Ubiquitin E3 Ligase Itch Negatively Regulates Osteoclast Formation by Promoting Deubiquitination of Tumor Necrosis Factor (TNF) Receptor-associated Factor 6

Abstract

Itch is a ubiquitin E3 ligase that regulates protein stability. Itch−/− mice develop an autoimmune disease phenotype characterized by itchy skin and multiorgan inflammation. The role of Itch in the regulation of osteoclast function has not been examined. We report that Itch−/− bone marrow and spleen cells formed more osteoclasts than cells from WT littermates in response to receptor activator of NF-κB ligand (RANKL) and was associated with increased expression of the osteoclastogenic transcription factors c-fos and Nfatc1. Overexpression of Itch in Itch−/− cells rescued increased osteoclastogenesis. RANKL increased Itch expression, which can be blocked by a NF-κB inhibitor. The murine Itch promoter contains NF-κB binding sites. Overexpression of NF-κB p65 increased Itch expression, and RANKL promoted the binding of p65 onto the NF-κB binding sites in the Itch promoter. Itch−/− osteoclast precursors had prolonged RANKL-induced NF-κB activation and delayed TNF receptor-associated factor 6 (TRAF6) deubiquitination. In WT osteoclast precursors, Itch bound to TRAF6 and the deubiquitinating enzyme cylindromatosis. Adult Itch−/− mice had normal bone volume, but they had significantly increased LPS-induced osteoclastogenesis and bone resorption. Thus, Itch is a new RANKL target gene that is induced during osteoclastogenesis. Itch interacts with the deubiquitinating enzyme and is required for deubiquitination of TRAF6, thus limiting RANKL-induced osteoclast formation.Background: TRAF6 activity is crucial for osteoclastogenesis, which is decreased by deubiquitination. The role of Itch in this process is studied.Results: Itch−/− osteoclast precursors formed more osteoclasts, had prolonged RANKL-induced NF-κB activation, and had delayed TRAF6 deubiquitination. Itch bound to the deubiquitinating enzyme cylindromatosis.Conclusion: Itch inhibits osteoclastogenesis by binding to cylindromatosis and prompting TRAF6 deubiquitination.Significance: Itch is a new inhibitor of osteoclastogenesis. Itch is a ubiquitin E3 ligase that regulates protein stability. Itch−/− mice develop an autoimmune disease phenotype characterized by itchy skin and multiorgan inflammation. The role of Itch in the regulation of osteoclast function has not been examined. We report that Itch−/− bone marrow and spleen cells formed more osteoclasts than cells from WT littermates in response to receptor activator of NF-κB ligand (RANKL) and was associated with increased expression of the osteoclastogenic transcription factors c-fos and Nfatc1. Overexpression of Itch in Itch−/− cells rescued increased osteoclastogenesis. RANKL increased Itch expression, which can be blocked by a NF-κB inhibitor. The murine Itch promoter contains NF-κB binding sites. Overexpression of NF-κB p65 increased Itch expression, and RANKL promoted the binding of p65 onto the NF-κB binding sites in the Itch promoter. Itch−/− osteoclast precursors had prolonged RANKL-induced NF-κB activation and delayed TNF receptor-associated factor 6 (TRAF6) deubiquitination. In WT osteoclast precursors, Itch bound to TRAF6 and the deubiquitinating enzyme cylindromatosis. Adult Itch−/− mice had normal bone volume, but they had significantly increased LPS-induced osteoclastogenesis and bone resorption. Thus, Itch is a new RANKL target gene that is induced during osteoclastogenesis. Itch interacts with the deubiquitinating enzyme and is required for deubiquitination of TRAF6, thus limiting RANKL-induced osteoclast formation. Background: TRAF6 activity is crucial for osteoclastogenesis, which is decreased by deubiquitination. The role of Itch in this process is studied. Results: Itch−/− osteoclast precursors formed more osteoclasts, had prolonged RANKL-induced NF-κB activation, and had delayed TRAF6 deubiquitination. Itch bound to the deubiquitinating enzyme cylindromatosis. Conclusion: Itch inhibits osteoclastogenesis by binding to cylindromatosis and prompting TRAF6 deubiquitination. Significance: Itch is a new inhibitor of osteoclastogenesis.