DDIAS suppresses TRAIL-mediated apoptosis by inhibiting DISC formation and destabilizing caspase-8 in cancer cells.

DNA damage-induced apoptosis suppressor (DDIAS) has an anti-apoptotic function during DNA damage in lung cancer. However, the anti-apoptotic mechanism of DDIAS in cancer cells under other conditions has not been reported. We report here that DDIAS protects cancer cells from tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis by two distinct mechanisms in non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC) cells. DDIAS depletion sensitized NSCLC and HCC cells to TRAIL-mediated apoptosis, an effect that was abrogated by pharmacological or genetic inhibition of caspase-8 and was independent of caspase-9, p53, or mitogen-activated protein kinase signaling. Interestingly, we found that the N terminus of DDIAS interacted with the death effector domain of Fas-associated protein death domain (FADD) and prevented its recruitment to the death-inducing signaling complex (DISC), thereby blocking caspase-8 activation. DDIAS knockdown also suppressed epidermal growth factor-induced phosphorylation of p90 ribosomal S6 kinase (RSK) 2 and stabilized caspase-8 by preventing its ubiquitination and proteasomal degradation. This effect was abolished by RSK2 overexpression. Taken together, DDIAS has dual functions in inhibiting DISC formation as well as in destabilizing caspase-8, thereby suppressing TRAIL-mediated apoptosis of cancer cells. Thus, we suggest that DDIAS can serve as an effective therapeutic target in the treatment of NSCLC and HCC.