[Show abstract][Hide abstract] ABSTRACT: The Set8/PR-Set7/KMT5a methyltransferase plays critical roles in governing transcriptional regulation, cell cycle progression and tumorigenesis. Although CRL4(Cdt2) was reported to regulate Set8 stability, deleting the PIP motif only led to partial resistance to ultraviolet-induced degradation of Set8, indicating the existence of additional E3 ligase(s) controlling Set8 stability. Furthermore, it remains largely undefined how DNA damage-induced kinase cascades trigger the timely destruction of Set8 to govern tumorigenesis. Here, we report that SCF(β-TRCP) earmarks Set8 for ubiquitination and degradation in a casein kinase I-dependent manner, which is activated by DNA-damaging agents. Biologically, both CRL4(Cdt2) and SCF(β-TRCP)-mediated pathways contribute to ultraviolet-induced Set8 degradation to control cell cycle progression, governing the onset of DNA damage-induced checkpoints. Therefore, like many critical cell cycle regulators including p21 and Cdt1, we uncover a tight regulatory network to accurately control Set8 abundance. Our studies further suggest that aberrancies in this delicate degradation pathway might contribute to aberrant elevation of Set8 in human tumours.
Preview · Article · Dec 2015 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: S1, a novel BH3 mimetic, can induce apoptosis dependent on Bax/Bak through inhibition of Bcl-2 in various tumors. S1 also induces autophagy through interrupting the interaction of Bcl-2 and Beclin1. Our results showed that S1 induces apoptosis in human ovarian cancer SKOV3 cells in a time- and dose-dependent manner. Autophagy precedes apoptosis, in SKOV3 cells treated with S1 (6 μmol/L), autophagy reached the maximum peak at 12 h after treatment and decreased to 24 h. In SKOV3 cells treated with different concentrations of S1 for 24 h, the highest level of autophagy was observed with 5 μmol/L and decreased to 10 μmol/L. Autophagy inhibitors 3-MA and CQ enhanced apoptosis induced by S1 in SKOV3 cells. However, overactivation of caspases in apoptosis induced by S1 may inhibit the autophagy-inducing function of Beclin1. Because the pan-caspase inhibitor Z-VAD recovered the autophagy-inducing function of Beclin1 through reduction of activated caspase-mediated cleavage of Beclin1. Furthermore, the Beclin1 cleavage products could further increase apoptosis induced by S1 in SKOV3 cells. This indicates that apoptosis induced by high doses and long exposure of S1 causes the overactivation of caspases and subsequent cleavage of Beclin1, and inhibits the protection of autophagy. Moreover, the cleaved product of Beclin1 further promotes apoptosis induced by S1 in SKOV3 cells. Our results suggest this may be a molecular mechanism for enhancing the sensitivity of cancer cells to apoptosis induced by small molecular compound targeting Bcl-2.
[Show abstract][Hide abstract] ABSTRACT: The mechanism of cisplatin resistance in ovarian cancer is not fully understood. In the present study, we showed a critical role for endoplasmic reticulum (ER) stress tolerance in mediating cisplatin resistance in human ovarian cancer cells. We found cisplatin to inhibit the proliferation of two ovarian cancer cell lines: cisplatin-sensitive SKOV3 cells and cisplatin‑resistant SKOV3/DDP cells. However, the effect was greater in the cisplatin-sensitive SKOV3 cells. Cisplatin treatment induced ER stress in the SKOV3 cells but not in the SKOV3/DDP cells. Cisplatin-induced Ca2+ flow from the ER into mitochondria caused mitochondrial calcium overload, which amplified proapoptotic signaling in the cisplatin-sensitive SKOV3 cells. ER stress-mediated apoptosis and mitochondrial pathway-dependent apoptosis were induced in the cisplatin-sensitive SKOV3 cells, but not in the cisplatin-resistant SKOV3/DDP cells. Moreover, there were more ER-mitochondria contacts in the cisplatin-treated SKOV3 cells. Collectively, our data indicated that tolerance to cisplatin-induced ER stress inhibits ER stress-mediated apoptosis, prevents an imbalance in ER and mitochondrial calcium homeostasis and maintains cell survival, thus leading to cisplatin resistance in ovarian cancer cells.
