INTEGRIN SYNTHESIS AND UTILIZATION IN CULTURED HUMAN OSTEOBLASTS

This study describes the adhesion of human osteoblasts, cultured in vi tro, to proteins of the extracellular matrix, the biosynthesis of inte grins, their topography and organization in focal contacts. The adhesi on of osteoblasts to laminin, type I collagen, vitronectin and fibrone ctin was 77-100%, in 2 h and at 55 nM substrata concentration, and it was accompained 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 ad hesion only to fibronectin. Using a panel of polyclonal antibodies aga inst alpha 2, alpha 3, alpha 5, alpha v, beta 1 and beta 3 integrins w e 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 metabolic ally 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 s erum we showed organization of beta 3 and alpha v integrins in focal c ontacts. 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 c ontacts. (C) 1996 Academic Press Limited