5468

PPARG

epithelial-mesenchymal transition (EMT) was shown to confer tumor cells with abilities essential for metastasis, including migratory phenotype, invasiveness, resistance to apoptosis, evading immune surveillance, and tumor stem cell traits. Therefore, inhibition of EMT can be an important therapeutic strategy to inhibit tumor metastasis. Here, we show that activation of peroxisome proliferator-activated receptor gamma (PPAR-gamma) inhibits transforming growth factor beta (TGF-beta)-induced EMT in lung cancer cells and prevents metastasis by antagonizing Smad3 function. Activation of PPAR-gamma by synthetic ligands (troglitazone and rosiglitazone) or by a constitutively active form of PPAR-gamma prevents TGF-beta-induced loss of E-cadherin expression and inhibits the induction of mesenchymal markers (vimentin, N-cadherin, fibronectin) and matrix metalloproteases. Consistently, activation of PPAR-gamma also inhibited EMT-induced migration and invasion of lung cancer cells. Furthermore, effects of PPAR-gamma ligands were attenuated by siRNA-mediated knockdown of PPAR-gamma, indicating that the ligand-induced responses are PPAR-gamma dependent. Selective knockdown of Smad2 and Smad3 by siRNA showed that TGF-beta-induced EMT is Smad3 dependent in lung cancer cells. Activation of PPAR-gamma inhibits TGF-beta-induced Smad transcriptional activity but had no effect on the phosphorylation or nuclear translocation of Smads. Consistently, PPAR-gamma activation prevented TGF-beta-induced transcriptional repression of E-cadherin promoter and inhibited transcriptional activation of N-cadherin promoter. Finally, treatment of mice with troglitazone or knockdown of Smad3 in tumor cells significantly inhibited TGF-beta-induced experimental metastasis in SCID-Beige mice. Together, with the low toxicity profile of PPAR-gamma ligands, our data show that these ligands may serve as potential therapeutic agents to inhibit metastasis.CI - (c)2010 AACR.

Chronic renal failure (CRF) mainly results from kidney fibrosis. epithelial-to-mesenchymal transition (EMT) occurs in stressed tubular epithelial cells and contributes to renal fibrosis. Transforming growth factor-beta1 (TGF-beta1) has been shown to initiate and complete the whole EMT process. Peroxisome proliferators-activated receptor-gamma (PPAR-gamma) exerts anti-inflammatory, anti-fibrotic and vaculo-protective effects on different renal diseases. Telmisartan is a member of angiotensin II (Ang II) receptor blocker (ARB) family. Recent studies show that Telmisartan has a partial agonistic effect on PPAR-gamma. Therefore, we tested the hypothesis that Telmisartan reverses the progression of induced EMT by TGF-beta1 in cultured human renal proximal tubular epithelial (HK-2) cells. Cultured HK-2 cells were treated with TGF-beta1 (3 ng/ml), a combination of TGF-beta1 and Telmisartan (10-200 umol/L) and a combination of TGF-beta1, Telmisartan and GW9662, a PPAR-gamma antagonist for 48 hours. EMT was determined by quantitative real-time PCR analysis of E-cadherin (E-cad), Connective Tissue Growth Factor (CTGF) and PPAR-gamma transcript expression and immunocytochemical analysis of E-cad, alpha-Smooth Muscle Actin (alpha-SMA) and PPAR-gamma protein expression. TGF-beta1 induced phenotypic EMT in cultured HK-2 cell line via significantly reduced E-cad expression and significantly increased CTGF, alpha-SMA expression in association with the loss of epithelial morphology. Telmisartan reversed all EMT markers in a dose-dependent manner which was inhibited by PPAR antagonist GW9662. In the present study, it was suggested that Telmisartan attenuated TGF-beta1 induced EMT by agonistic activation of PPAR-gamma.

The importance of PPARgamma (peroxisome proliferator-activated receptor gamma) in gastric cancer (GC) is unclear. We investigated the role of PPARgamma in GC cell lines and an animal model, and its prognostic significance of PPARgamma in GC patients. We controlled PPARgamma and galectin-9 expression by using siRNAs and lentiviral constructs. Interaction between PPARgamma and galectin-9 was evaluated using luciferase and chromatin immunoprecipitation assays. PPARgamma expression in GCs was determined by immunohistochemical staining of tissue microarrays and survival analysis was done. Overexpression of PPARgamma was accompanied by increased galectin-9. Enhanced PPARgamma or galectin-9 expression increased E-cadherin expression; decreased expression of N-cadherin, fibronectin, snail, twist and slug and reduced cell invasion and migration. PPARgamma bound to the galectin-9 promoter region. Galectin-9 activity increased in PPARgamma-overexpressing cells but decreased in PPARgamma siRNA-treated cells. In a zebrafish xenograft model, the number of migrated cancer cells and number of fish with AGS cells in the tail vein were reduced in PPARgamma-overexpressing GC cells. PPARgamma was expressed in 462 of the 688 patients (69.2%) with GC. In 306 patients with intestinal-type GC, those with PPARgamma-positive tumors had lower overall and cancer-specific mortalities than those with PPARgamma-negative tumors. PPARgamma expression was an independent prognostic factor for overall and GC-specific mortality in patients with intestinal-type GC (adjusted hazard ratio, 0.42; 95% CI, 0.22-0.81). PPARgamma inhibits cell invasion, migration and epithelial-mesenchymal transition through upregulation of galectin-9 in vitro and in vivo.CI - (c) 2014 UICC.

