c-Fms and the αvβ3 integrin collaborate during osteoclast differentiation
Roberta Faccio, … , F. Patrick Ross, Steven L. Teitelbaum
Roberta Faccio, … , F. Patrick Ross, Steven L. Teitelbaum
Published March 1, 2003
Citation Information: J Clin Invest. 2003;111(5):749-758. https://doi.org/10.1172/JCI16924.
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Article Bone biology

c-Fms and the αvβ3 integrin collaborate during osteoclast differentiation

Abstract

β3 integrin–null osteoclasts are dysfunctional, but their numbers are increased in vivo. In vitro, however, the number of β3–/– osteoclasts is reduced because of arrested differentiation. This paradox suggests cytokine regulation of β3–/– osteoclastogenesis differs in vitro and in vivo. In vitro, additional MCSF, but not receptor activator of NF-κB ligand (RANKL), completely rescues β3–/– osteoclastogenesis. Similarly, activation of extracellular signal-regulated kinases (ERKs) and expression of c-Fos, both essential for osteoclastogenesis, are attenuated in β3–/– preosteoclasts, but completely restored by additional MCSF. In fact, circulating and bone marrow cell membrane-bound MCSFs are enhanced in β3–/– mice, correlating with the increase in the osteoclast number. To identify components of the MCSF receptor that is critical for osteoclastogenesis in β3–/– cells, we retrovirally transduced authentic osteoclast precursors with chimeric c-Fms constructs containing various cytoplasmic domain mutations. Normalization of osteoclastogenesis and ERK activation, in β3–/– cells, uniquely requires c-Fms tyrosine 697. Finally, like high-dose MCSF, overexpression of c-Fos normalizes the number of β3–/– osteoclasts in vitro, but not their ability to resorb dentin. Thus, while c-Fms and αvβ3 collaborate in the osteoclastogenic process via shared activation of the ERK/c-Fos signaling pathway, the integrin is essential for matrix degradation.

Authors

Roberta Faccio, Sunao Takeshita, Alberta Zallone, F. Patrick Ross, Steven L. Teitelbaum

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c-FmsY697 is specifically required for osteoclastogenesis in the absence...
c-FmsY697 is specifically required for osteoclastogenesis in the absence of αvβ3. (a) Equal numbers of β3+/+ and β3–/– BMMs were retrovirally transduced with vector alone, nonmutated EpoR/c-Fms (WT), or EpoR/c-Fms carrying individual tyrosine-to-phenylalanine point mutation. Cells were selected in puromycin for 3 days and exposed for 3 days to RANKL and low-dose MCSF. The cells were then placed in serum-free medium for 2 hours, exposed to 25 U/ml Epo for varying times, and lysed. Equivalent expression of c-Fms and mutated forms of EpoR/c-Fms was established by immunoblot using a C-terminal anti–c-Fms antibody. (b) Puromycin-selected cells were cultured for 7 days in the optimal osteoclastogenic concentration of Epo (25 ng/ml) and RANKL (100 ng/ml). Osteoclastogenesis was measured by TRAP assay and expressed as a percentage of the value obtained with control (WT) EpoR/c-Fms transductants. While EpoR/c-FmsY697F was as effective as control in inducing β3+/+ osteoclastogenesis, the same mutant dampened the process 3.5-fold in β3–/– cells. In contrast, EpoR/c-FmsY721F did not impact the osteoclastogenic process. *P < 0.001 vs. vector; **P < 0.05 vs. vector.