Multiple myeloma (MM), a malignancy of plasma cells, still remains incurable; immunotherapies are expected to open a new avenue for MM treatment paradigm. TRAIL-based immunotherapy is one such approach against MM. Although MM extensively induces RANK ligand-mediated systemic osteoclastic bone destruction, the effects of TRAIL agonists on osteoclasotgenesis remain largely unknown. The present study was therefore undertaken to clarify the impact of TRAIL on osteoclastogenesis and MM-osteoclast (OC) interaction. RANK ligand induced editing of death receptor5 (DR5), a mouse TRAIL receptor, and c-FLIP, an endogenous caspase 8 inhibitor, in murine RAW264.7 preosteoclastic cells. Interestingly, addition of rTRAIL enhanced RANK ligand-mediated osteoclastogenesis, and did not induce apoptosis in mature OCs, while inducing apoptotic cell death with caspase8 cleavage in MM cells. rTRAIL and RANK ligand cooperatively phosphorylated TGF-beta-activated kinase-1 (TAK-1) and thereby degraded IκBα. However, the TAK-1 inhibitor LLZ1640-2 abrogated the NF-κB activation and c-FLIP induction, which triggered rTRAIL-induced apoptosis in OCs. We recently found Pim-2 as a critical mediator of MM survival and osteoclastogenesis (Leukemia, 2011, 2015). rTRAIL as well as RANK ligand induced Pim-2 expression in RAW264.7 cells. However, LLZ1640-2 abolished the Pim-2 up-regulation and suppressed osteoclastogensis induced by rTRAIL as well as RANK ligand, suggesting a critical role of the TAK-1-Pim-2 pathway. Cocultures with OCs enhanced MM cell growth and survival along with Pim-2 up-regulation in MM cells; however, LLZ1640-2 substantially reduced Pim-2 expression and potentiated rTRAIL-induced MM cell death even in cocultures with OCs. These results demonstrate that osteoclastic lineage cells utilize TRAIL for their differentiation and activation in combination with RANK ligand through tilting TRAIL-mediated caspase8-dependent apoptosis into activation of the NF-κB survival signaling, and suggest that TAK1 inhibition subverts TRAIL- and RANK ligand-mediated NF-κB activation in OCs to regain TRAIL-induced apoptosis in OCs as well as MM cells.