Fibronectin-rhamm interactions, which are required for cell motility, regulate podosome formation

grantor: University of TorontoInvadopodia or podosomes have been identified as sites for the local release of matrix metalloproteinases required for the initiation of cell motility and invasion. In this study, we confirm that the cell surface expression of the hyaluronan receptor RHAMM occurs transiently and report that fibronectin (FN) upregulates this expression by stabilizing the retention of RHAMM within podosomes. Further, anti-RHAMM antibodies block podosome formation suggesting FN-RHAMM interactions play a key role in the organization of these structures. RHAMM binds directly to the carboxy-terminal heparin-binding domain of FN via an imperfect leucine zipper motif encoded by exon 3. Peptides mimicking this sequence disrupt FN-RHAMM interactions resulting in both the inhibition of podosome formation as detected by cortactin and p130CAS staining within these structures and the reduction of random cell motility. Overexpression of RHAMM modifies the FN-induced tyrosine phosphorylation profile of proteins; notably, cortactin phosphorylation is enhanced. However, exon 3-mimicking peptide could not block these RHAMM-induced phosphorylation changes. Thus, we conclude that cell surface RHAMM plays a structural role in controlling podosome integrity independent of phosphotyrosine signaling.M.Sc