Sterols regulate 3β-hydroxysterol Δ24-reductase (DHCR24) via dual sterol regulatory elements: cooperative induction of key enzymes in lipid synthesis by Sterol Regulatory Element Binding Proteins.
ABSTRACT 3β-Hydroxysterol Δ24-reductase (DHCR24) catalyzes a final step in cholesterol synthesis, and has been ascribed diverse functions, such as being anti-apoptotic and anti-inflammatory. How this enzyme is regulated transcriptionally by sterols is currently unclear. Some studies have suggested that its expression is regulated by Sterol Regulatory Element Binding Proteins (SREBPs) while another suggests it is through the Liver X Receptor (LXR). However, these transcription factors have opposing effects on cellular sterol levels, so it is likely that one predominates. Here we establish that sterol regulation of DHCR24 occurs predominantly through SREBP-2, and identify the particular region of the DHCR24 promoter to which SREBP-2 binds. We demonstrate that sterol regulation is mediated by two sterol regulatory elements (SREs) in the promoter of the gene, assisted by two nearby NF-Y binding sites. Moreover, we present evidence that the dual SREs work cooperatively to regulate DHCR24 expression by comparison to two known SREBP target genes, the LDL receptor with one SRE, and farnesyl-diphosphate farnesyltransferase 1, with two SREs.
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ABSTRACT: 3β-hydroxysterol Δ24-reductase (DHCR24) catalyzes the reduction of the C-24 double bond of sterol intermediates during cholesterol biosynthesis. DHCR24 has also been involved in cell growth, senescence and cellular response to oncogenic and oxidative stress. Despite its important roles, little is known about the transcriptional mechanisms controlling DHCR24 gene expression. We analyzed the proximal promoter region and the cholesterol-mediated regulation of DHCR24. A putative sterol regulatory element (SRE) at -98/-90 bp of the transcription start site was identified. Other putative regulatory elements commonly found in SRE-binding protein (SREBP)-targeted genes were also identified. Sterol responsiveness was analyzed by luciferase reporter assays of ~1 kb 5'-flanking region of the human DHCR24 gene in HepG2 and SK-N-MC cells. EMSA and ChiP assays demonstrated cholesterol-dependent recruitment and binding of SREBPs to the putative SRE. Given the presence of several CACCC-boxes in the DHCR24 proximal promoter, we assessed the role of KLF5 in androgen-regulated DHCR24 expression. Dihydrotestosterone increased DHCR24 expression synergistically with lovastatin. However, dihydrotestosterone was unable to activate the DHCR24 proximal promoter, whereas KLF5 did, indicating that this mechanism is not involved in the androgen-induced stimulation of DHCR24 expression. These results allow to elucidate the mechanism of regulation of the DHCR24 gene by cholesterol availability and to identify other putative cis-acting elements which may be relevant for the regulation of DHCR24 expression.Bioscience Reports 10/2012; · 1.88 Impact Factor