Wnt signaling stimulates cell proliferation by promoting the G1/S transition of
Wnt signaling stimulates cell proliferation by promoting the G1/S transition of the cell cycle through -catenin/TCF4-mediated gene transcription. Y), indicating that endogenous Wnt signaling is under cell cycle control peaking at G2/M 13, 14. In line with this, protein levels of -catenin and Axin-2 also reach their maximum levels at G2/M 15, 16. However, a physiological role for this basal and cell cycle-regulated Wnt signaling has not been revealed so far. Intriguingly, most recently it was found that Wnt signaling can contribute to the stabilization of proteins other than -catenin 9, 17. In particular, this occurs at G2/M and is now referred to as Wnt-dependent stabilization of proteins (Wnt/STOP) 18. However, this novel role of Wnt signaling is yet poorly understood and a specific role for the entry into or Tariquidar for the progression of mitosis has not been identified so far. In addition to that, several Wnt signaling proteins such as APC, Axin-2, Dvl and -catenin have been implicated as direct regulators of mitosis 13, 19. For instance, APC together with Dvl localizes at the microtubuleCkinetochore interface where they might contribute to proper microtubule binding to kinetochores 20, 21, 22. This function seems to be independent of Wnt signaling. However, APC and Dvl2 also associate with the mitotic cell cortex where they might help to anchor astral microtubules to the cortex in order to ensure proper orientation of the mitotic spindle. This function also involves the Wnt receptor Fzd Tariquidar and its co-receptor LRP6 21. Furthermore, -catenin and Axin-2 are present at mitotic centrosomes where they might be involved in centrosome function, microtubule nucleation and mitotic spindle assembly 23, 24, 25. Thus, Wnt signaling as well as particular Wnt signaling components appear to be involved in the regulation of mitosis, but the nature of their action remains largely elusive. It is conceivable that the proper progression of mitosis is CXCL5 essential for faithful chromosome segregation and the generation of euploid progenitors in normal somatic cells. On the other hand, aneuploidy as a consequence of mitotic chromosome missegregation is often associated with human diseases including cancer and neurodegenerative diseases 26. In particular, much effort has been undertaken to understand how chromosomes are missegregated in cancer cells, but the underlying mechanisms are still poorly Tariquidar understood 27. Recently, we identified a key mechanism leading to perpetual chromosome missegregation and aneuploidy in human cancer cells 28. In fact, we found that increased microtubule plus end assembly rates in mitosis are directly responsible for the generation of so-called lagging chromosomes during anaphase, which represent a common pre-stage of chromosome missegregation in somatic cells 28, 29. Thus, cells must ensure proper microtubule assembly rates during mitosis in order to maintain a stable karyotype. However, the molecular pathways that ensure proper microtubule plus end assembly during a normal mitosis are ill defined. In our work presented here, we reveal a requirement for Wnt?signaling during mitosis that is independent of canonical Wnt signaling for proper mitotic microtubule plus end assembly and for faithful chromosome segregation in human somatic cells. Results and Discussion Inhibition of basal Wnt signaling causes increased mitotic microtubule plus end assembly rates Tariquidar during mitosis Our previous work established proper microtubule plus end assembly rates during mitosis as an essential determinant for proper mitotic progression and faithful chromosome segregation 28. Therefore, we investigated a potential involvement of non-induced (=?basal or baseline) Wnt signaling in this process. We transfected HCT116 and non-transformed human retinal pigment epithelial (hTert-RPE1) cells with siRNAs targeting different Wnt signaling components (Supplementary Fig S1A and B), which did not affect cell proliferation or cell cycle progression (Supplementary Fig S1C). Subsequently, we determined microtubule plus end assembly rates by tracking EB3-GFP fusion proteins 30 in living cells (Supplementary Fig S1D). Interestingly, we found that partial repression of or or or (Fig?(Fig1C1C and ?andD,D, Supplementary Fig S1G). As an alternative approach to inhibit basal Wnt signaling, we treated cells with purified sFRP and DKK1 proteins 32 (Supplementary Fig S2C and D) and measured microtubule plus end assembly rates. In line with our first results, we found a significant increase in microtubule assembly rates.