EGF-R signaling through Fyn kinase disrupts the function of integrin 6 4 at hemidesmosomes: role in epithelial cell migration and carcinoma invasion

e have examined the mechanism and functional significance of hemidesmosome disassembly during normal epithelial cell migration and squamous carcinoma invasion. Our findings indicate that a fraction of EGF receptor (EGF-R) combines with the hemidesmosomal integrin 6 4 in both normal and neoplastic keratinocytes. Activation of the EGF-R causes tyrosine phosphorylation of the 4 cytoplasmic domain and disruption of hemidesmosomes. The Src family kinase inhibitors PP1 and PP2 prevent tyrosine phosphorylation of 4 and disassembly of hemidesmosomes without interfering with the activation of EGF-R. Coimmunoprecipitation experiments indicate that Fyn and, to a lesser extent, Yes combine with 6 4. By contrast, Src and Lck do not associate W with 6 4 to a significant extent. A dominant negative form of Fyn, but not Src, prevents tyrosine phosphorylation of 4 and disassembly of hemidesmosomes. These observations suggest that the EGF-R causes disassembly of hemidesmosomes by activating Fyn, which in turn phosphorylates the 4 cytoplasmic domain. Neoplastic cells expressing dominant negative Fyn display increased hemidesmosomes and migrate poorly in vitro in response to EGF. Furthermore, dominant negative Fyn decreases the ability of squamous carcinoma cells to invade through Matrigel in vitro and to form lung metastases following intravenous injection in nude mice. These results suggest that disruption of hemidesmosomes mediated by Fyn is a prerequisite for normal keratinocyte migration and squamous carcinoma invasion.