No preview · Article · Sep 2015 · Oncology Reports
[Show abstract][Hide abstract] ABSTRACT: Lysosomes are involved in promoting resistance of cancer cells to chemotherapeutic agents. However, the mechanisms underlying lysosomal influence of cisplatin resistance in ovarian cancer remain incompletely understood. We report that, compared with cisplatin-sensitive SKOV3 cells, autophagy increases in cisplatin-resistant SKOV3/DDP cells treated with cisplatin. Inhibition of early‑stage autophagy enhanced cisplatin-mediated cytotoxicity in SKOV3/DDP cells, but autophagy inhibition at a later stage by disturbing autophagosome-lysosome fusion is more effective. Notably, SKOV3/DDP cells contained more lysosomes than cisplatin‑sensitive SKOV3 cells. Abundant lysosomes and lysosomal cathepsin D activity were required for continued autolysosomal degradation and maintenance of autophagic flux in SKOV3/DDP cells. Furthermore, SKOV3/DDP cells contain abundant lysosomal ATP required for lysosomal function, and inhibition of lysosomal ATP accumulation impaired lysosomal function and blocked autophagic flux. Therefore, our findings suggest that lysosomes at least partially contribute to cisplatin resistance in ovarian cancer cells through their role in cisplatin-induced autophagic processes, and provide insight into the mechanism of cisplatin resistance in tumors.
No preview · Article · Sep 2015 · International Journal of Oncology
[Show abstract][Hide abstract] ABSTRACT: Nuclear factor-κB (NF-κB) is constitutively activated in most malignant gliomas and is involved in cancer progression and drug resistance to chemotherapy. Sulfasalazine (SAS) is a classic inhibitor of NF-κB. Apoptosis and autophagy were induced by SAS accompanied by inhibition of NF-κB signaling in U251 cells. Inhibition of autophagy by 3-MA suppressed the effects of SAS on NF-κB signaling and apoptosis in U251 cells. Multifunctional scaffold protein p62 is well known as an autophagy marker protein and provides crosstalk for important signaling pathways, including NF-κB signaling. SAS-induced decrease in the p62 protein levels may be the result of degradation through autophagy. SAS induced the inhibition of NF-κB signaling and apoptosis at least partly via a p62-dependent effect in U251 cells. Collectively, our data shed light on the link between p62 and the NF-κB signaling pathway, particularly in glioma cells. The results may facilitate the design of more effective targeted therapies for the treatment of tumors in which NF-κB signaling is altered.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to identify critical gene pathways that are associated with lung cancer metastasis to the brain.
The RNA-Seq approach was used to establish the expression profiles of a primary lung cancer, adjacent benign tissue, and metastatic brain tumor from a single patient. The expression profiles of these three types of tissues were compared to define differentially expressed genes, followed by serial-cluster analysis, gene ontology analysis, pathway analysis, and knowledge-driven network analysis. Reverse transcription-polymerase chain reaction (RT-PCR) was used to validate the expression of essential candidate genes in tissues from ten additional patients.
Differential gene expression among these three types of tissues was classified into multiple clusters according to the patterns of their alterations. Further bioinformatic analysis of these expression profile data showed that the network of the signal transduction pathways related to actin cytoskeleton reorganization, cell migration, and adhesion was associated with lung cancer metastasis to the brain. The expression of ACTN4 (actinin, alpha 4), a cytoskeleton protein gene essential for cytoskeleton organization and cell motility, was significantly elevated in the metastatic brain tumor but not in the primary lung cancer tissue.
