TGF-β1 induced activations of Smad2 and miRNAs inhibit SF-1- and LRH-1-dependent CYP19 expression in rat Leydig...

P450 aromatase, encoded by the Cyp19 gene, catalyzes the synthesis of estrogen, which is crucial for mammalian germ cell differentiation. We have previously shown that transforming growth factor beta 1 (TGF-β1) attenuated the accumulation of steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1) and eventually reduced the transcription of Cyp19 in rat Leydig cells (LCs). Here, we report that TGF-β1 treatment-induced phosphorylation of Smad2 and decreased the expression levels of SF-1 and LRH-1 by elevating the expression levels of microRNA-21-3p and microRNA-339-5p in vivo and in vitro. Furthermore, both TGF-β1 treatment and over-expression of Smad2 inhibited the SF-1 or LRH-1-regulated promoter activity of the Cyp19 gene, and p-Smad2 physically interacted with SF-1 and LRH-1. Our findings collectively suggest that TGF-β1 may inhibit the expression of CYP19 in LCs mainly through two ways. On the one hand, TGF-β1 acts through Smad2 to repress the accumulation of SF-1 and LRH-1 at post-transcriptional level by upregulating specific microRNAs. On the other hand, TGF-β1 inhibits the transcriptional activity of Cyp19 through the interaction of p-Smad2 with SF-1/LRH-1.