Integrin synthesis and utilization in cultured human osteoblasts.

This study describes the adhesion of human osteoblasts, cultured in vitro, to proteins of the extracellular matrix, the biosynthesis of integrins, their topography and organization in focal contacts. The adhesion of osteoblasts to laminin, type I collagen, vitronectin and fibronectin was 77-100%, in 2 h and at 55 nM substrata concentration, and it was accompanied by spreading of the cells. Adhesion to fibronectin (FN), laminin (LN) and type I collagen (COL) was inhibited by antibodies to the beta 1 integrin and antibodies to the alpha 5 chain affected adhesion only to fibronectin. Using a panel of polyclonal antibodies against alpha 2, alpha 3, alpha 5, alpha v, beta 1 and beta 3 integrins we detected synthesis of alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, and an alpha v beta 1-like dimer by immunoprecipitation of metabolically labelled cell lysates. Studies of immunolocalization demonstrated the presence of the same integrins identified in lysates, plus alpha 4, alpha 1 and beta 5 subunits. In cells adhering in the presence of serum we showed organization of beta 3 and alpha v integrins in focal contacts. In cells adhering to fibronectin alpha 5 and beta 1 integrins were localized in focal contacts. In cells spread on laminin or type I collagen none of the integrins investigated was localized in focal contacts.