The high affinity heparin-binding domain and the V region of fibronectin mediate invasion of human oral squamous cell carcinoma cells in vitro.

Fibronectin is an extracellular matrix molecule composed of repeating subunits that create functional domains. These domains contain multiple binding sites for heparin and for various cell-surface receptors that modulate cell function. To examine the role that the high affinity heparin-binding region and the alternatively spliced V region of fibronectin play in tumor invasion, we expressed and purified four complementary recombinant fibronectin proteins. These proteins either included or excluded the alternatively spliced V region and contained either a mutated, non-functional high affinity heparin-binding domain (Hep-) or an unmutated heparin-binding domain (Hep+). Cultured oral squamous cell carcinoma cells were assayed for invasion into a Matrigel/collagen matrix supplemented with these four purified recombinant proteins, and for spreading and motility on plastic. Increased invasion was observed in gels supplemented with the V-Hep+ protein when compared with the V-Hep- protein. Inclusion of the V region in the proteins enhanced the invasion and migration associated with both Hep+ and Hep- proteins, whereas cell spreading was enhanced with the Hep+ recombinant proteins. These data demonstrate that both the high affinity heparin-binding domain and the V region of fibronectin play important roles in invasion, motility, and spreading of oral squamous cell carcinoma cells.