Identification of integrin cell‐substratum adhesion receptors on cultured rat bone cells

The interactions of bone cells with their extracellular matrix is of major importance in bone development, repair, and disease. We examined the ability of rat calvarial bone cells to adhere to various matrix proteins and to define the role of integrin cell‐substrate adhesion receptors in these interactions. Isolated newborn rat calvarial bone cells prelabeled with 3 H‐thymidine and plated on plastic wells that had been precoated with serial dilutions of various substrates showed typical dose‐response adherence curves to fibronectin, fibrinogen, laminin, vitronectin, and collagen I and IV. Cell adherence to poly‐ D ‐lysine, a nonspecific cell adherent, was high at all substrate concentrations >0.0001 μg/ml. A polyclonal anti‐rat integrin antibody blocked cell adhesion to all substrates tested except poly‐ D ‐lysine. Isolated rat calvarial bone cells were surface labeled with 125 I, extracted, and immunoprecipitated with polyclonal antibodies made against the rat integrin complex and peptides derived from the cytoplasmic domains of the α 2 , α 3 , and α 5 subunits. Analysis by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (nonreduced) identified four bands representing a mixture of integrins including the α 1 β 1 laminin/collagen receptor, the α 5 β 1 fibronectin receptor, and the α v β 3 (or possibly α v β 5 ) vitronectin receptor. These experiments show that bone cells adhere to a wide variety of extracellular matrix proteins via specific integrins. Increased knowledge about the regulation of these receptors and the mechanisms by which they transmit information to the cell will be important for a more complete understanding of bone physiology and pathophysiology.