IDENTIFICATION OF INTEGRIN RECEPTORS ON CULTURED HUMAN BONE-CELLS

The interactions of bone cells with their surrounding extracellular mi croenvironment may be mediated by integrins, a family of heterodimeric glycoproteins consisting of a and p subunits that noncovalently inter act to form cell-substratum adhesion receptors. We previously describe d the integrins on calvarial bone cells in rats with use of polyclonal antibodies against some integrin subunits. In the present study, we e xpanded this initial characterization by employing a more complete pan el of monoclonal antibodies to identify integrins on human bone cells. Minced fragments of trabecular bone obtained during total knee arthro plasty were grown in culture until bone cells became confluent. The ce lls then were dissociated, plated again, grown to confluence, and assa yed for alkaline phosphatase activity, response of cyclic adenosine mo nophosphate to stimulation with parathyroid hormone, and osteocalcin c ontent. The percentage of the cells that adhered to various substrates was measured; 60-70% adhered to type-I collagen, fibronectin, vitrone ctin, and poly-D-lysine; 40-50% adhered to type-IV collagen, laminin? and gelatin; and only 10% adhered to fibrinogen. Flow cytometric analy sis with anti-integrin monoclonal antibodies and sodium dodecyl sulfat e-polyacryamide gel electrophoresis analysis of immunoprecipitates of the human bone cells revealed high levels of alpha(1) beta(1), alpha(3 ) beta(1), alpha(5) beta(1), and alpha(V) beta(5) integrins and much l ower levels of alpha(2) beta(1), alpha(4) beta(1), alpha(V) beta(1), a nd alpha(V) beta(3) integrins. This description of the integrin repert oire of cultured human bone cells represents the first step toward an understanding of the role played by integrins in the growth, maintenan ce, and repair of bone.