Interaction of COUP-TF II with the Rat Carnitine Palmitoyltransferase I β Promoter in Neonatal Rat Cardiac Myocytes

Summary

The rat muscle isoform of carnitine palmitoyltransferase I β (CPT-I β) demon-strates a modest (three-fold) up-regulation of transcriptional activity when neonatal rat cardiac myocytes are co-transfected with the CPT-I β luciferase reporter gene and Peroxisomal Proliferator-Activated Receptor-α (PPAR- α). Neonatal cardiac myocytes contain undetectable levels of PPAR- α protein by immunoblotting. Cotransfection of CPT-I β luciferase with Retinoid X Receptor- α (PJCR- α) alone fails to increase promoter gene expression, con-sistent with the low amounts of PPAR- α in neonatal rat heart. COUP-TF II, but not COUP-TF I, inhibits the activation of the CPT-I β luciferase reporter gene expression, indicating that the repressor effects are isoform specific. Anti-sense COUP-TF II transfection augments CPT-I β reporter gene expression by 80%. Mutation of the PPAR-α/PJCR-α site increases CPT-I β gene expression in neonatal cardiac myocytes. Luciferase expression of both the wild type and mutant promoters is significantly inhibited by co-transfection of COUP-TF II. The data suggest that COUP-TF II represses CPT-I β activation in neonatal heart myocytes by occupying the PPAR-α/PJCR-α binding site within the wild type promoter. The data also support mediation by COUP-TF II of promoter repression by interacting with other transacting factors on the CPT-I β promoter in neonatal heart.