USE OF A PCR-BASED METHOD TO CHARACTERIZE PROTEIN-KINASE-C ISOFORM EXPRESSION IN CARDIAC-CELLS

Molecular cloning has identified at least nine unique isozymes of protein kinase C (PKC) designated alpha, betaI, betaII, gamma, delta, epsilon, zeta, and eta/L, with the recent addition of the theta-isoform. Previous attempts to characterize PKC isoform expression in heart have been limited by low levels of protein and perhaps by the presence of novel isoforms. Thus to critically examine the diversity of PKC expression in cardiac cells, we developed a reverse transcriptase-polymerase chain reaction (RT-PCR) approach that would amplify regions of the target cDNA of all the PKC isozymes in a single reaction. Degenerate oligonucleotide primers were designed to recognize sequences in the conserved regions of the PKC sequence motif. the cysteine-rich and the ATP-binding regions. Amplification of target PKC cDNA sequences resulted in PCR products with unique sizes and restriction digestion properties. The system was validated by identifying PCR products that correspond to all of the PKC isoform transcripts, except PKC-zeta, in a single reaction with cDNA derived from hippocampus. Cardiac cDNA was RT-PCR amplified, and the products were analyzed by a combination of restriction mapping and DNA sequencing that revealed the presence of only the alpha, delta, epsilon, and eta isoforms in adult rat cardiac myocytes and cultured neonatal ventricular myocytes. A unique nondegenerate primer pair was synthesized to recognize PKC-zeta cDNA. Results with these primers show that PKC-zeta is present in both cardiac myocyte preparations as well. The RT-PCR method developed here is an efficient approach that is broadly useful to examine PKC expression in many tissues, including the identification of potentially novel isoforms. This method has been used to provide the first comprehensive characterization of PKC expression in cardiac cells.