XIAP and cancer: Importantly, copper supplementation failed to sustain IL-17-induced phosphorylation of IκB in XIAP-deficient cells (Fig. 4d), and XIAP deficiency rendered Ls174t cells highly sensitive to 5-FU-induced caspase-3 activation (Fig. 4e), indicating that XIAP plays an important role in the IL17-induced effects of copper in cancer cells.