PP60(C-SRC) IS REQUIRED FOR CELL LOCOMOTION REGULATED BY THE HYALURONAN RECEPTOR RHAMM

The tyrosine kinase pp60(c-src) has been implicated as a regulator of focal adhesion formation and cell spreading. Here we show that c-src a lso regulates cell motility and is a key component in the signaling pa thway triggered by the motogenic hyaluronan receptor RHAMM, which has been shown to regulate focal adhesion turnover and to regulate ras. Fi broblasts derived from mice lacking src, (src (-/-), have a random loc omotion rate that is significantly slower than the corresponding wild- type fibroblasts. Cell locomotion in these mutant cells is restored by the expression of c-src containing a functional kinase domain, but no t by the expression of a kinase-deficient src or by a truncated src co ntaining only functional SH2 and SH3 domains. RHAMM is also required f or the restoration of src (-/-) cell locomotion. Thus, the motility of cells expressing c-src is reduced to src (-/-) levels by anti-RHAMM b locking antibodies while the cell locomotion of src (-/-) fibroblasts remains unaffected by anti-RHAMM antibodies. We predict that src acts downstream of RHAMM in the regulation of motility, since the expressio n of a dominant negative src significantly inhibits RHAMM-dependent ra s and serum regulated cell locomotion, the expression of v-src enhance s cell motility in a RHAMM independent fashion, and there is a physica l and functional association between src and RHAMM in ras-transformed cells. However, we suggest that RHAMM regulates focal adhesion turnove r via additional src-independent mechanisms. Thus, v-src is unable to turnover focal adhesions in the absence of RHAMM. These results direct ly demonstrate for the first time a role for src in the regulation of cell locomotion and confirm a key and complex role for src in the regu lation of the actin cycle.