Oral squamous cell carcinoma (OSCC) is the 6th most common cancer worldwide, with approximately 400,000 new cases each year. Current treatment regimens are, to a certain degree, inadequate, with a 5-year mortality rate of around 50%, and novel therapeutic targets are urgently required. Using gene microarrays, we identified the EPS8 gene as being over-expressed in OSCC cell lines relative to normal oral keratinocytes, and confirmed these findings using RT-PCR and Western blotting. In human tissues, we found that Eps8 was upregulated in OSCC (32% of primary tumors) compared with normal oral mucosa, and that expression correlated significantly with lymph node metastasis (p=0.032), suggesting a disease-promoting effect. Using OSCC cell lines we assessed the functional role of Eps8 in tumor cells: Although suppression of Eps8 produced no effect on cell proliferation, both cell spreading and migration were markedly inhibited. The latter cell functions may be modulated through the small GTP-ase, Rac1, and we used pull-down assays to investigate the role of Eps8 in Rac1 signaling. We found that ?v?6- and ?5?1-integrin-dependent activation of Rac1 was mediated through Eps8. Knockdown of either Eps8 or Rac1, inhibited integrin-dependent cell migration similarly, and transient expression of constitutively-active Rac1 significantly restored migration of cells in which Eps8 had been suppressed. We also showed, using an organotypic model of OSCC, that Eps8 promotes tumor cell invasion. These data suggest that Eps8 and Rac1 are part of an integrated signaling pathway modulating integrin-dependent tumour cell motility, and identify Eps8 as a possible therapeutic target
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