FLRG, a new ADAM12-associated protein, modulates osteoclast differentiation.
BACKGROUND
FLRG (follistatin-related gene) is a secreted glycoprotein that is highly homologous with follistatin. These proteins are involved in the regulation of various biological effects mediated by their binding to TGF-beta (transforming growth factor-beta) superfamily members, activin A and bone morphogenetic proteins. To characterize further the function of FLRG, we used a yeast two-hybrid screen to look for other possible functional partners.


RESULTS
We report a direct interaction between the cysteine-rich domain of FLRG and ADAM12 (a disintegrin and metalloprotease 12). ADAMs are metalloprotease-disintegrin proteins that have been implicated in cell adhesion, protein ectodomain shedding, matrix protein degradation and cell fusion. Several studies have reported that ADAM12 protein, as well as activin A, are important regulators of osteoclast differentiation. We observed that the expressions of ADAM12 and activin A are modulated during osteoclast formation, whereas the FLRG expression seemed to remain quite constant. We showed that the FLRG protein inhibits osteoclast differentiation from murine primary spleen cells and macrophage RAW264.7 cells cultured in the presence of RANK-L (receptor activator of nuclear factor kappaB ligand) and M-CSF (macrophage colony-stimulating factor). Addition of FLRG protein to precursors significantly reduces the number of osteoclasts, as well as the average number of nuclei in each osteoclast.


CONCLUSIONS
Our study indicates that the FLRG protein may contribute to bone formation by inhibiting osteoclast differentiation.
Bartholin
Laurent
L
Unité INSERM U590, Centre Léon Bérard, 69373 Lyon cedex 08, France.
Destaing
Olivier
O
Forissier
Stéphanie
S
Martel
Sylvie
S
Maguer-Satta
Véronique
V
Jurdic
Pierre
P
Rimokh
Ruth
R
D051722:ADAM Proteins; D000072199:ADAM12 Protein; D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D019556:COS Cells; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D038681:Follistatin / Q000378:metabolism; D038702:Follistatin-Related Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008666:Metalloendopeptidases / Q000378:metabolism; D051379:Mice; D010010:Osteoclasts / Q000502:physiology*; D011485:Protein Binding; D013154:Spleen / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D019485:Bone Morphogenetic Proteins; D038681:Follistatin; D038702:Follistatin-Related Proteins; D008565:Membrane Proteins; D016173:Macrophage Colony-Stimulating Factor; D051722:ADAM Proteins; D000072199:ADAM12 Protein; C000606480:ADAM12 protein, human; D008666:Metalloendopeptidases