Cloning and expression of the rat liver cDNA for peroxisomal enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase in lambda GT11. Transcriptional regulation of enzyme activity by Wy-14643 in primary cultures of rat hepatocytes.

Abstract

Proliferation of rat liver peroxisomes by the hypolipidemic drug Wy-14643 is associated with a concomitant induction of peroxisomal enzymes involved in the beta-oxidation of fatty acids. In order to explore the molecular mechanism of this induction process we have cloned the cDNA for the peroxisomal bifunctional enzyme enoyl-CoA hydratase, 3-hydroxyacyl-CoA dehydrogenase (ECH) in the lambda gt11 expression vector. The library was screened with the monospecific rabbit antiserum to ECH. Hybrid-selected-mRNA translation established that the immunoreactive clones contain the cDNA sequences of the ECH bifunctional enzyme. The cloned cDNA was used to define the early events associated with enzyme induction in primary cultures of rat hepatocytes. Dot-blot hybridization of the total hepatocyte RNA with the ECH cDNA probe showed that the ECH mRNA begins to rise at about 10-15 h following incubation with Wy-14643. At 24 h and 48 h of incubation the stimulation of the ECH mRNA over the vehicle-treated control reached 26-fold and 47-fold respectively. Run-off experiments in the isolated nuclei of hepatocytes showed no increase in the transcription rate of the ECH gene at 5 h after drug treatment and a 2-fold and 11-fold increase at 10 h and 20 h of drug treatment. From these results we conclude that the increase in ECH activity by Wy-14643 is due to an enhancement of the rate of transcription of the ECH gene. However, the relatively long lag period of about 10-15 h after exposure of hepatocytes to Wy-14643 suggests that the induction of the ECH mRNA may involve an indirect effect of the drug on the transcription of this gene.