Yin Yang 1 protein negatively regulates high-density lipoprotein receptor gene transcription by disrupting binding of sterol regulatory element binding protein to the sterol regulatory element

Because the high-density lipoprotein receptor (HDL-R) is a key element in cholesterol homeostasis and a potential therapeutic target for hypercholesterolemic drugs, an understanding of HDL-R regulation is essential. The sterol regulatory element (SRE) binding protein-1a (SREBP-1a) was shown to positively regulate HDL-R gene expression through two SREs. SREBP-1a requires the presence of a coactivator like simian-virus-40-protein-1 (Sp1) to promote maximum activation of the HDL-R promoter. Negative regulatory factors are also known to play a role in cholesterol homeostasis, and the ubiquitous Yin Yang-1 zinc finger transcription factor (YY1) has been shown to repress several sterol-responsive gene promoters. A search of the rat HDL-R promoter revealed two putative Wi binding sites (distal, -1329 to -1321; proximal, -1211 to -1203). Upon removal of both Wi binding sites, Wi was unable to repress HDL-R activation under basal (unstimulated) promoter conditions. However, Wi was still an efficient transcriptional repressor for SREBP-1a-induced activation. YY1 was able to attenuate the transcriptional synergy caused by the combined actions of SREBP-1a and Spl. Two-hybrid studies confirmed that Wi bound with high affinity to SREBP-1a, and mobility shift assays demonstrated that YY1 could disrupt SREBP-1a binding to both SREs. The molecular consequence of YY1 intervention seems to override any positive interactions between Sp-1 and SREBP-1a and results in the disruption of SREBP-1a binding to the SREs in the HDL-R promoter.