Maritoclax Enhances TRAIL-Induced Apoptosis via CHOP-Mediated Upregulation of DR5 and miR-708-Mediated Downregulation of cFLIP

Maritoclax, an active constituent isolated from marine bacteria, has been known to induce Mcl-1 downregulation through proteasomal degradation. In this study, we investigated the sensitizing effect of maritoclax on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human renal carcinoma cells. We found that combined treatment with maritoclax and TRAIL markedly induced apoptosis in renal carcinoma (Caki, ACHN and A498), lung cancer (A549) and hepatocellular carcinoma (SK-Hep1) cells. The upregulation of death receptor 5 (DR5) and downregulation of cellular FLICE-inhibitory protein (cFLIP) were involved in maritoclax plus TRAIL-induced apoptosis. Maritoclax-induced DR5 upregulation was regulated by induction of C/EBP homologous protein (CHOP) expression. Interestingly, maritoclax induced cFLIP downregulation through the increased expression of miR-708. Ectopic expression of cFLIP prevented combined maritoclax and TRAIL-induced apoptosis. Taken together, maritoclax sensitized TRAIL-induced apoptosis through CHOP-mediated DR5 upregulation and miR-708-mediated cFLIP downregulation.