Transcriptional regulation of methionine adenosyltransferase 2A by peroxisome proliferator-activated receptors in rat hepatic stellate cells.

ABSTRACT: Methionine adenosyltransferases (MATs) are critical enzymes that catalyze the formation of the methyl donor S-adenosyl methionine (SAM). The MAT2A gene, which encodes the catalytic subunit ?2, is induced in dedifferentiated liver. We previously demonstrated that MAT2A expression is enhanced in activated hepatic stellate cells (HSCs) and that silencing this gene reduces HSC activation. In this study, we examined the molecular mechanisms responsible for the transcriptional regulation of the MAT2A gene in HSCs. We identified peroxisome proliferator-activated receptor (PPAR) response elements (PPREs) in the rat MAT2A promoter. The PPAR? agonist rosiglitazone (RSG) promoted quiescence in the activated rat HSC cell line (BSC) or culture-activated primary rat HSCs, decreased MAT2A expression and promoter activity, and enhanced PPAR? binding to MAT2A PPREs. In vivo HSC activation in bile duct-ligated rats lowered PPAR? interaction with MAT2A PPREs. Silencing PPAR? increased MAT2A transcription, whereas overexpressing it had the opposite effect, demonstrating that PPAR? negatively controls this gene. Site-directed mutagenesis of PPREs abolished PPAR? recruitment to the MAT2A promoter and its inhibitory effect on MAT2A transcription in quiescent HSCs. PPRE mutations decreased the basal promoter activity of MAT2A in activated HSCs independent of PPAR?, indicating that other factors might be involved in PPRE interaction. We identified PPAR? binding to wild-type but not to mutated PPREs in activated cells. Furthermore, silencing PPAR? inhibited MAT2A expression and promoter activity. Forced expression of MAT2A in RSG-treated HSCs lowered PPAR? and enhanced PPAR? expression, thereby promoting an activated phenotype.We identified PPAR? as a negative regulator of MAT2A in quiescent HSCs. A switch from quiescence to activation abolishes this control and allows PPAR? to up-regulate MAT2A transcription.

SUBMITTER: Ramani K 

PROVIDER: S-EPMC3342421 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature