Interaction of COUP-TF II with the rat carnitine palmitoyltransferase I β promoter in neonatal rat cardiac myocytes

The rat muscle isoform of carnitine palmitoyltransferase I beta (CPT-I beta) demonstrates a modest (three-fold) up-regulation of transcriptional activity when neonatal rat cardiac myocytes are co-transfected with the CPT-I beta luciferase reporter gene and Peroxisomal Proliferator-Activated Receptor-alpha (PPAR-alpha). Neonatal cardiac myocytes contain undetectable levels of PPAR-a protein by immunoblotting. Cotransfection of CPT-I beta luciferase with Retinoid X Receptor-alpha (RXR-alpha) alone fails to increase Promoter gene expression, consistent with the low amounts of PPAR-alpha. in neonatal rat heart. COUP-TF II, but not COUP-TF I, inhibits the activation of the CPT-I beta luciferase reporter gene expression, indicating that the repressor effects are isoform specific. Anti-sense COLJP-TF II transfection augments CPT-I beta reporter gene expression by 80%. Mutation of the PPAP-alpha/RXR-alpha site increases CPT-I P 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 beta activation in neonatal heart myocytes by occupying the PPAR-alpha/RXR-alpha binding site within the wild type promoter. The data also support mediation by COLJP-TF II of promoter repression by interacting with other transacting factors on the CPT-I beta promoter in neonatal heart.