XIAP and cancer: XIAP prevents the activation of caspase-3 and -9 at different levels, including inhibition of substrate binding and proteasomal degradation of processed caspase-3 forms.43 Downregulation or inhibition of XIAP has been proposed as a mechanism of bortezomib-induced sensitisation to TRAIL in different cancer models.34,44,45 In our system, depletion of XIAP partially sensitised HPV+ cells to TRAIL and significantly enhanced the synergistic effect of bortezomib.