Med25 Is Required for RNA Polymerase II Recruitment to Specific Promoters, Thus Regulating Xenobiotic and Lipid Metabolism in Human Liver

Abstract

Hepatocyte nuclear factor 4α (HNF4α) controls the expression of many critical metabolic pathways, and the Mediator complex occupies a central role in recruiting RNA polymerase II (Pol II) to these gene promoters. An impaired transcriptional HNF4α network in human liver is responsible for many pathological conditions, such as altered drug metabolism, fatty liver, and diabetes. Here, we report that Med25, an associated member of the Mediator complex, is required for the association of HNF4α with Mediator, its several cofactors, and RNA Pol II. Further, increases and decreases in endogenous Med25 levels are reflected in the composition of the transcriptional complex, Pol II recruitment, and the expression of HNF4α-bound target genes. A novel feature of Med25 is that it imparts “selectivity.” Med25 affects only a significant subset of HNF4α target genes that selectively regulate drug and lipid metabolism. These results define a role for Med25 and the Mediator complex in the regulation of xenobiotic metabolism and lipid homeostasis.

ACKNOWLEDGMENTS

We thank Anton Jetten and Paul Wade for critical reading of the manuscript. We also thank and acknowledge the expertise and assistance of Jason Williams in the Protein Microcharacterization facility, Kevin Gerrish in the Microarray facility, and Jeff Tucker in the confocal microscopy core facility, NIEHS, and Benjamin Fontenot from CellzDirect/Invitrogen.

This study was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences, under NIH intramural project number Z01ES02124.

We declare that we have no conflict of interest.