The role of calpain in caspase activation during etoposide induced apoptosis in T cells

T cells treated with the drug etoposide undergo apoptotic death characteriz ed by early evidence of nuclear damage followed by loss of mitochondrial in tegrity and cell lysis. Calpains and caspases are cytoplasmic proteases and there is increasing evidence of cross-talk between these proteases in deat h pathways. In this study we have investigated the role of calpain, in etop oside-triggered apoptosis in the 2B4 murine T cell hybridoma. Cell permeabl e inhibitors of calpain, ALLnM, E64 and calpeptin that block Pas ligand-fas -mediated death in T cells, blocked etoposide-induced nuclear damage, loss of mitochondrial integrity and cell lysis. A broad spectrum peptide inhibit or of caspases, ZVAD-fmk, partially blocked nuclear damage but poorly inhib ited mitochondrial damage or cell lysis triggered by etoposide. Etoposide-i nduced expression of the cleaved, proteolytically active form of caspase 3, and DEVD-ase activity, detected prior to nuclear damage, were blocked in t he presence of calpain inhibitors. Collectively, these data describe a role for calpain in regulating etoposide-induced apoptosis via a caspase-depend ent pathway in T cells.