Glioma invasion in vitro is mediated by CD44-hyaluronan interactions

Invasion is a clinically important problem contributing to mortality and morbidity in patients with gliomas, but the mechanism(s) by which glioma cells invade surrounding brain structures is poorly understood. Various experimental models have been used in attempts to elucidate the process of glioma invasion. An in vitro model which is increasingly being employed involves measurement of the rate of invasion of tumour cells through Matrigel-a complex mixture of extracellular matrix components derived from the Engelbroth-Holm-Swarm (EHS) sarcoma. This model has been used to examine the possibility that extracellular hyaluronan (HA) might facilitate the invasive behaviour of human glioma cells. The major component of Matrigel is laminin, with smaller amounts of collagen IV, heparan sulphate proteoglycans, entactin, and nidogen but it lacks HA. In our experiments, we have incorporated HA into Matrigel and have measured its effect on the rate of invasion of human glioma cells in a modified Boyden chamber assay system. The incorporation of HA (50-800 mg/cm2) resulted in a dose-dependent increase in invasion. Invasion was enhanced by up to 70 per cent in comparison with HA-free Matrigel. Since CD44 is a major HA receptor expressed on gliomas, it might have a role in the HA-mediated facilitation of invasion. This was tested by blocking CD44 with specific antibody, which resulted in a 43 per cent reduction in invasion rate. We conclude that in an in vitro model system, HA enhances invasion of glioma cells and that the mechanism involves a CD44-HA interaction.