RESUMO
Peptides derived from protein kinase C (PKC) modulate its activity by interfering with critical protein-protein interactions within PKC and between PKC and PKC-binding proteins (Souroujon, M. C., and Mochly-Rosen, D. (1998) Nat. Biotechnol. 16, 919-924). We previously demonstrated that the C2 domain of PKC plays a critical role in these interactions. By focusing on epsilonPKC and using a rational approach, we then identified one C2-derived peptide that acts as an isozyme-selective activator and another that acts as a selective inhibitor of epsilonPKC. These peptides were used to identify the role of epsilonPKC in protection from cardiac and brain ischemic damage, in prevention of complications from diabetes, in reducing pain, and in protecting transplanted hearts. The efficacy of these two peptides led us to search for additional C2-derived peptides with PKC-modulating activities. Here we report on the activity of a series of 5-9-residue peptides that are derived from regions that span the length of the C2 domain of epsilonPKC. These peptides were tested for their effect on PKC activity in cells in vivo and in an ex vivo model of acute ischemic heart disease. Most of the peptides acted as activators of PKC, and a few peptides acted as inhibitors. PKC-dependent myristoylated alanine-rich C kinase substrate phosphorylation in epsilonPKC knock-out cells revealed that only a subset of the peptides were selective for epsilonPKC over other PKC isozymes. These epsilonPKC-selective peptides were also protective of the myocardium from ischemic injury, an epsilonPKC-dependent function (Liu, G. S., Cohen, M. V., Mochly-Rosen, D., and Downey, J. M. (1999) J. Mol. Cell. Cardiol. 31, 1937-1948), and caused selective translocation of epsilonPKC over other isozymes when injected systemically into mice. Examination of the structure of the C2 domain from epsilonPKC revealed that peptides with similar activities clustered into discrete regions within the domain. We propose that these regions represent surfaces of protein-protein interactions within epsilonPKC and/or between epsilonPKC and other partner proteins; some of these interactions are unique to epsilonPKC, and others are common to other PKC isozymes.