[Show abstract][Hide abstract] ABSTRACT: PKCβII controls the pathologic features of diabetic nephropathy, including glomerular mesangial cell hypertrophy. PKCβII contains the C-terminal hydrophobic motif site Ser-660. Whether this hydrophobic motif phosphorylation contributes to high glucose-induced mesangial cell hypertrophy has not been determined. Here we show that in mesangial cells, high glucose-increased phosphorylation of PKCβII at Ser-660 in a PI 3 kinase-dependent manner. Using siRNAs to downregulate PKCβII, dominant negative PKCβII and PKCβII hydrophobic motif phosphorylation deficient mutant, we found that PKCβII regulates activation of mTORC1 and mesangial cell hypertrophy by high glucose. PKCβII via its phosphorylation at Ser-660 regulated phosphorylation of Akt at both catalytic loop and hydrophobic motif sites, resulting in phosphorylation and inactivation of its substrate PRAS40. Specific inhibition of mTORC2 increased mTORC1 activity and induced mesangial cell hypertrophy. In contrast, inhibition of mTORC2 decreased the phosphorylation of PKCβII and Akt, leading to inhibition of PRAS40 phosphorylation and mTORC1 activity and prevented mesangial cell hypertrophy in response to high glucose; expression of constitutively active Akt or mTORC1 restored mesangial cell hypertrophy. Moreover, constitutively active PKCβII reversed the inhibition of high glucose-stimulated Akt phosphorylation and mesangial cell hypertrophy induced by suppression of mTORC2. Finally, using renal cortices from type 1 diabetic mice, we found that increased phosphorylation of PKCβII at Ser-660 was associated with enhanced Akt phosphorylation, and mTORC1 activation. Collectively, our findings identify a signaling route connecting PI 3 kinase to mTORC2 to phosphorylate PKCβII at the hydrophobic motif site necessary for Akt phosphorylation and mTORC1 activation, leading to mesangial cell hypertrophy.
Preview · Article · Jan 2016 · AJP Cell Physiology
[Show abstract][Hide abstract] ABSTRACT: Bone remodeling is controlled by dual actions of osteoclasts (OC) and osteoblasts (OB). The calcium sensitive NFATc1 transcription factor, as an OC signature gene, regulates differentiation of OC downstream of BMP-2-stimulated osteoblast-coded factors. To analyze a functional link between BMP-2 and NFATc1 we analyzed bones from the OB-specific BMP-2 knock out (BMP-2 cKO) mice for NFATc1 expression by immunohistochemical staining and found significant reduction in NFATc1 expression. This indicated a requirement of BMP-2 for NFATc1 expression in OB. We showed that BMP-2, via receptor-specific Smad pathway, regulates expression of NFATc1 in OB. PI 3 kinase/Akt signaling acting downstream of BMP-2 also drives NFATc1 expression and transcriptional activation. Under basal condition, NFATc1 is phosphorylated. Activation of NFAT requires dephosphorylation by calcium-dependent serine threonine phosphatase, calcineurin. We examined the role of calcium in BMP-2-stimulated regulation of NFATc1 in osteoblasts. BAPTA-AM, an inhibitor of intracellular calcium abundance blocked BMP-2-induced transcription of NFATc1. Interestingly, BMP-2 induced calcium release from intracellular stores and increased calcineurin phosphatase activity resulting in NFATc1 nuclear translocation. Cyclosporine A (CSA), which inhibits calcineurin upstream of NFATc1, blocked BMP-2-induced NFATc1 mRNA and protein expression. Expression of NFATc1 directly increased its transcription and VIVIT peptide, an inhibitor of NFATc1, suppressed BMP-2-stimulated NFATc1 transcription confirming its autoregulation. Together these data show a role of NFATc1 downstream of BMP-2 in mouse bone development and provide novel evidence for the presence of a cross-talk between Smad, PI 3 kinase/Akt and Ca(2+) signaling for BMP-2-induced NFATc1 expression through an autoregulatory loop.
