Meltrin-alpha, a fusion protein involved in multinucleated giant cell and osteoclast formation.
The formation of multinucleated cells such as myotubes, macrophage-derived giant cells (MGC), and osteoclasts is the result of cell-cell fusion of mononuclear precursors. Meltrin-alpha, -beta, and -gamma are members of a recently discovered family of proteins that contain disintegrin and metalloprotease domains and are related to fertilin, a protein involved in egg-sperm fusion. Based on this and evidence implicating meltrin-alpha in myoblast formation, we have investigated the possibility that meltrins may also play a role in the formation of MGC and osteoclasts. Using in situ RT-PCR, we have determined that murine mononuclear alveolar macrophages cultured under basal conditions express the transcript for meltrin-beta, but not for meltrin-alpha. However, meltrin-alpha mRNA appeared in mononuclear cells before cell fusion after treatment with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], a potent inducer of giant cell and osteoclast formation. Moreover, addition of meltrin-alpha antisense oligonucleotides to the cultures caused a 50% inhibition of giant cell formation. Similarly, meltrin-alpha antisense oligonucleotides inhibited by 70% the formation of multinucleated osteoclast-like cells expressing tartrate-resistant acid phosphatase (TRAP) in co-cultures of bone marrow cells and osteoblastic cells (2107) in the presence of 1,25(OH)2D3. Mononucleated TRAP-positive cells, induced by 1,25(OH)2D3 in the co-cultures, also expressed meltrin-alpha mRNA, but their number was not changed in the presence of meltrin-alpha antisense oligonucleotide. In contrast to mononuclear macrophages and osteoclast-like cells, murine bone marrow stroma and calvaria derived-cell lines (+/+ LDA.11 and 2107), primary cultures of calvaria cells, and primary cultures of bone marrow cells expressed both meltrin-alpha and -beta mRNA under basal conditions; whereas embryonic fibroblasts (NIH3T3) expressed only the meltrin-beta transcript. Upregulation of meltrin-alpha protein expression during cell fusion in alveolar macrophages and expression in osteoblastic cell lines were confirmed by Western blot analysis. These observations demonstrate that meltrins play a role in MGC and osteoclast formation from mononuclear precursors, as in the case with myotubes.
Abe
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Division of Endocrinology and Metabolism, John L. McClellan VA Geriatric Research, Education, and Clinical Center, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
Mocharla
H
H
Yamate
T
T
Taguchi
Y
Y
Manolagas
S C
SC
D051722:ADAM Proteins; D000072199:ADAM12 Protein; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002117:Calcitriol / Q000494:pharmacology; D002459:Cell Fusion / Q000235:genetics; D002478:Cells, Cultured; D018920:Coculture Techniques; D017931:DNA Primers / Q000737:chemistry; D019483:Disintegrins; D015726:Giant Cells / Q000201:enzymology*; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D008666:Metalloendopeptidases / Q000096:biosynthesis* / Q000235:genetics; D045726:Metalloproteases; D051379:Mice; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000235:genetics; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010010:Osteoclasts / Q000187:drug effects / Q000201:enzymology*; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000166:cytology
D017931:DNA Primers; D019483:Disintegrins; D008565:Membrane Proteins; D009124:Muscle Proteins; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D045726:Metalloproteases; D051722:ADAM Proteins; D000072199:ADAM12 Protein; C411902:ADAM19 protein, human; C096115:Adam12 protein, mouse; C096116:Adam19 protein, mouse; D008666:Metalloendopeptidases; D002117:Calcitriol