tumor recurrence in glioblastoma (GBM) is, in part, attributed to increased epithelial-to-mesenchymal transition (EMT) and enhanced tumor cell dissemination in adjacent brain parenchyma after ionizing radiation (IR). EMT is associated with aggressive behavior, increased stem-like characteristics and treatment resistance in malignancies; however, the underlying signaling mechanisms that regulate EMT are poorly understood. We identified grade-dependent p21-activated kinases 4 (PAK4) upregulation in gliomas and further determined its role in mesenchymal transition and radioresistance. IR treatment significantly elevated expression and nuclear localization of PAK4 in correlation with induction of reactive oxygen species (ROS) and mesenchymal transition in GBM cells. Stable PAK4 overexpression promoted mesenchymal transition by elevating EMT marker expression in these cells. Of note, transcription factor-DNA-binding arrays and chromatin immunoprecipitation experiments identified the formation of a novel nuclear PAK4/PPARgamma complex which was recruited to the promoter of Nox1, a peroxisome proliferator-activated receptor gamma (PPARgamma) target gene. In addition, IR further elevated PAK4/PPARgamma complex co-recruitment to Nox1 promoter, and increased Nox1 expression and ROS levels associated with mesenchymal transition in these cells. Conversely, specific PAK4 downregulation decreased PPARgamma-mediated Nox1 expression and suppressed EMT in IR-treated cells. In vivo orthotopic tumor experiments showed inhibition of growth and suppression of IR-induced PPARgamma and Nox1 expression by PAK4 downregulation in tumors. Our results provide the first evidence of a novel role for PAK4 in IR-induced EMT and suggest potential therapeutic efficacy of targeting PAK4 to overcome radioresistance in gliomas.

We have previously reported that perfluorooctanesulfonate (PFOS) causes cell apoptosis in renal tubular epithelial cells (RTCs). Here, we extend our findings and provide evidence of epithelial-mesenchymal transition (EMT)-associated renal fibrosis caused by PFOS and the protection by l-carnitine. Our results demonstrate that PFOS increased the expression of EMT and renal injury biomarkers (eg, N-cadherin, vimentin, Snail, Kim1, and Lcn2). In addition, PFOS caused EMT induction through Sirt1-mediated PPARgamma deacetylation and inactivation. l-carnitine reversed the EMT induction caused by PFOS and alleviated PFOS-mediated increases in cell migration by reactivating PPARgamma through the inhibition of Sirt1 activity. The critical role of Sirt1 in this process was validated by using Sirt1 overexpression, resveratrol (a pharmacologic activator of Sirt1), nicotinamide (a Sirt1 inhibitor) and siSirt1. Nicotinamide and siSirt1, but not Sirt1 overexpression and resveratrol, alleviated PFOS-mediated EMT induction, suggesting that increased Sirt1 activity contributed to the alterations. Furthermore, through PPARgamma overexpression and pharmacologic interventions, we validated the crucial role of increased PPARgamma deacetylation caused by aberrant increased Sirt1 activity in RTC transformation. Similar to PPARgamma overexpression, rosiglitazone (a PPARgamma agonist) alleviated the effects of PFOS on the EMT-related features, whereas GW9662 (a PPARgamma antagonist) mimicked the effects. The protective effect of l-carnitine was also verified in a mouse model of chronic PFOS exposure, in which decreased EMT biomarker levels and renal fibrosis by l-carnitine were observed in Western blot and histological analyses. Accordingly, l-carnitine alleviated EMT-associated renal fibrosis caused by PFOS through a Sirt1- and PPARgamma-dependent mechanism.CI - (c) The Author 2017. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Cyclin-dependent kinase 5 (CDK5) has been documented in podocyte injuries in diabetic nephropathy (DN), however its role in renal tubular epithelial cells has not been elucidated. We report here that CDK5 is detrimental and promotes tubulointerstitial fibrosis (TIF) via the extracellular signal-regulated kinase 1/2 (ERK1/2)/peroxisome proliferator-activated receptor gamma (PPRAgamma) pathway in DN. In high glucose cultured NRK52E cells, blocking CDK5 activity inhibited epithelial-to-mesenchymal transition (EMT) and fibrosis via ERK1/2/PPARgamma pathway. In diabetic rats, CDK5 inhibitor roscovitine decreased renal fibrosis and improved renal function as demonstrated by a decrease in levels of blood urine nitrogen (BUN), serum creatinine and beta2-microglobulin. Further studies revealed that improved renal fibrosis and function in diabetic rats were associated with inactivation of ERK1/2 and PPARgamma signaling pathways. In late staged DN patients, the upregulation of CDK5 and p35 activated phosphorylated ERK1/2 and PPARgamma, leading to decreased levels of E-cadherin but increased Vimentin and Collagen IV. Accordingly, renal fibrosis and function were worsened as revealed by decreased estimated glomerular filtration rate (eGFR) and increased serum BUN, creatinine, beta2-microglobulin, 24-hour proteinuria and urine albumin to creatinine ratio (UACR). These findings demonstrate a novel mechanism that CDK5 increases tubulointerstitial fibrosis by activating the ERK1/2/PPARgamma pathway and EMT in DN. CDK5 might have therapeutic potential in diabetic nephropathy.