Calmodulin-binding peptide PEP-19 modulates activation of calmodulin kinase II in situ

PEP-19 is a 6 kDa polypeptide that is highly expressed in select population s of neurons that sometimes demonstrate resistance to degeneration. These i nclude the granule cells of the hippocampus and the Purkinje cells of the c erebellum. Its only identified activity to date is that of binding apo-calm odulin. As a consequence, it has been demonstrated to act as an inhibitor o f calmodulin-dependent neuronal nitric oxide synthase in vitro, although PE P-19 regulation of calmodulin-dependent enzymes has never been characterize d in intact cells. The activation of the calmodulin-dependent enzyme calmod ulin kinase II (CaM kinase II) was studied in PC12 cells that had been tran sfected so as to express physiological levels of PEP-19. The expression of PEP-19 yielded a stable phenotype that failed to activate CaM kinase II upo n depolarization in high K+. However, CaM kinase II could be fully activate d when calcium influx was achieved with ATP. The effect of PEP-19 on CaM ki nase II activation was not attributable to changes in the cellular expressi on of calmodulin. The cellular permeability of the transfected cells to cal cium ions also appeared essentially unchanged. The results of this study de monstrated that PEP-19 can regulate CaM kinase II in situ in a manner that was dependent on the stimulus used to mobilize calcium. The selective natur e of the regulation by PEP-19 suggests that its function is not to globally suppress calmodulin activity but rather change the manner in which differe nt stimuli can access this activity.