Phosphorylation of peroxisome proliferator-activated receptor alpha in ratFao cells and stimulation by ciprofibrate

The basic mechanism(s) by which peroxisome proliferators activate peroxisom e proliferator-activated receptors (PPARs) is (are) not yet fully understoo d. Given the diversity of peroxisome proliferators, several hypotheses of a ctivation have been proposed. Among them is the notion that peroxisome prol iferators could activate PPARs by changing their phosphorylation status. In fact, it is well known that several members of the nuclear hormone recepto r superfamily are regulated by phosphorylation. In this report, we show tha t the rat Fao hepatic-derived cell line, known to respond to peroxisome pro liferators, exhibited a high content of PPAR alpha. Alkaline phosphatase tr eatment of Fao cell lysate as well as immunoprecipitation of PPAR alpha fro m cells prelabeled with [P-32] orthophosphate clearly showed that PPAR alph a is indeed a phosphoprotein in vivo. Moreover, treatment of rat Fao cells with ciprofibrate, a peroxisome proliferator, increased the phosphorylation level of the PPAR alpha. In addition, treatment of Fao cells with phosphat ase inhibitors (okadaic acid and sodium orthovanadate) decreased the activi ty of ciprofibrate-induced peroxisomal acyl-coenzyme A oxidase, an enzyme e ncoded by a PPAR alpha target gene. Our results suggest that the gene expre ssion controlled by peroxisome proliferators could be mediated in part by a modulation of the PPARa effect via a modification of the phosphorylation l evel of this receptor. BIOCHEM PHARMACOL 58;6:1001-1008, 1999. (C) 1999 Els evier Science Inc.