The integrin alpha(v)beta(5) is expressed on avian osteoclast precursors and regulated by retinoic acid

Osteoclasts arise by proliferation, differentiation, and subsequent fusion of marrow-derived precursors, all processes requiring attachment to matrix, Integrins are important mediators of cell-matrix recognition and bone is r ich in proteins containing the Arg-Gly-Asp moth, recognized primarily by al pha(v) integrins. Thus, we determined if avian osteoclast precursors expres s integrins capable of mediating initial attachment to matrix proteins. Ear ly, marrow-derived osteoclast precursors, when first isolated, contain no d etectable alpha(v)beta(3), but express an alpha(v) integrin with an 80 kDa associated beta subunit, Immunoprecipitation with an antibody raised agains t the conserved beta(5) cytoplasmic tail sequence indicates the the alpha(v ) associated the integrin is alpha(v)beta(5). Retinoic acid is a resorptive steroid, and its exposure to early osteoclast precursors prompts a time- a nd dose-dependent decrease in alpha(v)beta(5) expression, while simultaneou sly stimulating alpha(v)beta(3) expression. Northern analysis reveals that retinoic acid decreases beta(5) steady-state mRNA, nontranscriptionally, wi thout altering that of alpha(v). The finding alpha(v)beta(5) expression dec reases under the influence of retinoic acid, an osteoclastogenic steroid, w hile those of alpha(v)beta(3) rise, suggests that these closely related int egrins play separate and complementary roles during osteoclast differentiat ion.