PROTEOLYTIC CLEAVAGE OF RAS GTPASE-ACTIVATING PROTEIN DURING APOPTOSIS

p120-ras GTPase-activating protein (rasGAP) associates with Ras and ne gatively regulates Ras signaling by stimulating the intrinsic rate of Ras GTPase activity. rasGAP also associates with other cellular signal ing proteins which suggest that rasGAP may play a role in coordinating other signal transduction pathways. Disruption of rasGAP in vivo resu lts in extensive apoptosis. Fas-mediated apoptosis results in the acti vation of caspases that cleave cellular substrates which are important for maintaining cytoplasmic and nuclear integrity. We show here that rasGAP is proteolytically cleaved by caspases early in Fas-induced apo ptosis of Jurkat cells. rasGAP was also cleaved by DNA-damaging chemot herapeutic agents and TN F-related apoptosis inducing ligand (TRAIL), also known as Apo2L. Based on the size of the products generated by cl eavage of deletion mutants of rasGAP we predict that cleavage of rasGA P occurs in the hydrophobic region and between the SH2(2) and ras-p21 interacting domain which would leave an intact ras-p21 interacting dom ain. Interestingly, cleavage of rasGAP in vitro enhanced rasGAP hydrol ysis activity. Our results demonstrate that diverse apoptotic stimuli cause caspase-mediated cleavage of rasGAP early in apoptosis.