Functional expression of the voltage-gated Na+-channel Nav1.7 is necessary for EGF-mediated invasion in human non-small cell lung cancer cells

Various ion channels are expressed in human cancers where they are intimately involved in proliferation, angiogenesis, invasion and metastasis. Expression of functional voltage-gated Na+ channels (Na-v) is implicated in the metastatic potential of breast, prostate, lung and colon cancer cells. However, the cellular mechanisms that regulate Na-v expression in cancer remain largely unknown. Growth factors are attractive candidates; they not only play crucial roles in cancer progression but are also key regulators of ion channel expression and activity in non-cancerous cells. Here, we examine the role of epidermal growth factor receptor (EGFR) signalling and Na-v in non-small cell lung carcinoma (NSCLC) cell lines. We show unequivocally, that functional expression of the a subunit Na(v)1.7 promotes invasion in H460 NSCLC cells. Inhibition of Na(v)1.7 activity (using tetrodotoxin) or expression (by using small interfering RNA), reduces H460 cell invasion by up to 50%. Crucially, non-invasive wild type A549 cells lack functional Nav, whereas exogenous overexpression of the Na(v)1.7 a subunit is sufficient to promote TTX-sensitive invasion of these cells. EGF/EGFR signalling enhances proliferation, migration and invasion of H460 cells but we find that, specifically, EGFR-mediated upregulation of Na(v)1.7 is necessary for invasive behaviour in these cells. Examination of Na(v)1.7 expression at mRNA, protein and functional levels further reveals that EGF/EGFR signalling via the ERK1/2 pathway controls transcriptional regulation of channel expression to promote cellular invasion. Immunohistochemistry of patient biopsies confirms the clinical relevance of Na(v)1.7 expression in NSCLC. Thus, Na(v)1.7 has significant potential as a new target for therapeutic intervention and/or as a diagnostic or prognostic marker in NSCLC.