Full-text · Article · Oct 2015 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: We examined the effect of rapamycin on the life span of a mouse model of type 2 diabetes, db/db mice. At 4 months of age, male and female C57BLKSJ-lepr
db/db mice (db/db) were placed on either a control diet, lacking rapamycin or a diet containing rapamycin and maintained on these diets over
their life span. Rapamycin was found to reduce the life span of the db/db mice. The median survival of male db/db mice fed the control and rapamycin diets was 349 and 302 days, respectively, and
the median survival of female db/db mice fed the control and rapamycin diets was 487 and 411 days, respectively. Adjusting for gender differences, rapamycin
increased the mortality risk 1.7-fold in both male and female db/db mice. End-of-life pathological data showed that suppurative inflammation was the main cause of death in the db/db mice, which is enhanced slightly by rapamycin treatment.
Full-text · Article · Oct 2015 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Increase in protein synthesis contributes to kidney hypertrophy and matrix protein accumulation in diabetes. We have previously
shown that high glucose-induced matrix protein synthesis is associated with inactivation of glycogen synthase kinase 3β (GSK3β)
in renal cells and in the kidneys of diabetic mice. We tested whether activation of GSK3β by sodium nitroprusside (SNP) mitigates
kidney injury in diabetes. Studies in kidney-proximal tubular epithelial cells showed that SNP abrogated high glucose-induced
laminin increment by stimulating GSK3β and inhibiting Akt, mTORC1, and events in mRNA translation regulated by mTORC1 and
ERK. NONOate, an NO donor, also activated GSK3β, indicating that NO may mediate SNP stimulation of GSK3β. SNP administered
for 3 weeks to mice with streptozotocin-induced type 1 diabetes ameliorated kidney hypertrophy, accumulation of matrix proteins,
and albuminuria without changing blood glucose levels. Signaling studies showed that diabetes caused inactivation of GSK3β
by activation of Src, Pyk2, Akt, and ERK; GSK3β inhibition activated mTORC1 and downstream events in mRNA translation in the
kidney cortex. These reactions were abrogated by SNP. We conclude that activation of GSK3β by SNP ameliorates kidney injury
induced by diabetes.
No preview · Article · Oct 2014 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Enhanced TGFβ activity contributes to the accumulation of matrix proteins including collagen I (α2) by proximal tubular epithelial cells in progressive kidney disease. Although TGFβ rapidly activates its canonical Smad signaling pathway, it also recruits noncanonical pathway involving mTOR kinase to regulate renal matrix expansion. The mechanism by which chronic TGFβ treatment maintains increased mTOR activity to induce the matrix protein collagen I (α2) expression is not known. Deptor is an mTOR interacting protein that suppresses mTOR activity in both mTORC1 and mTORC2. In proximal tubular epithelial cells, TGFβ reduced deptor levels in a time-dependent manner with concomitant increase in both mTORC1 and mTORC2 activities. Expression of deptor abrogated activity of mTORC1 and mTORC2, resulting in inhibition of collagen I (α2) mRNA and protein expression via transcriptional mechanism. In contrast, neutralization of endogenous deptor by shRNAs increased activity of both mTOR complexes and expression of collagen I (α2) similar to TGFβ treatment. Importantly, downregulation of deptor by TGFβ increased the expression of Hif1α by increasing translation of its mRNA. TGFβ-induced deptor downregulation promotes Hif1α binding to its cognate hypoxia responsive element in the collagen I (α2) gene to control its protein expression via direct transcriptional mechanism. Interestingly, knockdown of raptor to specifically block mTORC1 activity significantly inhibited expression of collagen I (α2) and Hif1α while inhibition of rictor to prevent selectively mTORC2 activation did not have any effect. Critically, our data provide evidence for the requirement of TGFβ-activated mTORC1 only by deptor downregulation, which dominates upon the bystander mTORC2 activity for enhanced expression of collagen I (α2). Our results also suggest the presence of a safeguard mechanism involving deptor-mediated suppression of mTORC1 activity against developing TGFβ-induced renal fibrosis.
