Direct activation of TGF-beta1 transcription by androgen and androgen receptor complex in Huh7 human hepatoma cells and its tumor in nude mice

Abstract

Importance of androgen for promotion of hepatocelullar carcinoma (HCC) has long been supported by clinical and experimental evidences. However, mechanisms involved in the carcinogenesis have not yet been fully elucidated. Moreover, unbalanced expression of TGF-beta1 during tumor progression results in prooncogenic rather than growth inhibition. To investigate the effect of androgen on transcriptional regulation of TGF-beta1, we isolated rat TGF-beta1 promoter, based on our previous report (GenBank AF249327), and examined regulation of its promoter activity by dihydrotestosterone in Huh7, LNCaP, and PC3 cells. Several putative transcription factor-binding sites were found, but no TATA box. When the full-length (-4784 to +68) and variously deleted promoter DNAs were evaluated, the promoter region spanning from -2732 to -1203 showed the highest activity towards dihydrotestosterone in a dose-dependent manner in both Huh7 and PC3 cells with androgen receptor (AR) expression. Putative androgen response sequence half site (5'-TGTCCT-3') was identified to be located within -1932 to -1927, proved by mutant (5'-AGACCT-3') analysis and chromatin immunoprecipitation (ChIP) assay. AR mediated upregulation of TGF-beta1 expression was confirmed by HCC developed in nude mice with AR-overexpressed Huh7-cells. This work presents in vivo and in vitro evidences of activation of TGF-beta1 expression by androgen and AR, and implicates the modulation of hepatocarcinogenesis by AR through the regulation of TGF-beta1 expression.