miR-122 Regulates LHR Expression in Rat Granulosa Cells by Targeting Insig1 mRNA

Luteinizing hormone/chorionic gonadotropin receptor (LHR) expression in the ovary is regulated by a messenger RNA (mRNA) binding protein, which specifically binds to the coding region of LHR mRNA. We have shown that miR-122, a short noncoding RNA, mediates LHR mRNA levels by modulating the expression of LHR mRNA-binding protein (LRBP) through the regulation of sterol regulatory element binding protein (SREBP) activation. The present results show that miR-122 regulates LRBP levels by increasing the processing of SREBP through the degradation of Insig1, the anchoring protein of SREBP. We present evidence showing that mRNA and protein levels of Insig1 undergo a time-dependent increase following the treatment of rat granulosa cells with follicle-stimulating hormone (FSH), which leads to a decrease in LRBP levels. Furthermore, overexpression of miR-122 using an adenoviral vector (AdmiR-122) abolished FSH-induced increases in Insig1 mRNA and protein. We further confirmed the role of Insig1 by showing that inhibition of Insig1 using a specific small interfering RNA prior to FSH treatment resulted in the abrogation of LHR upregulation. Silencing of Insig1 also reversed FSH-mediated decreases in SREBP and LRBP activation. These results show that decreased levels of miR-122 increase Insig1 and suppress SREBP processing in response to FSH stimulation of rat granulosa cells.