Invasive tumour cells, such as gliomas, frequently express EGF (epidermal growth factor) receptor at a high level and they exhibit enhanced cell migration in response to EGF. We reported previously that tumour cell migration is associated with ectodomain cleavage of CD44, the major adhesion molecule that is implicated in tumour invasion and metastasis, and that the cleavage is enhanced by ligation of CD44. In the present study, we show that EGF promotes CD44 cleavage and CD44-dependent cell migration. Introduction of a dominant-negative mutant of the small GTPase Rac1 or depletion of Rac1 by RNAi (RNA interference) abrogated CD44 cleavage induced by EGF. Treatment with PD98059, an inhibitor for MEK (mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase), also suppressed the CD44 cleavage. Furthermore, RNAi studies showed that EGF induced ADAM10 (a disintegrin and metalloproteinase 10)-dependent CD44 cleavage and cell migration. These results indicate that EGF induces ADAM10-mediated CD44 cleavage through Rac1 and mitogen-activated protein kinase activation, and thereby promotes tumour cell migration and invasion.

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