The signaling pathways involved in the regulation of cytoskeleton reorganization, cell motility, and focal adhesion play a role in the process of lung cancer metastasis to the brain. The contribution of ACTN4 to the process of lung cancer metastasis to the brain could be mainly through regulation of actin cytoskeleton reorganization, cell motility, and focal adhesion.
[Show abstract][Hide abstract] ABSTRACT: Hyperbaric oxygen (HBO) is emerging as a therapy for brain ischemia, although its benefits are still debated. The present study aimed to investigate the effect of HBO on brain damage in a rat model of transient focal cerebral ischemia and its underlying mechanism of action. Male Wistar rats, which had suffered 1.5 h of transient middle cerebral artery occlusion (tMCAO) and had a Longa’s neuron score of 3, were given pure oxygen at 3.0 atm absolute, for 60 minutes after the third hour of reperfusion. After 24 h of reperfusion, rat brains were removed and studied. 2,3,5-triphenyltetrazolium chloride (TTC) and hematoxylin and eosin staining revealed that the infarct ratio in the HBO group increased remarkably when compared with the MCAO group. Up-regulation of extracellular signal-regulated kinase 1/2 (ERK1/2) activation was detected in the HBO group because of reactive oxygen species (ROS) generation. Autophagy appeared to be obstructed in the HBO group. Administration of the ERK1/2 inhibitor U0126 decreased the infarct ratio and improved protein clearance by autophagy in the HBO group. Collectively, these results suggest that HBO enlarges the area of brain damage via reactive oxygen species-induced activation of ERK1/2, which interrupts autophagy flux.
No preview · Article · Apr 2014 · European journal of pharmacology
[Show abstract][Hide abstract] ABSTRACT: Metastasis suppressor 1 (MTSS1) is an important tumor suppressor protein, and loss of MTSS1 expression has been observed in several types of human cancers. Importantly, decreased MTSS1 expression is associated with more aggressive forms of breast and prostate cancers, and with poor survival rate. Currently, it remains unclear how MTSS1 is regulated in cancer cells, and whether reduced MTSS1 expression contributes to elevated cancer cell proliferation and migration. Here we report that the SCFβ-TRCP regulates MTSS1 protein stability by targeting it for ubiquitination and subsequent destruction via the 26S proteasome. Notably, depletion of either Cullin 1 or β-TRCP1 led to increased levels of MTSS1. We further demonstrated a crucial role for Ser322 in the DSGXXS degron of MTSS1 in governing SCFβ-TRCP-mediated MTSS1 degradation. Mechanistically, we defined that Casein Kinase Iδ (CKIδ) phosphorylates Ser322 to trigger MTSS1's interaction with β-TRCP for subsequent ubiquitination and degradation. Importantly, introducing wild-type MTSS1 or a non-degradable MTSS1 (S322A) into breast or prostate cancer cells with low MTSS1 expression significantly inhibited cellular proliferation and migration. Moreover, S322A-MTSS1 exhibited stronger effects in inhibiting cell proliferation and migration when compared to ectopic expression of wild-type MTSS1. Therefore, our study provides a novel molecular mechanism for the negative regulation of MTSS1 by β-TRCP in cancer cells. It further suggests that preventing MTSS1 degradation could be a possible novel strategy for clinical treatment of more aggressive breast and prostate cancers.
[Show abstract][Hide abstract] ABSTRACT: Neural stem cells (NSCs) are usually affected by a number of biological functions in neural traumatic and degenerative diseases. Autophagy may be involved in these diseases. However, whether autophagy could affect NSCs is largely unknown. Therefore, we aimed to investigate intracellular microstructures, proliferation, axon extension, and Beclin-1 expression of rat NSCs by basic culture medium and conditioned medium without epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF). Transmission electron microscopy showed the formation of autophagic vacuoles in conditioned medium. Compared to the control group with normal medium, the number of secondary neurosphere was significantly reduced whereas the expression of Beclin-1 was enhanced. The majority of NSCs were nestin-positive when EGF/bFGF was withdrawn for 3 days and showed enhanced neurite extension, which was suppressed by autophagy antagonist 3-methyladenine. Our findings revealed that a short-term paucity of mitogens in microenvironments could induce autophagy of NSCs, which facilitated NSCs' axonal growth.
