Cleavage of PITSLRE kinases by ICE/CASP-1 and CPP32/CASP-3 during apoptosis induced by tumor necrosis factor

Emerging evidence suggests that multiple aspartate-specific cysteine proteases (caspases (CASPs)) play a crucial role in programmed cell death. Many cellular proteins have been identified as their substrates and serve as markers to assay the activation of CASPs during the death process. However, no substrate has yet been unambiguously identified as an effector molecule in apoptosis. PITSLRE kinases are a superfamily of Cdc2-like kinases that have been implicated in apoptotic signaling and tumorigenesis. In this paper we report that tumor necrosis factor (TNF)-mediated apoptosis is associated with a CrmA- and Bcl-2-inhibitable cleavage of PITSLRE kinases, indicating a role for CASPs. Testing of seven murine CASPs for their ability to cleave p110 PITSLRE kinase alpha 2-1 in vitro revealed that only CASP-1 (ICE (interleukin-1 beta-converting enzyme)) and CASP-3 (CPP32) were able to produce the same 43-kDa cleavage product as observed in cells undergoing TNF-induced apoptosis. Mutational analysis revealed that cleavage of p110 PITSLRE kinase alpha 2-1 occurred at Asp(393) within the sequence YVPDS, which is similar to that involved in the CASP-1-mediated cleavage of prointerleukin-1 beta. TNF-induced proteolysis of PITSLRE kinases was still observed in fibroblasts from GASP-1(0/0) mice. These data implicate CASP-3 as a potentially important CASP family protease responsible for the cleavage of PITSLRE kinases during TNF-induced apoptosis.