The protein Usurpin, an endogenous mammalian regulator of the process of apoptotic cell suicide, is provided. Provided are three Usurpin proteins having an amino acid sequence selected from the group consisting of: SEQ.ID.NO.:4, SEQ.ID.NO.:5, and SEQ.ID.NO.:6 that arise from alternative splicing of the Usurpin gene. The full-length Usurpin polypeptide (Usurpin-α) has features in common with pro-caspase-8 and -10, including tandem 'death effector domains' (DEDs) on the N-terminus and a large subunit/small subunit caspase-like domain, but it lacks key residues that are necessary for caspase proteolytic activity. However, Usurpin heterodimerizes with pro-caspase-8 and precludes pro-caspase-8 recruitment by the FADD/MORT1 adapter protein, thus blocking an important interaction in the CD95 (Fas/APO-1) apoptotic process. Therefore, Usurpin is useful as a modulator of the sensitivity of cells to CD95 (Fas/APO-1)-mediated apoptosis. Accordingly, the present invention also provides methods of modulating apoptosis by introducing Usurpin polypeptides into cells. Also provided are various purified nucleotide sequences encoding Usurpin. Also provided are methods of identifying inhibitors of the interaction between Usurpin and pro-caspase-8. Such inhibitors will be useful in controlling the interaction between Usurpin and pro-caspase-8, thus modulating apoptosis.
展开▼
