bims-micesi 2023-12-24 papers

Issue of 2023–12–24
four papers selected by
Valentina Piano, Uniklinik Köln

J Cell Biol. 2024 Feb 05. pii: e202108070. [Epub ahead of print]223(2):

NuSAP regulates microtubule flux and Kif2A localization to ensure accurate chromosome congression.

Mengjie Sun, Yao Wang, Guangwei Xin, Biying Yang, Qing Jiang, Chuanmao Zhang.

Precise chromosome congression and segregation requires the proper assembly of a steady-state metaphase spindle, which is dynamic and maintained by continuous microtubule flux. NuSAP is a microtubule-stabilizing and -bundling protein that promotes chromosome-dependent spindle assembly. However, its function in spindle dynamics remains unclear. Here, we demonstrate that NuSAP regulates the metaphase spindle length control. Mechanistically, NuSAP facilitates kinetochore capture and spindle assembly by promoting Eg5 binding to microtubules. It also prevents excessive microtubule depolymerization through interaction with Kif2A, which reduces Kif2A spindle-pole localization. NuSAP is phosphorylated by Aurora A at Ser-240 during mitosis, and this phosphorylation promotes its interaction with Kif2A on the spindle body and reduces its localization with the spindle poles, thus maintaining proper spindle microtubule flux. NuSAP knockout resulted in the formation of shorter spindles with faster microtubule flux and chromosome misalignment. Taken together, we uncover that NuSAP participates in spindle assembly, dynamics, and metaphase spindle length control through the regulation of microtubule flux and Kif2A localization.

DOI: https://doi.org/10.1083/jcb.202108070

BMC Cancer. 2023 Dec 21. 23(1): 1263

Endosulfine alpha maintains spindle pole integrity by recruiting Aurora A during mitosis.

Seul Kim, Kyoungho Jun, Ye-Hyun Kim, Kwan-Young Jung, Jeong Su Oh, Jae-Sung Kim.

BACKGROUND: The maintenance of spindle pole integrity is essential for spindle assembly and chromosome segregation during mitosis. However, the underlying mechanisms governing spindle pole integrity remain unclear.
METHODS: ENSA was inhibited by siRNA or MKI-2 treatment and its effect on cell cycle progression, chromosome alignment and microtubule alignment was observed by immunohistochemical staining and western blotting. PP2A-B55α knockdown by siRNA was performed to rescue the phenotype caused by ENSA inhibition. The interaction between ENSA and Aurora A was detected by in situ PLA. Furthermore, orthotopic implantation of 4Tl-luc cancer cells was conducted to confirm the consistency between the in vitro and in vivo relationship of the ENSA-Aurora A interaction.
RESULTS: During mitosis, p-ENSA is localized at the spindle poles, and the inhibition of ENSA results in mitotic defects, such as misaligned chromosomes, multipolar spindles, asymmetric bipolar spindles, and centrosome defects, with a delay in mitotic progression. Although the mitotic delay caused by ENSA inhibition was rescued by PP2A-B55α depletion, spindle pole defects persisted. Notably, we observed a interaction between ENSA and Aurora A during mitosis, and inhibition of ENSA reduced Aurora A expression at the mitotic spindle poles. Injecting MKI-2-sensitized tumors led to increased chromosomal instability and downregulation of the MASTL-ENSA-Aurora A pathway in an orthotopic breast cancer mouse model.
CONCLUSIONS: These findings provide novel insights into the regulation of spindle pole integrity by the MASTL-ENSA-Aurora A pathway during mitosis, highlighting the significance of ENSA in recruiting Aurora A to the spindle pole, independent of PP2A-B55α.

Keywords: Aurora A; ENSA; MASTL; Mitosis; Spindle pole integrity

DOI: https://doi.org/10.1186/s12885-023-11742-0

Nature. 2023 Dec 20.

Cryo-EM structures of PP2A:B55-FAM122A and PP2A:B55-ARPP19.

Sathish K R Padi, Margaret R Vos, Rachel J Godek, James R Fuller, Thomas Kruse, Jamin B Hein, Jakob Nilsson, Matthew S Kelker, Rebecca Page, Wolfgang Peti.

Progression through the cell cycle is controlled by regulated and abrupt changes in phosphorylation1. Mitotic entry is initiated by increased phosphorylation of mitotic proteins, a process driven by kinases2, whereas mitotic exit is achieved by counteracting dephosphorylation, a process driven by phosphatases, especially PP2A:B553. Although the role of kinases in mitotic entry is well established, recent data have shown that mitosis is only successfully initiated when the counterbalancing phosphatases are also inhibited4. Inhibition of PP2A:B55 is achieved by the intrinsically disordered proteins ARPP195,6 and FAM122A7. Despite their critical roles in mitosis, the mechanisms by which they achieve PP2A:B55 inhibition is unknown. Here, we report the single-particle cryo-electron microscopy structures of PP2A:B55 bound to phosphorylated ARPP19 and FAM122A. Consistent with our complementary NMR spectroscopy studies, both intrinsically disordered proteins bind PP2A:B55, but do so in highly distinct manners, leveraging multiple distinct binding sites on B55. Our extensive structural, biophysical and biochemical data explain how substrates and inhibitors are recruited to PP2A:B55 and provide a molecular roadmap for the development of therapeutic interventions for PP2A:B55-related diseases.

DOI: https://doi.org/10.1038/s41586-023-06870-3

DNA Repair (Amst). 2023 Dec 05. pii: S1568-7864(23)00165-9. [Epub ahead of print]133 103611

FBH1 deficiency sensitizes cells to WEE1 inhibition by promoting mitotic catastrophe.

Lucy Jennings, Heather Andrews Walters, Tyler J McCraw, Joshua L Turner, Jennifer M Mason.

WEE1 kinase phosphorylates CDK1 and CDK2 to regulate origin firing and mitotic entry. Inhibition of WEE1 has become an attractive target for cancer therapy due to the simultaneous induction of replication stress and inhibition of the G2/M checkpoint. WEE1 inhibition in cancer cells with high levels of replication stress results in induction of replication catastrophe and mitotic catastrophe. To increase potential as a single agent chemotherapeutic, a better understanding of genetic alterations that impact cellular responses to WEE1 inhibition is warranted. Here, we investigate the impact of loss of the helicase, FBH1, on the cellular response to WEE1 inhibition. FBH1-deficient cells have a reduction in ssDNA and double strand break signaling indicating FBH1 is required for induction of replication stress response in cells treated with WEE1 inhibitors. Despite the defect in the replication stress response, FBH1-deficiency sensitizes cells to WEE1 inhibition by increasing mitotic catastrophe. We propose loss of FBH1 is resulting in replication-associated damage that requires the WEE1-dependent G2 checkpoint for repair.

Keywords: DNA repair; FBH1; Mitosis; Replication; Replication catastrophe; WEE1

DOI: https://doi.org/10.1016/j.dnarep.2023.103611