DELTA AND EPSILON ISOZYMES IN HEART

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Protein kinase C (PKC) has been implicated in a number of cardiac functions. These include regulation of the strength and rate of contraction, expression of myofibril proteins, organization of cytoskeleton, regulation of cell size during normal development, and protection from hypoxia-induced cell death. We found that there are at least six different PKC isozymes in neonatal heart. These isozymes share long stretches of sequence homologies. In addition, each isozyme has unique sequences that are quite well conserved in evolution. It is therefore likely that individual PKC isozymes play specific roles in cardiac function, and that the isozyme-unique sequences determine the specificity of individual isozymes for each function. In this proposal, we plan to focus on determining the role of delta and epsilonPKC isozymes. We found that on activation, deltaPKC associates with fibrillar and perinuclear structures, and epsilonPKC isozyme associates with the myofibrils, perinucleus and cell-cell contact structures. Our recent data suggest that one of the unique regions in epsilonPKC contains the binding site for epsilonPKC, specific binding proteins at the perinucleus, myofibril and cell-cell contact. Similarly, we predict that the deltaPKC-specific binding site is in the corresponding unique region of deltaPKC. Here, we plan to identify the sequences within the above isozyme-unique regions that are required for isozyme-specific association of their sites of translocation. We will identify PKC fragments and peptides that inhibit the translocation of specific PKC isozymes to these sites. We have previously demonstrated that inhibition of translocation of PKC inhibits PKC-mediated functions. Therefore, using these delta and epsilon-specific translocation inhibitors, we will determine the role of the respective isozymes in protection of cardiac myocytes from hypoxia-induced cell death, cardiac contraction, organization of cytoskeletal elements, and regulation of cell size. PKC modulates pathological heart conditions including protection from ischemic damage, dysrhythmia and hypertrophy. By identifying isozyme- specific translocation inhibitors, the role of individual PKC isozymes in normal and malfunctioning heart can be determined. Moreover, this approach may lead to the generation of very specific and novel therapeutic agents.