to the peroxiredoxin reductase activity of SESN2 [19], but later studies could not confirm this finding [50]. However, SESN2 increases the expression of sulfiredoxin, a reductase for hyperoxidized peroxiredoxin under the transcription control of NRF2 [22,59]. Bae et al. studied the missing link between SESN2 and NRF2 and showed that the degradation of KEAP-1 by autophagy is promoted by SESN2. ...
... Oxidants and electrophiles disrupt the correct conformational binding between NRF2 and KEAP-1 necessary for the ubiquitination and degradation of NRF2 and facilitate nuclear translocation and induction of transcription of antioxidant genes ( Figure 5). The induction of KEAP-1 degradation by forced induction of SESN2 is dependent on P62 [22]. P62 or sequestosome 1 (SQSTM1) is an autophagy adapter with a KIR domain capable of binding with and tagging KEAP-1 for autophagic degradation. ...
A timely and adequate response to stress is inherently present in each cell and is important for maintaining the proper functioning of the cell in changing intracellular and extracellular environments. Disruptions in the functioning or coordination of defense mechanisms against cellular stress can reduce the tolerance of cells to stress and lead to the development of various pathologies. Aging also reduces the effectiveness of these defense mechanisms and results in the accumulation of cellular lesions leading to senescence or death of the cells. Endothelial cells and cardiomyocytes are particularly exposed to changing environments. Pathologies related to metabolism and dynamics of caloric intake, hemodynamics, and oxygenation, such as diabetes, hypertension, and atherosclerosis, can overwhelm endothelial cells and cardiomyocytes with cellular stress to produce cardiovascular disease. The ability to cope with stress depends on the expression of endogenous stress-inducible molecules. Sestrin2 (SESN2) is an evolutionary conserved stress-inducible cytoprotective protein whose expression is increased in response to and defend against different types of cellular stress. SESN2 fights back the stress by increasing the supply of antioxidants, temporarily holding the stressful anabolic reactions, and increasing autophagy while maintaining the growth factor and insulin signaling. If the stress and the damage are beyond repair, SESN2 can serve as a safety valve to signal apoptosis. The expression of SESN2 decreases with age and its levels are associated with cardiovascular disease and many age-related pathologies. Maintaining sufficient levels or activity of SESN2 can in principle prevent the cardiovascular system from aging and disease.
... In recent years, some studies have reported that Sesn2 promotes p62-dependent autophagy to degrade Keap1, thereby upregulating Nrf2 signaling and reducing ROS accumulation [46][47][48]. However, the results in this study showed that Keap1 and Nrf2 mRNA expression was not changed after NR treatments (Fig. 1a). ...
... It is reported in the literature that Sesn2 can regulate autophagy and mitophagy through Sqstm1 and Parkin [41,42,47]. Sesn2 can degrade Keap1 through Sqstm1-dependent autophagy, thereby increasing the level of Nrf2 in the cell [47]. ...
... It is reported in the literature that Sesn2 can regulate autophagy and mitophagy through Sqstm1 and Parkin [41,42,47]. Sesn2 can degrade Keap1 through Sqstm1-dependent autophagy, thereby increasing the level of Nrf2 in the cell [47]. Sesn2 can also promote the translocation of Parkin to mitochondria and induce mitophagy [41]. ...
Mitochondrial unfold protein response (UPRmt) can induce mitophagy to protect cell from unfold protein. However, how UPRmt induces mitophagy to protect cell is not yet clear. Herein, Sesn2 was considered to be a key molecule that communicated UPRmt and mitophagy in the intervertebral disc. Silencing of Sesn2 was able to reverse the protective effects of Nicotinamide riboside (NR) on nucleus pulposus (NP) cells and inhibit mitophagy induced by UPRmt. UPRmt upregulated Sesn2 through Eif2ak4/eIF2α/Atf4, and further induced mitophagy. Sesn2 promoted the translocation of cytosolic Parkin and Sqstm1 to the defective mitochondria respectively, thereby enhancing mitophagy. The translocation of cytosolic Sqstm1 to the defective mitochondria was dependent on Parkin. The two functional domains of Sesn2 were necessary for the interaction of Sesn2 with Parkin and Sqstm1. The cytosolic interaction of Sesn2 between Parkin and Sqstm1 was independent on Pink1 (named as PINK1 in human) but the mitochondrial translocation was dependent on Pink1. Sesn2-/- mice showed a more severe degeneration and NR did not completely alleviate the intervertebral disc degeneration (IVDD) of Sesn2-/- mice. In conclusion, UPRmt could attenuate IVDD by upregulation of Sesn2-induced mitophagy. This study will help to further reveal the mechanism of Sesn2 regulating mitophagy, and open up new ideas for the prevention and treatment of IVDD.
... To further explore the protective impact of the ACE2-Ang-(1-7) axis in the SAE condition, we evaluated the Nrf2 and Sestrin2 proteins, which are partially regulated by ACE2-Ang-(1-7) and highly relevant to neuroinflammation and cerebral oxidative stress [22][23][24]. Immunoblot data confirmed that CLP surgery resulted in a marked increase in the protein expressions of Nrf2 and Sestrin2 in comparison with sham surgery (Fig. 6a, b), and this effect was significantly enhanced in ACE2-TG mice (Fig. 6a), but weakened in ACE2-KO mice after CLP surgery (Fig. 6b). Consistently, immunoblotting assays verified that ACE2-KO BM → WT chimeric mice expressed lower levels of Nrf2 and sestrin2 proteins, while ACE2-TG BM → WT mice expressed higher levels of the Nrf2 and sestrin2 proteins compared with WT BM → WT mice (Fig. 6c). ...
... Nrf2, once activated by exposure to harmful factors, initiates the transcription of downstream genes and ultimately exerts compensatory effects [34,35]. Sestrin2 is an Nrf2-targeted antioxidant protein that facilitates Nrf2 activation in return [22,35,36]. Additionally, augmenting sestrin2 is a novel approach for the resolution of Ang-II-induced pathological changes, and its function comprises inhibiting apoptosis, pyroptosis, and ferroptosis while promoting mitophagy [23,24,39]. ...
Neuroinflammation and oxidative stress contribute to the progression of sepsis-associated encephalopathy (SAE). Angiotensin-converting enzyme 2 (ACE2) is considered to be a neuroprotective factor due to its anti-inflammatory and antioxidant properties. However, the role of ACE2 on myeloid cells in regulating SAE and the underlying mechanism warrants further exploration. SAE was induced in ACE2 transgenic (TG), knockout (KO), and bone marrow (BM) chimeric mice by cecal ligation and puncture (CLP). The expression levels of apoptosis-, oxidation- and neuroinflammation-associated mediators and morphological changes were monitored by quantitative real-time PCR analyses and histological examinations in the cortex of septic mice. The contents of angiotensin (Ang) II and Ang-(1–7) along with the activity of ACE2 were examined with commercial kits. The expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Sestrin2 was detected by immunoblotting analysis. Our results indicated that the expression of cortical ACE2 was significantly reduced in the early phase of CLP-induced sepsis. Moreover, ACE2 overexpression in TG mice conferred neuroprotection against sepsis, as evidenced by alleviated neuronal apoptosis, oxidative stress, and proinflammatory M1-like microglial polarization, accompanied by upregulation of the Ang-(1–7), Nrf2, and Sestrin2 protein levels. Conversely, ACE2 deficiency in KO mice exacerbated SAE. The neuroprotective effects of ACE2 were further confirmed in wild-type mice transplanted with ACE2-TG and KO BM cells. Therefore, our data suggest that myeloid ACE2 exerts a protective role in the pathogenesis of SAE, potentially by activating Ang-(1–7)-Nrf2/sestrin2 signaling pathway, and highlight that upregulating ACE2 expression and activity may represent a promising approach for the treatment of SAE in patients with sepsis.
... Because the PCR array revealed antioxidant-associated DEGs responsive to FF treatment, selected components of the antioxidant response were analyzed using real-time PCR and Western blotting techniques ( Figure 4). First, we determined the expression of Nuclear factor erythroid 2-Related Factor 2 (NRF2), a transcription factor that activates the expression of antioxidant response genes [11]. The mRNA ( Figure 4a) and protein levels ( Figure 4b) of NRF2 were similar in the renal cortex tissue of young and old rats. ...
... Both doses of FF decreased mRNA levels of Nrf2 in young but not old animals (Figure 4a), however, FF did not affect NRF2 protein levels in either young or old rats ( Figure 4b). Next, we analyzed the protein levels of sestrin 2 (SESN2), which stimulates NRF2 by targeting its repressor Kelch-like ECH-Associated Protein 1 (Keap1) for autophagosomal degradation [11,12]. Sesn2 mRNA expression levels were similar in young and old control rats (Figure 4a), whereas SESN2 protein levels were two-fold higher in the old animals ( Figure 4b). ...
We investigated the age-related effects of the lipid-lowering drug fenofibrate on renal stress-associated effectors. Young and old rats were fed standard chow with 0.1% or 0.5% fenofibrate. The kidney cortex tissue structure showed typical aging-related changes. In old rats, 0.1% fenofi-brate reduced the thickening of basement membranes, but 0.5% fenofibrate exacerbated interstitial fibrosis. The PCR array for stress and toxicity-related targets showed that 0.1% fenofibrate mildly downregulated, whereas 0.5% upregulated multiple genes. In young rats, 0.1% fenofibrate increased some antioxidant genes' expression and decreased the immunoreactivity of oxidative stress marker 4-HNE. However, the activation of cellular antioxidant defenses was impaired in old rats. Fenofibrate modulated the expression of factors involved in hypoxia and osmotic stress signaling similarly in both age groups. Inflammatory response genes were variably modulated in the young rats, whereas old animals presented elevated expression of proinflammatory genes and TNFα immunoreactivity after 0.5% fenofibrate. In old rats, 0.1% fenofibrate more prominently than in young animals induced phospho-AMPK and PGC1α levels, and upregulated fatty acid oxidation genes. Our results show divergent effects of fenofibrate in young and old rat kidneys. The activation of multiple stress-associated effectors by high-dose fenofibrate in the aged kidney warrants caution when applying fenofibrate therapy to the elderly.
... Other non-canonical autophagy regulatory proteins like Sestrin2 (Bae et al., 2013) and tripartite motif-containing protein 16 (TRIM16) (Kimura et al., 2015) also participate in the regulation of Nrf2 and mTOR via direct or indirect interactions, providing novel targets for pondering the connection between autophagy and the Nrf2 antioxidant pathway. ...
... Studies have shown that Sestrin2 overexpression can induce autophagic degradation of Keap1, leading to the upregulation of Nrf2 activity (Bae et al., 2013). In addition, this process requires the phosphorylation of the UBA domain of SQSTM1 at Ser409 (Polito et al., 2014;Rhee and Bae, 2015), resulting in the degradation of LC3-SQSTM1-Keap1 aggregates by selective autophagy. ...
Macroautophagy/autophagy is a lysosome-dependent catabolic pathway for the degradation of intracellular proteins and organelles. Autophagy dysfunction is related to many diseases, including lysosomal storage diseases, cancer, neurodegenerative diseases, cardiomyopathy, and chronic metabolic diseases, in which increased reactive oxygen species (ROS) levels are also observed. ROS can randomly oxidize proteins, lipids, and DNA, causing oxidative stress and damage. Cells have developed various antioxidant pathways to reduce excessive ROS and maintain redox homeostasis. Treatment targeting only one aspect of diseases with autophagy dysfunction and oxidative stress shows very limited effects. Herein, identifying the bridging factors that can regulate both autophagy and antioxidant pathways is beneficial for dual-target therapies. This review intends to provide insights into the current identified bridging factors that connect autophagy and Nrf2 antioxidant pathway, as well as their tight interconnection with each other. These factors could be potential dual-purpose targets for the treatment of diseases implicated in both autophagy dysfunction and oxidative stress.
... Sestrins are a family of stress-responsive proteins consisting of Sestrin 1 (SESN1), Sestrin 2 (SESN2), and Sestrin 3 (SESN3) (Budanov and Karin, 2008;Budanov et al., 2010). SESN1 and SESN2 have been shown to inhibit the accumulation of reactive oxygen species (ROS) and oxidative stress (OS) via autophagic degradation of Keap 1 and subsequent activation of the Nrf2 pathway, resulting in the induction of antioxidant enzyme genes (Bae et al., 2013;Rhee and Bae, 2015). Similarly, it is reported that SESN2 can inhibit mTORC1 activation, reducing the buildup of ROS (Rhee and Bae, 2015). ...
... Sestrins belong to a family of stress-responsive proteins that are activated by stress including oxidative stress, DNA damage, and hypoxia (Budanov and Karin, 2008;Budanov et al., 2010). In recent years, Sestrin isoforms such as SESN1 and SESN2 have been correlated with antioxidative properties and activity (Bae et al., 2013;Budanov et al., 2004;Li et al., 2010) while SESN3 has been identified as a molecular link between brain damage and increased risk for seizures (Huang et al., 2018) and seizure generation in post-ischemic seizure incidence (Shi et al., 2021). Similarly, Johnson et al. (2015) demonstrated that SESN3 is a positive regulator of the proconvulsant gene network in temporal lobe epilepsy patients. ...
Epilepsy affects approximately 1% of the global population, with 30% of patients experiencing uncontrolled seizures despite treatment. Reactive oxygen species (ROS) and oxidative stress have been implicated in the pathogenesis of epilepsy. Sestrins are stress-inducible proteins that regulate the ROS response. In particular, Sestrin 3 (SESN3) has been implicated in ROS accumulation and the regulation of proconvulsant genes. To investigate the role of SESN3 in epilepsy, we studied its involvement in rat models of acute seizures and temporal lobe epilepsy. Our results showed that downregulation of SESN3 reduced the oxidative stress induced by seizure activity in neuronal cultures. After acute seizure activity, SESN3 protein levels temporarily increased as early as 3 h after the seizure, whereas kainic acid-induced status epilepticus led to a significant and persistent increase in SESN3 protein levels in the cortex and hippocampus for up to 2 weeks post-status epilepticus. In the chronic epilepsy phase, when spontaneous seizures emerge, SESN3 protein expression is significantly increased in both regions 6 and 12 weeks after status epilepticus. Interestingly, immunohistochemical staining showed a predominant increase in the oxidative stress marker 8-OHdG in neurons in both regions after an acute seizure, whereas following status epilepticus, the marker was detected in both neurons and astrocytes. Our findings suggest that SESN3 may contribute to the development and establishment of epilepsy, and could be a potential therapeutic target for more effective treatments.