[Show abstract][Hide abstract] ABSTRACT: High glucose-induced Akt acts as a signaling hub for mesangial cell hypertrophy and matrix expansion that are recognized as cardinal signatures for development of diabetic nephropathy. How mesangial cells sustain the activated state of Akt is not clearly understood. Here we show Akt-dependent phosphorylation of the transcription factor FoxO1 by high glucose. Phosphorylation deficient constitutively active FoxO1 inhibited high glucose-induced phosphorylation of Akt to suppress phosphorylation/inactivation of PRAS40 and mTORC1 activity. In contrast, dominant negative FoxO1 increased phosphorylation of Akt resulting in increased mTORC1 activity similar to high glucose treatment. Notably, FoxO1 regulates high glucose-induced protein synthesis, hypertrophy and, expression of fibronectin and PAI-1. High glucose paves the way for complications of diabetic nephropathy through production of reactive oxygen species (ROS). We considered whether the FoxO1 target antioxidant enzyme catalase contributes to sustained activation of Akt. High glucose-inactivated FoxO1 decreases the expression of catalase to increase production of ROS. Moreover, we show that catalase blocks high glucose-stimulated Akt phosphorylation to attenuate inactivation of FoxO1 and PRAS40, resulting in inhibition of mTORC1 and mesangial cell hypertrophy, and, fibronectin and PAI-1 expression. Finally, using kidney cortex from type 1 diabetic OVE26 mice, we show that increased FoxO1 phosphorylation is associated with decreased catalase expression and increased fibronectin and PAI-1 expression. Together our results provide the first evidence for the presence of a positive feedback loop for sustained activation of Akt involving inactivated FoxO1 and decrease in catalase expression, leading to increased ROS and mesangial cell hypertrophy and matrix protein expression.
No preview · Article · Oct 2014 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Renal cancer metastasis may result from oncogenic forces that contribute to the primary tumor. We have recently identified microRNA-21 as an oncogenic driver of renal cancer cells. The mechanism by which miR-21 controls renal cancer cell invasion is poorly understood. We show that miR-21 directly downregulates the proapoptotic protein PDCD4 to increase migration and invasion of ACHN and 786-O renal cancer cells as a result of phosphorylation/activation of Akt and IKKβ, which activate NFκB-dependent transcription. Constitutively active (CA) Akt or CA IKKβ blocks PDCD4-mediated inhibition and restores renal cancer cell migration and invasion. PDCD4 inhibits mTORC1 activity, which was reversed by CA IKKβ. Moreover, CA mTORC1 restores cell migration and invasion inhibited by PDCD4- and dominant negative IKKβ. Moreover, PDCD4 negatively regulates mTORC2-dependent Akt phosphorylation upstream of this cascade. We show that PDCD4 forms a complex with rictor, an exclusive component of mTORC2, and that this complex formation is reduced in renal cancer cells due to increased miR-21 expression resulting in enhanced phosphorylation of Akt. Thus our results identify a previously unrecognized signaling node where high miR-21 levels reduce rictor-PDCD4 interaction to increase phosphorylation of Akt and contribute to metastatic fitness of renal cancer cells.
No preview · Article · Jul 2014 · Experimental Cell Research
[Show abstract][Hide abstract] ABSTRACT: Platelet-derived growth factor BB and its receptor (PDGFRβ) play pivotal role in development of renal glomerular mesangial cells. Their roles in increased mesangial cell proliferation during mesangioproliferative glomerulonephritis have long been noted; but the signaling mechanism regulating these changes remains poorly understood. We examined the role of a recently identified MAPK, Erk5, in this process. PDGF increased the activating phosphorylation of Erk5 and tyrosine phosphorylation of proteins in a time-dependent manner. A pharmacologic inhibitor of Erk5, XMD8-92, abrogated PDGF-induced DNA synthesis and mesangial cell proliferation. Similarly, expression of dominant negative Erk5 or siRNAs against Erk5 blocked PDGF-stimulated DNA synthesis and proliferation. Inhibition of Erk5 attenuated expression of cyclin D1 mRNA and protein, resulting in suppression of CDK4-mediated phosphorylation of the tumor suppressor protein pRb. Expression of cyclin D1 or CDK4 prevented the dominant negative Erk5- or siErk5-mediated inhibition of DNA synthesis and mesangial cell proliferation induced by PDGF. We have previously shown that PI 3 kinase contributes to PDGF-induced proliferation of mesangial cells. Inhibition of PI 3 kinase blocked PDGF-induced phosphorylation of Erk5. Since PI 3 kinase acts through Akt, we determined the role of Erk5 on Akt phosphorylation. XMD8-92, dominant negative Erk5 and siErk5 inhibited phosphorylation of Akt by PDGF. Interestingly, we found inhibition of PDGF-induced Erk5 phosphorylation by a pharmacological inhibitor of Akt kinase and kinase dead Akt in mesangial cells. Thus our data unfold the presence of a positive feedback microcircuit between Erk5 and Akt downstream of PI 3 kinase nodal point for PDGF-induced mesangial cell proliferation.
