Abstract
Diazepam-binding inhibitor/acyl-CoA-binding protein (DBI/ACBP), a highly conserved 10-kDa polypeptide, has been implicated in various physiological processes including gamma-aminobutyric acid type A receptor binding, acyl-CoA binding and transport, steroidogenesis, and peptide hormone release. Both in LNCaP prostate cancer cells and 3T3-L1 preadipocytes, the expression of DBI/ACBP is stimulated under conditions that promote lipogenesis (treatment with androgens and insulin, respectively) and that involve the activation of sterol regulatory element-binding proteins (SREBPs). Accordingly, we investigated whether DBI/ACBP expression is under the direct control of SREBPs. Analysis of the human and rat DBI/ACBP promoter revealed the presence of a conserved sterol regulatory element (SRE)-like sequence. Gel shift analysis confirmed that this sequence is able to bind SREBPs. In support of the functionality of SREBP binding, coexpression of SREBP-1a with a DBI/ACBP promoter-reporter gene resulted in a 50-fold increase in transcriptional activity in LNCaP cells. Disruption of the SRE decreased basal expression and abolished SREBP-1a-induced transcriptional activation. In agreement with the requirement of a co-regulator for SREBP function, transcriptional activation by SREBP-1a overexpression was severely diminished when a neighboring NF-Y site was mutated. Cholesterol depletion or androgen treatment, conditions that activate SREBP function in LNCaP cells, led to an increase in DBI/ACBP mRNA expression and SRE-dependent transcriptional activation. These findings indicate that the promoter for DBI/ACBP contains a functional SRE that allows DBI/ACBP to be coregulated with other genes involved in lipid metabolism.
Highlights
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) X94563
In view of the postulated role of Diazepam-binding inhibitor (DBI)/acyl-CoA-binding protein (ACBP) in fatty acid and cholesterol metabolism and its induction under conditions that involve sterol regulatory element-binding proteins (SREBPs) activation, we explored whether DBI/ACBP is directly controlled by SREBPs
Identification of a SREBP-binding Site in the DBI/ACBP Promoter—Examination of the nucleotide sequences of the human DBI/ACBP promoter for potential SREBP sites revealed a sequence CTCGCCCGAG at positions Ϫ127 to Ϫ118 of the published sequence [25], resembling the 10-base pair sterol regulatory element (SRE) found in other SREBP-regulated genes (Fig. 1)
Summary
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) X94563. Transcriptional Regulation of DBI/ACBP Promoter-Reporter Genes by Coexpressed SREBP—In order to determine whether SREBP binding is functional, we transiently transfected LNCaP cells with a DBI/ACBP promoter-reporter construct harboring the SRE site (pDBI-264luc, here referred to as wt), together with a plasmid encoding -galactosidase and increasing amounts of pSREBP-1a1–460, a plasmid encoding transcriptionally active SREBP-1a.
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