RGC-32 mediates transforming growth factor-beta-induced epithelial-mesenchymal transition in human renal proximal tubular cells.
Epithelial-mesenchymal transition (EMT) occurs in several disease states, including renal fibrosis and carcinogenesis. Myofibroblasts produced from EMT of renal tubular cells are responsible for the deposition of extracellular matrix components in a large portion of renal interstitial fibrosis. Transforming growth factor-beta (TGF-beta) plays an essential role in the EMT of renal tubular cells, but the molecular mechanism governing this process remains largely unknown. In this study, we found that RGC-32 (response gene to complement 32) is critical for TGF-beta-induced EMT of human renal proximal tubular cells (HPTCs). RGC-32 is not normally expressed in the HPTCs. However, TGF-beta stimulation markedly activates RGC-32 while inducing an EMT, as shown by the induction of smooth muscle alpha-actin (alpha-SMA) and extracellular matrix proteins collagen I and fibronectin, as well as the reduction of epithelial marker E-cadherin. TGF-beta function is mediated by several signaling pathways, but RGC-32 expression in HPTCs appears to be mainly regulated by Smad. Functionally, RGC-32 appears to mediate TGF-beta-induced EMT of HPTCs. Blockage of RGC-32 using short hairpin interfering RNA significantly inhibits TGF-beta induction of myofibroblast marker gene alpha-SMA while repressing the expression of E-cadherin. In contrast, overexpression of RGC-32 induces alpha-SMA expression while restoring E-cadherin. RGC-32 also inhibits the expression of another adherens junction protein, N-cadherin, suggesting that RGC-32 alone induces the phenotypic conversion of renal epithelial cells to myofibroblasts. Additional studies show that RGC-32 stimulates the production of extracellular matrix components fibronectin and collagen I. Mechanistically, RGC-32 induces EMT via the activation of other transcription factors such as Snail and Slug. RGC-32 knockdown inhibits the expression of Snail and Slug during TGF-beta-induced EMT. Taken together, our data demonstrate for the first time that RGC-32 plays a critical role in TGF-beta-induced EMT of renal tubular cells.
Huang
Wen-Yan
WY
Department of Physiology, The University of Georgia College of Veterinary Medicine, Athens, Georgia 30602, USA.
Li
Zu-Guo
ZG
Rus
Horea
H
Wang
Xiaoyan
X
Jose
Pedro A
PA
Chen
Shi-You
SY
D015820:Cadherins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis / Q000235:genetics; D005353:Fibronectins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D051785:Smad Proteins / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D015820:Cadherins; D018797:Cell Cycle Proteins; D016326:Extracellular Matrix Proteins; D005353:Fibronectins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; C115049:RGCC protein, human; D051785:Smad Proteins; D016212:Transforming Growth Factor beta