OXIDATIVE STRESS INHIBITS CALPAIN ACTIVITY IN-SITU

In this study, the effects of oxidative stress on calpain-mediated pro teolysis and calpain I autolysis in situ were examined. Calpain activi ty was stimulated in SH-SY5Y human neuroblastoma cells with the calciu m ionophore, ionomycin, Calpain-mediated proteolysis of the membrane-p ermeable fluorescent substrate eucyl-L-valyl-L-tyrosine-7-amido-4-meth ylcoumarin, as well as the endogenous protein substrates microtubule-a ssociated protein 2, tau and spectrin, was measured. Oxidative stress, induced by addition of either doxorubicin or 2-mercaptopyridine N-oxi de, resulted in a significant decrease in the extent of ionophore-stim ulated calpain activity of both the fluorescent compound and the endog enous substrates compared with control, normoxic conditions, Addition of glutathione ethyl ester, as well as other antioxidants, resulted in the retention/recovery of calpain activity, indicating that oxidation -induced calpain inactivation was preventable/reversible. The rate of autolytic conversion of the large subunit of calpain I from 80 to 78 t o 76 kDa was decreased during oxidative stress; however, the extent of calpain autolysis was not altered, These data indicate that oxidative stress may reversibly inactivate calpain I in vivo.