Mch3, a novel human apoptotic cysteine protease highly related to CPP32

Recent evidence suggests that mammalian cysteine proteases related to Caenorhabditis elegans CED-3 are key components of mammalian programmed cell death or Apoptosis. We have shown recently that the CPP32 and Mch2 alpha cysteine proteases cleave the apoptotic markers poly(ADP-ribose) polymerase (PARP) and lamins, respectively. Here we report the cloning of a new Ced-3/interleukin 1 beta-converting enzyme-related gene, designated Mch3, that encodes a protein with the highest degree of homology to CPP32 compared to Other family members. An alternatively spliced isoform, named Mch3 beta, was also identified. Bacterially expressed recombinant Mch3 has intrinsic autocatalytic/autoactivation activity. The specific activity of Mch3 alpha toward the peptide substrate DEVD-7-amino-4-methylcoumarin and PARP resembles that of CPP32. Like interleukin 1 beta-converting Enzyme and CPP32, the active Mch3 alpha is made of two subunits derived from a precursor (proMch3 alpha). It was of interest that recombinant CPP32-p17 subunit can form an active heteromeric Enzyme complex with recombinant Mch3 alpha-p12 subunit and vice versa, as determined by the ability of the heteromeric complexes to induce Apoptosis in Sf9 cells. These data suggest that proMch3 alpha and proCPP32 can interact to form an active Mch3 alpha/CPP32 heteromeric complex. We also provide evidence that CPP32 can efficiently cleave proMch3 alpha, but not the opposite, suggesting that Mch3 alpha activation in vivo may depend in part on CPP32 activity. The high degree of conservation in structure and specific activity and the coexistence of Mch3 alpha and CPP32 in the same cell suggests that the PARP cleavage activity observed during Apoptosis cannot solely be attributed to CPP32 but could also be an activity of Mch3 alpha.