Mitotic phosphorylation of PRC1 at Thr470 is required for PRC1 oligomerization and proper central spindle organization

During cell division, chromosome segregation is orchestrated by the interaction of spindle microtubules with the centromere. A dramatic remodeling of interpolar microtubules into an organized central spindle between the separating chromatids is required for the initiation and execution ofcytokinesis. Central spindle organization requires mitotic kinesins, the chromosomal passenger protein complex, and microtubule bundling protein PRC 1. PRC 1 is phosphorylated by Cdc2 at Thr470 and Thr481 during mitosis. However, the functional relevance of PRC 1 phosphorylation at Thr470 has remained elusive. Here we show that expression of the non-phosphorylatable mutant PRC 1T470A but not the phospho-mimicking mutant PRC 1^T470E causes aberrant organization of the central spindle. Immunoprecipitation experiment indicates that both PRC 1^T470A and PRC 1^T470E mutant proteins associate with wild-type PRC 1, suggesting that phosphorylation of Thr470 does not alter PRC 1 self-association. In addition, in vitro co-sedimentation experiment showed that PRC 1 binds to microtubule independent of the phosphorylation state of Thr470. Gel-filtration experiment suggested that phosphorylation of Thr470 promotes oligomerization of PRC 1. Given the fact that prevention of the Thr470 phosphorylation inhibits PRC 1 oligomerization in vitro and causes an aberrant organization of central spindle in vivo, we propose that this phosphorylation-dependent PRC 1 oligomerization ensures that central spindle assembly occurs at the appropriate time in the cell cycle.

AMPK regulates anaphase central spindle Length by phosphorylation of KIF4A

AMP-activated protein kinase （AMPK） is an energy sensor that couples the cellular energy state with basic biological processes. AMPK is thought to be linked with cell division although the underlying mechanisms remain largely unknown. Here, we show that AMPK functionally participates throughout cell division and that AMPK catalytic subunits, especially α2, are sequentially associated with separate mitotic apparatus. Using quantitative phosphoproteomics analysis, we found that the strong direct sub- strate KIF4A is phosphorylated by AMPK at Set801. Further analysis revealed that AMPK and Aurora B competitively phosphore- gulates KIF4A during mitotic phase due to overlapping recognition motifs, resulting in the elaborate phosphoregutation for KIF4A-dependent central spindle length control. Given the intrinsic energy-sensing function of AMPK, our study links the KIF4A- dependent control of central spindle length with cellular glucose stress.

Mitotic motor CENP-E cooperates with PRC1 in temporal control of central spindle assembly

Error-free cell division depends on the accurate assembly of the spindle midzone from dynamic spindle microtubules to ensure chromatid segregation during metaphase-anaphase transition.However,the mechanism underlying the key transition from the mitotic spindle to central spindle before anaphase onset remains elusive.Given the prevalence of chromosome instability phenotype in gastric tumorigenesis,we developed a strategy to model context-dependent cell division using a combination of light sheet microscope and 3D gastric organoids.Light sheet microscopic image analyses of 3D organoids showed that CENP-E inhibited cells undergoing aberrant metaphase-anaphase transition and exhibiting chromosome segregation errors during mitosis.Highresolution real-time imaging analyses of 2D cell culture revealed that CENP-E inhibited cells undergoing central spindle splitting and chromosome instability phenotype.Using biotinylated syntelin as an affinity matrix,we found that CENP-E forms a complex with PRC1 in mitotic cells.Chemical inhibition of CENP-E in metaphase by syntelin prevented accurate central spindle assembly by perturbing temporal assembly of PRC1 to the midzone.Thus,CENP-E-mediated PRC1 assembly to the central spindle constitutes a temporal switch to organize dynamic kinetochore microtubules into stable midzone arrays.These findings reveal a previously uncharacterized role of CENP-E in temporal control of central spindle assembly.Since CENP-E is absent from yeast,we reasoned that metazoans evolved an elaborate central spindle organization machinery to ensure accurate sister chromatid segregation during anaphase and cytokinesis.