The integrin α(v)β₅ 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 rich in proteins containing the Arg-Gly-Asp motif, recognized primarily by α(v) integrins. Thus, we determined if avian osteoclast precursors express integrins capable of mediating initial attachment to matrix proteins. Early, marrow-derived osteoclast precursors, when first isolated, contain no detectable α(v)β₃, but express an α(v) integrin with an 80 kDa associated β subunit. Immunoprecipitation with an antibody raised against the conserved β₅ cytoplasmic tail sequence indicates the the α(v) associated the integrin is α(v)β₅. Retinoic acid is a resorptive steroid, and its exposure to early osteoclast precursors prompts a time- and dose-dependent decrease in α(v)β₅ expression, while simultaneously stimulating α(v)β₃ expression. Northern analysis reveals that retinoic acid decreases β₅ steady-state mRNA, nontranscriptionally, without altering that of α(v). The finding α(v)β₅ expression decreases under the influence of retinoic acid, an osteoclastogenic steroid, while those of α(v)β₃ rise, suggests that these closely related integrins play separate and complementary roles during osteoclast differentiation.