Hyaluronate Receptors Mediating Glioma Cell Migration and Proliferation
The extracellular matrix (ECM) of the central nervous system (CNS) is enriched in hyaluronate (HA). Ubiquitous receptors for HA are CD44 and the Receptor for HA-Mediated Motility known as RHAMM. In the present study, we have investigated the potential role of CD44 and RHAMM in the migration and proliferation of human astrocytoma cells. HA-receptor expression in brain tumor cell lines and surgical specimens was determined by immunocytochemistry and western blot analyses. The ability of RHAMM to bind ligand was determined through cetylpyridinium chloride (CPC) precipitations of brain tumor lysates in HA-binding assays. The effects of HA, CD44 blocking antibodies, and RHAMM soluble peptide on astrocytoma cell growth and migration was determined using MTT and migration assays. Our results show that the expression of the HA-receptors, CD44, and RHAMM, is virtually ubiquitous amongst glioma cell lines, and glioma tumor specimens. There was a gradient of expression amongst gliomas with high grade gliomas expressing more RHAMM and CD44 than did lower grade lesions or did normal human astrocytes or non-neoplastic specimens of human brain. Specific RHAMM variants of 85- and 58-kDa size were shown to bind avidly to HA following CPC precipitations. RHAMM soluble peptide inhibited glioma cell line proliferation in a dose-dependent fashion. Finally, while anti-CD44 antibodies did not inhibit the migration of human glioma cells, soluble peptides directed at the HA-binding domain of RHAMM inhibited glioma migration both on and off an HA-based ECM. These data support the notion that HA-receptors contribute to brain tumor adhesion, proliferation, and migration, biological features which must be better understood before more effective treatment strategies for these tumors can be found.
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