TRANSLOCATION INHIBITORS DEFINE SPECIFICITY OF PROTEIN-KINASE-C ISOENZYMES IN PANCREATIC BETA-CELLS

The protein kinase C (PKC) family consists of 11 isoenzymes. Following activation, each isoenzyme translocates and binds to a specific recep tor for (a) under bar ctivated (C) under bar (k) under bar inase (RACK ) (Mochly-Rosen, D. (1995) Science 268, 247-251) that provides an anch oring site in close proximity to the isoenzyme's specific substrate. P ancreatic islet cells contain at least six PKC isoenzymes (Knutson, K. L., and Hoenig, M. (1994) Endocrinology 135, 881-886). Although PKC a ctivation enhances insulin release, the specific function of each isoe nzyme is unknown. Here we show that following stimulation with glucose , alpha PKC and epsilon PKC translocate to the cell's periphery, while delta PKC and zeta PKC translocate to perinuclear sites. beta C2-4, a peptide derived from the RACK1 binding site in the C2 domain of beta PKC, inhibits translocation of alpha PKC and reduces insulin response to glucose. Likewise, epsilon V1-2, an epsilon PKC derived peptide con taining the site for its specific RACK, inhibits translocation of epsi lon PKC and reduces insulin response to glucose. Inhibition of islet-g lucose metabolism with mannoheptulose blocks translocation of both alp ha PKC and epsilon PKC and diminishes insulin response to glucose whil e calcium-free buffer inhibits translocation of alpha PKC but not epsi lon PKC and lowers insulin response by 50%. These findings illustrate the unique ability of specific translocation inhibitors to elucidate t he isoenzyme-specific functions of PKC in complex signal transduction pathways.