Expression of alpha v and beta 3 integrin subunits in rat osteoclasts in situ.

Recent findings suggest that the vitronectin receptor, a member of the integrin family, plays an important role in the attachment of osteoclasts to bone matrix. We report here the localization by in situ hybridization of the mRNA for the alpha and beta subunits of the vitronectin receptor in rat bone sections. To generate the rat-specific RNA probes used in this study, we cloned cDNA fragments of integrin chains alpha v, beta 3, and beta 5 by the polymerase chain reaction from rat cDNA. These fragments share 86-91% homology with the respective human sequences. In situ hybridization localized the alpha v and beta 3 mRNAs to regions undergoing extensive bone resorption. The histologic appearance and prestaining of bone sections for tartrate-resistant acid phosphatase (TRAP) indicated the presence of these mRNAs in osteoclasts. These observations support immunohistochemical findings that osteoclasts express high levels of the vitronectin receptor, confirm the identity of this receptor as integrin alpha v/beta 3, and suggest that osteoclasts may actively synthesize these molecules.