Mechanisms of fibronectin-mediated attachment of osteoblasts to substrates in vitro.

Adhesive proteins of plasma and the extracellular matrix, such as fibronectin, adsorbed onto surfaces mediate cell/substrate adhesion. In a series of experiments, the roles of the type III connecting segment (IIICS) adhesion sites (specifically, CS1 and CS5 peptides) of fibronectin, heparan sulfate proteoglycan, endogenous proteins, and passive attachment in fibronectin-mediated osteoblast attachment were examined in vitro. The CS1 and CS5 peptides of the IIICS of fibronectin had no effect on osteoblast attachment. Blocking the heparin-binding domains of fibronectin inhibited osteoblast attachment by 40-45%, which is complementary to inhibition results previously obtained with the RGDS tetrapeptide. Endogenously synthesized and secreted proteins played a role in maintaining and repairing the osteoblast surface. Osteoblast attachment to fibronectin, but not to the nonadhesive protein albumin, occurred via active mechanisms in that the process was dependent on free sulfhydryl groups, divalent cations and temperature.