EphB3 suppresses non-small-cell lung cancer metastasis via a PP2A/RACK1/Akt signalling complex

Eph receptors are implicated in regulating the malignant progression of cancer. Here we find that despite overexpression of EphB3 in human non-small-cell lung cancer, as reported previously, the expression of its cognate ligands, either ephrin-B1 or ephrin-B2, is significantly downregulated, leading to reduced tyrosine phosphorylation of EphB3. Forced activation of EphB3 kinase in EphB3-overexpressing non-small-cell lung cancer cells inhibits cell migratory capability in vitro as well as metastatic seeding in vivo. Furthermore, we identify a novel EphB3-binding protein, the receptor for activated C-kinase 1, which mediates the assembly of a ternary signal complex comprising protein phosphatase 2A, Akt and itself in response to EphB3 activation, leading to reduced Akt phosphorylation and subsequent inhibition of cell migration. Our study reveals a novel tumour-suppressive signalling pathway associated with kinase-activated EphB3 in non-small-cell lung cancer, and provides a potential therapeutic strategy by activating EphB3 signalling, thus inhibiting tumour metastasis.