... Whereas upon oxidative stress, the canonical KEAP1-NRF2 pathway activation is mediated by the release of NRF2 from KEAP1, then NRF2 translocates into the nucleus to activate antioxidant genes such as NAD(P)H quinone dehydrogenase 1 (NQO1) and HMOX1/HO-1 heme oxygenase 1 (HO1) [14,22]. The noncanonical KEAP1-NRF2 pathway activation is mediated by p62/SQSTM1, an autophagy receptor protein that competitively binds with and degrades KEAP1 to activate NRF2 [22][23][24]. Indeed, NRF2-p62 system and selective autophagy are vital in tolerance of tumor microenvironmental stress [25,26]. ER stress inducing agents, such as ER Ca 2+ pump inhibitor TG (Thapsigargin) and the N-glycosylation inhibitor TM (Tunicamycin), increase ROS production and trigger tumor cell apoptosis [20]. ...
... Consistently, we found that TG or TM treatment induced NRF2 activation, thus the expression of NRF2 target genes (HO1 and NQO1) were increased during ER stress. The KEAP1-NRF2 signaling can be activated by 1) KEAP1 disassociation from NRF2; 2) NRF2 phosphorylation regulation [27]; 3) KEAP1 degradation [23,24], etc. Recent studies have revealed that TRIM25 as a RING-type E3 ubiquitin ligase facilitates tumor cell survival by activating NRF2 signaling through ubiquitination and degradation of KEAP1 during ER stress, providing a promising therapeutic approach targeting TRIM25 concurrently with NRF2 inhibition [53]. ...
Cancer cells consistently utilize the unfolded protein response (UPR) to encounter the abnormal endoplasmic reticulum (ER) stress induced by the accumulation of misfolded proteins. Extreme activation of the UPR could also provoke maladaptive cell death. Previous reports have shown that NRF2 antioxidant signaling is activated by UPR and serves as noncanonical pathway to defense and reduce excessive ROS levels during ER stress. However, the mechanisms of regulating NRF2 signaling upon ER stress in glioblastoma have not been fully elucidated. Here we identify that SMURF1 protects against ER stress and facilitates glioblastoma cell survival by rewiring KEAP1-NRF2 pathway. We show that ER stress induces SMURF1 degradation. Knockdown of SMURF1 upregulates IRE1 and PERK signaling in the UPR pathway and prevents ER-associated protein degradation (ERAD) activity, leading to cell apoptosis. Importantly, SMURF1 overexpression activates NRF2 signaling to reduce ROS levels and alleviate UPR-mediated cell death. Mechanistically, SMURF1 interacts with and ubiquitinates KEAP1 for its degradation (NRF2 negative regulator), resulting in NRF2 nuclear import. Moreover, SMURF1 loss reduces glioblastoma cell proliferation and growth in subcutaneously implanted nude mice xenografts. Taken together, SMURF1 rewires KEAP1-NRF2 pathway to confer resistance to ER stress inducers and protect glioblastoma cell survival. ER stress and SMURF1 modulation may provide promising therapeutic targets for the treatment of glioblastoma.
... In addition, ROS could also enhance the level of autophagy by increasing the expression of Beclin 1 or activating the transcription factor p53 (Abida and Gu, 2008;Fernández et al., 2018). Activated autophagy relieves oxidative stress through two major pathways: one is the selective degradation of intracellular damaged macromolecules and organelles, particularly the depolarized mitochondria, which are a major source of excessive ROS (Liu et al., 2014); and the other is the p62-Keap1-Nrf2-ARE signaling pathway, which initiates gene transcription of phase II detoxification enzymes and antioxidant enzymes to alleviate oxidative stress (Komatsu et al., 2010;Taguchi et al., 2012;Bae et al., 2013). ...
... Autophagy has been reported to execute its protective function by eliminating intracellular abnormal macromolecules, damaged organelles and invading pathogens, recycling the degradation products, and activating other self-protection responses such as the antioxidant defense system and immune system (Bae et al., 2013;Klionsky et al., 2016;Mizushima and Levine, 2020). As oxidative stress caused by excessive ROS was regarded as the potential mechanism of BDE-47 toxic effects on B. plicatilis (Wang et al., 2015;2021;Zhang et al., 2013;2016b), the present study tended to study the role of autophagy in B. plicatilis' coping BDE-47 exposure from the perspective of oxidative stress. ...
2,2',4,4'-Tetrabromodiphenyl ether (BDE-47) is a persistent organic pollutant that spreads widely in the marine environment. Our previous studies found that it had adverse effects on the marine rotifer Brachionus plicatilis and caused a series of stress responses. The present study was performed to verify the occurrence of autophagy and explore its role in B. plicatilis' coping with BDE-47 exposure. Rotifers were exposed to 0.05, 0.2, 0.8, and 3.2 mg/L BDE-47 for 24 h, respectively. Detections of the autophagy marker protein LC3 by western blot and autophagosomes by MDC staining demonstrated the occurrence of autophagy. The levels of autophagy were significantly increased in BDE-47-treated groups with a peak in 0.8 mg/L group. A series of indicators responded to BDE-47 exposure, including reactive oxygen species (ROS), GSH/GSSG ratio, superoxide dismutase (SOD) activity, and malonaldehyde (MDA), collectively indicating the occurrence of oxidative stress. The potential interplay between autophagy and oxidative stress in B. plicatilis was explored in the 0.8 mg/L group through a series of additions. The ROS level was significantly decreased by the addition of the ROS generation inhibitor diphenyleneiodonium chloride, to a level even lower than that in the blank control, and concomitantly, autophagosome was almost undetectable, indicating that a certain level of ROS was essential for the occurrence of autophagy. Autophagy was weakened by the addition of the autophagy inhibitor 3-methyladenine coincident with the great elevation of ROS, indicating that activated autophagy contributed to reducing the ROS level. Additional proof of this relation was obtained from the direct opposite effects of the autophagy inhibitor bafilomycin A1 and the autophagy activator rapamycin: the former increased the MDA content significantly, whereas the latter decreased it significantly. The combined results suggested that autophagy alleviated oxidative stress and might be a newly discovered protective mechanism in B. plicatilis coping with BDE-47 exposure.
... A possible mechanism for SESN2-regulated autophagy to ease oxidative stress may be that SESN2 physically associates with ULK1 and autophagic cargo receptor p62/sequestosome-1 (SQSTM1) to form a complex, facilitating p62/SQSTM1 phosphorylation at Ser403 and autophagic degradation of p62/SQSTM1 and its substrates [42], such as Kelch-like ECH-associated protein 1 (Keap1), a Nrf2 suppressor that can exclusively bind to the evolutionarily conserved N-terminal Neh2 regulatory domain of Nrf2 and facilitate its ubiquitylation and degradation in cytoplasm with the collaboration of Cullin3 and ring-box 1 (RBX1) [43,44]. The autophagic degradation of Keap1 can promote the expression of Nrf2 downstream genes, including sulfiredoxin (Srx), glutathione-Stransferase (GST), and NQO1 [45]. More specifically, SESN2 can activate mitophagy, a mitochondrion-selective autophagic machinery, to remove damaged mitochondria for restoring redox homeostasis. ...
... SESN2 is an important endogenous defender with prominent antioxidant capacity. Bae et al. found that SESN2 enhances p62/ SQSTM1-mediated autophagic degradation of Keap1 and facilitates Nrf2 release and activation, thereby alleviating oxidative liver damage [45]. Han et al. further verified that pharmacological induction of SESN2 by liraglutide promotes the transduction of Nrf2/HO-1 pathway and initiates the translation of downstream targets, including catalase (CAT), NQO1, and glutamate cysteine ligase modifier subunit (GCLM), in livers of HFD mice, which contributes to the recovery of redox balance [97]. ...
Sestrin2 (SESN2), a highly conserved stress-responsive protein, can be triggered by various noxious stimuli, such as hypoxia, DNA damage, oxidative stress, endoplasmic reticulum (ER) stress, and inflammation. Multiple transcription factors regulate SESN2 expression, including hypoxia-inducible factor 1 (HIF-1), p53, nuclear factor E2-related factor 2 (Nrf2), activating transcription factor 4 (ATF4), ATF6, etc. Upon induction, SESN2 generally leads to activation of adenosine monophosphate-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin complex 1 (mTORC1). To maintain cellular homeostasis, SESN2 and its downstream molecules directly scavenge reactive oxygen species or indirectly influence the expression patterns of key genes associated with redox, macroautophagy, mitophagy, ER stress, apoptosis, protein synthesis, and inflammation. In liver diseases including acute liver injury, fatty liver diseases, hepatic fibrosis, and hepatocellular carcinoma (HCC), SESN2 is abnormally expressed and correlated with disease progression. In NAFLD, SESN2 helps with postponing disease progression through balancing glycolipid metabolism and macroautophagy (lipophagy), and rectifying oxidative damage and ER stress. During hepatic fibrosis, SESN2 represses HSCs activation and intrahepatic inflammation, hindering the occurrence and progress of fibrogenesis. However, the role of SESN2 in HCC is controversial due to its paradoxical pro-autophagic and anti-apoptotic effects. In conclusion, this review summarizes the biological functions of SESN2 in hypoxia, genotoxic stress, oxidative stress, ER stress, and inflammation, and specifically emphasizes the pathophysiological significance of SESN2 in liver diseases, aiming to providing a comprehensive understanding for SESN2 as a potential therapeutic target in liver diseases.
... Activation of SESN2 can reduce the accumulation of ROS, maintain energy balance, reduce protein synthesis, and retard metabolic disease progression. 15, 16 Chen et al. found that up-regulation of SESN2 protected bovine mammary epithelial cells from hydrogen peroxide (H 2 O 2 )-induced oxidative damage through the kelch-like ECH-associated protein 1 (Keap1)nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. 17 Fan et al. have found that SESN2 protects retinal ganglion cells from H 2 O 2 -induced oxidative stress in glaucoma. ...
Objective
We aimed to explore the effect and potential mechanism of Sestrin 2 (SESN2) in human lens epithelial cells (HLECs).
Methods
To mimic the oxidative stress environment, SAR01/04 cells were treated with 200 μM hydrogen peroxide (H2O2) for 24 h. Cell viability and apoptosis were checked by cell counting kit-8 and flow cytometry. Western blot was taken to check the protein changes of SESN2, B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X (Bax), mechanistic target of rapamycin (mTOR), phosphorylated (p)-mTOR, ribosomal protein S6 kinase B1 (p70S6K), p-p70S6K, and nuclear factor erythroid 2-related factor 2 (Nrf2). Superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and reactive oxygen species (ROS) were detected via the corresponding reagent kit. The levels of interleukin (IL)-1β, IL-18, and tumor necrosis factor (TNF)-α were measured using enzyme-linked immunosorbent assay.
Results
SESN2 was down-regulated in cataract lens tissue and up-regulated in SAR01/04 cells treated with H2O2. Under treatment of H2O2, up-regulation of SESN2 improved cell viability, enhanced the activity of SOD and CAT, inhibited cell apoptosis, and reduced the levels of MDA, ROS, IL-1β, IL-18, and TNF-α, while down-regulation of SESN2 caused the contrary effects. Further bioinformatics analysis suggested that SESN2 regulated the mTOR signaling pathway. Treatment of H2O2 inhibited p-mTOR and p-p70S6K protein expression, while overexpression of SESN2 increased p-mTOR and p-p70S6K protein expression in the H2O2 group and down-regulation of SESN2 further decreased p-mTOR and p-p70S6K protein expression in the H2O2 group. Additionally, H2O2 increased Nrf2 protein expression, and overexpression of SESN2 further increased Nrf2 protein expression in the H2O2 group. Importantly, rapamycin (an inhibitor of mTOR signaling pathway) and knockdown of Nrf2 reversed the promotive effects of SESN2 on cell viability and the inhibitive effects of SESN2 on cell apoptosis, oxidative stress, and inflammatory reaction.
Conclusion
SESN2 protected HLECs damage induced by H2O2, which was related to the activation of mTOR/Nrf2 pathway.
... Sestrins, initially identified as p53 target genes that decline with aging [13], have been implicated in an array of cellular functions, including response to nutritional stress (liver) [14], metabolic regulation, and autophagy [15]. Sestrins are known to be potent antioxidants, primarily through the activation of the Nrf2-Keap1 pathway, promoting p62-dependent autophagic degradation [16]. Sestrins are also important negative regulators of rapamycin mTOR complex 1 (mTORC1) [17] aiding in the detoxification of harmful reactive oxygen species (ROS) [18] via activating adenosine monophosphate-activated protein kinase (AMPK) [19] which exerts an antiaging influence [20]. ...
Background
Sestrins have been implicated in regulating aging in various organs through multiple pathways. However, their roles in ovarian aging remain unrevealed.
Methods
Female Sestrin1−/−, Sestrin2−/−, and Sestrin3−/− mice were generated using the CRISPR-Cas9 system. Body weights, little sizes, ovarian weights, estrous cyclicity, and follicle number in female mice were observed. ELISA was utilized to measure serum anti-Müllerian hormone (AMH) levels. Real time PCR, western blot, immunofluorescence, and Masson trichrome staining were employed for assessment of aging-related change.
Results
The deletion of Sestrin 1, 2, or 3 had no discernible impact on body weights,or serum AMH levels in female mice at the age of 12 months. And there were no discernible differences in litter sizes or estrous cyclicity which were assessed at the age of 8 months. At the age of 12 months, no significant differences were observed in ovarian weights or follicle numbers among the knockout mice. Consistently, the extent of fibrosis within the ovaries remained comparable across all experimental groups at this age. Additionally, autophagy, apoptosis, DNA damage, and inflammation within the ovaries were also found to be comparable to those in wild-type mice of the same age.
Conclusions
The loss of Sestrin 1, 2, or 3 does not exert a noticeable influence on ovarian function during the aging process. Sestrin1, 2, and 3 are not essential for female fertility in mice.
... [43]There are some compounds that can regulate the activations of Nrf2 by p62 signaling pathway. As an example, LPS in RAW cells and overexpression of Sens2 protein in HEK293 and MEF cells can increase the Nrf2 activation [44,45]. However, impairment in autophagy and increase in p62 phosphorylation which can activate Nrf2 sustained, promotes antineoplastic drug chemoresistance to doxorubicin, cisplatin, erastin, sorafenib, buthionine sulfoxamine and carfilzomib which it leads to cancer cell proliferation; although mutation in KIR domain in p62 that prevents Keap1-p62 interaction, is associated with ROS increase and the etiology of amyotrophic lateral sclerosis [35,42,[46][47][48][49][50][51]. ...
Carbamate (CBs) is a class of insecticides which is being known as an important cause of intentional or accidental poisoning. CBs, cause carbamylation of acetylcholinesterase at neuronal synapses and neuromuscular junction. Exposure to CBs through skin contact, inhalation, or ingestion can result in significant cholinergic toxicity. This is due to the elevation of acetylcholine levels at ganglionic synapses found in both the sympathetic and parasympathetic nervous systems, as well as muscarinic receptors located in target organs of the parasympathetic nervous system, nicotinic receptors situated in skeletal muscle tissue, and the central nervous system. The association between human illnesses and environmental exposures to CBs have been extensively studied in several studies. Although CBs-triggered toxicity leads to overproduction of reactive oxygen species (ROS), the detailed association between the toxicity under CBs exposure and NFE2-related factor 2 (Nrf2) signaling pathways has not been completely clarified. In this review we aimed to summarize the latest findings on the functional interrelationship between carbamates compounds and Nrf2 signaling.
