Identification of a hormone response element that mediates suppression of APOF by LXR and PPAR? agonists.

ABSTRACT: Apolipoprotein F (ApoF) regulates cholesteryl ester transfer protein activity. We previously observed that hepatic APOF mRNA levels are decreased by high fat, cholesterol-enriched diets. Here we show in human liver C3A cells that APOF mRNA levels are reduced by agonists of LXR and PPAR? nuclear receptors. This negative regulation requires co-incubation with the RXR agonist, retinoic acid. Bioinformatic analysis of the ~2 kb sequence upstream of the APOF promoter identified one potential LXR and 4 potential PPAR? binding sites clustered between nucleotides -2007 and -1961. ChIP analysis confirmed agonist-dependent binding of LXR?, PPAR?, and RXR? to this hormone response element complex (HREc). A luciferase reporter containing the 2 kb 5' APOF sequence was negatively regulated by LXR and PPAR? ligands as seen in cells. This regulation was maintained in constructs lacking the ~1700 nucleotides between the HREc and the APOF proximal promoter. Mutations of the HREc that disrupted LXR? and PPAR? binding led to the loss of reporter construct inhibition by agonists of these nuclear receptors. siRNA knockdown studies showed that APOF gene regulation by LXR? or PPAR? agonists did not require an interaction between these two nuclear receptors. Thus, APOF is subject to negative regulation by agonist-activated LXR or PPAR? nuclear receptors binding to a regulatory element ~1900 bases 5' to the APOF promoter. High fat, cholesterol-enriched diets likely reduce APOF gene expression via these receptors interacting at this regulatory site.

SUBMITTER: Liu Y 

PROVIDER: S-EPMC6957717 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature