Apoptosis, or programmed cell death, is related to many diseases, such as cancer. Apoptosis is triggered by a variety of stimuli including members in the TNF family and can be prevented by the inhibitor of apoptosis (IAP) proteins. IAP proteins form a conserved gene family that binds to and inhibits cell death proteases. The X-chromosome linked inhibitor of apoptosis (XIAP) contains 3 baculoviral IAP repeat (BIR) motifs that are essential and sufficient for the binding and inhibition of caspases-3, -7, and -9. Upregulation of XIAP expression can protect cells from apoptosis induced by low level radiation; conversely, decreased XIAP expression by antisense targeting resulted in increased cell death following low level radiation. Two negative regulators, termed XAF-1 and Smac, can bind and inhibit XIAP activity.