... This complex facilitates the phosphorylation and degradation of p62/SQSTM1 and its associated substrate, Kelch-like ECH-associated protein 1 (Keap1), which is a major suppressor of Nrf2 [55]. Consequently, the stabilization of Nrf2 initiates an antioxidative response that safeguards cells from oxidative stress and the accumulation of cellular damage, thereby preventing the development of malignancies [56] (Figure 4). In the absence of oxidative stress, Nrf2 is bound to Keap1, which triggers the degradation of Nrf2. ...
Simple Summary
Cells experience various stress conditions, including replicative stress, oxidative stress, toxin-induced damage, and pathogen exposure. The tumor suppressor p53 initiates intricate cellular responses to mitigate such stress. Sestrins, induced by p53, play a pivotal role in these responses. The Sestrin family has three members, with Sestrin 2 being the most extensively studied. Here, all three Sestrins are considered, with a special focus on Sestrin 2. Sestrins trigger complex signaling cascades involving kinases and kinase complexes such as mTORC, AMP-activated kinase (AMPK), and Unc-51-like protein kinase 1 (ULK1). These kinase-driven responses enable cells to defend against cellular stress, facilitate repairs, and adapt to changing conditions, preventing damage accumulation in macromolecules such as nucleic acids, proteins, and lipids, and thereby averting malignant transformation. Thus, Sestrins essentially contribute to the prevention of cancer development. Because Sestrins also support adaptation to cellular stress and can thereby promote cell survival, these stress responses can also protect malignant tumor cells. Therefore, such anti-stress responses are a double-edged sword—on the one hand they prevent the onset of neoplasia, but on the other hand they can also shield an already established malignancy from the induction of cell death.
Abstract
p53, a crucial tumor suppressor and transcription factor, plays a central role in the maintenance of genomic stability and the orchestration of cellular responses such as apoptosis, cell cycle arrest, and DNA repair in the face of various stresses. Sestrins, a group of evolutionarily conserved proteins, serve as pivotal mediators connecting p53 to kinase-regulated anti-stress responses, with Sestrin 2 being the most extensively studied member of this protein family. These responses involve the downregulation of cell proliferation, adaptation to shifts in nutrient availability, enhancement of antioxidant defenses, promotion of autophagy/mitophagy, and the clearing of misfolded proteins. Inhibition of the mTORC1 complex by Sestrins reduces cellular proliferation, while Sestrin-dependent activation of AMP-activated kinase (AMPK) and mTORC2 supports metabolic adaptation. Furthermore, Sestrin-induced AMPK and Unc-51-like protein kinase 1 (ULK1) activation regulates autophagy/mitophagy, facilitating the removal of damaged organelles. Moreover, AMPK and ULK1 are involved in adaptation to changing metabolic conditions. ULK1 stabilizes nuclear factor erythroid 2-related factor 2 (Nrf2), thereby activating antioxidative defenses. An understanding of the intricate network involving p53, Sestrins, and kinases holds significant potential for targeted therapeutic interventions, particularly in pathologies like cancer, where the regulatory pathways governed by p53 are often disrupted.
... Autophagy activation is required for the antioxidant effects of Sestrin2 (61). After activated by the JNK pathways (62), Sestrin2 is involved in modulation of autophagy through AMPK/mTORC1, Keap1/Nrf2, p53/Sestrin2 and PI3K/AKT/mTOR pathways (63)(64)(65). ...
Diabetes is a global health problem which is accompanied with multi-systemic complications. It is of great significance to elucidate the pathogenesis and to identify novel therapies of diabetes and diabetic complications. Sestrin2, a stress-inducible protein, is primarily involved in cellular responses to various stresses. It plays critical roles in regulating a series of cellular events, such as oxidative stress, mitochondrial function and endoplasmic reticulum stress. Researches investigating the correlations between Sestrin2, diabetes and diabetic complications are increasing in recent years. This review incorporates recent findings, demonstrates the diverse functions and regulating mechanisms of Sestrin2, and discusses the potential roles of Sestrin2 in the pathogenesis of diabetes and diabetic complications, hoping to highlight a promising therapeutic direction.
... More specifically, the Tumor Protein 53-Induced Nuclear Protein 1 (TP53INP1), a target of P53, plays a key role in antioxidant defense by participating in the elimination of ROS-producing altered mitochondria [85,86]. Moreover, the functions of the key antioxidant regulator NRF2 can be attenuated by P53 mutant proteins ( Figure 5A) [87][88][89]. ...
Pancreatic ductal adenocarcinoma (PDAC) is a devastating tumor type where a very high proportion of people diagnosed end up dying from cancer. Surgical resection is an option for only about 20% of patients, where the 5-year survival increase ranges from 10 to 25%. In addition to surgical resection, there are adjuvant chemotherapy schemes, such as FOLFIRINOX (a mix of Irinotecan, oxaliplatin, 5-Fluorouraci and leucovorin) or gemcitabine-based treatment. These last two drugs have been compared in the NAPOLI-3 clinical trial, and the NALIRIFOX arm was found to have a higher overall survival (OS) (11.1 months vs. 9.2 months). Despite these exciting improvements, PDAC still has no effective treatment. An interesting approach would be to drive ferroptosis in PDAC cells. A non-apoptotic reactive oxygen species (ROS)-dependent cell death, ferroptosis was first described by Dixon et al. in 2012. ROS are constantly produced in the tumor cell due to high cell metabolism, which is even higher when exposed to chemotherapy. Tumor cells have detoxifying mechanisms, such as Mn-SOD or the GSH-GPX system. However, when a threshold of ROS is exceeded in the tumor cell, the cell’s antioxidant systems are overwhelmed, resulting in lipid peroxidation and, ultimately, ferroptosis. In this review, we point out ferroptosis as an approach to consider in PDAC and propose that altering the cellular ROS balance by combining oxidizing agents or with inhibitors of the main cellular detoxifiers triggers ferroptosis in PDAC.
... (reverse), 5′-CATTGAGAGG-CAGCTCCTCC-3′; GPX4 (forward), 5′-GCTGTGGAAGTGGATGAAGA-3′; GPX4 (reverse), 5′-CAGCCGTTCTTGTCGATGA-3′; β-Actin (forward), 5′-CTGGCACC-CAGCACAATG-3′; β-Actin (reverse), 5′-GCCGATCCACACGGAGTACT-3′. The NQO1 sequence was referenced by Bae et al. [34]. All primers, except for GPX4, were purchased from Cosmo Genetech (Korea). ...
Ferroptosis, a type of cell death induced by lipid peroxidation, has emerged as a novel anti-cancer strategy. Cancer cells frequently acquire resistance to ferroptosis. However, the underlying mechanisms are poorly understood. To address this issue, we conducted a thorough investigation of the genomic and transcriptomic data derived from hundreds of human cancer cell lines and primary tissue samples, with a particular focus on non-small cell lung carcinoma (NSCLC). It was observed that mutations in Kelch-like ECH-associated protein 1 ( KEAP1 ) and subsequent nuclear factor erythroid 2-related factor 2 (NRF2, also known as NFE2L2) activation are strongly associated with ferroptosis resistance in NSCLC. Additionally, AIFM2 gene, which encodes ferroptosis suppressor protein 1 (FSP1), was identified as the gene most significantly correlated with ferroptosis resistance, followed by multiple NRF2 targets. We found that inhibition of NRF2 alone was not sufficient to reduce FSP1 protein levels and promote ferroptosis, whereas FSP1 inhibition effectively sensitized KEAP1 -mutant NSCLC cells to ferroptosis. Furthermore, we found that combined inhibition of FSP1 and NRF2 induced ferroptosis more intensely. Our findings imply that FSP1 is a crucial suppressor of ferroptosis whose expression is partially dependent on NRF2 and that synergistically targeting both FSP1 and NRF2 may be a promising strategy for overcoming ferroptosis resistance in cancer.
... Impaired autophagy induces gene expression of antioxidant proteins involved in defense, accompanied by abnormal accumulation and aggregation of proteins. A remarkable amount of p62 accumulates in tissues with autophagy dysfunction, while previous studies have clarified a correlation between p62-mediated selective autophagy and the oxidative stress response system Keap1-Nrf2 pathway (Jain et al., 2010;Komatsu et al., 2010;Lau et al., 2010;Taguchi et al., 2012;Bae et al., 2013;Ichimura et al., 2013). This interaction inhibits the degradation of transcription factors that promote gene expression of antioxidant proteins, and excessive accumulation of p62 in cells indirectly induces gene expression of antioxidant proteins. ...
Objective: This study clarified the risk factors and pathophysiology of pancreatic cancer by examining the factors associated with fatty pancreas.
Methods: The degree of fatty pancreas, background factors, and incidence of pancreatic cancer were examined among nonalcoholic fatty liver disease (NAFLD) patients (n = 281) and intraductal papillary mucinous neoplasm (IPMN) patients with a family history of pancreatic cancer (n = 38). The presence of fatty pancreas was confirmed by the pancreatic CT value/splenic CT value ratio (P/S ratio). Immunohistochemical staining was performed on 10 cases with fatty pancreas, confirmed via postoperative pathology.
Results: Fatty pancreas occurred in 126 patients (44.8%) in the NAFLD group who were older ( p = 0.0002) and more likely to have hypertension ( p < 0.0001). The IPMN group had 18 patients (47.4%) with fatty pancreas, included more men than women ( p = 0.0056), and was more likely to have patients with hypertension ( p = 0.0010). On histological examination, a significant infiltration of adipocytes into the acini from the pancreatic interstitium induced atrophy of the pancreatic parenchyma, and both M1 and M2 macrophages were detected in the area where adipocytes invaded the pancreatic parenchyma. Accumulation of p62 and increased positive staining of NQO1 molecules related to autophagy dysfunction were detected in pancreatic acinar cells in the fatty area, acinar-ductal metaplasia, and pancreatic cancer cells. The rate of p62-positive cell area and that of NQO1-positive cell area were significantly higher in the fatty pancreatic region than those in the control lesion (pancreatic region with few adipocyte infiltration). Furthermore, the rate of p62-positive cell area or that of NQO1-positive cell area showed strong positive correlations with the rate of fatty pancreatic lesion. These results suggest that adipocyte invasion into the pancreatic parenthyme induced macrophage infiltration and autophagy substrate p62 accumulation. High levels of NQO1 expression in the fatty area may be dependent on p62 accumulation.
Conclusion: Hypertension was a significant risk factor for fatty pancreas in patients with NAFLD and IPMN. In fatty pancreas, fatty infiltration into the pancreatic parenchyme might induce autophagy dysfunction, resulting in activation of antioxidant proteins NQO1. Thus, patients with fatty pancreas require careful follow-up.
... The regulation of Keap1 cytoplasmic levels by SQSTM1/p62 has been demonstrated through both SQSTM1/p62 overexpression and knockdown experiments [27]. The SQSTM1/p62-mediated degradation of Keap1 is also dependent on Sestrin1 and Ses-trin2 [28]. The positive feedback loop between Nrf2 and autophagy is further strengthened by the regulation of the SQSTM1/p62 expression levels by Nrf2 itself [29]. ...
Dimethyl fumarate (DMF) is a well-characterized molecule that exhibits immuno-modulatory, anti-inflammatory, and antioxidant properties and that is currently approved for the treatment of psoriasis and multiple sclerosis. Due to its Nrf2-dependent and independent mechanisms of action, DMF has a therapeutic potential much broader than expected. In this comprehensive review, we discuss the state-of-the-art and future perspectives regarding the potential repurposing of DMF in the context of chronic inflammatory diseases of the intestine, such as inflammatory bowel disorders (i.e., Crohn’s disease and ulcerative colitis) and celiac disease. DMF’s mechanisms of action, as well as an exhaustive analysis of the in vitro/in vivo evidence of its beneficial effects on the intestine and the gut microbiota, together with observational studies on multiple sclerosis patients, are here reported. Based on the collected evidence, we highlight the new potential applications of this molecule in the context of inflammatory and immune-mediated intestinal diseases.
... Total RNA extraction and RT-qPCR [35]. All primers, except for GPX4, were purchased from Cosmo Genetech (Korea). ...
Ferroptosis, a type of cell death induced by lipid peroxidation, has emerged as a novel anti-cancer strategy. Cancer cells frequently acquire resistance to ferroptosis. However, the underlying mechanisms are poorly understood. To address this issue, we conducted a thorough investigation of the genomic and transcriptomic data derived from hundreds of human cancer cell lines and primary tissue samples, with a particular focus on non-small cell lung carcinoma (NSCLC). It was observed that mutations in Kelch-like ECH-associated protein 1 ( KEAP1 ) and subsequent nuclear factor erythroid 2-related factor 2 (NRF2, also known as NFE2L2) activation are strongly associated with ferroptosis resistance in NSCLC. Additionally, AIFM2 gene, which encodes ferroptosis suppressor protein 1 (FSP1),was identified as the gene most significantly correlatedwith ferroptosis resistance, followed by multiple NRF2 targets. We found that inhibition of NRF2 alone was not sufficient to reduce FSP1 protein levels and promote ferroptosis, whereas FSP1 inhibition effectively sensitized KEAP1 -mutant NSCLC cells to ferroptosis. Furthermore, we found that combined inhibition of FSP1 and NRF2 induced ferroptosis more intensely. Our findings imply that FSP1 is a crucial suppressor of ferroptosis independent of NRF2 and that synergistically targeting both FSP1 and NRF2 may be a promising strategy for overcoming ferroptosis resistance in cancer.
... Normally, Nrf2 is inactivated, and it is bound to its repressor Kelchlike ECH-associated protein 1 (KEAP1) [333]. Sestrin2 can act as a positive regulator of Nrf2 by promoting the SQSTM1/p62-mediated autophagic degradation of KEAP1 [334,335]. Sestrin2 overexpression was found to suppress cell inflammation and oxidative stress, and to activate AMPK/Nrf2 signaling [336]. Sestrin2 signaling appears to work through Nrf2 [337]. ...
Musculoskeletal health is directly linked to independence and longevity, but disease and aging impairs muscle mass and health. Complete repair after a pathological or physiological muscle injury is critical for maintaining muscle function, yet muscle repair is compromised after disuse, or in conditions such as metabolic diseases, cancer, and aging. Regeneration of damaged tissue is critically dependent upon achieving the optimal function of satellite cells (muscle stem cells, MSCs). MSC remodeling in muscle repair is highly dependent upon its microenvironment, and metabolic health of MSCs, which is dependent on the functional capacity of their mitochondria. Muscle repair is energy demanding and mitochondria provide the primary source for energy production during regeneration. However, disease and aging induce mitochondrial dysfunction, which limits energy production during muscle regeneration. Nevertheless, the role of mitochondria in muscle repair likely extends beyond the production of ATP and mitochondria could provide potentially important regulatory signaling to MSCs during repair from injury. The scope of current research in muscle regeneration extends from molecules to exosomes, largely with the goal of understanding ways to improve MSC function. This review focuses on the role of mitochondria in skeletal muscle myogenesis/regeneration and repair. A therapeutic strategy for improving muscle mitochondrial number and health will be discussed as a means for enhancing muscle regeneration. Highlights: (a). Mitochondrial dysfunction limits muscle regeneration; (b). Muscle stem cell (MSC) function can be modulated by mitochondria; (c). Enhancing mitochondria in MSCs may provide a strategy for improving muscle regeneration after an injury.
