Transcriptional Regulation of Cholesterol Biosynthetic Gene by Nuclear Receptors

点击翻译按钮获取中文摘要

Luciferase assay using deleted rat and human squalene epoxidase (SE) promoter, reveals that SE gene is regulated by SREBP and NF-Y.Over-expression of LXR cause reduction of SE gene expression. Next we tested the changes of LXRE and SE promoter expression, using LXRβ, RXRα and LXRα mutants. Over-expression of LXRα, LXRβ, RXRα and co-overexpression of LXRs and RXRα cause the induction of LXRE.But LXRα mutant 1 and mutant-2 did not show any induction of LXRE as well as very slight induction with RXR cotransfection. These results strongly suggest that mutant 1 and 2 of LXRα functioned as a dominant negative mutants to LXRE expression. LXRE induction reciprocally correlated with the suppression of SE promoter reporter plasmid, indicating the LXR involvement of SE gene expression.To identify possible LXRα ligands, we tested for ability to activate LXRE expression. As shown in this slide, significant activation of LXRE chimeras was obtained in transfected HeLa cells treated with 24(S), 25-epoxycholesterol and 22(R)-hydroxycholesterol, but 20α-hydroxycholesterol and 22(S)-hydroxycholesterol was less effective. This suggests 24(S), 25-epoxycholesterol and 22(R)-hydroxycholesterol are candidates of LXR ligands. Suppression of SE promoter expression also correlated again with LXRE reporter plasmid induction, provided another support for LXR participation in SE promoter suppression.