[Show abstract][Hide abstract] ABSTRACT: Increase in matrix protein content in the kidney is a cardinal feature of diabetic kidney disease. While renal matrix protein content is increased by chronic hyperglycemia, whether it is regulated by acute elevation of glucose and insulin has not been addressed. In this study, we aimed to evaluate if short duration of combined hyperglycemia and hyperinsulinemia, mimicking metabolic environment of pre-diabetes and early type 2 diabetes, induces kidney injury. Normal rats were subjected to either saline infusion (control, n=4) or seven hours of combined hyperglycemic-hyperinsulinemic clamp (HG+HI clamp; n=6). During the clamp, plasma glucose and plasma insulin were maintained at about 350 mg/dl and 16 ng/ml, respectively. HG+HI clamp increased the expression of renal cortical TGFβ and renal matrix proteins, laminin and fibronectin. This was associated with the activation of SMAD3, Akt, mTOR complexes and Erk signaling pathways and their downstream target events in the initiation and elongation phases of mRNA translation, an important step in protein synthesis. Additionally, HG+HI clamp provoked renal inflammation as shown by the activation of toll like receptor 4 (TLR4) and infiltration of CD68 positive monocytes. Urinary F2t isoprostane excretion, an index of renal oxidant stress, was increased in the HG+HI clamp rats. We conclude that even a short duration of hyperglycemia and hyperinsulinemia contributes to activation of pathways that regulate matrix protein synthesis, inflammation and oxidative stress in the kidney. This finding could have implications for the control of short term rises in blood glucose in diabetic individuals at risk of developing kidney disease.
Preview · Article · Oct 2013 · AJP Cell Physiology
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs regulate post-transcriptomic landscape in many tumors including renal cell carcinoma. We have recently shown significantly increased expression of miR-21 in renal tumors and that this miRNA contributes to the proliferation of renal cancer cells in culture. However, the mechanism by which miR-21 regulates renal cancer cells proliferation is poorly understood. Addiction to constitutive NFκB activity is hallmark of many cancers including renal cancer. Using miR-21 Sponge in renal cancer cells to block endogenous function of miR-21, we show inhibition of phosphorylation of p65 subunit of NFκB, IKKβ and IκB, which results in attenuation of NFκB transcriptional activity. Subtle reduction in the tumor suppressor PTEN has been linked to various malignancies. We showed previously that miR-21 targeted PTEN in renal cancer cells. Inhibition of PTEN by siRNAs restored miR-21 Sponge-induced suppression of phosphorylation of p65, IKKβ, IκB and NFκB transcriptional activity along with reversal of miR-21 Sponge-reduced phosphorylation of Akt. Expression of constitutively active Akt protected against miR-21 Sponge- and PTEN-mediated decrease in p65/IKKβ/IκB phosphorylation and NFκB transcriptional activity. Furthermore, IKKβ and p65 were required for miR-21-induced renal cancer cell proliferation. Interestingly, miR-21 controlled the expression of cyclin D1 through NFκB-dependent transcription. Finally, we demonstrate that miR-21-regulated renal cancer cell proliferation is mediated by cyclin D1 and CDK4. Together, our results establish a molecular order of a phosphatase-kinase couple involving PTEN/Akt/IKKβ and NFκB-dependent cyclin D1 expression for renal carcinoma cell proliferation by increased miR-21 levels.