... Sestrins are expressed in mammalian cells in three isoforms: sestrin1 (SESN1), sestrin2 (SESN2), and sestrin3 (SESN3) [14]. SESN2 was first described to be part of the hypoxia-induced gene 95 family (Hi95) [15] and is a powerful autophagy inducer able to activate the antioxidant system and maintain cell homeostasis [16]. The gene is present on chromosome 1, at Cytoband p35.3, and encodes 481 amino acids. ...
(1) Background: Glioma is among the most common brain tumors, and is difficult to eradicate with current therapeutic strategies due to its highly invasive and aggressive characteristics. Sestrin2 (SESN2) is an autophagy inducer. The effect of SESN2 on glioma is controversial and unclear. (2) Methods: We downloaded related RNA-seq data from the TCGA and GTEx databases. Bioinformatic analyses including differential gene expression analysis, KM survival curve analysis, univariate and multivariate Cox regression analyses, nomogram analysis, ROC curve analysis, gene function enrichment analysis, and immune cell infiltration analysis were conducted. In addition, data from the Human Protein Atlas (HPA) database were collected to validate SESN2 expression in glioma. (3) Results: In comparison with normal tissue, expression of SESN2 in glioma tissue was higher, and those with higher expressions had significantly lower overall survival rates. The results of univariate Cox regression analyses showed that SESN2 can be a disadvantageous factor in poor glioma prognosis. Both nomograms and ROC curves confirmed these findings. Meanwhile, according to gene function analysis, SESN2 may be involved in immune responses and the tumor microenvironment (TME). Based on the HPA database results, SESN2 is localized in the cytosol and shows high expression in glioma. (4) Conclusions: The expression of SESN2 in gliomas was positively relevant to a poorer prognosis, suggesting that SESN2 could be used as a prognostic gene.
... When Hepa1c1c7 cells are exposed to fenofibrate, Keap1 is degraded via macroautophagy approximately 18 hr after exposure (Park et al., 2015). It has also been reported that ROS are generated in the liver of mice 16 hr after fasting and refeeding and that Keap1 is degraded by p62-mediated macroautophagy (Bae et al., 2013). Therefore, most previous studies indicate that the degradation of the Keap1 protein starts relatively later. ...
Tributyltin (TBT) is an environmental chemical, which was used as an antifouling agent for ships. Although its use has been banned, it is still persistently present in ocean sediments. Although TBT reportedly causes various toxicity in mammals, few studies on the mechanisms of biological response against TBT toxicity exist. The well-established Keap1–Nrf2 pathway is activated as a cytoprotective mechanism under stressful conditions. The relationship between TBT and the Keap1–Nrf2 pathway remains unclear. In the present study, we evaluated the effect of TBT on the Keap1–Nrf2 pathway. TBT reduced Keap1 protein expression in Neuro2a cells, a mouse neuroblastoma cell line, after 6 hr without altering mRNA expression levels. TBT also promoted the nuclear translocation of Nrf2, a transcription factor for antioxidant proteins, after 12 hr and augmented the expression of heme oxygenase 1, a downstream protein of Nrf2. Furthermore, TBT decreased Keap1 levels in mouse embryonic fibroblast (MEF) cells, with the knockout of Atg5, which is essential for macroautophagy, as well as in wild-type MEF cells. These results suggest that TBT activates the Keap1–Nrf2 pathway via the reduction in the Keap1 protein level in a macroautophagy-independent manner. The Keap1–Nrf2 pathway is activated by conformational changes in Keap1 induced by reactive oxygen species or electrophiles. Furthermore, any unutilized Keap1 protein is degraded by macroautophagy. Understanding the novel mechanism governing the macroautophagy-independent reduction in Keap1 by TBT may provide insights into the unresolved biological response mechanism against TBT toxicity and the activation mechanism of the Keap1–Nrf2 pathway.
... Keap1 contains several highly reactive cysteine residues, and classic Nrf2 activators electrophilically modify the cysteine residues and thereby induce conformational changes in Keap1 to release Nrf2, leading to the nuclear localization of Nrf2. Such electrophilic modifications have also been demonstrated to accelerate the degradation of Keap1 by autophagy [31][32][33]. To investigate the mechanism underlying the induction of nuclear translocation of Nrf2 by febuxostat, we first examined the role of omaveloxolone in Keap1 degradation. ...
Xanthine oxidoreductase (XOR) is a rate-limiting enzyme in purine catabolism that acts as a novel regulator of adipogenesis. In pathological states, xanthine oxidoreductase activity increases to produce excess reactive oxygen species (ROS). The nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical inducer of antioxidants, which is bound and repressed by a kelch-like ECH-associated protein 1 (Keap1) in the cytoplasm. The Keap1-Nrf2 axis appears to be a major mechanism for robust inducible antioxidant defenses. Here, we demonstrate that febuxostat, a xanthine oxidase inhibitor, alleviates the increase in adipose tissue mass in obese mouse models with a high-fat diet or ovariectomy. Febuxostat disrupts in vitro adipocytic differentiation in adipogenic media. Adipocytes appeared at day 7 in absence or presence of febuxostat were 160.8 ± 21.2 vs. 52.5 ± 12.7 (p < 0.01) in 3T3–L1 cells, and 126.0 ± 18.7 vs. 55.3 ± 13.4 (p < 0.01) in 10T1/2 cells, respectively. Adipocyte differentiation was further enhanced by the addition of hydrogen peroxide, which was also suppressed by febuxostat. Interestingly, febuxostat, but not allopurinol (another xanthine oxidase inhibitor), rapidly induced the nuclear translocation of Nrf2 and facilitated the degradation of Keap1, similar to the electrophilic Nrf2 activator omaveloxolone. These results suggest that febuxostat alleviates adipogenesis under oxidative conditions, at least in part by suppressing ROS production and Nrf2 activation. Regulation of adipocytic differentiation by febuxostat is expected to inhibit obesity due to menopause or overeating.
... in EBV-infected NPCs, higher p62 protein levels destroy the interaction between Keap1 and NRF2, which causes high levels of NRF2 [24]. Consequently, more NRF2 is observed to translocate into the infected nuclei, which induces a higher level of GPX4 [22]. ...
Apoptosis, necrosis, or autophagy are diverse types of regulated cell death (RCD), recognized as the strategies that host cells use to defend against pathogens such as viruses, bacteria, or fungi. Pathogens can induce or block different types of host cell RCD, promoting propagation or evading host immune surveillance. Ferroptosis is a newly identified RCD. Evidence has demonstrated how pathogens regulate ferroptosis to promote their replication, dissemination, and pathogenesis. However, the interaction between ferroptosis and pathogenic infections still needs to be completely elucidated. This review summarizes the advances in the interaction between pathogenic infections and host ferroptotic processes, focusing on the underlying mechanisms of how pathogens exploit ferroptosis, and discussing possible therapeutic measures against pathogen-associated diseases in a ferroptosis-dependent manner.
... The phosphorylation of p62 can increase the binding affinity of Keap1 [100]. Recent study has shown that p62 can not only competitively bind to Keap1, but also directly promote the degradation of Keap1 through selective autophagy [101]. ...
Cerebral ischemic stroke is characterized by acute ischemia in a certain part of the brain, which leads to brain cells necrosis, apoptosis, ferroptosis, pyroptosis, etc. At present, there are limited effective clinical treatments for cerebral ischemic stroke, and the recovery of cerebral blood circulation will lead to cerebral ischemia-reperfusion injury (CIRI). Cerebral ischemic stroke involves many pathological processes such as oxidative stress, inflammation, and mitochondrial dysfunction. Nuclear factor erythroid 2-related factor 2 (Nrf2), as one of the most critical antioxidant transcription factors in cells, can coordinate various cytoprotective factors to inhibit oxidative stress. Targeting Nrf2 is considered as a potential strategy to prevent and treat cerebral ischemia injury. During cerebral ischemia, Nrf2 participates in signaling pathways such as Keap1, PI3K/AKT, MAPK, NF-κB, and HO-1, and then alleviates cerebral ischemia injury or CIRI by inhibiting oxidative stress, anti-inflammation, maintaining mitochondrial homeostasis, protecting the blood–brain barrier, and inhibiting ferroptosis. In this review, we have discussed the structure of Nrf2, the mechanisms of Nrf2 in cerebral ischemic stroke, the related research on the treatment of cerebral ischemia through the Nrf2 signaling pathway in recent years, and expounded the important role and future potential of the Nrf2 pathway in cerebral ischemic stroke.
Diabetic retinopathy (DR) is a significant complication of diabetes that often leads to blindness, impacting Müller cells, the primary retinal macroglia involved in DR pathogenesis. Reactive oxygen species (ROS) play a crucial role in the development of DR. The objective of this study was to investigate the involvement of sestrin2 in DR using a high‐glucose (HG)‐induced Müller cell model and assessing cell proliferation with 5‐ethynyl‐2‐deoxyuridine (EdU) labeling. Following this, sestrin2 was upregulated in Müller cells to investigate its effects on ROS, tube formation, and inflammation both in vitro and in vivo, as well as its interaction with the nuclear factor erythroid2‐related factor 2 (Nrf2) signaling pathway. The findings demonstrated a gradual increase in the number of EdU‐positive cells over time, with a subsequent decrease after 72 h of exposure to high glucose levels. Additionally, the expression of sestrin2 exhibited a progressive increase over time, followed by a decrease at 72 h. The rh‐sestrin2 treatment suppressed the injury of Müller cells, decreased ROS level, and inhibited the tube formation. Rh‐sestrin2 treatment enhanced the expression of sestrin2, Nrf2, heme oxygenase‐1 (HO‐1), and glutamine synthetase (GS); however, the ML385 treatment reversed the protective effect of rh‐sestrin2. Finally, we evaluated the effect of sestrin2 in a DR rat model. Sestrin2 overexpression treatment improved the pathological injury of retina and attenuated the oxidative damage and inflammatory reaction. Our results highlighted the inhibitory effect of sestrin2 in the damage of retina, thus presenting a novel therapeutic sight for DR.
Aims
Neuroblastoma (NB) is the most common extracranial solid tumor in children, with a 5‐year survival rate of <50% in high‐risk patients. MYCN amplification is an important factor that influences the survival rate of high‐risk patients. Our results indicated MYCN regulates the expression of SESN1. Therefore, this study aimed to investigate the role and mechanisms of SESN1 in NB.
Methods
siRNAs or overexpression plasmids were used to change MYCN, SESN1, or MyD88's expression. The role of SESN1 in NB cell proliferation, migration, and invasion was elucidated. Xenograft mice models were built to evaluate SESN1's effect in vivo. The correlation between SESN1 expression and clinicopathological data of patients with NB was analyzed. RNA‐Seq was done to explore SESN1's downstream targets.
Results
SESN1 was regulated by MYCN in NB cells. Knockdown SESN1 promoted NB cell proliferation, cell migration, and cell invasion, and overexpressing SESN1 had opposite functions. Knockdown SESN1 promoted tumor growth and shortened tumor‐bearing mice survival time. Low expression of SESN1 had a positive correlation with poor prognosis in patients with NB. RNA‐Seq showed that Toll‐like receptor (TLR) signaling pathway, and PD‐L1 expression and PD‐1 checkpoint pathway in cancer were potential downstream targets of SESN1. Knockdown MyD88 or TLRs inhibitor HCQ reversed the effect of knockdown SESN1 in NB cells. High expression of SESN1 was significantly associated with a higher immune score and indicated an active immune microenvironment for patients with NB.
Conclusions
SESN1 functions as a new tumor suppressor gene via TLR signaling pathway in NB.
Postoperative cognitive dysfunction (POCD) is a prevalent central nervous system complication predominantly observed in elderly patients. Sevoflurane, a general anaesthetic agent, has been implicated in the development of POCD, yet the underlying regulatory mechanisms potentially involving Sestrin1 (SESN1), a stress‐responsive protein that plays a critical role in cellular homeostasis and protection against stress‐induced damage, including oxidative stress and DNA damage, remain elusive. This study endeavoured to elucidate the impact of SESN1 on sevoflurane‐induced cognitive impairment in rats. Employing a model in which SESN1 was transfected into SD male rats and cognitive dysfunction was induced by sevoflurane. The Morris Water Maze test was used for behavioural evaluation, Enzyme‐Linked Immunosorbent Assay, Western blotting and immunofluorescence were applied to assess the influence of SESN1 on the inflammatory response and mitophagy in the rat hippocampus. The study further aimed to uncover the putative mechanism by which SESN1, through SIRT1, might modulate cognitive function. Concurrently, levels of malondialdehyde, superoxide dismutase and mitochondrially produced ATP within the rat hippocampus were quantified. Experimental outcomes suggested that SESN1 overexpression significantly mitigated the deleterious effects of sevoflurane anaesthesia, ameliorated neuroinflammation and inflammasome activation, modified mitochondrial function and facilitated mitophagy. Additionally, SESN1, via the activation of SIRT1, may suppress inflammasome activation and mitochondrial dysfunction. Collectively, these findings underscore SESN1's integral role in counteracting sevoflurane‐induced cognitive impairment, impeding inflammasome activation, enhancing mitochondrial function and fostering mitophagy, which appear to be intricately linked to SESN1‐mediated SIRT1 activation. SESN1 is a novel therapeutic target for POCD, potentially advancing neuroprotective strategies in clinical settings.
This chapter entitled “P53, ROS-Redox Regulation Signaling, Metabolic Reprogramming, and Autophagy in Cancer” initially shows P53 regulation with MDM2, and its tumor suppressor role has been discussed through its activation/deactivation and apoptosis. Cellular redox homeostasis through the p53 antioxidant and prooxidant function has been discussed. As most cancers have mutant p53, its redox regulation functional changes have been discussed as gain of function (GOF) and loss of function (LOF) linking to cancer therapy. Further, p53 regulation of reprogramming of metabolism in cancer has been discussed both in wild type and mutant p53. p53-mediated, autophagy signaling pathways and regulation in cancer have also been taken up.
