6498

SKIL

epithelial-mesenchymal transition (EMT) is a fundamental cellular process that contributes to epithelial tissue morphogenesis during normal development and in tumor invasiveness and metastasis. The transcriptional regulator SnoN robustly influences EMT in response to the cytokine TGFbeta, but the mechanisms that regulate the fundamental role of SnoN in TGFbeta-induced EMT are not completely understood. Here we employ interaction proteomics to uncover the signaling protein TIF1gamma as a specific interactor of SnoN1 but not the closely related isoform SnoN2. A 16-amino acid peptide within a unique region of SnoN1 mediates the interaction of SnoN1 with TIF1gamma. Strikingly, although TIF1gamma is thought to act as a ubiquitin E3 ligase, we find that TIF1gamma operates as a small ubiquitin-like modifier (SUMO) E3 ligase that promotes the sumoylation of SnoN1 at distinct lysine residues. Importantly, TIF1gamma-induced sumoylation is required for the ability of SnoN1 to suppress TGFbeta-induced EMT, as assayed by the disruption of the morphogenesis of acini in a physiologically relevant three-dimensional model of normal murine mammary gland (NMuMG) epithelial cells. Collectively, our findings define a novel TIF1gamma-SnoN1 sumoylation pathway that plays a critical role in EMT and has important implications for our understanding of TGFbeta signaling and diverse biological processes in normal development and cancer biology.CI - (c) 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

The transcriptional regulator SnoN (also known as SKI-like proto-oncogene, SKIL), a member of the Ski family, has been reported to influence epithelial-mesenchymal transition (EMT) in response to TGF-beta. In the present study, we investigated the role of SnoN in bladder cancer (BC). Differential expression of SnoN was not detected in BC tissues compared with that noted in adjacent non-cancerous tissues. SnoN was upregulated in response to TGF-beta treatment, but had no effect on the TGF-beta pathway, which may be explained by the low level of SnoN SUMOylation. TIF1gamma, which catalyzes the SUMOylation of SnoN, was downregulated in BC tissues. Overexpression of TIF1gamma restored the ability of SnoN to suppress the TGF-beta pathway. Furthermore, TGF-beta-induced EMT and invasion of BC cells were suppressed by TIF1gamma in the presence of SnoN. Collectirely, our data suggest that SnoN suppresses TGF-betainduced EMT and invasion of BC cells in a TIF1gammadependent manner and may serve as a novel therapeutic option for the treatment of BC.

It has been reported that transforming growth factor-beta1 (TGF-beta1) signaling plays an important role in the development of diabetic nephropathy (DN). The nuclear transcription co-repressor Ski-related novel protein N (SnoN) is a critical negative regulator of TGF-beta1/Smad signal pathway, involving in tubule epithelial-mesenchymal transition (EMT), extracellular matrix (ECM) accumulation, and tubulointerstitial fibrosis. In this study, we focused on miR-23a as a regulator of SnoN. Our purpose is to study the effects of miR-23a on high glucose (HG)-induced EMT process and ECM deposition in HK2 cells. We found that miR-23a was up-regulated in renal tissues of diabetic patients and HG-induced HK2 cells. Besides, the high level of miR-23a was closely associated with decreased SnoN expression. Knockdown of miR-23a increased SnoN expression and in turn suppressed HG-induced EMT and renal fibrogenesis. Introduction of miR-23a decreased SnoN expression and enhanced the profibrogenic effects of HG on HK2 cells. Next, bioinformatics analysis predicted that the SnoN was a potential target gene of miR-23a. Luciferase reporter assay demonstrated that miR-23a could directly target SnoN. We demonstrated that overexpression of SnoN was sufficient to inhibit HG-induced EMT and renal fibrogenesis in HK2 cells. Furthermore, down-regulation of SnoN partially reversed the protective effect of miR-23a knockdown on HG-induced EMT and renal fibrogenesis in HK2 cells. Collectively, miR-23a and SnoN significantly impact on the progression of HG-induced EMT and renal fibrogenesis in vitro, and they may represent novel targets for the prevention strategies of renal fibrosis in the context of DN.