Cloning of AIP1, a novel protein that associates with the apoptosis-linkedgene ALG-2 in a Ca2+-dependent reaction

ALG-2 is a 22-kDa calcium-binding protein necessary for cell death induced by different stimuli in 3DO T-cell hybridoma 3DO cell clones depleted of AL G-2 protein exhibit normal caspases activation, suggesting that ALG-2 funct ion is required downstream or is independent of caspase proteases activity for apoptosis to occur. Using the yeast two-hybrid screening system, we hav e isolated and characterized the mouse cDNA encoding for ALG-2 interacting protein 1 (AIP1), a novel protein that interacts with ALG-2. ALG-2 and AIP1 colocalize in the cytosol and the presence of calcium is an indispensable requisite for their association. Sequence align ment shows that AIP1 is hig hly similar to BRO1, a yeast protein related to components of the Pkc1p-MAP kinase cascade. Overexpression of a truncated form of AIP1 protects two different cell type s from death induced by trophic factors withdrawal; thus, our data indicate that AIP1 cooperates with ALG-1 in executing the calcium-dependent require ments along the cell death pathway.