COVID‐19 is caused by a novel SARS‐CoV‐2 leading to pulmonary and extra‐pulmonary manifestations due to oxidative stress (OS) development and hyperinflammation. COVID‐19 is primarily asymptomatic though it may cause acute lung injury (ALI), acute respiratory distress syndrome (ARDS), systemic inflammation, and thrombotic events in severe cases. SARS‐CoV‐2‐induced OS triggers the activation of different signaling pathways, which counterbalances this complication. One of these pathways is nuclear factor erythroid 2‐related factor 2 (Nrf2), which induces a series of cellular interactions to mitigate SARS‐CoV‐2‐mediated viral toxicity and OS‐induced cellular injury. Nrf2 pathway inhibits the expression of pro‐inflammatory cytokines and the development of cytokine storm in COVID‐19. Therefore, Nrf2 activators may play an essential role in reducing SARS‐CoV‐2 infection‐induced inflammation by suppressing NLRP3 inflammasome in COVID‐19. Furthermore, Nrf2 activators can attenuate endothelial dysfunction (ED), renin‐angiotensin system (RAS) dysregulation, immune thrombosis, and coagulopathy. Thus this mini‐review tries to clarify the possible role of the Nrf2 activators in the management of COVID‐19. Nrf2 activators could be an effective therapeutic strategy in the management of Covid‐19. Preclinical and clinical studies are recommended in this regard.
Duchenne muscular dystrophy (DMD), a progressive muscle disease caused by the absence of functional dystrophin protein, is associated with multiple cellular, physiological, and metabolic dysfunctions. As an added complication to the primary insult, obesity/insulin resistance (O/IR) is frequently reported in DMD patients; however, how IR impacts disease severity is unknown. We hypothesized a high-fat, high sucrose diet (HFHSD) would induce O/IR, exacerbate disease severity, and cause metabolic alterations in dystrophic mice. To test this hypothesis, we treated 7-wk old mdx (disease model) and C57 mice with a control diet (CD) or a HFHSD for 15 weeks. The HFHSD induced insulin resistance, glucose intolerance and hyperglycemia in C57 and mdx mice. Of note, mdx mice on CD were also insulin resistant. Additionally, visceral adipose tissue weights were increased with HFHSD in C57 and mdx mice though differed by genotype. Serum creatine kinase activity and histopathological analyses using Masson's trichrome staining in diaphragm indicated muscle damage was driven by dystrophin deficiency but was not augmented by diet. In addition, markers of inflammatory signaling, mitochondrial abundance, and autophagy were impacted by disease but not diet. Despite this, in addition to disease signatures in CD-fed mice, metabolomic and lipidomic analyses demonstrated a HFHSD caused some common changes in C57 and mdx mice and some unique signatures of O/IR within the context of dystrophin deficiency. In total, these data revealed that in mdx mice, 15 weeks of a HFHSD did not overtly exacerbate muscle injury but further impaired the metabolic status of dystrophic muscle.
Although the use of iodinated contrast agents is sometimes unavoidable for accurate diagnosis, contrast-induced acute kidney injury (CI-AKI) is a possible complication of its administration. The pathogenesis of CI-AKI has not been fully elucidated, but oxidative stress is thought to be a major factor. Sestrin2 plays an important role in cellular and mitochondrial homeostasis by regulating oxidative stress. In this study, we aimed to investigate whether recombinant adenovirus containing sestrin2 (RS) can attenuate CI-AKI by reducing oxidative stress in a CI-AKI mice model. Our results showed that RS decreases oxidative stress, pro-inflammatory cytokines (TNF-α, IL-1α, IL-1β and IL-6) and apoptosis (Bax/Bcl2 and cleaved caspase-3) in the CI-AKI model. Additionally, RS alleviated mitochondrial damage, as evidenced by morphological changes, are restored ATP synthesis. Furthermore, RS administration resulted in a decrease in mitochondrial fission marker (Drp1) that was increased in the CI-AKI model, while the mitochondrial fusion marker (Mfn2) increased, indicating a restoration of mitochondrial dynamics. Decreased relative blood volume, as evaluated on computed tomography (CT), significantly increased compared to the CI-AKI group after RS administration. Finally, renal injury markers such as Kim-1, Ngal, IL-18 also decreased and kidney function was preserved with RS. These results suggested that RS can mitigate the deterioration of renal function in CI-AKI model.
Cancer development and progression of cancer is closely associated with the activation of oncogenes and loss of tumor suppressor genes. Nucleic acid drugs (e.g., siRNA, mRNA, and DNA) have been widely used for cancer therapy due to their specific ability to regulate the expression of any cancer‐associated genes. However, nucleic acid drugs are negatively charged biomacromolecules that are susceptible to serum nucleases and could not cross cell membrane. Therefore, specific delivery tools are required to facilitate the intracellular delivery of nucleic acid drugs. In the past few decades, a variety of nanoparticles (NPs) have been designed and developed for nucleic acid delivery and cancer therapy. In particular, the polymeric NPs in response to the abnormal redox status in cancer cells have garnered much more attention as their potential in redox‐triggered nanostructure dissociation and rapid intracellular release of nucleic acid drugs. In this review, we briefly introduce the important genes or signaling pathways regulating the abnormal redox status in cancer cells and systemically summarize the recent development of redox‐responsive NPs for nucleic acid delivery and cancer therapy. We also discuss the future development of NPs‐mediated nucleic acid delivery and their challenges in clinical translation.
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Cardiac aging is accompanied by changes in the heart at the cellular and molecular levels, leading to alterations in cardiac structure and function. Given today's increasingly aging population, the decline in cardiac function caused by cardiac aging has a significant impact on quality of life. Anti-aging therapies to slow the aging process and attenuate changes in cardiac structure and function have become an important research topic. Treatment with drugs, including metformin, spermidine, rapamycin, resveratrol, astaxanthin, Huolisu oral liquid, and sulforaphane, has been demonstrated be effective in delaying cardiac aging by stimulating autophagy, delaying ventricular remodeling, and reducing oxidative stress and the inflammatory response. Furthermore, caloric restriction has been shown to play an important role in delaying aging of the heart. Many studies in cardiac aging and cardiac aging-related models have demonstrated that Sestrin2 has antioxidant and anti-inflammatory effects, stimulates autophagy, delays aging, regulates mitochondrial function, and inhibits myocardial remodeling by regulation of relevant signaling pathways. Therefore, Sestrin2 is likely to become an important target for anti-myocardial aging therapy.
Chronic inflammation is a major contributor to the development of metabolic disorders and is commonly seen in studies of diet-induced obesity in humans and rodents. Exercise has been shown to have anti-inflammatory properties, though the exact mechanisms are still not fully understood. Sestrins and Nrf2 are of interest to researchers as they are known to protect against inflammation and oxidative stress. In this study, we aim to explore the interconnection between Sestrin2 (SESN2) and Nrf2 and their roles in exercise benefits on chronic inflammation. Our data showed that SESN2 knockout aggravated the abnormalities of body weight, fat mass, and serum lipid that were induced by a high-fat diet (HFD), and a concomitant increase of TNF-α, IL-1β and IL-6 in both serum and skeletal muscle. Notably, exercise was found to reverse these changes, and SESN2 was found to be necessary for exercise to reduce the inflammatory response in skeletal muscles, though not in serum. Immunoprecipitation and bioinformatics prediction experiments further revealed that SESN2 directly binds to Nrf2, indicating a protein-protein interaction between the two. Furthermore, our data demonstrated that SESN2 protein is necessary for exercise-induced effects on Nrf2 pathway in HFD-fed mice, and Nrf2 protein is necessary to enable SESN2 to reduce the inflammation caused by palmitic acid (PA)+ oleic acid (OA) treatment in vitro. Our findings indicate that exercise mitigates chronic inflammation induced by HFD through SESN2 in an Nrf2-dependent manner. Our study reveals a novel molecular mechanism whereby the SESN2/Nrf2 pathway mediates the positive impact of exercise on chronic inflammation.
Ethnopharmacological relevance:
Panax japonicus (T. Nees) C.A. Mey. (PJ) has been used as a tonic traditional Chinese medicine (TCM) for years. Based on its meridian tropism in liver, spleen, and lung, PJ was popularly used to enhance the function of these organs. It is originally recorded with detoxicant effect on binge drink in Ben Cao Gang Mu Shi Yi, a persuasive Chinese materia medica. And binge dink has a close relationship with alcoholic liver disease (ALD). Hence, it's meaningful to investigate whether PJ exerts liver protection against binge drink toxicity.
Aim of the study:
This investigation was carried out not only to emphasize the right recognition of total saponins from PJ (SPJ), but also to study on its sober-up effectiveness and defensive mechanism against acute alcoholic liver injury in vivo and in vitro.
Materials and methods:
SPJ constituents were verified by HPLC-UV analysis. In vivo, acute alcoholic liver oxidative stress and hepatosteatosis were established by continuous ethanol gavage to C57BL/6 mice for 3 days. SPJ was pre-administered for 7 days to investigate its protective efficacy. Loss of righting reflex (LORR) assay was employed to assess anti-inebriation effect of SPJ. Transaminases levels and hematoxylin and eosin (H&E) staining were measured to indicate the alcoholic liver injury. Antioxidant enzymes were measured to evaluate the oxidative stress degree in liver. Measurement of hepatic lipid accumulation was based on Oil Red O staining. Levels of inflammatory cytokines were evaluated by enzyme-linked immunosorbent assay (ELISA). In vitro, HepG2 cells were treated with ethanol for 24 h, and SPJ was pre-administered for 2 h. 2,7-dichlorofluorescein diacetate (DCFH-DA) was used as a probe to indicate reactive oxygen species (ROS) generation. Nrf2 activation was verified by the favor of specific inhibitor, ML385. The nuclear translocation of Nrf2 was indicated with immunofluorescence analysis. Proteins expressions of related pathways were determined by Western blotting.
Results:
Oleanane-type saponins are the most abundant constituents of SPJ. In this acute model, SPJ released inebriation of mice in a dose dependent manner. It decreased levels of serum ALT and AST, and hepatic TG. Besides, SPJ inhibited CYP2E1 expression and reduced MDA level in liver, with upregulations of antioxidant enzymes GSH, SOD and CAT. p62-related Nrf2 pathway was activated by SPJ with downstream upregulations of GCLC and NQO1 in liver. AMPK-ACC/PPARα axis was upregulated by SPJ to alleviate hepatic lipidosis. Hepatic IL-6 and TNF-α levels were downregulated by SPJ, which indicated a regressive lipid peroxidation in liver. In HepG2 cells, SPJ reduced ethanol-exposed ROS generation. Activated p62-related Nrf2 pathway was verified to contribute to the alleviation of alcohol-induced oxidative stress in hepatic cells.
Conclusion:
This attenuation of hepatic oxidative stress and steatosis suggested the therapeutic value of SPJ for ALD.
Aims:
Obese patients are highly sensitive to adriamycin (ADR)-induced cardiotoxicity. However, the potential mechanism of superimposed toxicity remains to be elucidated. Sestrin 2 (SESN2), a potential antioxidant, could attenuate stress-induced cardiomyopathy; therefore, this study aims to explore whether SESN2 enhances cardiac resistance to ADR-induced oxidative damage in high fat diet (HFD)-induced obese mice.
Results:
The results revealed that obesity decreased SESN2 expression in ADR-exposed heart. And, HFD mice may predispose to ADR-induced cardiotoxicity which probably associated with inhibiting AKT, GSK-3β phosphorylation and subsequently blocking nuclear localization of NRF2, ultimately resulting in cardiac oxidative damage. However, these destructive cascades and cardiac damaged effects induced by HFD/sodium palmitate combined with ADR were blocked by overexpression of SESN2. Moreover, the antioxidant effect of SESN2 could be largely abolished by sh-Nrf2 or wortmannin, respectively. And sulforaphane (SFN), an NRF2 agonist, could remarkably reverse cardiac pathological and functional abnormalities caused by ADR in obese mice.
Innovation and conclusion:
The present study demonstrated that SESN2 might be a promising therapeutic target for improving anthracycline-related cardiotoxicity in obesity by up-regulating activity of NRF2 via AKT/GSK-3β/FYN signaling pathway.
Background: The government’s role in influencing policies related to COVID-19 vaccine distribution and handwashing uptake is essential in controlling the spread of the virus. This study aims to systematically review published studies to determine how government policies have influenced hand washing and vaccine uptake in Kenya, Uganda and Tanzania in relation to COVID-19 prevention and control.
Methods and analysis: Using systematic approach, this study reviewed 136 published research papers to examine and understand how government policies have influenced hand washing and COVID-19 vaccine uptake in Kenya, Uganda and Tanzania in relation to COVID-19 prevention and control. The search strategy was applied in three databases, papers were selected using strict inclusion and exclusion criteria including papers published between December 2019 and January 2023. The review was undertaken according to the PRISMA-P 2015 checklist and the PRISMA flow diagram was used for research article selection and screening.
Findings: Eleven of the initial records were found eligible for review. The findings reveal that the government has a role in influencing policies related to COVID-19 vaccine distribution and handwashing uptake. Study results indicate that employment of public health campaigns and communication strategies by the government in Uganda increased vaccine acceptance and hand hygiene uptake. Similarly, results revealed that government efforts in making hand hygiene accessible increases uptake of handwashing. In Kenya, government efforts show informal settlements access soap and clean water at markets, results revealed that government incentives such as cash could increase vaccination rates and vaccination reminders combined with cash incentives increased childhood immunization coverage. Studies have indicated monitoring and enforcing compliance increases vaccine and handwashing uptake.
Conclusion: The government’s role in influencing policies that promote handwashing and vaccine uptake. The effectiveness of these polices are also influenced by various factors including safety and efficacy, access to information among other. It is important to address these factors to successfully implementation these policies.
Registration: PROSPERO ID CRD42023396319; registered on 2nd February 2023
Cardiac ischemia/reperfusion(I/R) induced-cardiac vascular endothelial injury is an important pathological process that appears in the early stage of cardiac I/R injury. The autophagy-lysosomal pathway is essential for the maintenance of cellular homeostasis. However, in cardiac I/R injury, the role of the autophagy-lysosomal pathway is controversial. The present study aimed to use oxygen-glucose deprivation/oxygen-glucose resupply(OGD/OGR) in human coronary artery endothelial cells(HCAECs) with I/R injury to assess the role of the autophagy-lysosomal pathway in I/R-induced endothelial injury. The results revealed lysosomal dysfunction and impaired autophagic flux in endothelial cells exposed to OGD/OGR. Meanwhile, our data showed that the levels of cathepsin D(CTSD) decreased time-dependently. Knockdown of CTSD caused lysosomal dysfunction and impaired autophagic flux. Conversely, restoration of CTSD levels protected HCAECs against OGD/OGR induced-defects in autophagy-lysosomal function and cellular damage. Our findings indicated that I/R induced-impaired autophagic flux, rather than excessive autophagic initiation, mediates endothelial cells injury. The maintenance of autophagy-lysosomal function is critical to protect endothelial cells against I/R injury, and CTSD is a key regulator. Thus, strategies focused on restoring CTSD function are potentially novel treatments for cardiac reperfusion injury.
