PP2A--B55γ counteracts Cdk1 and regulates proper spindle orientation through the cortical dynein adaptor NuMA

• Published in: Journal of cell science Vol. 133; no. 14
• Main Authors: Keshri, Riya, Rajeevan, Ashwathi, Kotak, Sachin
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists Ltd 31.07.2020
• Subjects: CDC2 Protein Kinase - genetics; CDC2 Protein Kinase - metabolism; Cell Cycle Proteins - metabolism; Dyneins - genetics; Dyneins - metabolism; Humans; Mitosis; Nuclear Matrix-Associated Proteins - genetics; Nuclear Matrix-Associated Proteins - metabolism; Protein Phosphatase 2 - genetics; Spindle Apparatus - genetics; Spindle Apparatus - metabolism; Cdk1; Spindle orientation; PP2A; Mitosis; NuMA; Dynein
• ISSN: 0021-9533; 1477-9137
• DOI: 10.1242/jcs.243857

Proper orientation of the mitotic spindle is critical for accurate development and morphogenesis. In human cells, spindle orientation is regulated by the evolutionarily conserved protein NuMA, which interacts with dynein and enriches it at the cell cortex. Pulling forces generated by cortical dynein orient the mitotic spindle. Cdk1-mediated phosphorylation of NuMA at threonine 2055 (T2055) negatively regulates its cortical localization. Thus, only NuMA not phosphorylated at T2055 localizes at the cell cortex. However, the identity and the mechanism of action of the phosphatase complex involved in T2055 dephosphorylation remains elusive. Here, we characterized the PPP2CA-B55γ (PPP2R2C)-PPP2R1B complex that counteracts Cdk1 to orchestrate cortical NuMA for proper spindle orientation. reconstitution experiments revealed that this complex is sufficient for T2055 dephosphorylation. Importantly, we identified polybasic residues in NuMA that are critical for T2055 dephosphorylation, and for maintaining appropriate cortical NuMA levels for accurate spindle elongation. Furthermore, we found that Cdk1-mediated phosphorylation and PP2A-B55γ-mediated dephosphorylation at T2055 are reversible events. Altogether, this study uncovers a novel mechanism by which Cdk1 and its counteracting PP2A-B55γ complex orchestrate spatiotemporal levels of cortical force generators for flawless mitosis.