Various ion channels are expressed in human cancers where they are intimately involved in proliferation, angiogenesis, migration and invasion. Expression of functional voltage-gated sodium (Nav) channels is implicated in the metastatic potential of breast, prostate, colon, cervical and lung cancer cells. However, the cellular mechanisms that regulate Nav channel 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, the role of epidermal growth factor receptor (EGFR) signalling and Nav channels in non-small cell lung cancer (NSCLC) cell lines have been examined. It is shown that functional expression of Nav1.7 promotes invasion in strongly metastatic H460 NSCLC cells. However, in non-invasive A549 NSCLC cells, Nav1.7 is completely absent. Inhibition of Nav1.7 either pharmacologically by tetrodotoxin (TTX) or genetically by small interfering RNA (siRNA) reduces H460 cell invasion by up to 50%. Whilst EGFR signalling enhances proliferation, migration and invasion of H460 cells, EGFR-mediated upregulation of Nav1.7 specifically, is required to promote invasive behaviour in these cells. Examination of Nav1.7 expression at the mRNA, protein and functional levels further reveals that EGFR signalling via the ERK1/2 pathway controls transcriptional regulation of Nav1.7 expression to promote cellular invasion in NSCLC. The role of Nav channels in promoting cancer cell invasion is also unclear. Therefore, the effect of Nav channel activity on two likely downstream contributors to cellular invasion, intracellular calcium concentration, [Ca2+]i, and intracellular pH, pHi, have been examined. It is shown that functional expression of Nav1.7 likely drives H460 NSCLC cell invasion via H+ efflux from the cell in an uncharacterised mechanism potentially involving NHE1, resulting in extracellular acidification of the perimembrane space. However, much more work is needed to understand this Na+-dependent invasive mechanism. Immunohistochemistry (IHC) of patient biopsies confirms the clinical relevance of Nav1.7 expression in NSCLC. Thus, Nav1.7 has significant potential as a novel target for therapeutic intervention, possibly in conjunction with existing EGFR inhibitors, and/or as a diagnostic/prognostic marker in NSCLC.
|Date of Award||1 Aug 2013|
- The University of Manchester
|Supervisor||Liz Fitzgerald (Supervisor)|