Apoptosis of Jurkat T cells induced the caspase-mediated proteolytic cleavage of p21-activated kinase 2 (PAK2). Cleavage occurred between the amino-terminal regulatory domain and the carboxyl-terminal catalytic domain, which generated a constitutively active PAK2 fragment. Stable Jurkat cell lines that expressed a dominant-negative PAK mutant were resistant to the Fas-induced formation of apoptotic bodies, but had an enhanced externalization of phosphatidlyserine at the cell surface. Thus, proteolytic activation of PAK2 represents a guanosine triphosphatase-independent mechanism of PAK regulation that allows PAK2 to regulate morphological changes that are seen in apoptotic cells.