Background:
Sestrin-2 (SESN2) is a antioxidant protein that can be activated by a number of conditions, including DNA damage and hypoxia.
Aims:
Our objective was to evaluate maternal serum SESN2 levels in patients with intrauterine growth restriction (IUGR) and its association with adverse perinatal outcomes.
Methods:
This prospective study included a total of 87 pregnant women admitted to our tertiary care center between 2018 August and 2019 July. The study group consisted of a total of 44 patients who had been diagnosed with IUGR. Forty-three low-risk and gestational age-matched pregnant women were taken as control group. Demographic data, maternal serum SESN2 levels, and maternal-neonatal outcomes were evaluated. SESN2 levels were analyzed by the enzyme-linked immunosorbent assay (ELISA) method and compared between groups.
Results:
Maternal serum SESN2 levels were significantly higher in the IUGR group compared to control group (22.38 ng/ml vs. 13.0 ng/ml, p < 0.001). In correlation analysis, a negative significant correlation was found between SESN2 levels and gestational week at delivery (r = - 0.387, p < 0.001). The ideal cut-off value for detecting IUGR was 9.5 ng/ml, and the area under the curve was 0.719 (95%CI: 0.610-0.827). Birth interval, gestational week at birth, birth weight, and 1-5-min Apgar scores were lower in the IUGR group (p < 0.001).
Conclusions:
Maternal serum SESN2 levels are elevated in IUGR and are associated with adverse neonatal outcome. Considering that SESN2 is involved in pathogenesis, it can be used as a new marker for the evaluation of IUGR.
Background:
Combination therapy with other antineoplastic agent is a favorable approach for targeting the molecules involved in sorafenib resistance.
Purpose:
In the present study, we determined whether tiliroside, a natural flavonoid glycoside isolated from oriental paperbush flower, could improve the sensitivity of hepatocellular carcinoma (HCC) cells to sorafenib. Furthermore, we investigated the mechanisms and identified the potential drug targets of tiliroside.
Methods:
Synergy was performed using CalcuSyn. Transcriptomic studies were adopted to investigate whether tiliroside could induce ferroptosis and inhibit the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway in HCC cells. Ferroptosis was analyzed using western blotting, flow cytometry, and transmission electron microscopy. Immunofluorescence, co-immunoprecipitation, and Nrf2 knockdown or overexpression were performed to confirm the involvement of Nrf2 in tiliroside-induced ferroptosis. Additionally, molecular docking and biolayer interferometry-based measurements were used to confirm the direct target of tiliroside. Finally, subcutaneous xenograft and orthotopic xenograft tumors in nude mice were used to assess the effects of tiliroside in vivo.
Results:
Tiliroside significantly enhanced the anti-HCC activity of sorafenib without any discernible side effects. Moreover, the combination of tiliroside and sorafenib induced synergistic effects against HCC in vitro. The inhibitory effects of tiliroside on HCC were antagonized by N-acetylcysteine and the ferroptosis inhibitor liproxstatin-1. Studies on the mechanism of action revealed that tiliroside could directly bind to TANK-binding kinase 1 (TBK1) and inhibit its enzymatic activity. Inhibition of TBK1 by tiliroside decreased the phosphorylation of serine 349 on sequestosome-1 (p62) and the affinity of p62 for kelch like ECH-associated protein 1 (Keap1) and promoted Keap1-mediated Nrf2 ubiquitination and degradation. The downstream target proteins of Nrf2, including glutathione peroxidase 4, ferritin heavy chain 1, and glucose-6-phosphate dehydrogenase, demonstrated similar results to that of Nrf2 protein, inducing ferroptosis in tiliroside-treated HCC cells. We extended these findings in vivo and found that tiliroside inhibited the growth of HepG2 tumors in both subcutaneous xenograft and orthotopic xenograft tumor models of HCC.
Conclusion:
Our findings imply that tiliroside is a potent TBK1 inhibitor and a candidate natural anti-cancer product that could function as a sensitizer of sorafenib in HCC treatment by targeting TBK1 to induce ferroptosis.
The rapid increase in both the lifespan and proportion of older adults is accompanied by the unprecedented rise in age-associated chronic diseases, including sarcopenia and obesity. Aging is also manifested by increased susceptibility to multiple endogenous and exogenous stresses enabling such chronic conditions to develop. Among the main physiological regulators of cellular adaption to various stress stimuli, such as DNA damage, hypoxia, and oxidative stress, are sestrins (Sesns), a family of three evolutionarily conserved proteins, Sesn1, 2, and 3. Age-associated sarcopenia and obesity are characterized by two key processes: (i) accumulation of senescent cells in the skeletal muscle and adipose tissue and (ii) creation of a systemic, chronic, low-grade inflammation (SCLGI). Presumably, failed SCLGI resolution governs the development of these chronic conditions. Noteworthy, Sesns activate senolytics, which are agents that selectively eliminate senescent cells, as well as specialized pro-resolving mediators, which are factors that physiologically provide inflammation resolution. Sesns reveal clear beneficial effects in pre-clinical models of sarcopenia and obesity. Based on these observations, we propose a novel treatment strategy for age-associated sarcopenia and obesity, complementary to the conventional therapeutic modalities: Sesn activation, SCLGI resolution, and senescent cell elimination.
Nelumbo nucifera Gaertn. is an important aquatic vegetable, and its dried stamen (Nelumbinis stamen, NS) is a valuable nutraceutical usually used as a herbal tea. Here, we used ultrahigh-performance liquid chromatography (UPLC)-quadrupole time-of-flight mass spectrometry and high-performance liquid chromatography (HPLC) to chemically profile NS and quantify their main constituent flavonoids, respectively. In total, 44 components were identified, including organic acids, flavonoids, monoterpene glycosides, and fatty acids. Experimental mice were induced with fatigue by exposure to chronic restraint stress (CRS) for 8 h daily for 15 days and then treated with an aqueous extract of NS (0.5 and 1 g/kg) via gavage. NS significantly mitigated CRS-induced skeletal muscle dysfunction and fatigue in mice possibly by lowering serum corticosterone levels and restoring Sestrin2 expression in the gastrocnemius to regulate metabolism, preserve mitochondrial homeostasis, and promote antioxidant capacity. These results demonstrate that NS can be used as a nutraceutical or supplement for controlling stress-induced muscle dysfunction and fatigue.
Dimethyl fumarate (DMF) is a small molecule currently approved and used in the treatment of psoriasis and multiple sclerosis due to its immuno-modulatory, anti-inflammatory, and antioxidant properties. As an Nrf2 activator through Keap1 protein inhibition, DMF unveils a potential therapeutical use that is much broader than expected so far. In this comprehensive review we discuss the state-of-art and future perspectives regarding the potential repositioning of this molecule in the panorama of eye pathologies, including Age-related Macular Degeneration (AMD). The DMF’s mechanism of action, an extensive analysis of the in vitro and in vivo evidence of its beneficial effects, together with a search of the current clinical trials, are here reported. Altogether, this evidence gives an overview of the new potential applications of this molecule in the context of ophthalmological diseases characterized by inflammation and oxidative stress, with a special focus on AMD, for which our gene–disease (KEAP1-AMD) database search, followed by a protein–protein interaction analysis, further supports the rationale of DMF use. The necessity to find a topical route of DMF administration to the eye is also discussed. In conclusion, the challenge of DMF repurposing in eye pathologies is feasible and worth scientific attention and well-focused research efforts.
Intrinsic antioxidant defences are important for neuronal longevity. We show that synaptic activity, acting via NMDA receptor (NMDAR) signaling, boosts antioxidant defences through changes to the thioredoxin-peroxiredoxin system. Synaptic activity enhances thioredoxin activity, facilitates the reduction of overoxidized peroxiredoxins, and promotes resistance to oxidative stress. Resistance is mediated by coordinated transcriptional changes: synaptic NMDAR activity inactivates a novel FOXO target gene, the thioredoxin inhibitor Txnip. Conversely, NMDAR blockade upregulates Txnip in vivo and in vitro, where it binds thioredoxin and promotes vulnerability to oxidative damage. Synaptic activity also up-regulates the peroxiredoxin re-activating genes Sestrin2 and Sulfiredoxin, via C/EBPβ and AP-1 respectively. Mimicking these expression changes is sufficient to strengthen antioxidant defences. Trans-synaptic stimulation of synaptic NMDARs is crucial for boosting antioxidant defences: chronic bath activation of all (synaptic and extrasynaptic) NMDARs induces no antioxidative effects. Thus, synaptic NMDAR activity may influence the progression of pathological processes associated with oxidative damage.
The Kelch-like ECH-associated protein 1 (Keap1)-NF-E2-related factor 2 (Nrf2) system is essential for cytoprotection against oxidative and electrophilic insults. Under unstressed conditions, Keap1 serves as an adaptor for ubiquitin E3 ligase and promotes proteasomal degradation of Nrf2, but Nrf2 is stabilized when Keap1 is inactivated under oxidative/electrophilic stress conditions. Autophagy-deficient mice show aberrant accumulation of p62, a multifunctional scaffold protein, and develop severe liver damage. The p62 accumulation disrupts the Keap1-Nrf2 association and provokes Nrf2 stabilization and accumulation. However, individual contributions of p62 and Nrf2 to the autophagy-deficiency-driven liver pathogenesis have not been clarified. To examine whether Nrf2 caused the liver injury independent of p62, we crossed liver-specific Atg7::Keap1-Alb double-mutant mice into p62- and Nrf2-null backgrounds. Although Atg7::Keap1-Alb::p62(-/-) triple-mutant mice displayed defective autophagy accompanied by the robust accumulation of Nrf2 and severe liver injury, Atg7::Keap1-Alb::Nrf2(-/-) triple-mutant mice did not show any signs of such hepatocellular damage. Importantly, in this study we noticed that Keap1 accumulated in the Atg7- or p62-deficient mouse livers and the Keap1 level did not change by a proteasome inhibitor, indicating that the Keap1 protein is constitutively degraded through the autophagy pathway. This finding is in clear contrast to the Nrf2 degradation through the proteasome pathway. We also found that treatment of cells with tert-butylhydroquinone accelerated the Keap1 degradation. These results thus indicate that Nrf2 accumulation is the dominant cause to provoke the liver damage in the autophagy-deficient mice. The autophagy pathway maintains the integrity of the Keap1-Nrf2 system for the normal liver function by governing the Keap1 turnover.
Peroxiredoxins (Prxs) are a family of peroxidases that reduce peroxides, with a conserved cysteine residue (the peroxidatic Cys) serving as the site of oxidation by peroxides. Peroxides oxidize the peroxidatic Cys-SH to Cys-SOH, which then reacts with another cysteine residue (typically the resolving Cys [C(R)]) to form a disulfide that is subsequently reduced by an appropriate electron donor. On the basis of the location or absence of the C(R), Prxs are classified into 2-Cys, atypical 2-Cys, and 1-Cys Prx subfamilies. In addition to their peroxidase activity, members of the 2-Cys Prx subfamily appear to serve as peroxide sensors for other proteins and as molecular chaperones. During catalysis, the peroxidatic Cys-SOH of 2-Cys Prxs is occasionally further oxidized to Cys-SO(2)H before disulfide formation, resulting in inactivation of peroxidase activity. This hyperoxidation, which is reversed by the ATP-dependent enzyme sulfiredoxin, modulates the sensor and chaperone functions of 2-Cys Prxs. The peroxidase activity of 2-Cys Prxs is extensively regulated via tyrosine and threonine phosphorylation, which allows modulation of the local concentration of the intracellular messenger H(2)O(2). Finally, 2-Cys Prxs interact with a variety of proteins, with such interaction having been shown to modulate the function of the binding partners in a reciprocal manner.
Autophagy is an evolutionarily conserved process by which cytoplasmic proteins and organelles are catabolized. During starvation, the protein TOR (target of rapamycin), a nutrient-responsive kinase, is inhibited, and this induces autophagy. In autophagy, double-membrane autophagosomes envelop and sequester intracellular components and then fuse with lysosomes to form autolysosomes, which degrade their contents to regenerate nutrients. Current models of autophagy terminate with the degradation of the autophagosome cargo in autolysosomes, but the regulation of autophagy in response to nutrients and the subsequent fate of the autolysosome are poorly understood. Here we show that mTOR signalling in rat kidney cells is inhibited during initiation of autophagy, but reactivated by prolonged starvation. Reactivation of mTOR is autophagy-dependent and requires the degradation of autolysosomal products. Increased mTOR activity attenuates autophagy and generates proto-lysosomal tubules and vesicles that extrude from autolysosomes and ultimately mature into functional lysosomes, thereby restoring the full complement of lysosomes in the cell-a process we identify in multiple animal species. Thus, an evolutionarily conserved cycle in autophagy governs nutrient sensing and lysosome homeostasis during starvation.
The accumulation of ubiquitin-positive protein aggregates has been implicated in the pathogenesis of neurodegenerative diseases, heart disease and diabetes. Emerging evidence indicates that the autophagy lysosomal pathway plays a critical role in the clearance of ubiquitin aggregates, a process that is mediated by the ubiquitin binding protein p62. In addition to binding ubiquitin, p62 also interacts with LC3 and transports ubiquitin conjugates to autophagosomes for degradation. The exact regulatory mechanism of this process is still largely unknown. Here we report the identification of Keap1 as a binding partner for p62 and LC3. Keap1 inhibits Nrf2 by sequestering it in the cytosol and preventing its translocation to the nucleus and activation of genes involved in the oxidative stress response. In this study, we found that Keap1 interacts with p62 and LC3 in a stress-inducible manner, and that Keap1 colocalizes with LC3 and p62 in puromycin-induced ubiquitin aggregates. Moreover, p62 serves as a bridge between Keap1 and ubiquitin aggregates and autophagosomes. Finally, genetic ablation of Keap1 leads to the accumulation of ubiquitin aggregates, increased cytotoxicity of misfolded protein aggregates, and defective activation of autophagy. Therefore, this study assigns a novel positive role of Keap1 in upregulating p62-mediated autophagic clearance of ubiquitin aggregates.
The p62/SQSTM1 (sequestosome 1) protein, which acts as a cargo receptor for autophagic degradation of ubiquitinated targets, is up-regulated by various stressors. Induction of the p62 gene by oxidative stress is mediated by NF-E2-related factor 2 (NRF2) and, at the same time, p62 protein contributes to the activation of NRF2, but hitherto the mechanisms involved were not known. Herein, we have mapped an antioxidant response element (ARE) in the p62 promoter that is responsible for its induction by oxidative stress via NRF2. Chromatin immunoprecipitation and gel mobility-shift assays verified that NRF2 binds to this cis-element in vivo and in vitro. Also, p62 docks directly onto the Kelch-repeat domain of Kelch-like ECH-associated protein 1 (KEAP1), via a motif designated the KEAP1 interacting region (KIR), thereby blocking binding between KEAP1 and NRF2 that leads to ubiquitylation and degradation of the transcription factor. The KIR motif in p62 is located immediately C-terminal to the LC3-interacting region (LIR) and resembles the ETGE motif utilized by NRF2 for its interaction with KEAP1. KIR is required for p62 to stabilize NRF2, and inhibition of KEAP1 by p62 occurs from a cytoplasmic location within the cell. The LIR and KIR motifs cannot be engaged simultaneously by LC3 and KEAP1, but because p62 is polymeric the interaction between KEAP1 and p62 leads to accumulation of KEAP1 in p62 bodies, which is followed by autophagic degradation of KEAP1. Our data explain how p62 contributes to activation of NRF2 target genes in response to oxidative stress through creating a positive feedback loop.
