Cyclin B1-Cdk1 facilitates MAD1 release from the nuclear pore to ensure a robust spindle checkpoint

Abstract

How the cell rapidly and completely reorganizes its architecture when it divides is a problem that has fascinated researchers for almost 150 yr. We now know that the core regulatory machinery is highly conserved in eukaryotes, but how these multiple protein kinases, protein phosphatases, and ubiquitin ligases are coordinated in space and time to remodel the cell in a matter of minutes remains a major question. Cyclin B1-Cdk is the primary kinase that drives mitotic remodeling; here we show that it is targeted to the nuclear pore complex (NPC) by binding an acidic face of the kinetochore checkpoint protein, MAD1, where it coordinates NPC disassembly with kinetochore assembly. Localized cyclin B1-Cdk1 is needed for the proper release of MAD1 from the embrace of TPR at the nuclear pore so that it can be recruited to kinetochores before nuclear envelope breakdown to maintain genomic stability.

Cyclin B1 scaffolds MAD 1 at the kinetochore corona to activate the mitotic checkpoint

“…This was sufficient to co‐recruit Cyclin B1 in a manner that was dependent on a region between amino acids 41–92 of MAD1 (Fig F and G). Therefore, these data are consistent with earlier reports that Cyclin B1 localises to unattached kinetochores (Bentley et al , ; Chen et al , ) in a manner that is dependent on the N‐terminus of MAD1 (Alfonso‐Perez et al , ; Jackman et al , ).…”

Rashomon at the kinetochore: Function(s) of the Mad1–cyclin B1 complex

“…Viewpoint 1: Mad1-associated cyclin B1-Cdk1 releases Mad1 from nuclear pore complexes Mad1 localizes to nuclear pore complexes in interphase through an interaction with the nuclear basket protein Tpr/Megator. Jackman et al (2020) suggest that cyclin B1 association is critical for the timely release of Mad1 from nuclear pores ( Fig. 1 Bi).…”

“…The results of Alfonso-Pérez et al (2019) also have implications for the model proposed by Jackman et al (2020). The N-terminal deletion of Mad1 they analyzed, in addition to removing the cyclin B1 interaction motif, is also predicted to reduce nuclear pore localization (Rodriguez-Bravo et al, 2014).…”

“…Of note, Alfonso-Pérez et al's localization analysis was conducted using in situ-tagged Mps1, which overcomes limitations imposed by antibody-based detection of this dynamically localized kinase. Unlike Jackman et al (2020) and Allan et al (2020), Alfonso-Pérez et al (2019) did not identify and selectively mutate a specific cyclin B1 interaction motif in Mad1. Thus, a caveat of their analysis is that the deleted region may affect other functions; for example, this region is suggested to be important for Mad1 nuclear localization (Sze et al, 2008).…”

“…Viewpoint 3: Cyclin B1 scaffolds Mad1 at the kinetochore corona Allan et al (2020) identify the same cyclin B1 association motif as Jackman et al (2020) and employ biochemical reconstitutions with purified components to establish a direct Mad1 interaction with cyclin B1 that is dependent on this motif; notably, Cdk1 is not required for the interaction. The precise binding mechanism involved will be important to elucidate, as it may potentially reveal a new general mode of cyclin binding.…”