PKC-dependent activation of p44/p42 MAPKs during myocardial ischemia-reperfusion in conscious rabbits

Using conscious rabbits, we examined the effect of ischemic preconditioning (PC) on p44 and p42 mitogen-activated protein kinases (MAPKs). We found th at both isoforms contribute significantly to total MAPK activity in the hea rt (in-gel kinase assay: p44, 59 +/- 1%; p42, 41 +/- 1%). Ischemic PC (6 cy cles of 4-min occlusion/4-min reperfusion) elicited a pronounced increase i n total cellular MAPK activity (+89%). This increase, which occurred exclus ively in the nuclear fraction, was contributed by both isoforms (in-gel kin ase assay: p44, +97%; p42, +210%) and was accompanied by migration of the t wo proteins from the cytosolic to the nuclear compartment. In control rabbi ts, MAPK kinase (MEK)1 and MEK2, direct activators of p44 and p42 MAPKs, we re located almost exclusively in the cytosolic fraction. Ischemic PC induce d a marked increase in cytosolic MEK activity (+164%), whereas nuclear MEK activity did not change, indicating that MEK-induced activation of MAPKs oc curred in the cytosolic compartment. Activation of MAPKs after ischemic PC was completely blocked by the protein kinase C (PKC) inhibitor chelerythrin e. Selective overexpression of PKC-epsilon in adult rabbit cardiomyocytes i nduced activation of both p44 and p42 MAPKs and reduced lactate dehydrogena se release during simulated ischemia-reperfusion, which was abolished by th e MEK inhibitor PD-98059. The results demonstrate that 1) ischemic PC induc es a rapid activation of p44 and p42 MAPKs in hearts of conscious rabbits; 2) the mechanism of this phenomenon involves activation of p44 and p42 MAPK s in the cytosol and their subsequent translocation to the nucleus; and 3) it occurs via a PKC-mediated signaling pathway. The in vitro data implicate PKC-epsilon as the specific isoform responsible for PKC-induced MAPK activ ation and suggest that p44/p42 MAPKs contribute to PKC-epsilon-mediated pro tection against simulated ischemia. The results are compatible with the hyp othesis that p44 and p42 MAPKs may play a role in myocardial adaptations to ischemic stress.