PKC-dependent activation of p46/p54 JNKs during ischemic preconditioning in conscious rabbits

A conscious rabbit model was used to study the effect of ischemic precondit ioning (PC) on stress-activated kinases [c-Jun NH2-terminal kinases (JNKs) and p38 mitogen-activated protein kinase (MAPK)] in an environment free of surgical trauma and attending external stress. Ischemic PC (6 cycles of 4-m in ischemia/4-min reperfusion) induced significant activation of protein ki nase C (PKC)-epsilon in the particulate fraction, which was associated with activation of p46 JNK in the nuclear fraction and p54 JNK in the cytosolic fraction; all of these changes were completely abolised by the PKC inhibit or chelerythrine. Selective enhancement of PKC-epsilon activity in adult ra bbit cardiac myocytes resulted in enhanced activity of p46/p54 JNKs, provid ing direct in vitro evidence that PKC-epsilon is coupled to both kinases. S tudies in rabbits showed that the activation of p46 JNK occurred during isc hemia, whereas that of p54 JNK occurred after reperfusion. A single 4-min p eriod of ischemia induced a robust activation of the p38 MAPK cascade, whic h, however, was attenuated after 5 min of reperfusion and disappeared after six cycles of 4-min ischemia/reperfusion. Overexpression of PKC-E in cardi ac myocytes failed to increase the p38 MAPK activity. These results demonst rate that ischemic PC activates p46 and p54 JNKs via a PKC-epsilon-dependen t signaling pathway and that there are important differences between p46 an d p54 JNKs with respect to the subcellular compartment (cytosolic vs, nucle ar) and the mechanism (ischemia vs. reperfusion) of their activation after ischemic PC.