No preview · Article · Jul 2013 · Journal of Biochemical and Molecular Toxicology
[Show abstract][Hide abstract] ABSTRACT: Abstract Primary objective: p62/ZIP as the autophagy receptor can transport the misfolded proteins to a macroautophagy-lysosome system for degradation and also create a positive feedback loop between p62/ZIP and Nrf2. However, the role of p62/ZIP on cerebral ischaemia is unclear. The aim of this study was to evaluate the role of p62/ZIP in the regulation of endoplasmic reticulum(ER) stress induced by cerebral ischaemia/reperfusion. Research design: Different ischemic periods were designed by transient middle cerebral artery occlusion (tMCAO) using the suture method. Methods and procedures: At 24 hours after reperfusion, the ischaemic brain tissue was studied histologically and biochemically for autophagic, ER stress and Keap1-Nrf2-ARE signalling pathway markers. Main outcomes and results: Prolongation of ischaemia significantly increased the cortical injury observed in rats and was associated with a gradual increase in the protein expression of ubiquitin-aggregates, Grp78, GADD153/CHOP and p62/ZIP. Autophagy marker Atg12-Atg5 and LC3-PE increased and then decreased. Moreover, p62/ZIP mRNA expression increased and then decreased and was consistent with Nrf2 activation. Conclusions: p62/ZIP not only plays a key role in scavenging protein aggregates during autophagy, but it may also be involved in preventing oxidative injury and alleviating ER stress through the Keap1-Nrf2-ARE signalling pathway during cerebral ischaemia/reperfusion injury.
[Show abstract][Hide abstract] ABSTRACT: Diabetes mellitus (DM) is a chronic metabolic disease, and its incidence is growing worldwide. The endoplasmic reticulum (ER) is a central component of cellular functions and is involved in protein folding and trafficking, lipid synthesis, and maintenance of calcium homeostasis. The ER is also a sensor of both intra- and extracellular stress and thus participates in monitoring and maintaining cellular homeostasis. Therefore, the ER is one site of interaction between environmental signals and a cell's biological function. The ER is tightly linked to autophagy, inflammation, and apoptosis, and recent evidence suggests that these processes are related to the pathogenesis of DM and its complications. Thus, the ER has been considered an intersection integrating multiple stress responses and playing an important role in metabolism-related diseases including DM. Here, we review the relationship between the ER and autophagy, inflammation, and apoptosis in DM to better understand the molecular mechanisms of this disease.
Preview · Article · May 2013 · Journal of Diabetes Research
[Show abstract][Hide abstract] ABSTRACT: Cadmium (Cd) is an important nephrotoxic pollutant. To examine late effects on the kidney of individuals previously exposed to chronic Cd at very low levels, male Wistar rats were given 20 nmol/kg i.p. injections of Cd every other day for 4 weeks. At the 20(th), 28(th), 36(th), 44(th) and 52(nd) week of the study, renal metal accumulation, morphology and function were examined. Immunochemical staining was performed to detect renal 3-nitrotyrosine (3-NT) accumulation, metallothionein (MT) expression, cell proliferation and global DNA methylation. Results showed that renal Cd concentration and MT expression along with 3-NT accumulation were significantly higher in the Cd group than that in the control. Histopathologically renal tubule damage at the early stage and hyperplasia at the late stage were observed in the Cd group. Renal fibrosis in glomeruli was evident in the Cd group, particularly at the late stage of the study. Immunoreactivity of global DNA methylation was markedly diminished in the Cd group at both 20(th) and 52(nd) weeks. These results suggest that previous exposure to chronic Cd at very low level induced persistent damaging effects on the kidney along with increases in cell proliferation and global DNA hypomethylation.
