Transcriptional regulation of human oxysterol 7α-hydroxylase by sterol response element binding protein

Abstract

Oxysterol 7α-hydroxylase (CYP7B1) metabolizes oxysterols, potent regulators of lipid homeostasis. Very little is known about transcriptional regulation of human CYP7B1. The present results indicate that sterol response element binding protein (SREBP), a family of oxysterol-responsive transcription factors that stimulates cholesterol synthesis, may be an important regulator of CYP7B1. SREBP suppressed a human CYP7B1 luciferase reporter gene in several cell lines, most markedly in rat hepatoma McA-RH7777 cells. An SREBP-1-responsive region was mapped to a GC-rich sequence in the proximal CYP7B1 promoter, containing binding sites for the basal transcriptional activator Sp1. Mutagenesis of this sequence abolished SREBP-1-mediated suppression. Data indicated that SREBP does not bind this sequence but affects the gene indirectly, probably via interaction with Sp1. Our findings indicate that CYP7B1 transcription is controlled by SREBP and reveal a link between oxysterol-sensitive regulators and oxysterol metabolism. We propose that CYP7B1 is important for regulating cellular sterol content and protects against oxysterol-mediated toxicity.