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Int. J. Mol. Sci. 2017, 18(10), 2054;

Blocking of the Ubiquitin-Proteasome System Prevents Inflammation-Induced Bone Loss by Accelerating M-CSF Receptor c-Fms Degradation in Osteoclast Differentiation

Department of Microbiology, Laboratory of Bone Metabolism and Control, Yeungnam University College of Medicine, Daegu 42415, Korea
Department of Biomedical Engineering, College of Health Science, Institute of Medical Engineering, Yonsei University, Wonju 26493, Korea
IHBR, Department of Oral Pathology, School of Dentistry, Kyungpook National University, Daegu 41940, Korea
These authors contributed equally to this work.
Author to whom correspondence should be addressed.
Received: 9 August 2017 / Revised: 20 September 2017 / Accepted: 23 September 2017 / Published: 25 September 2017
(This article belongs to the Section Biochemistry, Molecular and Cellular Biology)
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Anti-osteoporotic activity of a blocker of the ubiquitin-proteasome system, bortezomib, has known to be achieved by directly opposed action in increased bone formation by osteoblasts and in decreased bone destruction by osteoclasts. However, the mechanisms underlying the proteasome blocker inhibition of osteoclast differentiation and function are not fully understood. Here, we observed that proteasome inhibitors, such as MG132 and bortezomib, in osteoclasts accelerated the degradation of c-Fms, a cognate receptor of macrophage colony-stimulating factor (M-CSF), and did not affect the amount of receptor activator of nuclear factor kappa-B (RANK), a receptor of receptor activator of nuclear factor kappa-B ligand (RANKL). c-Fms degradation induced by proteasome inhibitors was controlled by the activation of p38/tumor necrosis factor-alpha converting enzyme (TACE)-mediated regulated intramembrane proteolysis (RIPping). This was validated through the restoration of c-Fms using specific inhibitors of p38 and TACE, and a stimulation of p38-dependent TACE. In addition, c-Fms degradation by proteasome inhibition completely blocked M-CSF-mediated intrinsic signalling and led to the suppression of osteoclast differentiation and bone resorption. In a mouse model with intraperitoneal administration of lipopolysaccharide (LPS) that stimulates osteoclast formation and leads to bone loss, proteasome blockers prevented LPS-induced inflammatory bone resorption due to a decrease in the number of c-Fms-positive osteoclasts. Our study showed that accelerating c-Fms proteolysis by proteasome inhibitors may be a therapeutic option for inflammation-induced bone loss. View Full-Text
Keywords: proteasome inhibitors; c-Fms; osteoclast; bone resorption proteasome inhibitors; c-Fms; osteoclast; bone resorption

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Lee, K.; Kim, M.Y.; Ahn, H.; Kim, H.-S.; Shin, H.-I.; Jeong, D. Blocking of the Ubiquitin-Proteasome System Prevents Inflammation-Induced Bone Loss by Accelerating M-CSF Receptor c-Fms Degradation in Osteoclast Differentiation. Int. J. Mol. Sci. 2017, 18, 2054.

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