[Show abstract][Hide abstract] ABSTRACT: CLIC4/mtCLIC (referred to here as CLIC4) is one of the seven-member family of chloride intracellular channels (CLIC). CLIC4 localizes to the mitochondria, nucleus, cytoplasm and other organellular compartments and participates in the apoptotic response to stress. However, the role of CLIC4 in oxidative stress and apoptosis is not well understood. In this study, we showed the important role of CLIC4 in apoptosis of C6 glioma cells induced by hydrogen peroxide (H2O2). Our results showed that CLIC4 protein expression was upregulated following H2O2-induced C6 cell apoptosis. The upregulation of CLIC4 protein expression was paralleled with an increased Bax/Bcl-2 ratio, cytochrome c and cleaved caspase-3 protein expression upon H2O2-induced C6 cell apoptosis. Suppression of CLIC4 expression by RNA interference enhanced cell apoptosis, but the ratio of Bax/Bcl-2 was not involved in this process. Dissipation of mitochondrial membrane potential and nuclear translocation of CLIC4 were involved in the activation of apoptosis induced by H2O2. Our data indicate that CLIC4 protein may be a key element in the apoptotic response to oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: NaYF4:Yb3+,Er3+@Ag core–shell nanocomposites were prepared. Due to the outer shell of Ag, some modifications were found on the upconversion (UC) processes of NaYF4:Yb3+,Er3+ core nanoparticles (NPs) caused by the co-interaction of surface effect, surface plasma absorption effect and local thermal effect under infrared radiation. Upon 980 nm excitation, the relative UC intensity of the green (2H11/2, 4S3/2–4I15/2) to red (4F9/2–4I15/2) and the slope of power-dependence increased intensively, and three-photon population process for the green level appeared.
No preview · Article · Jan 2013 · Materials Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Rabies is an acute viral infection of the central nervous system (CNS) and is typically fatal in humans and animals; however, its pathogenesis remains poorly understood. In this study, the morphological changes of dendrites and dendritic spines in the CA1 region of the hippocampus were investigated in mice that were intracerebrally infected with an MRV strain of the street rabies virus. Hematoxylin-eosin and fluorescent staining analysis of brain sections from the infected mice showed very little morphological changes of neuronal bodies and neuronal processes. However, we found a significant decrease in the number of dendritic spines. Primary neuronal cultures derived from the hippocampus of mice (embryonic day 16.5) that were infected with the virus also showed an obvious decrease in the number of dendritic spines. Furthermore, the decrease in the number of dendritic spines was related to the depolymerization of actin filaments (F-actin). We propose that the observed structural changes can partially explain the severe clinical disease that was found in experimental models of street rabies virus infections.
Full-text · Article · Oct 2012 · Journal of General Virology
[Show abstract][Hide abstract] ABSTRACT: CLIC4/mtCLIC, a chloride intracellular channel protein, localizes to mitochondria, endoplasmic reticulum (ER), nucleus and cytoplasm, and participates in the apoptotic response to stress. Apoptosis and autophagy, the main types of the programmed cell death, seem interconnected under certain stress conditions. However, the role of CLIC4 in autophagy regulation has yet to be determined. In this study, we demonstrate upregulation and nuclear translocation of the CLIC4 protein following starvation in U251 cells. CLIC4 siRNA transfection enhanced autophagy with increased LC3-II protein and puncta accumulation in U251 cells under starvation conditions. In that condition, the interaction of the 14-3-3 epsilon isoform with CLIC4 was abolished and resulted in Beclin 1 overactivation, which further activated autophagy. Moreover, inhibiting the expression of CLIC4 triggered both mitochondrial apoptosis involved in Bax/Bcl-2 and cytochrome c release under starvation and endoplasmic reticulum stress-induced apoptosis with CHOP and caspase-4 upregulation. These results demonstrate that CLIC4 nuclear translocation is an integral part of the cellular response to starvation. Inhibiting the expression of CLIC4 enhances autophagy and contributes to mitochondrial and ER stress-induced apoptosis under starvation.