XIAP (X-linked inhibitor of apoptosis)

X-linked inhibitor of apoptosis (XIAP), also referred to as BIRC4 or IAP3, is one of the most studied members among the proteins known as Inhibitors of Apoptosis Proteins (IAPs). This protein family portrays its main role by preventing apoptotic cell death through direct or indirect inhibition of caspase activity. All members of the IAPs carry at least one BIR domain in their structure, which are generally responsible for caspase interaction. XIAP has three BIR domains, enabling interaction with both initiation and effector caspases. Moreover, it is also structured with a RING finger domain, which functions as a ubiquitin ligase (E3), and one UBA domain, for binding to ubiquitin, further rendering XIAP a central role in the ubiquitination process and, thus, implicating such IAP in multiple signaling pathways, including cell death, autophagy, immunity, inflammation, cell cycle, and cell migration. XIAP overexpression is found in a variety of cancer types and is frequently associated with chemoresistance and increased risk of relapse. Furthermore, there are many evidences that XIAP inhibition may sensitize tumor cells to chemotherapy agents, which make this protein a potential target in cancer