XIAP Associated Factor 1 (XAF1)

X-linked inhibitor of apoptosis (XIAP) is a potent member of the IAP family. All members of this family possess baculoviral IAP (BIR) repeats, cysteine-rich domains of approximately 80 amino acids that bind and inhibit caspases. XIAP has 3 BIR domains and a C-terminal RING zinc finger that possesses E3 ubiquitin ligase activity. XAF1 antagonizes the anticaspase activity of XIAP and may be important in mediating apoptosis resistance in cancer cells.

The BIRC4-XAF1 complex mediates down-regulation of BIRC5/survivin; the process requires the E3 ligase activity of BIRC4. Seems to be involved in cellular sensitivity to the proapoptotic actions of TRAIL. May be a tumor suppressor by mediating apoptosis resistance of cancer cells