No preview · Article · Aug 2013 · Cellular Signalling
[Show abstract][Hide abstract] ABSTRACT: Activation of glomerular mesangial cells (MCs) by angiotensin II (Ang II) leads to extracellular matrix accumulation. Here, we demonstrate that, in MCs, Ang II induces endothelial nitric oxide synthase (eNOS) uncoupling with enhanced generation of reactive oxygen species (ROS) and decreased production of nitric oxide (NO). Ang II promotes a rapid increase in 3-nitrotyrosine formation and uric acid attenuates Ang II-induced decrease in NO bioavailability, demonstrating that peroxynitrite mediates the effects of Ang II on eNOS dysfunction. Ang II rapidly up-regulates Nox4 protein. Inhibition of Nox4 abolishes the increase in ROS and peroxynitrite generation as well as eNOS uncoupling triggered by Ang II, indicating that Nox4 is upstream of eNOS. This pathway contributes to Ang II-mediated fibronectin accumulation in MCs. Ang II also elicits an increase in mitochondrial abundance of Nox4 protein and the oxidase contributes to ROS production in mitochondria. Overexpression of mitochondrial superoxide dismutase (MnSOD) prevents the stimulatory effects of Ang II on mitochondrial ROS production, loss of NO availability and MC fibronectin accumulation, whereas MnSOD depletion increases mitochondrial ROS, NO deficiency and fibronectin synthesis basally and in cells exposed to Ang II. This work provides the first evidence that uncoupled eNOS is responsible for Ang II-induced MC fibronectin accumulation and identifies Nox4 and mitochondrial ROS as mediators of eNOS dysfunction. These data shed light on molecular processes underlying the oxidative signaling cascade engaged by Ang II and identify potential targets for intervention to prevent renal fibrosis.
No preview · Article · Aug 2013 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Podocyte apoptosis is a critical mechanism for excessive loss of urinary albumin that eventuates in kidney fibrosis. Pharmacological doses of the mTOR inhibitor rapamycin reduce albuminura in diabetes. We explored the hypothesis that mTOR mediates podocyte injury in diabetes. High glucose (HG) induces apoptosis of podocytes, inhibits AMPK activation, inactivates tuberin and activates mTOR. HG also increases the levels of Nox4 and Nox1 and NADPH oxidase activity. Inhibition of mTOR by low dose rapamycin decreases HG-induced Nox4 and Nox1, NADPH oxidase activity and podocyte apoptosis. Inhibition of mTOR had no effect on AMPK or tuberin phosphorylation indicating that mTOR is downstream of these signaling molecules. In isolated glomeruli of OVE26 mice, there is similar decrease in the activation of AMPK and tuberin and activation of mTOR with increase in Nox4 and NADPH oxidase activity. Inhibition of mTOR by small dose of rapamycin reduces podocyte apoptosis, attenuates glomerular injury and albuminuria. Our data provide evidence for a novel function of mTOR in Nox4-derived ROS generation and podocyte apoptosis that contributes to urinary albumin excretion in type 1 diabetes. Thus mTOR and or NADPH oxidase inhibition may represent a therapeutic modality of diabetic kidney disease.
[Show abstract][Hide abstract] ABSTRACT: In many renal diseases, TGFβ-stimulated canonical Smad 3 and noncanonical mTOR promote increased protein synthesis and mesangial cell hypertrophy. The cellular underpinnings involving these signaling molecules to regulate mesangial cell hypertrophy are not fully understood. Deptor has recently been identified as an mTOR interacting protein and functions as an endogenous inhibitor of the kinase activity for both TORC1 and TORC2. Prolonged incubation of mesangial cells with TGFβ reduced the levels of deptor concomitant with increase in TORC1 and TORC2 activity. Sustained TGFβ activation was required to inhibit association of deptor with mTOR while rapid activation had no effect. Using mTOR inhibitor PP242, we found that TGFβ-induced both early and sustained activation of TORC1 and TORC2 were necessary for deptor suppression. PP242-induced reversal of deptor suppression by TGFβ was associated with significant inhibition of TGFβ-stimulated protein synthesis and hypertrophy. Interestingly, expression of siRNA against Smad 3 or Smad 7, which blocks TGFβ receptor-specific Smad 3 signaling, prevented TGFβ-induced suppression of deptor abundance and TORC1/2 activities. Furthermore, overexpression of Smad 3 decreased deptor expression similar to TGFβ stimulation concomitant with increased TORC1 and TORC2 activities. Finally, knockdown of deptor reversed Smad 7-mediated inhibition of protein synthesis and mesangial cell hypertrophy induced by TGFβ. These data reveal the requirement of both early and late activation of mTOR for TGFβ-induced protein synthesis. Our results support that TGFβ-stimulated Smad 3 acts as a key node to instill a feed back loop between deptor downregulation and TORC1/2 activation in driving mesangial cell hypertrophy.
