Compartmentalized control of Cdk1 drives mitotic spindle assembly

• Published in: Cell reports (Cambridge) 2022-01, Vol.38 (4), p.110305-110305, Article 110305
• Main Authors: Serpico, Angela Flavia, Febbraro, Francesco, Pisauro, Caterina, Grieco, Domenico
• Format: Article
• Language: English
• Subjects: CDC2 Protein Kinase - metabolism; Cdk1; cell cycle; compartmentalization; HeLa Cells; Humans; i-Cdk1; microtubule-associated proteins; Mitosis - physiology; mitotic spindle assembly; Phosphorylation; Spindle Apparatus - metabolism; spindle assembly checkpoint; Wee1
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2022.110305

During cell division, dramatic microtubular rearrangements driven by cyclin B-cdk1 (Cdk1) kinase activity mark the onset of mitosis leading to dismantling of the interphase microtubular cytoskeleton and assembly of the mitotic spindle. During interphase, Cdk1 accumulates in an inactive state, phosphorylated at inhibitory sites by Wee1/Myt1 kinases. At mitosis onset, Cdc25 phosphatase dephosphorylates and activates Cdk1. Once activated, Cdk1 clears cytoplasmic microtubules by inhibiting microtubule-stabilizing and growth-promoting microtubule-associated proteins (MAPs). Nevertheless, some of these MAPs are required for spindle microtubule growth and spindle assembly, creating quite a conundrum. We show here that a Cdk1 fraction bound to spindle structures escapes Cdc25 action and remains inhibited by phosphorylation (i-Cdk1) in mitotic human cells. Loss or restoration of i-Cdk1 inhibits or promotes spindle assembly, respectively. Furthermore, polymerizing spindle microtubules foster i-Cdk1 aggregating with Wee1 and excluding Cdc25. Our data reveal that spindle assembly relies on compartmentalized control of Cdk1 activity. [Display omitted] •A small fraction of Cdk1 is inhibited by phosphorylation in mitosis (i-Cdk1)•i-Cdk1 selectively localizes at the mitotic spindle and drives its formation•i-Cdk1 controls PP1 and microtubule-stabilizing MAPs to promote spindle assembly By cell fractionation, imaging, and genetic knockdown experiments in human cells, Serpico et al. find that a small fraction of Cdk1, the major M-phase promoting kinase, remains inhibited by phosphorylation in mitosis (i-Cdk1). i-Cdk1 is selectively localized at the mitotic spindle and necessary for its formation.