Ischemia-induced phosphorylation and translocation of stress protein αB-crystallin to Z lines of myocardium

It is becoming clear that stress proteins play a role in various aspects of postischemic myocardial recovery and that the cytoskeleton of cardiac myocytes is an important determinant for cellular survival during ischemia and energy depletion. In the present study, we addressed the question cf whether the cytoskeleton-binding stress protein alpha beta-crystallin may be involved in early cellular responses of rat and porcine myocardium to ischemia. Immunostaining and subcellular fractionation revealed a rapid ischemia-induced redistribution of alpha beta-crystallin from a cytosolic pool to intercalated disks and Z lines of the myofibrils. This striking translocation of alpha beta-crystallin from the cytosol to sites of the myofibrillar system that are known to be sensitive to ischemia-reperfusion injury was accompanied by a rapid shift of a fraction of alpha beta-crystallin to a more acidic isoelectric point. This shift is caused by alpha beta-crystallin phosphorylation, as identified by its augmentation in the presence of phosphatase inhibitors (vanadate, fluoride) and comigration of the acidic alpha beta-crystallin form with the phosphorylated B-1 form of lenticular alpha beta-crystallin. In view of the chaperone-like function of alpha beta-crystallin in conjunction with its high level of constitutive expression in the myocardium (1-2% of soluble protein content), we consider alpha beta-crystallin an excellent candidate to play a role in early aspects of the protection of the myocardial contractile apparatus against ischemia-reperfusion injury.