Full-text · Article · Jan 2013 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: We explored molecular events associated with aging-induced matrix changes in the kidney. C57BL6 mice were studied in youth, middle age, and old age. Albuminuria and serum cystatin C level (an index of glomerular filtration) increased with aging. Renal hypertrophy was evident in middle-aged and old mice and was associated with glomerulomegaly and increase in mesangial fraction occupied by extracellular matrix. Content of collagen types I and III and fibronectin was increased with aging; increment in their mRNA varied with the phase of aging. The content of ZEB1 and ZEB2, collagen type I transcription inhibitors, and their binding to the collagen type Iα2 promoter by ChIP assay also showed age-phase-specific changes. Lack of increase in mRNA and data from polysome assay suggested decreased degradation as a potential mechanism for kidney collagen type I accumulation in the middle-aged mice. These changes occurred with increment in TGFβ mRNA and protein and activation of its SMAD3 pathway; SMAD3 binding to the collagen type Iα2 promoter was also increased. TGFβ-regulated microRNAs (miRs) exhibited selective regulation. The renal cortical content of miR-21 and miR-200c, but not miR-192, miR-200a, or miR-200b, was increased with aging. Increased miR-21 and miR-200c contents were associated with reduced expression of their targets, Sprouty-1 and ZEB2, respectively. These data show that aging is associated with complex molecular events in the kidney that are already evident in the middle age and progress to old age. Age-phase-specific regulation of matrix protein synthesis occurs and involves matrix protein-specific transcriptional and post-transcriptional mechanisms.
[Show abstract][Hide abstract] ABSTRACT: Kidney injury is one of the most serious complications of diabetes. Current therapies only slow down but do not stop its progression to end stage kidney failure; thus, there is a need for novel approaches. Accumulation of extracellular matrix proteins, e.g., laminin, fibronectin, contributes to the loss of functioning parenchyma and progressive loss of kidney function in diabetes. We have recently reported that H2S inhibits high glucose-induced increase in synthesis of proteins including matrix proteins (H.J. Lee et al., J. Biol. Chem. 287 (2012) 4451). We wish to identify H2S generating agents that can be used in humans to treat diabetic kidney disease. We hypothesized that tadalafil, a H2S donor and phosphodiesterase 5 (PDE5) inhibitor, inhibits high glucose stimulation of synthesis of proteins including ECM proteins by generating H2S in mouse kidney podocytes. High glucose (30 mM), but not equimolar mannitol, significantly promoted global protein synthesis, cellular hypertrophy and expression of laminin-γ1 and fibronectin. These events were inhibited by 10 μM tadalafil. Because mRNA translation is rate-limiting for protein synthesis, we examined tadalafil effect on events in translation. Tadalafil abrogated high glucose-induced mTORC1 activation as indicated by phosphorylation of p70S6 kinase and 4E-BP1; both these events are important for the initiation phase of translation. Tadalafil reversed high glucose-induced changes in the phosphorylation of eEF2 and eEF2 kinase, which regulate the elongation phase of translation. Upstream regulators of mTORC1 were investigated. Tadalafil stimulated activating phosphorylation of AMPK in a dose dependent manner, peaking at 10 μM. Pre-incubation with Compound C, an AMPK inhibitor, completely abolished tadalafil effect on high glucose stimulation of events in mRNA translation as well as global protein and laminin synthesis. Tadalafil-induced AMPK phosphorylation was abolished by dl-propargylglycine (PAG), an inhibitor of cystathionine γ lyase (CSE), a H2S generating enzyme. Tadalafil rapidly increased CSE protein expression in 1 h which was inhibited by cycloheximide but not actinomycin-D, suggesting regulation at the level of mRNA translation. In an enzymatic assay, PAG abrogated tadalafil stimulation of generation of H2S. PAG completely abolished tadalafil effect on high glucose stimulation of events in mRNA translation as well as global protein and laminin synthesis. Tadalafil is a PDE5 inhibitor that increases cGMP content. ODQ, an inhibitor of guanylyl cyclase that generates cGMP, abolished tadalafil induction of AMPK phosphorylation. ODQ abrogated tadalafil inhibition of high glucose-induced increase in laminin expression. Renal cortical content of cystathionine β synthase (CBS) and CSE, H2S generating enzymes, was significantly reduced in the kidney in mice with type 1 or type 2 diabetes. Our data show that tadalafil stimulates H2S-AMPK axis to inhibit mTORC1 and mRNA translation leading to amelioration of high glucose-induced global and matrix protein increment in renal podocytes. It is likely that tadalafil stimulation of H2S is cGMP-dependent in the podocyte. Future work is needed to define whether tadalafil can ameliorate kidney injury in animal models of diabetes.
