bims-micesi 2023-05-07 papers

Issue of 2023–05–07
four papers selected by
Valentina Piano, Uniklinik Köln

Curr Biol. 2023 Apr 28. pii: S0960-9822(23)00469-4. [Epub ahead of print]

BUB-1-bound PLK-1 directs CDC-20 kinetochore recruitment to ensure timely embryonic mitoses.

Jack Houston, Midori Ohta, J Sebastián Gómez-Cavazos, Amar Deep, Kevin D Corbett, Karen Oegema, Pablo Lara-Gonzalez, Taekyung Kim, Arshad Desai.

During mitosis, chromosomes assemble kinetochores to dynamically couple with spindle microtubules.1,2 Kinetochores also function as signaling hubs directing mitotic progression by recruiting and controlling the fate of the anaphase promoting complex/cyclosome (APC/C) activator CDC-20.3,4,5 Kinetochores either incorporate CDC-20 into checkpoint complexes that inhibit the APC/C or dephosphorylate CDC-20, which allows it to interact with and activate the APC/C.4,6 The importance of these two CDC-20 fates likely depends on the biological context. In human somatic cells, the major mechanism controlling mitotic progression is the spindle checkpoint. By contrast, progression through mitosis during the cell cycles of early embryos is largely checkpoint independent.7,8,9,10 Here, we first show that CDC-20 phosphoregulation controls mitotic duration in the C. elegans embryo and defines a checkpoint-independent temporal mitotic optimum for robust embryogenesis. CDC-20 phosphoregulation occurs at kinetochores and in the cytosol. At kinetochores, the flux of CDC-20 for local dephosphorylation requires an ABBA motif on BUB-1 that directly interfaces with the structured WD40 domain of CDC-20.6,11,12,13 We next show that a conserved "STP" motif in BUB-1 that docks the mitotic kinase PLK-114 is necessary for CDC-20 kinetochore recruitment and timely mitotic progression. The kinase activity of PLK-1 is required for CDC-20 to localize to kinetochores and phosphorylates the CDC-20-binding ABBA motif of BUB-1 to promote BUB-1-CDC-20 interaction and mitotic progression. Thus, the BUB-1-bound pool of PLK-1 ensures timely mitosis during embryonic cell cycles by promoting CDC-20 recruitment to the vicinity of kinetochore-localized phosphatase activity.

Keywords: APC/C; Bub1; Cdc20; Plk1; cell cycle; centromere; embryogenesis; kinetochore; mitosis; spindle assembly checkpoint

DOI: https://doi.org/10.1016/j.cub.2023.04.021

J Cell Biol. 2023 Jun 05. pii: e202110124. [Epub ahead of print]222(6):

Repression of CENP-A assembly in metaphase requires HJURP phosphorylation and inhibition by M18BP1.

Julio C Flores Servin, Rachel R Brown, Aaron F Straight.

Centromeres are the foundation for mitotic kinetochore assembly and thus are essential for chromosome segregation. Centromeres are epigenetically defined by nucleosomes containing the histone H3 variant CENP-A. CENP-A nucleosome assembly is uncoupled from replication and occurs in G1, but how cells control this timing is incompletely understood. The formation of CENP-A nucleosomes in vertebrates requires CENP-C and the Mis18 complex which recruit the CENP-A chaperone HJURP to centromeres. Using a cell-free system for centromere assembly in X. laevis egg extracts, we discover two activities that inhibit CENP-A assembly in metaphase. HJURP phosphorylation prevents the interaction between HJURP and CENP-C in metaphase, blocking the delivery of soluble CENP-A to centromeres. Non-phosphorylatable mutants of HJURP constitutively bind CENP-C in metaphase but are not sufficient for new CENP-A assembly. We find that the M18BP1.S subunit of the Mis18 complex also binds to CENP-C to competitively inhibit HJURP's access to centromeres. Removal of these two inhibitory activities causes CENP-A assembly in metaphase.

DOI: https://doi.org/10.1083/jcb.202110124

Mol Biol Cell. 2023 Apr 26. mbcE23040130

The role of kinetochore dynein in checkpoint silencing is restricted to disassembly of the corona.

Amy H Ide, Keith F DeLuca, O'Neil Wiggan, Steven M Markus, Jennifer G DeLuca.

During mitosis, kinetochore-microtubule attachments are monitored by a molecular surveillance system known as the spindle assembly checkpoint. The prevailing model posits that dynein evicts checkpoint proteins (e.g., Mad1, Mad2) from stably attached kinetochores by transporting them away from kinetochores, thus contributing to checkpoint silencing. However, the mechanism by which dynein performs this function, and its precise role in checkpoint silencing remain unresolved. Here, we find that dynein's role in checkpoint silencing is restricted to evicting checkpoint effectors from the fibrous corona, and not the outer kinetochore. Dynein evicts these molecules from the corona in a manner that does not require stable, end-on microtubule attachments. Thus, by disassembling the corona through indiscriminate microtubule encounters, dynein primes the checkpoint signaling apparatus so it can respond to stable end-on microtubule attachments, and permit cells to progress through mitosis. Accordingly, we find that dynein function in checkpoint silencing becomes largely dispensable in cells in which checkpoint effectors are excluded from the corona.

DOI: https://doi.org/10.1091/mbc.E23-04-0130

Genes Cells. 2023 Apr 29.

The toxicity of dysregulated Plk1 activity revealed by its suppressor mutations.

Nana Kamakura, Motoko Takahashi, Minji Jo.

Polo-like kinase 1 (Plk1) is a mitotic kinase that has multiple functions throughout the cell cycle. Catalytic activation of Plk1 is known to be regulated by phosphorylation of the kinase domain, including Thr210, and by releasing the kinase domain from its inhibitory polo-box domain. However, how Plk1 is activated to fulfill its proper roles, in time and space, is not well understood. In this study, we unintentionally found that the expression of a constitutively active form of human Plk1 is toxic to bacterial cells, such that cells contained point mutations that alleviate the kinase activity. Structural prediction revealed that these mutations are adjacent to the amino acids supporting the kinase activity. When human cells express these mutants, we found decreased levels of Plk1's substrate phosphorylation, resulting in mitotic defects. Moreover, unlike in bacterial cells, the expression of activated Plk1 mutants did not affect cell proliferation in human cells unless localized at the right place in mitosis. Our observations identified new suppressor mutations and underscored the importance of spatiotemporal regulation in Plk1, providing a basis for how we might intervene in this kinase for therapeutic purpose in human cells.

Keywords: Plk1; kinase domain; kinetochore; mitotic kinase

DOI: https://doi.org/10.1111/gtc.13032