Antioxidant treatment induces transcription and expression of transforminggrowth factor beta in cultured renal proximal tubular cells

Transforming growth factor beta (TCF-beta) plays an important role in the d evelopment of tubulointerstitial fibrosis in chronic renal disease. We were interested whether interference with oxygen radicals may modulate TGF-beta expression. Unexpectedly, we discovered that diphenylene iodine (DIP), an inhibitor of NADP(H) oxidase, induces a robust increase in TGF-beta transcr ipt expression in cultured mouse proximal tubular cells (MCT cells), A simi lar increase was seen with EUK-8, a synthetic salen-manganese complex with high oxyradical scavenger activities. This induction of TCF-beta1 mRNA was paralleled by increasing protein expression, Transient transfection of MCT cells with a reporter construct in which murine TCF-beta1 enhancer/promoter elements were cloned in front of the luciferase gene, revealed that DIP, E UK-3, and Tiron all stimulated transcription of the TGF-beta1 gene whereas exogenous H2O2 suppressed transcription. Antisense oligonucleotides against p22phox, but not sense oligonucleotides, also increased transcriptional ac tivity of TCF-beta1, Mutagenesis of Sp1 binding sites in the mouse TGF-beta 1 enhancer/promoter abolished the stimulatory effect of the antioxidants, G el shift experiments revealed that DIP as well as EUK-3 activated binding o f nuclear proteins to Spl consensus sequence. Our data provide evidence tha t TGF-beta1 transcription is negatively regulated in MCT cells under basal conditions by NADP(H) oxidase-mediated oxygen radicals. Thus, antioxidant t herapy may increase local synthesis of TGF-beta1 in the tubulointerstitium. (C) 2001 Federation of European Biochemical Societies. Published by Elsevi er Science B.V. All rights reserved.