Requirement of the hyaluronan receptor RHAMM in neurite extension and motility as demonstrated in primary neurons and neuronal cell lines

The recently cloned and characterized hyaluronan (HA) receptor RHAMM (receptor for HA-mediated motility) has been shown to play a critical role in mechanisms underlying the motile capacity of a variety of peripheral cell types. Similarities in molecular processes that govern cell locomotion and growth cone migration prompted us to investigate whether RHAMM also contributes to neurite migration in vitro. In immunohistochemical studies of PC12 cells, NG108–15 cells and a neuroblastoma/spinal cord neuronal hybrid cell line (NSC-34 cells) as well as rat and human primary neurons, a punctiform RHAMM labeling pattern was detected in cell bodies, along processes, and at growth cones. By Western blot analysis, the cells lines expressed major RHAMM forms with apparent MW of 60, 75, and 116 kDa. Treatment of NG108–15 cells with dibutyryl-cAMP led to a clear increase in immunolabeling for RHAMM and enhanced expression of the 60 and 75 kDa forms. A polyclonal anti-RHAMM antibody that interferes with HA/RHAMM interaction significantly reduced neurite migration of each cell type examined, while another directed against a RHAMM repeat sequence thought to promote RHAMM receptor aggregation significantly stimulated neurite migration of NSC-34 and rat primary neurons. Different monoclonal anti- RHAMM antibodies had differential inhibitory actions on neurite movement. Low concentrations (ng/ml) of a peptide corresponding to an HA binding domain within RHAMM inhibited neurite migration. These results are the first to implicate RHAMM in the mediation of neurite motility and migration and to point to the potential importance of HA in this process.