Involvement of calmodulin- and protein kinase C-related mechanism in an induction process of peroxisomal fatty acid oxidation-related enzymes by hypolipidemic peroxisome proliferators

Abstract

Trifluoperazine, a calmodulin antagonist, suppressed the clofibric acid-evoked induction of the peroxisomal cyanide-insensitive fatty acyl-CoA oxidizing system and carnitine acetyltransferase in rat liver and also in cultured rat hepatocytes. H-7, a potent inhibitor of protein kinase C, also suppressed the induction of these enzymes by clofibric acid, burafibrate, Wy14,643 or mono(2-ethylhexyl)phthalate in cultured rat hepatocytes. This suppressive effect was also confirmed by the protein composition of hepatocytes treated with clofibric acid and these antagonists, where the increase in the amount of peroxisomal bifunctional enzyme by peroxisome proliferator was markedly suppressed by above two antagonists. Profile of the time-dependent changes in the activities of the two enzymes after clofibric acid treatment showed that there might be two phases in the induction process. The initial phase (0–3 days after the treatment) showed a relative low inducing rate and subsequent phase (3–5 days after the treatment) showed an abrupt induction. The suppressive effect of the above two antagonists was significant in the later phase. In a time course study of the induction process of peroxisomal catalase, bifunctional enzyme or 69 kDa integral membrane protein using immunochemical detection, the induction of the membrane protein by clofibric acid was delayed compared with that of the bifunctional enzyme, where the induction was inhibited almost completely by nicardipine. These experimental results suggest that calmodulin- and protein kinase C-dependent processes play an important role in the process of marked induction of peroxisomal enzymes and membrane protein by drugs in rat liver.