Sestrins are conserved proteins that accumulate in cells exposed to stress, potentiate adenosine monophosphate–activated protein
kinase (AMPK), and inhibit activation of target of rapamycin (TOR). We show that the abundance of Drosophila sestrin (dSesn) is increased upon chronic TOR activation through accumulation of reactive oxygen species that cause activation
of c-Jun amino-terminal kinase and transcription factor Forkhead box O (FoxO). Loss of dSesn resulted in age-associated pathologies
including triglyceride accumulation, mitochondrial dysfunction, muscle degeneration, and cardiac malfunction, which were prevented
by pharmacological activation of AMPK or inhibition of TOR. Hence, dSesn appears to be a negative feedback regulator of TOR
that integrates metabolic and stress inputs and prevents pathologies caused by chronic TOR activation that may result from
diminished autophagic clearance of damaged mitochondria, protein aggregates, or lipids.
The livers of insulin-resistant, diabetic mice manifest selective insulin resistance, suggesting a bifurcation in the insulin signaling pathway: Insulin loses its ability to block glucose production (i.e., it fails to suppress PEPCK and other genes of gluconeogenesis), yet it retains its ability to stimulate fatty acid synthesis (i.e., continued enhancement of genes of lipogenesis). Enhanced lipogenesis is accompanied by an insulin-stimulated increase in the mRNA encoding SREBP-1c, a transcription factor that activates the entire lipogenic program. Here, we report a branch point in the insulin signaling pathway that may account for selective insulin resistance. Exposure of rat hepatocytes to insulin produced a 25-fold increase in SREBP-1c mRNA and a 95% decrease in PEPCK mRNA. Insulin-mediated changes in both mRNAs were blocked by inhibitors of PI3K and Akt, indicating that these kinases are required for both pathways. In contrast, subnanomolar concentrations of rapamycin, an inhibitor of the mTORC1 kinase, blocked insulin induction of SREBP-1c, but had no effect on insulin suppression of PEPCK. We observed a similar selective effect of rapamycin in livers of rats and mice that experienced an insulin surge in response to a fasting-refeeding protocol. A specific inhibitor of S6 kinase, a downstream target of mTORC1, did not block insulin induction of SREBP-1c, suggesting a downstream pathway distinct from S6 kinase. These results establish mTORC1 as an essential component in the insulin-regulated pathway for hepatic lipogenesis but not gluconeogenesis, and may help to resolve the paradox of selective insulin resistance in livers of diabetic rodents.
In response to oxidative stress, Nrf2 and p21(Cip1/WAF1) are both upregulated to protect cells from oxidative damage. Nrf2 is constantly ubiquitinated by a Keap1 dimer that interacts with a weak-binding (29)DLG motif and a strong-binding (79)ETGE motif in Nrf2, resulting in degradation of Nrf2. Modification of the redox-sensitive cysteine residues on Keap1 disrupts the Keap1-(29)DLG binding, leading to diminished Nrf2 ubiquitination and activation of the antioxidant response. However, the underlying mechanism by which p21 protects cells from oxidative damage remains unclear. Here we present molecular and genetic evidence suggesting that the antioxidant function of p21 is mediated through activation of Nrf2 by stabilizing the Nrf2 protein. The (154)KRR motif in p21 directly interacts with the (29)DLG and (79)ETGE motifs in Nrf2 and thus competes with Keap1 for Nrf2 binding, compromising ubiquitination of Nrf2. Furthermore, the physiological significance of our findings was demonstrated in vivo using p21-deficient mice.
The active-site cysteine of 2-Cys peroxiredoxins (Prxs), a subgroup of the Prx family, is reversibly hyperoxidized to cysteine sulfinic acid during catalysis with concomitant loss of peroxidase activity. The reduction of sulfinic 2-Cys Prx enzymes, the first known biologic of such a reaction, has been reported to be catalyzed by either sulfiredoxin (Srx) or sestrin (Sesn) 2. The 13-kDa Srx and 60-kDa Sesn 2 show no sequence similarity, however. Whereas the reductase function of Srx has been confirmed by several studies, such is not the case for Sesn 2. We have now shown that (a) recombinant Sesn 2 did not catalyze the reduction of sulfinic Prx I in vitro, whereas Srx did; (b) overexpression of Sesn 2 in HeLa or A549 cells did not affect the reduction of 2-Cys Prxs, whereas overexpression of Srx markedly increased the reduction rate; and (c) the rate of sulfinic 2-Cys Prx reduction in embryonic fibroblasts derived from Sesn 2-knockout mice did not differ from that in those derived from wild-type mice. These results suggest that, unlike Srx, Sesn 2 is not a sulfinic Prx reductase.
Proteins contain thiol-bearing cysteine residues that are sensitive to oxidation, and this may interfere with biological function either as 'damage' or in the context of oxidant-dependent signal transduction. Cysteine thiols oxidized to sulphenic acid are generally unstable, either forming a disulphide with a nearby thiol or being further oxidized to a stable sulphinic acid. Cysteine-sulphenic acids and disulphides are known to be reduced by glutathione or thioredoxin in biological systems, but cysteine-sulphinic acid derivatives have been viewed as irreversible protein modifications. Here we identify a yeast protein of relative molecular mass M(r) = 13,000, which we have named sulphiredoxin (identified by the US spelling 'sulfiredoxin', in the Saccharomyces Genome Database), that is conserved in higher eukaryotes and reduces cysteine-sulphinic acid in the yeast peroxiredoxin Tsa1. Peroxiredoxins are ubiquitous thiol-containing antioxidants that reduce hydroperoxides and control hydroperoxide-mediated signalling in mammals. The reduction reaction catalysed by sulphiredoxin requires ATP hydrolysis and magnesium, involving a conserved active-site cysteine residue which forms a transient disulphide linkage with Tsa1. We propose that reduction of cysteine-sulphinic acids by sulphiredoxin involves activation by phosphorylation followed by a thiol-mediated reduction step. Sulphiredoxin is important for the antioxidant function of peroxiredoxins, and is likely to be involved in the repair of proteins containing cysteine-sulphinic acid modifications, and in signalling pathways involving protein oxidation.
Acting as a signal, hydrogen peroxide circumvents antioxidant defense by overoxidizing peroxiredoxins (Prxs), the enzymes
that metabolize peroxides. We show that sestrins, a family of proteins whose expression is modulated by p53, are required
for regeneration of Prxs containing Cys-SO2H, thus reestablishing the antioxidant firewall. Sestrins contain a predicted redox-active domain homologous to AhpD, the
enzyme catalyzing the reduction of a bacterial Prx, AhpC. Purified Hi95 (sestrin 2) protein supports adenosine triphosphate–dependent
reduction of overoxidized PrxI in vitro, indicating that unlike AhpD, which is a disulfide reductase, sestrins are cysteine
sulfinyl reductases. As modulators of peroxide signaling and antioxidant defense, sestrins constitute potential therapeutic
targets.
NF-E2 related factor (Nrf2) controls a pleiotropic cellular defense, where multiple antioxidant/detoxification pathways are
up-regulated in unison. Although small molecule inducers of Nrf2 activity have been reported to protect neurons in vitro, whether similar pathways can be accessed in vivo is not known. We have investigated whether in vivo toxicity of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) can be attenuated by constitutive and inducible
Nrf2 activity. The absence of Nrf2 function in Nrf2–/– mice resulted in 3-NP hypersensitivity that became apparent with time and increasing dose, causing motor deficits and striatal
lesions on a more rapid time scale than identically treated Nrf2+/+ and Nrf2+/– controls. Striatal succinate dehydrogenase activity, the target of 3-NP, was inhibited to the same extent in all genotypes
by a single acute dose of 3-NP, suggesting that brain concentrations of 3-NP were similar. Dietary supplementation with the
Nrf2 inducer tert-butylhydroquinone attenuated 3-NP toxicity in Nrf2+/– mice, but not Nrf2–/–, confirming the Nrf2-specific action of the inducer in vivo. Increased Nrf2 activity alone was sufficient to protect animals from 3-NP toxicity because intrastriatal adenovirus-mediated
Nrf2 overexpression significantly reduced lesion size compared with green fluorescent protein overexpressing controls. In
cultured astrocytes, 3-NP was found to increase Nrf2 activity leading to antioxidant response element-dependent gene expression
providing a potential mechanism for the increased sensitivity of Nrf2–/– animals to 3-NP toxicity in vivo. We conclude that Nrf2 may underlie a feedback system limiting oxidative load during chronic metabolic stress
Keap1 is a BTB-Kelch protein that functions as a substrate adaptor protein for a Cul3-dependent E3 ubiquitin ligase complex. Keap1 targets its substrate, the Nrf2 transcription factor, for ubiquitination and subsequent degradation by the 26 S proteasome. Inhibition of Keap1-dependent ubiquitination of Nrf2 increases steady-state levels of Nrf2 and enables activation of cytoprotective Nrf2-dependent genes. In this report, we demonstrate that Keap1 and three other BTB-Kelch proteins, including GAN1, ENC1, and Sarcosin, are ubiquitinated by a Cul3-dependent complex. Ubiquitination of Keap1 is markedly increased in cells exposed to quinone-induced oxidative stress, occurs in parallel with inhibition of Keap1-dependent ubiquitination of Nrf2, and results in decreased steady-state levels of Keap1, particularly in cells that are unable to synthesize glutathione. Degradation of Keap1 is independent of the 26 S proteasome, because inhibitors of the 26 S proteasome do not prevent loss of Keap1 following exposure of cells to quinone-induced oxidative stress. Our results suggest that a switch from substrate to substrate adaptor ubiquitination is a critical regulatory step that controls steady-state levels of both BTB-Kelch substrate adaptor proteins and their cognate substrates.
The prevalence and mechanistic significance of self-association among substrate adaptors for the Cul-Rbx family of ubiquitin
ligases remain unclear. We now report that it is as a homodimer that the substrate adaptor Keap1 interacts with Cul3. The
resulting complex facilitates ubiquitylation of the Nrf2 transcription factor but only when this substrate possesses within
its Neh2 domain a second cryptic Keap1-binding site, the DLG motif, in addition to its previously described ETGE site. Both
motifs recognize overlapping surfaces on Keap1, and the seven lysine residues of Nrf2 that act as ubiquitin acceptors lie
between them. Based on these data, we propose a “fixed-ends” model for Nrf2 ubiquitylation in which each binding site becomes
tethered to a separate subunit of the Keap1 homodimer. This two-site interaction between Keap1 and Nrf2 constrains the mobility
of the target lysine residues in the Neh2 domain, increasing their average concentration in the vicinity of the Rbx-bound
ubiquitin-conjugating enzyme, and thus the rate at which the transcription factor is ubiquitylated. We show that self-association
is a general feature of Cul3 substrate adaptors and propose that the fixed-ends mechanism is commonly utilized to recruit,
orientate, and ubiquitylate substrates upon this family of ubiquitin ligases.
Keap1-Nrf2-ARE signaling plays a significant role in protecting cells from endogenous and exogenous stresses. The development of Nrf2 knockout mice has provided key insights into the toxicological importance of this pathway. These mice are more sensitive to the hepatic, pulmonary, ovarian, and neurotoxic consequences of acute exposures to environmental agents and drugs, inflammatory stresses, as well as chronic exposures to cigarette smoke and other carcinogens. Under quiescent conditions, the transcription factor Nrf2 interacts with the actin-anchored protein Keap1, largely localized in the cytoplasm. This quenching interaction maintains low basal expression of Nrf2-regulated genes. However, upon recognition of chemical signals imparted by oxidative and electrophilic molecules, Nrf2 is released from Keap1, escapes proteasomal degradation, translocates to the nucleus, and transactivates the expression of several dozen cytoprotective genes that enhance cell survival. This review highlights the key elements in this adaptive response to protection against acute and chronic cell injury provoked by environmental stresses.
Protein degradation by basal constitutive autophagy is important to avoid accumulation of polyubiquitinated protein aggregates and development of neurodegenerative diseases. The polyubiquitin-binding protein p62/SQSTM1 is degraded by autophagy. It is found in cellular inclusion bodies together with polyubiquitinated proteins and in cytosolic protein aggregates that accumulate in various chronic, toxic, and degenerative diseases. Here we show for the first time a direct interaction between p62 and the autophagic effector proteins LC3A and -B and the related gamma-aminobutyrate receptor-associated protein and gamma-aminobutyrate receptor-associated-like proteins. The binding is mediated by a 22-residue sequence of p62 containing an evolutionarily conserved motif. To monitor the autophagic sequestration of p62- and LC3-positive bodies, we developed a novel pH-sensitive fluorescent tag consisting of a tandem fusion of the red, acid-insensitive mCherry and the acid-sensitive green fluorescent proteins. This approach revealed that p62- and LC3-positive bodies are degraded in autolysosomes. Strikingly, even rather large p62-positive inclusion bodies (2 microm diameter) become degraded by autophagy. The specific interaction between p62 and LC3, requiring the motif we have mapped, is instrumental in mediating autophagic degradation of the p62-positive bodies. We also demonstrate that the previously reported aggresome-like induced structures containing ubiquitinated proteins in cytosolic bodies are dependent on p62 for their formation. In fact, p62 bodies and these structures are indistinguishable. Taken together, our results clearly suggest that p62 is required both for the formation and the degradation of polyubiquitin-containing bodies by autophagy.
The mechanistic target of rapamycin (mTOR) signaling pathway senses and integrates a variety of environmental cues to regulate organismal growth and homeostasis. The pathway regulates many major cellular processes and is implicated in an increasing number of pathological conditions, including cancer, obesity, type 2 diabetes, and neurodegeneration. Here, we review recent advances in our understanding of the mTOR pathway and its role in health, disease, and aging. We further discuss pharmacological approaches to treat human pathologies linked to mTOR deregulation.
Metabolic stress results in p53 activation, which can trigger cell-cycle arrest, ROS clearance, or apoptosis. However, what determines the p53-mediated cell fate decision upon metabolic stress is not very well understood. We show here that PGC-1α binds to p53 and modulates its transactivation function, resulting in preferential transactivation of proarrest and metabolic target genes. Thus glucose starvation results in p53-dependent cell-cycle arrest and ROS clearance, but abrogation of PGC-1α expression results in extensive apoptosis. Additionally, prolonged starvation results in PGC-1α degradation concomitant with induction of apoptosis. We have also identified RNF2, a Polycomb group (PcG) protein, as the cognate E3 ubiquitin ligase. Starvation of mice where PGC-1α expression is abrogated results in loss of p53-mediated ROS clearance, enhanced p53-dependent apoptosis, and consequent severe liver atrophy. These findings provide key insights into the role of PGC-1α in regulating p53-mediated cell fate decisions in response to metabolic stress.
