Research ArticleMitosis

Mitotic phosphorylation by NEK6 and NEK7 reduces the microtubule affinity of EML4 to promote chromosome congression

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Science Signaling  13 Aug 2019:
Vol. 12, Issue 594, eaaw2939
DOI: 10.1126/scisignal.aaw2939

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NEKs and EML4 in cell division

Faithful cell division requires proper separation of duplicated chromosomes into daughter cells. When this process goes awry, the dividing cell or daughter cells carry too many or too few copies (known as aneuploidy), which can cause disease. Microtubule dynamics are critical to this process. The protein EML4, which is abnormally fused to other proteins in some cancers, binds to and stabilizes microtubules, and its presence in the cell is critical for mitotic progression. However, Adib et al. found that upon entry into mitosis, phosphorylation of EML4 by the kinases NEK6 and NEK7 induced its dissociation from microtubules to enable proper chromosome alignment at the spindle equator, ready for subsequent anaphase and cytokinesis. These findings reveal further insight into both the regulation of cell division and how NEKs promote tumor growth.

Abstract

EML4 is a microtubule-associated protein that promotes microtubule stability. We investigated its regulation across the cell cycle and found that EML4 was distributed as punctate foci along the microtubule lattice in interphase but exhibited reduced association with spindle microtubules in mitosis. Microtubule sedimentation and cryo–electron microscopy with 3D reconstruction revealed that the basic N-terminal domain of EML4 mediated its binding to the acidic C-terminal tails of α- and β-tubulin on the microtubule surface. The mitotic kinases NEK6 and NEK7 phosphorylated the EML4 N-terminal domain at Ser144 and Ser146 in vitro, and depletion of these kinases in cells led to increased EML4 binding to microtubules in mitosis. An S144A-S146A double mutant not only bound inappropriately to mitotic microtubules but also increased their stability and interfered with chromosome congression. In addition, constitutive activation of NEK6 or NEK7 reduced the association of EML4 with interphase microtubules. Together, these data support a model in which NEK6- and NEK7-dependent phosphorylation promotes the dissociation of EML4 from microtubules in mitosis in a manner that is required for efficient chromosome congression.

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