The role of Eg5 in EML4-ALK driven lung cancer

EML4-ALK fusions are found in approximately 5% of lung cancer patients. Multiple variants of the EML4-ALK fusion exist due to alternate breakpoints in the EML4 gene. EML4-ALK variant 3 (V3) is a significant clinical risk factor being associated with accelerated metastasis, heightened resistance to ALK inhibitor treatment and worse survival rates compared to other common variants, such as V1. Interestingly, EML4-ALK V3 but not V1 binds interphase microtubules. Cells expressing EML4-ALK V3 display a more mesenchymal-like morphology and exhibit enhanced migration. These phenotypic changes rely on EML4-ALK V3 interaction and activation of the NEK9 and NEK7 kinases. However, the downstream substrates of this pathway and how they contribute to oncogenic progression remain unclear.

Here, we have tested the hypothesis that the mitotic kinesin, Eg5, is a downstream substrate of the EML4-ALK V3:NEK9:NEK7 pathway. NEK7 is known to phosphorylate Eg5 to promote centrosome separation in mitosis and dendrite extension in post-mitotic neurons. Strikingly, we found that in proliferating cells, Eg5 is recruited to interphase microtubules in cells expressing EML4-ALK V3 but not V1. Furthermore, this recruitment was reduced upon depletion of NEK7 from V3 cells. The mesenchymal morphology of V3 cells was also lost upon chemical inhibition of Eg5 or expression of a phosphonull-Eg5 mutant. We therefore propose that Eg5 is a downstream substrate of the EML4-ALK V3:NEK9:NEK7 pathway that contributes to microtubule-dependent morphological changes in cells expressing V3.

We also investigated whether EML4-ALK V3 has a role at the centrosome based on recent published findings that cells expressing V3 exhibit centrosome amplification and enhanced microtubule nucleation. Strikingly, we found EML4-ALK V3 but not V1 co-localised with interphase centrosomes but that this was not associated with recruitment of Eg5. Together, our data provide new mechanistic insights that reveal novel therapeutic opportunities for treatment of lung cancer patients with EML4-ALK V3.