The catalytic activity of the Src family kinases is required to disrupt cadherin-dependent cell-cell contacts

Despite the importance of epithelial cell contacts in determining cell beha vior, we still lack a detailed understanding of the assembly and disassembl y of intercellular contacts. Here we examined the role of the catalytic act ivity of the Src family kinases at epithelial cell contacts in vitro. Like E- and P-cadherin, Ca2+ treatment of normal and tumor-derived human keratin ocytes resulted in c-Yes (and c-Src and Fyn), as well as their putative sub strate p120(CTN), being recruited to cell-cell contacts. A tyrosine kinase inhibitor with selectivity against the Src family kinases, PD162531, and a dominant-inhibitory c-Src protein that interferes with the catalytic functi on of the endogenous Src kinases induced cell- cell contact and E-cadherin redistribution, even in low Ca2+ which does not normally support stable cel l- cell adhesion. Time-lapse microscopy demonstrated that Src kinase inhibi tion induced stabilization of transiently formed intercellular contacts in low Ca2+. Furthermore, a combination of E- and P-cadherin-specific antibodi es suppressed cell-cell contact, indicating cadherin involvement. As a cons equence of contact stabilization, normal cells were unable to dissociate fr om an epithelial sheet formed at high density and repair a wound in vitro, although individual cells were still motile. Thus, cadherin-dependent conta cts can be stabilized both by high Ca2+ and by inhibiting Src activity in l ow (0.03 mM) Ca2+ in vitro.