XIAP and cancer: The most direct evidence supporting its role as an autophagy negative-regulator came from a study by Huang et al. In this study, XIAP was shown to be capable of inhibiting autophagy via a XIAP-Mouse double minute 2 homolog (Mdm2)-p53 signaling pathway in the wild-type p53 (p53WT)-expressing HCT116 cancer cells, but not in the p53−/− HCT116 cancer cells [40].