Expression and genetic analysis of XIAP-associated factor 1 (XAF1) in cancer cell lines

X-linked inhibitor of apoptosis protein (XIAP) is a potent modulator of pro grammed cell death. XIAP specifically binds and inhibits the function of ca spase-3, -7, and -9, key effector proteases of apoptosis. We recently isola ted, by yeast two-hybrid screening, a novel 34-kDa zinc finger protein, XIA P-associated factor 1 (XAF1). Both the caspase inhibiting and the anti-apop totic abilities of XIAP were found to be blocked by overexpressed XAF1. Her e, we report the isolation and characterization of the human XAF1 gene. The xaf1 gene consists of seven exons spanning 18 kb. Fluorescence in situ hyb ridization analysis localized the xaf1 locus at 17p13.2, telomeric to the p 53 gene. The xaf1 locus was further refined to YAC 746C10, approximately 3 cM distal to TP53. Microsatellite analysis of the xaf1 locus using the NCI6 0 cell line panel revealed significantly decreased heterozygosity at all th ree polymorphic markers tested, suggesting that allelic loss of the xaf1 ge ne is prevalent in cancer cell lines. Examination of the same NCI cell line panel for xaf1 RNA expression demonstrated that cancer cell lines exhibite d very low levels of mRNA relative to normal human liver. In contrast, XIAP mRNA levels were relatively high in the majority of cancer cell lines test ed. We propose that a high level of XIAP to XAF1 expression in cancer cells may provide a survival advantage through the relative increase of XIAP ant i-apoptotic function. (C) 2000 Academic Press.