[Show abstract][Hide abstract] ABSTRACT: Transforming growth factor-β (TGFβ) promotes glomerular hypertrophy and matrix expansion, leading to glomerulosclerosis. MicroRNAs are well suited to promote fibrosis because they can repress gene expression, which negatively regulate the fibrotic process. Recent cellular and animal studies have revealed enhanced expression of microRNA, miR-21, in renal cells in response to TGFβ. Specific miR-21 targets downstream of TGFβ receptor activation that control cell hypertrophy and matrix protein expression have not been studied. Using 3'UTR-driven luciferase reporter, we identified the tumor suppressor protein PTEN as a target of TGFβ-stimulated miR-21 in glomerular mesangial cells. Expression of miR-21 Sponge, which quenches endogenous miR-21 levels, reversed TGFβ-induced suppression of PTEN. Additionally, miR-21 Sponge inhibited TGFβ-stimulated phosphorylation of Akt kinase, resulting in attenuation of phosphorylation of its substrate GSK3β. Tuberin and PRAS40, two other Akt substrates, and endogenous inhibitors of mTORC1, regulate mesangial cell hypertrophy. Neutralization of endogenous miR-21 abrogated TGFβ-stimulated phosphorylation of tuberin and PRAS40, leading to inhibition of phosphorylation of S6 kinase, mTOR and 4EBP-1. Moreover, downregulation of miR-21 significantly suppressed TGFβ-induced protein synthesis and hypertrophy, which were reversed by siRNA-targeted inhibition of PTEN expression. Similarly, expression of constitutively active Akt kinase reversed the miR-21 Sponge-mediated inhibition of TGFβ-induced protein synthesis and hypertrophy. Furthermore, expression of constitutively active mTORC1 prevented the miR-21 Sponge-induced suppression of mesangial cell protein synthesis and hypertrophy by TGFβ. Finally, we show that miR-21 Sponge inhibited TGFβ-stimulated fibronectin and collagen expression. Suppression of PTEN expression and expression of both constitutively active Akt kinase and mTORC1 independently reversed this miR-21-mediated inhibition of TGFβ-induced fibronectin and collagen expression. Our results uncover an essential role of TGFβ-induced expression of miR-21, which targets PTEN to initiate a non-canonical signaling circuit involving Akt/mTORC1 axis for mesangial cell hypertrophy and matrix protein synthesis.
[Show abstract][Hide abstract] ABSTRACT: Increasing evidence shows the beneficial effects of fish oil on breast cancer growth and invasion in vitro and in animal models. Expression of CSF-1 (colony stimulating factor-1) by breast cancer cells acts as potent activator of malignancy and metastasis. In this report, we used two human breast cancer cell lines, MDA-MB-231 and MCF-7, to show that the bioactive fish oil component DHA (docosahexaenoic acid) inhibits expression of CSF-1 and its secretion from these cancer cells. We found that the tumor suppressor protein PTEN regulates CSF-1 expression through PI 3 kinase/Akt signaling via a transcriptional mechanism. The enhanced abundance of microRNA-21 (miR-21) in breast cancer cells contributes to the growth and metastasis. Interestingly, DHA significantly inhibited expression of miR-21. miR-21 Sponge, which derepresses the miR-21 targets, markedly decreased expression of CSF-1 and its secretion. Furthermore, miR-21-induced upregulation of CSF-1 mRNA and its transcription were prevented by expression of PTEN mRNA lacking 3'-untranslated region (UTR) and miR-21 recognition sequence. Strikingly, miR-21 reversed DHA-forced reduction of CSF-1 expression and secretion. Finally, we found that expression of miR-21 as well as CSF-1 was significantly attenuated in breast tumors of mice receiving a diet supplemented with fish oil. Our results reveal a novel mechanism for the therapeutic function of fish oil diet that blocks miR-21, thereby increasing PTEN levels to prevent expression of CSF-1 in breast cancer.