Promoter analysis of the DHCR24 (3β-hydroxysterol Δ24-reductase) gene: characterization of SREBP (sterol-regulatoryelement-binding protein)-mediated activation

Abstract

Synopsis DHCR24 (3β-hydroxysterol24 -reductase) catalyses 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 analysed the proximal promoter region and the cholesterol-mediated regulation of DHCR24. A putative SRE (sterol-regulatory element) at − 98/ − 90 bp of the transcription start site was identified. Other putative regulatory elements commonly found in SREBP (SRE-binding protein)-targeted genes were also identified. Sterol responsiveness was analysed by luciferase reporter assays of approximately 1 kb 5 -flanking region of the human DHCR24 gene in HepG2 and SK-N-MC cells. EMSAs (electrophoretic mobility-shift assays) and ChIP (chromatin immunoprecipitation) 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 (Krüppel-like factor 5) in androgen-regulated DHCR24 expression. DHT (dihydrotestosterone) increased DHCR24 expression synergistically with lovastatin. However, DHT 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. The results of the present study allow the elucidation of the mechanism of regulation of the DHCR24 gene by cholesterol availability and identification of other putative cis-acting elements which may be relevant for the regulation of DHCR24 expression.

Dietary lipids modulate the expression of miR‐107, a miRNA that regulates the circadian system

“…The functionality of this SREBP-binding site needs to be experimentally validated. However, the proximity of this binding site to the TSS, as well as the presence of close SP-1 and NF-Y binding sites support the hypothesis of the SREBP modulation by miR-107 levels, since this structure is characteristic of SREBP modulated promoters [62]. Additionally, we found binding sites for other metabolically important transcription factors such as CREBP, myogenin, c-Fos/c-Jun, and GATA3.…”

Dietary lipids modulate the expression of miR-107, an miRNA that regulates the circadian system

“…The functionality of this SREBP binding site needs to be experimentally validated. However, the proximity of this binding site to the TSS, as well as the presence of close SP‐1 and NF‐Y binding sites support the hypothesis of the SREBP modulation by miR‐107 levels, since this structure is characteristic of SREBP‐modulated promoters . Additionally, we found binding sites for other metabolically important transcription factors such as CREBP, myogenin, c‐Fos/c‐Jun, and GATA3.…”

Involvement of microRNA214 and transcriptional regulation in reductions in mevalonate pyrophosphate decarboxylase mRNA levels in stroke-prone spontaneously hypertensive rat livers

“…11,12) SREBPs in the endoplasmic reticulum (ER) membrane require proteolytic processing (two-steps proteolytic process of cleavage after transfer from ER to Golgi complex) to release N-terminal bHLH-Zip domains into the nucleus, and the N-terminal domains of SREBP bind to target genes (sterol regulatory element : SRE) in order to activate the transcription of fatty acids or cholesterol synthesis. 13) SREBP processing is regulated by changes in the content of cholesterol in the liver or the amount of cholesterol absorbed from the small intestine. Increases in cellular cholesterol synthetic enzymes and receptors (LDL-receptor) involved in the uptake of serum cholesterol by the liver have been attributed to the stimulation of SREBP processing by the depletion of cholesterol levels in liver or the amount of cholesterol (small amount) absorbed from the small intestine.…”