title: MicroRNAs 125a and 455 repress lipoprotein-supported steroidogenesis by targeting scavenger receptor class B type I in steroidogenic cells.
abstract: We sought to identify and characterize microRNA (miRNAs) that posttranscriptionally regulate the expression of scavenger receptor class B type I (SR-BI) and SR-BI-linked selective high-density lipoprotein (HDL) cholesteryl ester (CE) transport and steroidogenesis. Four miRNAs (miRNA-125a, miRNA-125b, miRNA-145, and miRNA-455) with a potential to regulate SR-BI were identified in silico and validated by quantitative real-time PCR (qRT-PCR), Western blot analysis, and SR-BI 3' untranslated region (UTR) reporter assays. In vitro treatment of primary rat granulosa cells and MLTC-1 cells with cyclic AMP (cAMP) or in vivo treatment of rat adrenals with adrenocorticotropic hormone (ACTH) decreased the expression of miRNA-125a, miRNA-125b, and miRNA-455 and reciprocally increased SR-BI expression. Using luciferase constructs containing the 3' untranslated region of SR-BI combined with miRNA overexpression and mutagenesis, we have provided evidence that steroidogenic SR-BI is a direct target of miRNA-125a and miRNA-455. Moreover, the transfection of Leydig tumor cells with precursor miRNA 125a (pre-miRNA-125a) or pre-miRNA-455 resulted in the suppression of SR-BI at both the transcript and protein levels and reduced selective HDL CE uptake and HDL-stimulated progesterone production. Transfection of liver Hepa 1-6 cells with pre-miRNA-125a significantly reduced SR-BI expression and its selective transport function. In contrast, overexpression of miRNA-145 did not affect SR-BI expression or selective HDL CE uptake mediated by SR-BI in steroidogenic cell lines. These data suggest that a trophic hormone and cAMP inversely regulate the expression of SR-BI and miRNA-125a and miRNA-455 in steroidogenic tissues/cells and that both miRNA-125a and miRNA-455, by targeting steroidogenic SR-BI, negatively regulate selective HDL CE uptake and HDL CE-supported steroid hormone production.
authors.affiliation: Geriatric Research, Education and Clinical Center, VA Palo Alto Health Care System, Palo Alto, California, USA.
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Hu
authors.forename: Wen-Jun
authors.initials: WJ
authors.lastname: Shen
authors.forename: Fredric B
authors.initials: FB
authors.lastname: Kraemer
authors.forename: Salman
authors.initials: S
authors.lastname: Azhar
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002478:Cells, Cultured; D002788:Cholesterol Esters / Q000378:metabolism; D015536:Down-Regulation; D005260:Female; D006107:Granulosa Cells / Q000378:metabolism; D007985:Leydig Cells / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism*; D011374:Progesterone / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D051122:Scavenger Receptors, Class B / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D013256:Steroids / Q000096:biosynthesis*; D014162:Transfection
chemical_list: D020413:3' Untranslated Regions; D002788:Cholesterol Esters; C059714:HDL cholesteryl ester; D008075:Lipoproteins, HDL; D035683:MicroRNAs; C495125:Scarb1 protein, rat; D051122:Scavenger Receptors, Class B; D013256:Steroids; D011374:Progesterone