title: Feedback inhibition of human scavenger receptor class B type I gene expression by glucocorticoid in adrenal and ovarian cells.
abstract: Scavenger receptor class B type I (SR-BI) facilitates the reverse transport of excess cholesterol from peripheral tissues to the liver via high-density lipoproteins. In steroidogenic tissues, SR-BI supplies cholesterol for steroid hormone production. We show here that the transcription of the human SR-BI gene is subject to feedback inhibition by glucocorticoid in adrenal and ovarian cells. SR-BI mRNA levels were increased in adrenals from corticosterone-insufficient Crh(-/-) mice, whereas corticosterone replacement by oral administration inhibited SR-BI gene expression in these mice. SR-BI mRNA levels were increased in adrenals from wild-type mice treated with metyrapone, a drug that blocks corticosterone synthesis. Experiments in adrenocortical H295R and ovarian SKOV-3 cells using cycloheximide and siRNA-mediated gene silencing revealed that glucocorticoid-mediated inhibition of SR-BI gene transcription requires de novo protein synthesis and the glucocorticoid receptor (GR). No direct binding of GR to the SR-BI promoter could be demonstrated in vitro and in vivo, suggesting an indirect mechanism of repression of SR-BI gene transcription by GR in adrenal cells. Deletion analysis established that the region of the human SR-BI promoter between nucleotides -201 and -62 is sufficient to mediate repression by glucocorticoid. This region contains putative binding sites for transcriptional repressors that could play a role in SR-BI gene regulation in response to glucocorticoid. In summary, this is the first report showing that glucocorticoid suppress SR-BI expression suggesting that steroidogenic tissues maintain steroid hormone homeostasis by prohibiting SR-BI-mediated high-density lipoprotein cholesterol uptake when the endogenous levels of glucocorticoid are elevated.
authors.affiliation: Department of Basic Sciences, Foundation of Research and Technology-Hellas, Heraklion 71003, Greece.
authors.forename: Sofia
authors.initials: S
authors.lastname: Mavridou
authors.forename: Maria
authors.initials: M
authors.lastname: Venihaki
authors.forename: Olga
authors.initials: O
authors.lastname: Rassouli
authors.forename: Christos
authors.initials: C
authors.lastname: Tsatsanis
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kardassis
mesh_terms: D000311:Adrenal Glands / Q000166:cytology*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010053:Ovary / Q000166:cytology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051122:Scavenger Receptors, Class B / Q000235:genetics / Q000378:metabolism*
chemical_list: D005938:Glucocorticoids; D034741:RNA, Small Interfering; D011965:Receptors, Glucocorticoid; D051122:Scavenger Receptors, Class B