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Abstract

The integrin family of cell adhesion molecules are a series of cell surface glycoproteins that recognize a range of cell surface and extracellular matrix (ECM)-associated ligands. To date, the precise role of individual integrin molecules in bone cell–ECM interactions remains unclear. Cell binding assays were performed to examine the ability of normal human bone cells (NHBCs) to adhere to different ECM proteins in vitro. NHBCs displayed preferential adhesion to fibronectin over collagen types I, IV, and vitronectin and showed low affinity binding to laminin and collagen type V. No binding was observed to collagen type III. The integrin heterodimers α1β1, α2β1, α3β1, α5β1, αvβ3, and αvβ5 were found to be constitutively expressed on the cell surface of NHBCs by flow cytometric analysis. The integrins α4β1 and α6β1 were not expressed by NHBCs. Subsequent binding studies showed that NHBC adhesion to collagen and laminin was mediated by multiple integrins where cell attachment was almost completely inhibited in the presence of a combination of function-blocking monoclonal antibodies (Mabs) to α1β1, α2β1, α3β1, and β1. In contrast, the adhesion of NHBCs to fibronectin was only partially inhibited (50%) in the presence of blocking Mabs to α3β1, α5β1, and β1. The attachment of NHBCs to collagen, laminin, fibronectin, and vitronectin was also found to be unaffected in the presence of a function-blocking Mab to αvβ3. The results of this study indicate that β1 integrins appear to be the predominant adhesion receptor subfamily utilized by human osteoblast-like cells to adhere to collagen and laminin and in part to fibronectin.