SMAD3 inhibits SF-1-dependent activation of the CYP17 promoter in H295R cells.
Cytochrome P450c17, encoded by the CYP17 gene, is a component of 17alpha-hydroxylase/17,20 lyase which catalyses 17alpha-hydroxylation of pregnenolone or progesterone, required for glucocorticosteroid and androgen synthesis. It has been reported that transforming growth factor beta (TGF-beta) decreases both basal and cAMP-stimulated levels of CYP17 mRNA, but the mechanism of TGF-beta action on CYP17 expression remains unknown. We investigated an inhibitory effect of TGF-beta on CYP17 expression in H295R cells using constructs containing the CYP17 promoter region fused with the luciferase gene. In the H295R cells, TGF-beta decreased endogenous SF-1 level and inhibited activity of the 300 bp fragment of CYP17 promoter, which was stimulated by coexpression of SF-1. Overexpression of SMAD3 caused an inhibition of SF-1-stimulated CYP17 promoter activity, whereas overexpression of SMAD7 was ineffective. In conclusion, our results suggest that the inhibitory action of TGF-beta on CYP17 transcription involve at least two mechanisms: SMAD3 dependent inactivation of CYP17 promoter activity and repression of SF-1 expression.
Derebecka-Holysz
Natalia
N
Department of Biochemistry and Molecular Biology, Medical University, 6 Swiecickiego St, Poznan, Poland.
Lehmann
Tomasz P
TP
Holysz
Marcin
M
Trzeciak
Wieslaw H
WH
D000302:Adrenal Cortex / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D006801:Humans; D011401:Promoter Regions, Genetic; D015398:Signal Transduction / Q000187:drug effects; D051900:Smad3 Protein / Q000502:physiology*; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics*; D054339:Steroidogenic Factor 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000494:pharmacology