The Role and Regulation of Cortactin in EML4-ALK V3 Non-Small Cell Lung Cancer

Lung cancer causes the largest number of cancer-related deaths, largely because it is often diagnosed after metastasis has occurred. Approximately 5% of lung adenocarcinomas are driven by the EML4-ALK oncogenic fusion protein of which variants exist due to differences in the EML4 gene breakpoint. The second most common variant, EML4-ALK V3, is associated with accelerated metastasis, resistance to treatment and poor patient outcome. Experiments undertaken in our laboratory revealed that EML4-ALK V3 leads to a change from epithelial to mesenchymal morphology in cells, as well as increased migration. These properties depend on microtubule-based interaction of EML4-ALK V3 with the NEK9 and NEK7 kinases and coincide with microtubule stabilization.

Here, we sought to characterise a potential downstream effector of this pathway, namely the actin regulator cortactin. Cortactin is required for the formation of F-actin branches and is often upregulated or modified in highly invasive tumours. We had identified cortactin as a substrate of NEK6, a highly related kinase to NEK7. This prompted us to hypothesise that activation of NEK7 may contribute to changes in morphology, migration and invasion of cancer cells expressing EML4-ALK V3 through regulation of cortactin.

Using a combination of advanced microscopy techniques in 2D and 3D cell culture, as well as in vitro biochemical assays, it was revealed that cortactin is essential for the development of the mesenchymal cell morphology and enhanced migration that occurs downstream of EML4-ALK V3, or constitutively active NEK9 or NEK7 kinases. In addition, it was demonstrated that cortactin is phosphorylated on serine residues in the actin-binding region by NEK7 and that this could alter the association of cortactin with F-actin subtypes. We therefore propose that the EML4(-ALK)-NEK9-NEK7 pathway may represent a novel regulator of microtubule-actin crosstalk, which may be important not only in the migration of cancer cells but also that of normal cells.