Osteoclasts utilize TRAIL for their NF-κB activation, but TAK1 inhibition resumes TRAIL-induced apoptosis in osteoclasts   — ASN Events
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Osteoclasts utilize TRAIL for their NF-κB activation, but TAK1 inhibition resumes TRAIL-induced apoptosis in osteoclasts   (#119)

Hirofumi Tenshin 1 2 , Jumpei Teramachi 3 , Asuka Oda 2 , Ryota Amachi 4 , Masahiro Hiasa 5 , Keiichiro Watanabe 4 , Shingen Nakamura 2 , Hirokazu Miki 6 , Shiro Fujii 2 , Kumiko Kagawa 2 , Masami Iwasa 2 , Ariunzaya Baterdene 2 , Itsuro Endo 2 , Eiji Tanaka 4 , Toshio Matsumoto 7 , Masahiro Abe 2
  1. Department of Orthodontics and Dentofacial Orthopedics, Graduate School of Oral Science, The University of Tokushima, Tokushima-shi, TOKUSHIMA, Japan
  2. Department of hematology, endocrinology and metabolism, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, Japan
  3. Department of Histology and Oral Histology, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokuhsima
  4. Department of Orthodontics and Dentofacial Orthopedics, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima
  5. Department of Biomaterials and Bioengineering, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima
  6. Division of Transfusion Medicine and Cell Therapy, Tokushima University Hospital, Tokushima
  7. Fujii Memorial Institute of Medical Sciences, Tokushima University, Tokushima, Japan

Multiple myeloma (MM) expands in bone with devastating osteoclastic bone destruction. We recently found that TRAIL rather enhances osteoclastogenesis, although TRAIL-based immunotherapy is regarded as a promising approach against MM. In the present study, we therefore aimed to dissect the mechanisms of osteoclastogenic actions by TRAIL and develop a maneuver to induce TRAIL-mediated apoptosis in osteoclasts (OCs) together with MM cells. RANK ligand concomitantly induced the TRAIL receptor DR5 and c-FLIP, an inhibitor for DISC formation and caspase-8 activation, in RAW264.7 cells. TRAIL further upregulated c-FLIP, and induced TAK1 phosphorylation and thereby IκBα degradation without inducing apoptosis in OCs. Immunoprecipitation analyses demonstrated that TRAIL preferentially formed the complex with FADD, TRAF2 and RIP (Complex II), an initiator of canonical NF-κB activation, but not DISC in OCs, while potently inducing DISC formation in MM cells. c-FLIP siRNA abolished the TRAIL-induced Complex II formation and triggered DISC formation and thereby apoptosis in OCs, indicating a predominant role of c-FLIP in blocking of apoptosis by TRAIL. The c-FLIP upregulation in OCs by TRAIL was abolished by the NF-κB inhibitor BAY11-7085 as well as terameprocol, an inhibitor of Sp-1, a transcription factor responsible for c-FLIP gene expression, suggesting the TRAIL-TAK1-NF-κB-Sp-1-c-FLIP induction axis in OCs. The TAK1 inhibitor LLZ1640-2 also resumed DISC formation in OCs by TRAIL along with the reduction of Sp-1 and c-FLIP which was restored by the caspase-8 inhibitor z-IETD-FMK, indicating enzymatic Sp-1 degradation and thereby c-FLIP reduction. In MM cells, TRAIL reduced Sp-1 and c-FLIP protein levels in a caspase-8-dependent manner, which was further enhanced by the TAK1 inhibition. These results collectively demonstrate that osteoclastic lineage cells tilt TRAIL-mediated apoptosis into the NF-κB survival signaling, and that TAK1 inhibition subverts TRAIL-mediated NF-κB activation in OCs to resume TRAIL-induced apoptosis in OCs while further potentiating it in MM cells.