Granulosa Cell-expressed BMPR1A and BMPR1B have Unique Functions in Regulating Fertility but Act Redundantly to Suppress Ovarian Tumor Development

摘要

Vitamin D receptor (VDR) is activated by natural ligands, 1 ? , 25-dihydroxy-vitamin D 3 (1 ? , 25(OH) 2 -D 3 ) and lithocholic acid (LCA).OurpreviousstudyshowsthatVDRisexpressedinhumanhepatocytes,andVDRligandsinhibitbileacidsynthesisandtranscriptionof the gene encoding cholesterol 7 ? -hydroxylase (CYP7A1). Primary human hepatocytes were used to study LCA and 1 ? ,25(OH) 2 -D 3 activation of VDR signaling. Confocal immunofluorescent microscopy imaging and immunoblot analysis showed thatLCA and 1 ? , 25(OH) 2 -D 3 induced intracellular translocation of VDR from the cytosol to the nucleus, and also plasma membranewhere VDR co-localized with caveolin-1. VDR ligands induced tyrosine phosphorylation of c-Src and VDR, and their interaction.Inhibition of c-Src abrogated VDR ligand-dependent inhibition of CYP7A1 mRNA expression. Kinase assays showed that VDRligands specifically activated the c-Raf/MEK1/2/ERK1/2 pathway, which stimulates serine phosphorylation of VDR and HNF4 ? , andtheir interaction. Mammalian two-hybrid assays showed a VDR ligand dependent interaction of nuclear receptor corepressor-1(NCoR-1)andsilencingmediatorofretinoidandthyroid(SMRT)withVDR/RXR ? .Chromatinimmunoprecipitationassaysrevealedthat an ERK1/2 inhibitor reversed VDR ligand-induced recruitment of VDR, RXR ? and corepressors to human CYP7A1 promoter.In conclusion, VDR ligands activate membrane VDR signaling to activate the MEK1/2/ERK1/2 pathway, which stimulates nuclearVDR/RXR ? recruitmentofco-repressorstoinhibitCYP7A1genetranscriptioninhumanhepatocytes.ThismembraneVDRsignalingpathway may be activated by bile acids to inhibit bile acid synthesis as a rapid response to protect hepatocytes from cholestaticliver injury.