Hyaluronan Receptor-Mediated Tumor Cell Motlity

Abstract

Hyaluronan (HA) is an evolutionarily conserved, large and negatively charged glycosaminoglycan that has been implicated in the locomotion of cells during morphogenesis, wound repair, and disease states such as tumorigenesis. Recently, we demonstrated that HA is produced in elevated levels in ras-transformed cells and is required for their motility. Furthermore, TGF-β₁ which stimulates locomotion of these cells requires HA for this effect. We have shown that RHAMM, a novel glycoprotein that was recently cloned from fibroblasts, mediates the locomotion of ras-transformed fibroblasts. Thus, blocking antibodies inhibit ras-transformed locomotion and conversely, cells transfected with a genomic RHAMM clone, that overexpress cell surface RHAMM, exhibit a two fold increased in cell locomotion and also display a loss of contact inhibition of locomotion, as demonstrated by a nuclear overlap ratio, and of growth as demonstrated by overgrowth at culture confluence. The mechanism(s) by which HA might regulate cell locomotion and contact inhibition are unknown. HA promotes transient increases in protein tyrosine phosphorylation, a phenomenon that is required for cell locomotion to occur. Concomitant with an increase in protein tyrosine phosphorylation is an increase in lamellae extension and the transient appearance of small point focal contacts. These structures show increased protein tyrosine content and contain focal adhesion kinase (FAK). Focal contacts disappear 10-15min after HA stimulation as cells begin to displace, suggesting that a key role of HA in stimulating locomotion is the regulation of focal contact turnover. Our results provide evidence for an important role of HA and of one of its HA receptors, RHAMM, in the contact and motility behavior of tumor cells and predict that these molecules play a critical role in tumor progression.