Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contributes to the pathophysiological development of kidney fibrosis. Although it was reported that TGF-β1 enhances β1 integrin levels in NMuMG cells, the detailed molecular mechanisms underlying TGF-β1-induced β1 integrin gene expression and the role of β1 integrin during EMT in the renal system are still unclear. In this study, we examined the role of β1 integrin in TGF-β1-induced EMT both in vitro and in vivo. TGF-β1-induced augmentation of β1 integrin expression was required for EMT in several epithelial cell lines, and knockdown of Smad3 inhibited TGF-β1-induced augmentation of β1 integrin. TGF-β1 triggered β1 integrin gene promoter activity as assessed by luciferase activity assay. Both knockdown of Smad3 and mutation of the Smad-binding element to block binding to the β1 integrin promoter markedly reduced TGF-β1-induced β1 integrin promoter activity. Chromatin immunoprecipitation assay showed that TGF-β1 enhanced Smad3 binding to the β1 integrin promoter. Furthermore, induction of unilateral ureteral obstruction triggered increases of β1 integrin in both renal epithelial and interstitial cells. In human kidney with chronic tubulointerstitial fibrosis, we also found a concomitant increase of β1 integrin and α-smooth muscle actin in tubule epithelia. Blockade of β1 integrin signaling dampened the progression of fibrosis. Taken together, β1 integrin mediates EMT and subsequent tubulointerstitutial fibrosis, suggesting that inhibition of β1 integrin is a possible therapeutic target for prevention of renal fibrosis.
All Science Journal Classification (ASJC) codes
- Pathology and Forensic Medicine