Calcium/calmodulin-dependent protein kinase IV is cleaved by caspase-3 and calpain in SH-SY5Y human neuroblastoma cells undergoing apoptosis

We have previously demonstrated cleavage of alpha-spectrin by caspase-3 and calpain during apoptosis in SH-SY5Y neuroblastoma cells (Nath, R, Raser, K, J., Stafford, D., Hajimohammadreza, I., Posner, A., Alien, H,, Talanian, R, V,, Yuen, P,, Gilbertsen, R. B,, and Wang, K, K, (1996) Biochem. J, 319, 683-690). We demonstrate here that calcium/calmodulin-dependent protein kinase IV (CaMK TV) is cleaved during apoptosis by caspase-3 and calpain, We challenged SH-SY5Y cells with the pro-apoptotic agent thapsigargin. Western blot analysis revealed major CaMK IV breakdown. products of 40, 38, and 33 kDa, Digestion of control SH-SY5Y lysate with purified caspase-3 produced a 38-kDa CaMK IV fragment; digestion with purified calpain produced a major fragment of 40 kDa, Pretreatment with carbobenzoxy-Asp-CH2OC(O)-2,6-dichlorobenzene or Z-Val-Ala-Asp-fluoromethylketone was able to block the caspase-3-mediated production of the 38-kDa fragment both in situ and in vitro. Calpain inhibitor II similarly blocked formation of the calpain-mediated 40-kDa fragment both in situ and in vitro. Digestion of recombinant CaMK TV by other caspase family members revealed that only caspase-3 produces a fragmentation pattern consistent to that seen in situ. The major caspase-3 and calpain cleavage sites are respectively identified as PAPD(176)*A and CG(201)*A, both within the CaMK TV catalytic domain. Furthermore, calmodulin-stimulated protein kinase activity decreases within 6 h in thapsigargin-treated SH-SY5Y, The loss of activity precedes cell death.