APIP: Proteins and Enzymes

The mammalian homologues of the key cell death gene CED-4 in C. elegans has been identified recently from human and mouse and designated Apaf1 (for apoptosis protease-activating factor 1) (1,2). Apaf1 binds to cytochrome c (Apaf2) and caspase-9 (Apaf3), which leads to caspase-9 activation. Activated caspase-9 in turn cleaves and activates caspase-3 that is one of the key proteases, being responsible for the proteolytic cleavage of many key proteins in apoptosis (3). Recently, Cho et al (4) have identified a new Apaf-1 Interactiong Protein (APIP) also known as CG129 and MMRP19, as a negative regulator of ischemic injury. APIP competes with Caspase-9 binding site of Apaf1. APIP is predicted to code for a 204 amino acid. An isoform of APIP, APIP2 encodes a 242 amino acid protein, which is an alternative splicing variant differing in its N-terminus from APIP. APIP transcript is ubiquitously expressed in most adult tissue with high expression in skeletal muscle, heart, and kidney.