Author:

Keywords:

Animals, Base Sequence, CCAAT-Enhancer-Binding Proteins, Carrier Proteins, Conserved Sequence, DNA-Binding Proteins, Diazepam Binding Inhibitor, Gene Expression Regulation, Genes, Reporter, Humans, Lipid Metabolism, Molecular Sequence Data, Nuclear Proteins, Promoter Regions (Genetics), RNA, Messenger, Rats, Sequence Alignment, Steroids, Sterol Regulatory Element Binding Protein 1, Trans-Activation (Genetics), Transcription Factors, Tumor Cells, Cultured, Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, DENSITY-LIPOPROTEIN RECEPTOR, CELL-LINE LNCAP, INDUCED INSULIN-SECRETION, AMINO-ACID SEQUENCE, ACYL-COA, MESSENGER-RNA, ADIPOCYTE DIFFERENTIATION, BENZODIAZEPINE RECEPTOR, ANDROGEN REGULATION, SYNTHASE PROMOTER, Promoter Regions, Genetic, Transcriptional Activation, 03 Chemical Sciences, 06 Biological Sciences, 11 Medical and Health Sciences, 31 Biological sciences, 32 Biomedical and clinical sciences, 34 Chemical sciences

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.