title: The downregulation of SnoN expression in human renal proximal tubule epithelial cells under high-glucose conditions is mediated by an increase in Smurf2 expression through TGF-β1 signaling.
abstract: Transforming growth factor (TGF)-β1 is a profibrotic cytokine that plays a critical role in the progression of diabetic nephropathy (DN). Previous studies have demonstrated that the Smad transcriptional co-repressor, Ski-related novel protein N (SnoN), an antagonizer of TGF-β1/Smad signaling, is downregulated in the kidneys of diabetic rats; however, the underlying molecular mechanisms remain elusive. In the present study, we demonstrated that the upregulation of Smad ubiquitination regulatory factor-2 (Smurf2), through TGF-β1/Smad signaling, contributes to the downregulation of SnoN under high-glucose conditions in primary human renal proximal tubule epithelial cells (hRPTECs). The hRPTECs were cultured in high-glucose (30 mmol/l D-glucose) medium in the presence or absence of either the proteasome inhibitor, MG132, or the TGF-β type I receptor kinase inhibitor, SB-431542. Small interfering RNA (siRNA) was used to silence Smurf2. The expression levels of SnoN, Smurf2, Smad2 and phosphorylated (p-)Smad2 were measured by western blot analysis and RT-qPCR. The protein levels of SnoN were markedly downregulated, while its mRNA levels were increased in the hRPTECs cultured under high-glucose conditions. The protein and mRNA levels of Smurf2 were significantly increased under high-glucose conditions. The knockdown of Smurf2 increased SnoN expression in the hRPTECs cultured in high-glucose medium. Moreover, MG132 partially inhibited SnoN degradation in the hRPTECs under high-glucose conditions and SB-431542 decreased the phosphorylation of Smad2 and the expression of Smurf2 induced under high-glucose conditions. Taken together, the findings of this study demonstrate that the downregulation of SnoN expression in hRPTECs under high-glucose conditions is mediated by the increased expression of Smurf2 through the TGF-β1/Smad signaling pathway.
authors.affiliation: Department of Nephrology, Beijing Friendship Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Xiuji
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Nephrology, Beijing Friendship Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Zongli
authors.initials: Z
authors.lastname: Diao
authors.affiliation: Department of Nephrology, Beijing Friendship Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Jiaxiang
authors.initials: J
authors.lastname: Ding
authors.affiliation: Department of Infectious Diseases, Beijing Friendship Hospital, Capital Medical University, Beijing, P.R. China.
authors.forename: Ruixia
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Nephrology, Beijing Friendship Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Liyan
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Nephrology, Beijing Tongren Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Wen
authors.initials: W
authors.lastname: Huang
authors.affiliation: Department of Nephrology, Beijing Friendship Hospital, Faculty of Kidney Diseases, Capital Medical University, Beijing, P.R. China.
authors.forename: Wenhu
authors.initials: W
authors.lastname: Liu
mesh_terms: D001549:Benzamides / Q000008:administration & dosage; D002478:Cells, Cultured; D004149:Dioxoles / Q000008:administration & dosage; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D007976:Leupeptins / Q000008:administration & dosage; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein / Q000096:biosynthesis; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis* / Q000235:genetics
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D004149:Dioxoles; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins; D011518:Proto-Oncogene Proteins; C060615:SKIL protein, human; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta; C471641:SMURF2 protein, human; D044767:Ubiquitin-Protein Ligases; D005947:Glucose; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde