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Epstein-Barr virus (EBV)-encoded Latent Membrane Protein 2A (LMP2A) is an EBV latency-associated protein regularly expressed in nasopharyngeal carcinoma (NPC). In B cells, LMP2A activity resembles that of a constitutively activated antigen receptor, which recruits the Syk tyrosine kinase to activate a set of downstream signaling pathways. LMP2A also downregulates cellular Syk levels. In the present study, we demonstrate that Syk interacts with the integrin β4 subunit (ITGβ4) of integrin α6β4 in epithelial cells and that concurrent LMP2A expression interferes with this interaction by competitive binding to Syk. We find that both Syk and LMP2A have an effect on ITGβ4 cell surface expression. However, in LMP2A expressing cells, ITGβ4 remains concentrated at the cellular protrusions, an expression pattern characteristic of motile cells, including NPC-derived epithelial cells. This effect of LMP2A on ITGβ4 localization is associated with a greater propensity for migration and invasion in-vitro, and may contribute to the invasive property of LMP2A-expressing NPC.

Early metastatic growth occurs at sites of vascular arrest of blood-borne cancer cells and is entirely intravascular. Here we show that lung colonization by B16-F10 cells is licensed by beta(4) integrin adhesion to the mouse lung endothelial Ca(2+)-activated chloride channel protein mCLCA1. In a manner independent of Met, beta(4) integrin-mCLCA1-ligation leads to complexing with and activation of focal adhesion kinase (FAK) and downstream signaling to extracellular signal-regulated kinase (ERK). FAK/ERK signaling is Src-dependent and is interrupted by adhesion blocking antibodies and by dominant-negative (dn)-FAK mutants. Levels of ERK activation in B16-F10 cells transfected with wild-type or mutant FAK are closely associated with rates of proliferation and bromodeoxyuridine (BrdUrd) incorporation of tumor cells grown in mCLCA1-coated dishes, the ability to form tumor cell colonies on CLCA-expressing endothelial cell monolayers, and the extent of pulmonary metastatic growth. Parallel with the transfection rates, B16-F10 cells transfected with dn-FAK mutants and injected intravenously into syngeneic mice generate approximately half the number and size of lung colonies that vector-transfected B16-F10 cells produce. For the first time, beta(4) integrin ligation to its novel CLCA-adhesion partner is shown to be associated with FAK complexing, activation, and signaling to promote early, intravascular, metastatic growth.