NONERYTHROID ALPHA-SPECTRIN BREAKDOWN BY CALPAIN AND INTERLEUKIN 1-BETA-CONVERTING-ENZYME-LIKE PROTEASE(S) IN APOPTOTIC CELLS - CONTRIBUTORY ROLES OF BOTH PROTEASE FAMILIES IN NEURONAL APOPTOSIS

The cytoskeletal protein non-erythroid alpha-spectrin is well document ed as an endogenous calpain substrate, especially under pathophysiolog ical conditions. In cell necrosis (e.g. maitotoxin-treated neuroblasto ma SH-SY5Y cells), a-spectrin breakdown products (SBDPs) of 150 kDa an d 145 kDa were produced by cellular calpains. In contrast, in neuronal cells undergoing apoptosis (cerebellar granule neurons subjected to l ow potassium and SH-SY5Y cells treated with staurosporine), an additio nal SBDP of 120 kDa was also observed. The formation of the 120 kDa SB DP was insensitive to calpain inhibitors but was completely blocked by an interleukin 1 beta-converting-enzyme (ICE)-like protease inhibitor , Z-Asp-CH2OC(O)-2,6-dichloro-benzene, Autolytic activation of both ca lpain and the ICE homologue CPP32 was also observed in apoptotic cells , alpha-Spectrin can also be cleaved in vitro by purified calpains to produce the SBDP doublet of 150/145 kDa and by ICE and ICE homologues [ICH-1, ICH-2 and CPP32(beta)] to produce a 150 kDa SBDP, In addition, CPP32 and ICE also produced a 120 kDa SBDP. Furthermore inhibition of either ICE-like protease(s) or calpain protects both granule neurons and SH-SY5Y cells against apoptosis. Our results suggest that both pro tease families participate in the expression of neuronal apoptosis.