XIAP and malignant colon neoplasm: Other ATRA pro-apoptotic actions were found in LoVo and SW1116 colon cancer cell lines where ATRA is able to induce the expression of X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1), a protein that functions as antagonist of XIAP by rescuing XIAP-suppressed caspase activity and inducing apoptotic growth suppression (Figure 3) [107].