JNK-dependent AP-1 activation is required for aristolochic acid-induced TGF-beta1 synthesis in human renal proximal epithelial cells

摘要

Chronic aristolochic acid ne-phropathy (CAAN) is a chronic and progressive tubulointerstitial nephropathy characterized by extensive interstitial fibrosis. Aristolochic acid (AA) could induce overexpression of transforming growth factor-beta1 (TGF-beta1) in a human renal proximal tubule epithelial cells line (HKC), which has been implicated in the pathogenesis of CAAN. The present studies in HKC cells showed 1) AA could activate JNK in time- and dose-dependent manners and JNK inhibitor SP600125 could inhibit AA-induced TGF-beta1 promoter activity and TGF-beta1 synthesis; 2) AA-induced JNK activation and TGF-beta1 synthesis were significantly inhibited by kinase-inactive mutants of MEKK4, MKK4, or MKK7; 3) AA could upregulate luciferase activity derived by a wild-type TGF-beta1 promoter, but not by an AP-1 binding-deficient TGF-beta1 promoter; and 4) AA could upregulate expression of c-Fos, phospho-c-Jun, and phospho-ATF2. The above data suggest AA-induced TGF-beta1 overexpression in HKC cells may be mainly mediated by the JNK signaling pathway. Both the upstream kinases of JNK including MEKK4, MKK4, and MKK7, and the downstream transcription factor of JNK, AP-1, may also participate in this process.