Nuclear receptor binding to the retinoic acid response elements of the phosphoenolpyruvate carboxykinase gene in vivo: effects of vitamin A deficiency

Abstract

Vitamin A deficiency decreases hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene expression in mice and expression is restored with retinoic acid treatment in vivo. This report examines further the mechanism of retinoid regulation of the PEPCK gene in vivo. We have identified nuclear receptors that bind to retinoic acid response elements (RAREs) in the PEPCK promoter by electrophoretic mobility shift assay and have verified these in vivo using chromatin immunoprecipitation (ChIP) in mouse liver. Based on the results of our ChIP assay, hepatic nuclear factor (HNF)-4α, retinoid X receptor (RXR) α, retinoic acid receptor (RAR) α, peroxisome proliferator-activated receptor (PPAR) α and chicken ovalbumin upstream promoter transcription factor (COUP-TF) II bind to the downstream retinoic acid response unit RARE1/RARE2, and PPARα and RXRα bind to the upstream RARE3 of the PEPCK gene. HNF-4α, RXRα, RARα, PPARα and COUP-TFII bind PEPCK RAREs in a specific pattern that, with the exception of PPARα, does not change significantly with vitamin A deficiency. PPARα binding to the upstream retinoic acid response element is decreased in the vitamin A-deficient liver, when compared to the vitamin A-sufficient state. These results provide the first in vivo measures of nuclear receptor binding to the upstream and downstream RAREs of the PEPCK gene under conditions where the nucleosomal structure of the chromatin is maintained and the nuclear receptors are physically cross-linked in situ to the PEPCK DNA in intact liver.