Translational upregulation of the X-linked inhibitor of apoptosis.

The X-linked inhibitor of apoptosis protein (XIAP) is the most potent and best studied intrinsic regulator of programmed cell death. The critical role XIAP plays in the control of apoptosis is also reflected in the complex ways the activity of XIAP is regulated. In addition to regulating the function of the protein, the synthesis of XIAP is also selectively regulated. XIAP is translated by a cap-independent mechanism of translation initiation that is mediated by a unique internal ribosome entry site (IRES) sequence element located in its 5' untranslated region. This allows XIAP mRNA to be actively translated during conditions of cellular stress when the majority of cellular protein synthesis is inhibited. The IRES regulation of XIAP translation points to an important mechanism in the control and regulation of apoptosis.