Specific targeting of PKCδ suppresses osteoclast differentiation by accelerating proteolysis of membrane-bound macrophage colony-stimulating factor receptor

• Published in: Scientific reports Vol. 9; no. 1; p. 7044
• Main Authors: Kim, Mi Yeong, Lee, Kyunghee, Shin, Hong-In, Jeong, Daewon
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.05.2019; Nature Publishing Group
• Subjects: 38/89; 692/163; 692/163/2743/316; 82; 82/80; 96/95; Acetophenones - pharmacology; AKT protein; Animals; Benzopyrans - pharmacology; Bone growth; Bone marrow; Bone remodeling; Bone resorption; Bone Resorption - drug therapy; Bone Resorption - metabolism; c-Jun protein; Calvaria; Cell Differentiation - drug effects; Cell Differentiation - genetics; Cells, Cultured; Colonies; Colony-stimulating factor; Extracellular signal-regulated kinase; Gene silencing; Humanities and Social Sciences; Inactivation; Innate immunity; Intracellular signalling; Isoforms; JNK protein; Kinases; Macrophage colony-stimulating factor; Macrophage Colony-Stimulating Factor - metabolism; Macrophage Colony-Stimulating Factor - pharmacology; Male; Mice, Inbred C57BL; mRNA; multidisciplinary; NF-κB protein; Osteoclastogenesis; Osteoclasts; Osteoclasts - cytology; Osteoclasts - drug effects; Osteoclasts - metabolism; Peptide inhibitors; Periosteum; Protein kinase C; Protein Kinase C-delta - antagonists & inhibitors; Protein Kinase C-delta - genetics; Protein Kinase C-delta - metabolism; Proteolysis - drug effects; Receptor, Macrophage Colony-Stimulating Factor - metabolism; RNA, Small Interfering; Science; Science (multidisciplinary); Signal transduction; Transcription factors
• DOI: 10.1038/s41598-019-43501-2
• ISSN: 2045-2322

c-Fms is the macrophage colony-stimulating factor (M-CSF) receptor, and intracellular signalling via the M-CSF/c-Fms axis mediates both innate immunity and bone remodelling. M-CSF-induced transient proteolytic degradation of c-Fms modulates various biological functions, and protein kinase C (PKC) signalling is activated during this proteolytic process via an unknown mechanism. Notably, the role of specific PKC isoforms involved in c-Fms degradation during osteoclast differentiation is not known. Here, we observed that inactivation of PKCδ by the biochemical inhibitor rottlerin, a cell permeable peptide inhibitor, and short hairpin (sh) RNA suppresses osteoclast differentiation triggered by treatment with M-CSF and receptor activator of NF-κB ligand. Interestingly, inhibition of PKCδ by either inhibitor or gene silencing of PKCδ accelerated M-CSF-induced proteolytic degradation of membrane-bound c-Fms via both the lysosomal pathway and regulated intramembrane proteolysis (RIPping), but did not affect c- fms expression at the mRNA level. Degradation of c-Fms induced by PKCδ inactivation subsequently inhibited M-CSF-induced osteoclastogenic signals, such as extracellular signal-regulated kinase (ERK), c-JUN N-terminal kinase (JNK), p38, and Akt. Furthermore, mice administered PKCδ inhibitors into the calvaria periosteum exhibited a decrease in both osteoclast formation on the calvarial bone surface and the calvarial bone marrow cavity, which reflects osteoclastic bone resorption activity. These data suggest that M-CSF-induced PKCδ activation maintains membrane-anchored c-Fms and allows the sequential cellular events of osteoclastogenic signalling, osteoclast formation, and osteoclastic bone resorption.