Mitotic WNT: aligning chromosomes through KIF2A

ABSTRACT

WNT signaling regulates cell cycle progression and fate determination through β-catenin dependent transcription, and its misregulation is often associated with tumorigenesis. Our recent work demonstrated that basal WNT activity is also required to ensure proper chromosome alignment during mitosis through the regulation of kinesin family member 2A (KIF2A).

Misregulation of the canonical WNT signaling pathway is causally involved in several diseases, including cancer.¹ The best-established output of this pathway is the stabilization of β-catenin by ligand-receptor complexes termed low-density lipoprotein receptor-related proteins 6 (LRP6) signalosomes.² The translocation and accumulation of β-catenin in the nucleus often leads to the transcription of target genes associated with cell cycle progression and fate determination, notably in stem cells.¹ Previous evidence demonstrated that WNT signaling activity also peaks in mitosis to stabilize other proteins beyond β-catenin via WNT-dependent stabilization of proteins (WNT/STOP).^3–5 In detail, LRP6 signalosome formation and stabilization is enhanced during mitosis by cyclin Y/cyclin dependent kinase 14/16 (CDK14/16), and by cyclin dependent kinase 1 (CDK1), which phosphorylate LRP6 and B-cell lymphoma 9 (BCL9), respectively.^4,5 However, the specific functions of mitotic WNT signaling remain largely uncharacterized.

In our recent study, we searched for novel WNT signaling targets in mitosis using phosphoproteomics.⁶ Among the candidates, we found that WNT promotes the phosphorylation of kinesin family member 2A (KIF2A) at serine 100. KIF2A is a minus-end microtubule depolymerase required in development for scaling the mitotic spindle and neurogenesis.^7,8 Mechanistically, KIF2A promotes microtubule depolymerization at the spindle poles, which generates pulling forces on attached kinetochores, thereby ensuring the congression, alignment and segregation of chromosomes.⁹ Interestingly, we identified that both ablation of serine 100 phosphorylation, as well as WNT inhibition by Dickkopf-related protein 1 (DKK1) led to decreased levels of KIF2A at the spindle, prompting us to investigate how KIF2A is modulated.

We found that the LRP6 signalosome component disheveled segment polarity protein 2 (DVL2) interacts with the N-terminal and motor domains of KIF2A. This interaction required the availability of serine 100 in KIF2A and was further promoted upon LRP6 signalosome formation during mitosis. We also identified that the LRP6 signalosomes form platforms for KIF2A interaction with and activation by polo like kinase 1 (PLK1), which is critical for the localization and function of the depolymerase at the spindle poles. Accordingly, inhibition of basal WNT activity impaired KIF2A recruitment to the mitotic spindle, thereby inducing a delay in chromosome congression and misalignment before the onset of mitosis. Even though, the phosphorylation of serine 100 was identified to be relevant for the interaction and function of KIF2A, it remains uncharacterized which kinase downstream of PLK1 is directly phosphorylating it (Figure 1). Taken together, our data support a model in which WNT signaling monitors KIF2A activity to ensure timely and faithful mitotic progression across different cell types, including pluripotent stem cells.⁶

Figure 1.

WNT signaling recruits KIF2A to the mitotic spindle for proper chromosome alignment. WNT ligands induce low-density lipoprotein receptor-related protein 5/6 (LRP) and frizzled clustering on disheveled (DVL) platforms, which are endocytosed in LRP6 signalosomes. Both polo like kinase 1 (PLK1) and kinesin family member 2A (KIF2A) are recruited to DVL, which facilitates KIF2A activation and localization to the spindle Poles. It is still unclear which kinase downstream of PLK1 phosphorylates KIF2A at serine 100 (P_S100). The correct positioning and activity of KIF2A is critical for proper chromosome alignment before cell division

We also identified that long-term depletion of KIF2A or LRP6 results in aneuploidy. However, whether the WNT-KIF2A-axis contributes to genome stability in development and tissue homeostasis remains unclear. Furthermore, given that factors, which affect signalosome formation such as ring finger protein 43 (RNF43), Adenomatous polyposis coli (APC), and axin 1 (AXIN1), are frequently mutated in cancer,¹ it would be important to study whether aberrant regulation of KIF2A contributes to the roles of oncogenic WNT signaling during tumor development. Finally, it remains to be uncovered whether WNT also regulates KIF2A functions in development such as spindle scaling, ciliogenesis and neurogenesis.^7,8

Funding Statement

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), SFB 1324, Project number 331351713. A.B. received a doctoral junior award sponsored by the Schmeil-Stiftung Heidelberg.

Disclosure statement

No potential conflict of interest were disclosed.