Sterol regulatory element-binding protein-1a binds to cis elements in the promoter of the rat high density lipoprotein receptor SR-BI gene.
The high density lipoprotein (HDL) receptor, or scavenger receptor class B type I (SR-BI), is critical for cholesterol transport and a potential target for hypercholesterolemic drugs. Thus, elucidation of the mechanism underlying regulation of the HDL receptor SR-BI gene is essential. It has been previously shown that there is a correlation between depletion in ovarian cholesteryl ester content and increased HDL receptor SR-BI expression in response to hormonal stimulation. We wanted to determine whether the levels of mature sterol response element-binding protein-1a (SREBP-1a), a key protein in the transcriptional regulation of several genes by sterols, are affected under these conditions. Thus, Western blot analysis was carried out. Consistent with the possibility that SREBP-1a may be involved in the regulation of the HDL receptor SR-BI gene, we found that mature SREBP-1a levels increased up to 11-fold in the ovary after treatment with 50 U hCG. This increase in mature SREBP-1a protein levels correlated with a 30% decrease in ovarian cholesterol levels. These changes in both SREBP-1a and cholesterol levels preceded a 2-fold induction of HDL receptor SR-BI protein levels. To determine whether SREBP-1a could directly regulate the expression of the rat HDL receptor SR-BI gene, approximately 2.2 kb of the receptor SR-BI promoter were cloned and sequenced, and deletion analysis and mobility shift assays were performed. The results of these studies demonstrate that the rat HDL receptor SR-BI promoter contains two sterol response elements (pSRE and dSRE) through which SREBP-1a can bind and activate transcription of this gene. These motifs are similar to known SRE motifs reported for sterol-sensitive genes, and the pSRE is located between two Sp1 sites, similar to the SRE-1 motif in the low density lipoprotein receptor. The cysteine protease inhibitor N-acetyl-leucyl-leucyl-norleucinal, which inhibits SREBP degradation, enhanced the effect of SREBP-1a on the regulation of the rat HDL receptor SR-BI gene. It has previously been shown that tropic hormones such as hCG can also influence gene expression by increasing cAMP levels. Consistent with this fact, we have recently shown that steroidogenic factor-1 (SF-1) mediates cAMP activation of the HDL receptor SR-BI gene. Thus, we decided to examine whether SREBP-1a could cooperate with SF-1 to enhance transcription this gene. The results confirm that indeed both SF-1 and SREBP-1a synergize to induce HDL receptor SR-BI gene expression.
Lopez
D
D
Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa 33606, USA.
McLean
M P
MP
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D018955:CD36 Antigens / Q000235:genetics*; D002352:Carrier Proteins; D002784:Cholesterol / Q000378:metabolism; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism* / Q000494:pharmacology; D010053:Ovary / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein / Q000235:genetics; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D054339:Steroidogenic Factor 1; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D018955:CD36 Antigens; D002352:Carrier Proteins; D006063:Chorionic Gonadotropin; D004268:DNA-Binding Proteins; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; C495125:Scarb1 protein, rat; D051122:Scavenger Receptors, Class B; C497389:Srebf1 protein, rat; D054339:Steroidogenic Factor 1; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; C031616:high density lipoprotein receptors; C515058:steroidogenic factor 1, mouse; C515060:steroidogenic factor 1, rat; C075197:high density lipoprotein binding protein; D004247:DNA; D002784:Cholesterol