Autophagy is the major intracellular degradation system by which cytoplasmic materials are delivered to and degraded in the lysosome. However, the purpose of autophagy is not the simple elimination of materials, but instead, autophagy serves as a dynamic recycling system that produces new building blocks and energy for cellular renovation and homeostasis. Here we provide a multidisciplinary review of our current understanding of autophagy's role in metabolic adaptation, intracellular quality control, and renovation during development and differentiation. We also explore how recent mouse models in combination with advances in human genetics are providing key insights into how the impairment or activation of autophagy contributes to pathogenesis of diverse diseases, from neurodegenerative diseases such as Parkinson disease to inflammatory disorders such as Crohn disease.
Metabolic homeostasis requires integration of multiple signals and cellular activities. Without this integration, conditions of obesity and diabetes often develop. Recent in vivo studies explore the molecular basis for metabolic homestasis, showing that p62 links autophagy and mTORC1 activation to regulate adipogenesis and energy control.
An antioxidant response element (ARE) or an electrophile responsive element (EpRE) regulate the transcriptional induction of a battery of drug-detoxifying enzymes that are protective against electrophiles. Based on the high similarity of the ARE consensus sequence to an erythroid gene regulatory element NF-E2 binding site, we have found that the transcription factor Nrf2 is indispensable for the ARE-mediated induction of drug-metabolizing enzymes. Recent genome-wide analysis demonstrated that Nrf2 regulates hundreds of genes that are involved in the cytoprotective response against oxidative stress. In-depth analysis of Nrf2 regulatory mechanisms has led us to the discovery of a novel protein, which we have named Keap1. Keap1 suppresses Nrf2 activity by specifically binding to its evolutionarily conserved N-terminal Neh2 regulatory domain. In this review article, we summarize the findings and observations that have lead to the discovery of the Nrf2-Keap1 system. Furthermore, we briefly discuss the function of the Nrf2-Keap1 system under the regulation of the endogenous electrophilic compound 15-deoxy-Δ¹²(,)¹⁴-prostaglandin J₂. We propose that Nrf2-Keap1 plays a significant physiological role in the response to endogenous, environmental, and pharmacological electrophiles.
In response to stress, cells can utilize several cellular processes, such as autophagy, which is a bulk-lysosomal degradation pathway, to mitigate damages and increase the chances of cell survival. Deregulation of autophagy causes upregulation of p62 and the formation of p62-containing aggregates, which are associated with neurodegenerative diseases and cancer. The Nrf2-Keap1 pathway functions as a critical regulator of the cell's defense mechanism against oxidative stress by controlling the expression of many cellular protective proteins. Under basal conditions, Nrf2 is ubiquitinated by the Keap1-Cul3-E3 ubiquitin ligase complex and targeted to the 26S proteasome for degradation. Upon induction, the activity of the E3 ubiquitin ligase is inhibited through the modification of cysteine residues in Keap1, resulting in the stabilization and activation of Nrf2. In this current study, we identified the direct interaction between p62 and Keap1 and the residues required for the interaction have been mapped to 349-DPSTGE-354 in p62 and three arginines in the Kelch domain of Keap1. Accumulation of endogenous p62 or ectopic expression of p62 sequesters Keap1 into aggregates, resulting in the inhibition of Keap1-mediated Nrf2 ubiquitination and its subsequent degradation by the proteasome. In contrast, overexpression of mutated p62, which loses its ability to interact with Keap1, had no effect on Nrf2 stability, demonstrating that p62-mediated Nrf2 upregulation is Keap1 dependent. These findings demonstrate that autophagy deficiency activates the Nrf2 pathway in a noncanonical cysteine-independent mechanism.
The endoplasmic reticulum (ER) is the major site in the cell for protein folding and trafficking and is central to many cellular functions. Failure of the ER's adaptive capacity results in activation of the unfolded protein response (UPR), which intersects with many different inflammatory and stress signaling pathways. These pathways are also critical in chronic metabolic diseases such as obesity, insulin resistance, and type 2 diabetes. The ER and related signaling networks are emerging as a potential site for the intersection of inflammation and metabolic disease.
Impaired selective turnover of p62 by autophagy causes severe liver injury accompanied by the formation of p62-positive inclusions and upregulation of detoxifying enzymes. These phenotypes correspond closely to the pathological conditions seen in human liver diseases, including alcoholic hepatitis and hepatocellular carcinoma. However, the molecular mechanisms and pathophysiological processes in these events are still unknown. Here we report the identification of a novel regulatory mechanism by p62 of the transcription factor Nrf2, whose target genes include antioxidant proteins and detoxification enzymes. p62 interacts with the Nrf2-binding site on Keap1, a component of Cullin-3-type ubiquitin ligase for Nrf2. Thus, an overproduction of p62 or a deficiency in autophagy competes with the interaction between Nrf2 and Keap1, resulting in stabilization of Nrf2 and transcriptional activation of Nrf2 target genes. Our findings indicate that the pathological process associated with p62 accumulation results in hyperactivation of Nrf2 and delineates unexpected roles of selective autophagy in controlling the transcription of cellular defence enzyme genes.
Although metabolic alterations have been observed in cancer for almost a century, only recently have the mechanisms underlying these changes been identified and the importance of metabolic transformation realized. p53 has been shown to respond to metabolic changes and to influence metabolic pathways through several mechanisms. The contributions of these activities to tumour suppression are complex and potentially rather surprising: some reflect the function of basal p53 levels that do not require overt activation and others might even promote, rather than inhibit, tumour progression.
The cysteine residue at the active site of peroxiredoxin (Prx) I, Prx II, or Prx III is reversibly hyperoxidized to cysteine sulfinic acid, with concomitant loss of peroxidase activity, during normal catalysis. Sulfiredoxin (Srx) is the enzyme responsible for reversing this hyperoxidation. We now show that the expression of Srx at both the mRNA and protein levels is increased markedly in the lungs of mice exposed to hyperoxia. This hyperoxia-induced expression of Srx was not evident in mice deficient in the transcription factor Nrf2, indicating an essential role for an Nrf2 signaling pathway in this effect. Hyperoxia also elicited the accumulation of the sulfinic form of the mitochondrial enzyme Prx III, but not that of the cytosolic enzymes Prx I or Prx II, in lung tissue. This selective hyperoxidation of Prx III is likely due either to mitochondria being the major site of the hyperoxia-induced production of reactive oxygen species or to the translocation of Srx from the cytosol into mitochondria being rate limiting for the reduction of sulfinic Prx III. Hyperoxia induced the degradation of Prx III in Nrf2-deficient mice but not in wild-type animals, suggesting that, in the absence of a sufficient amount of Srx, sulfinic Prx III is converted to a form that is susceptible to proteolysis.
The tumor suppressor p53 is activated upon genotoxic and oxidative stress and in turn inhibits cell proliferation and growth through induction of specific target genes. Cell growth is positively regulated by mTOR, whose activity is inhibited by the TSC1:TSC2 complex. Although genotoxic stress has been suggested to inhibit mTOR via p53-mediated activation of mTOR inhibitors, the precise mechanism of this link was unknown. We now demonstrate that the products of two p53 target genes, Sestrin1 and Sestrin2, activate the AMP-responsive protein kinase (AMPK) and target it to phosphorylate TSC2 and stimulate its GAP activity, thereby inhibiting mTOR. Correspondingly, Sestrin2-deficient mice fail to inhibit mTOR signaling upon genotoxic challenge. Sestrin1 and Sestrin2 therefore provide an important link between genotoxic stress, p53 and the mTOR signaling pathway.
Hepatic lipid synthesis is known to be regulated by food consumption. In rodents fasting decreases the synthesis of cholesterol as well as fatty acids. Refeeding a high carbohydrate/low fat diet enhances fatty acid synthesis by 5- to 20-fold above the fed state, whereas cholesterol synthesis returns only to the prefasted level. Sterol regulatory element binding proteins (SREBPs) are transcription factors that regulate genes involved in cholesterol and fatty acid synthesis. Here, we show that fasting markedly reduces the amounts of SREBP-1 and -2 in mouse liver nuclei, with corresponding decreases in the mRNAs for SREBP-activated target genes. Refeeding a high carbohydrate/low fat diet resulted in a 4- to 5-fold increase of nuclear SREBP-1 above nonfasted levels, whereas nuclear SREBP-2 protein returned only to the nonfasted level. The hepatic mRNAs for fatty acid biosynthetic enzymes increased 5- to 10-fold above nonfasted levels, a pattern that paralleled the changes in nuclear SREBP-1. The hepatic mRNAs for enzymes involved in cholesterol synthesis returned to the nonfasted level, closely following the pattern of nuclear SREBP-2 regulation. Transgenic mice that overproduce nuclear SREBP-1c failed to show the normal decrease in hepatic mRNA levels for cholesterol and fatty acid synthetic enzymes upon fasting. We conclude that SREBPs are regulated by food consumption in the mouse liver and that the decline in nuclear SREBP-1c upon fasting may explain in part the decrease in mRNAs encoding enzymes of the fatty acid biosynthetic pathway.
Obesity and its associated comorbidities are among the most prevalent and challenging conditions confronting the medical profession in the 21st century. A major metabolic consequence of obesity is insulin resistance, which is strongly associated with the deposition of triglycerides in the liver. Hepatic steatosis can either be a benign, noninflammatory condition that appears to have no adverse sequelae or can be associated with steatohepatitis: a condition that can result in end-stage liver disease, accounting for up to 14% of liver transplants in the US. Here we highlight recent advances in our understanding of the molecular events contributing to hepatic steatosis and nonalcoholic steatohepatitis.
Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis in the absence of a history of significant alcohol use or other known liver disease. Nonalcoholic steatohepatitis (NASH) is the progressive form of NAFLD. The Pathology Committee of the NASH Clinical Research Network designed and validated a histological feature scoring system that addresses the full spectrum of lesions of NAFLD and proposed a NAFLD activity score (NAS) for use in clinical trials. The scoring system comprised 14 histological features, 4 of which were evaluated semi-quantitatively: steatosis (0-3), lobular inflammation (0-2), hepatocellular ballooning (0-2), and fibrosis (0-4). Another nine features were recorded as present or absent. An anonymized study set of 50 cases (32 from adult hepatology services, 18 from pediatric hepatology services) was assembled, coded, and circulated. For the validation study, agreement on scoring and a diagnostic categorization ("NASH," "borderline," or "not NASH") were evaluated by using weighted kappa statistics. Inter-rater agreement on adult cases was: 0.84 for fibrosis, 0.79 for steatosis, 0.56 for injury, and 0.45 for lobular inflammation. Agreement on diagnostic category was 0.61. Using multiple logistic regression, five features were independently associated with the diagnosis of NASH in adult biopsies: steatosis (P = .009), hepatocellular ballooning (P = .0001), lobular inflammation (P = .0001), fibrosis (P = .0001), and the absence of lipogranulomas (P = .001). The proposed NAS is the unweighted sum of steatosis, lobular inflammation, and hepatocellular ballooning scores. In conclusion, we present a strong scoring system and NAS for NAFLD and NASH with reasonable inter-rater reproducibility that should be useful for studies of both adults and children with any degree of NAFLD. NAS of > or =5 correlated with a diagnosis of NASH, and biopsies with scores of less than 3 were diagnosed as "not NASH."
Polyphenols are characterized by the presence of more than one phenolic group and are widely distributed in many fruits and vegetables. They possess antioxidant properties and interact with cellular defense systems through the antioxidant-responsive element/electrophile-responsive element (ARE/EpRE) although the precise mechanism by which polyphenols influence transcription factor complexes to target ARE is poorly understood. In the present study, we chose a typical polyphenol, quercetin, to investigate the mechanism in human HepG2 cells. Quercetin enhanced the ARE binding activity and Nrf2-mediated transcription activity. Molecular evidence revealed that quercetin not only up-regulated the expression of Nrf2 mRNA and protein, but also stabilized Nrf2 protein by inhibiting the ubiquitination and proteasomal turnover of Nrf2. At the same time, quercetin markedly reduced the level of Keap1 protein in posttranslational levels through the formation of modified Keap1 protein, rather than 26S proteasome-dependent degradation mechanisms, without affecting the dissociation of Keap1-Nrf2. Silencing Keap1 using Keap1 siRNA significantly increased the Nrf2-dependent ARE activity, whereas silencing Nrf2 using Nrf2 siRNA markedly reduced the ARE activity under both baseline and quercetin-induced conditions. Thus, we conclude that the pathway of quercetin-induced ARE activity involves up-regulation of Nrf2 through the regulation of both transcription and posttranscription sites and repression of Keap1 by affecting the posttranscription site, revealing some substantial differences between oxidative inducers. Thus, the findings provide an insight into the mechanisms underlying polyphenolic compounds in cytoprotection and cancer chemoprevention.
Mammalian target of rapamycin, mTOR, is a major sensor of nutrient and energy availability in the cell and regulates a variety of cellular processes, including growth, proliferation, and metabolism. Loss of the tuberous sclerosis complex genes (TSC1 or TSC2) leads to constitutive activation of mTOR and downstream signaling elements, resulting in the development of tumors, neurological disorders, and at the cellular level, severe insulin/IGF-1 resistance. Here, we show that loss of TSC1 or TSC2 in cell lines and mouse or human tumors causes endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR). The resulting ER stress plays a significant role in the mTOR-mediated negative-feedback inhibition of insulin action and increases the vulnerability to apoptosis. These results demonstrate ER stress as a critical component of the pathologies associated with dysregulated mTOR activity and offer the possibility to exploit this mechanism for new therapeutic opportunities.
DeCaprio for Rbx1 mutants, and T. Johansen for p62 mutants. This work was supported by National Honor Scientist program grant 2006-05106 and Bio R&D program grant
- + Mefs
- D Kwiatkowsky
- Mefs
- M Komatsu
- M Lee
- + Atg
- M Mefs
- D Hannink
- Rbx1 Zhang
- J Keap1 Cdnas
+/+ and p62 À/À MEFs, D. Kwiatkowsky for TSC2 +/+ and TSC2 À/À MEFs, M. Komatsu and M. Lee for Atg7 +/+ and Atg7 À/À MEFs, M. Hannink and D. Zhang for Rbx1 and Keap1 cDNAs, J. DeCaprio for Rbx1 mutants, and T. Johansen for p62 mutants. This work was supported by National Honor Scientist program grant 2006-05106 and Bio R&D program grant M10642040001-07N4204-00110 (S.G.R.) as well as the BK21 program of the Korean government (S.H.B. and H.E.L.).