A Novel Hyperactive Nud1 Mitotic Exit Network Scaffold Causes Spindle Position Checkpoint Bypass in Budding Yeast

Abstract

Mitotic exit is a critical cell cycle transition that requires the careful coordination of nuclear positioning and cyclin B destruction in budding yeast for the maintenance of genome integrity. The mitotic exit network (MEN) is a Ras-like signal transduction pathway that promotes this process during anaphase. A crucial step in MEN activation occurs when the Dbf2-Mob1 protein kinase complex associates with the Nud1 scaffold protein at the yeast spindle pole bodies (SPBs; centrosome equivalents) and thereby becomes activated. This requires prior priming phosphorylation of Nud1 by Cdc15 at SPBs. Cdc15 activation, in turn, requires both the Tem1 GTPase and the Polo kinase Cdc5, but how Cdc15 associates with SPBs is not well understood. We have identified a hyperactive allele of NUD1, nud1-A308T, that recruits Cdc15 to SPBs in all stages of the cell cycle in a CDC5-independent manner. This allele leads to early recruitment of Dbf2-Mob1 during metaphase and requires known Cdc15 phospho-sites on Nud1. The presence of nud1-A308T leads to loss of coupling between nuclear position and mitotic exit in cells with mispositioned spindles. Our findings highlight the importance of scaffold regulation in signaling pathways to prevent improper activation.

Centrosomes act as organizing centers to promote Polo kinase-mediated adaptation to persistent DNA damage

“…Nud1 may contribute to this pathway by 1) recruiting Cdc5 at SPBs to facilitate transduction of a crucial signal that overrides DNA damage checkpoint activation, and 2) acting as a MEN scaffold that induces mitotic exit when the G2/M checkpoint is silenced and cells become receptive to cell cycle re-entry with lingering DNA damage (Hu et al, 2001; Valerio-Santiago et al, 2013). The observation that a hyperactive Nud1 allele (i.e., nud1-A308T) can trigger partial spindle assembly checkpoint (SAC) bypass and robust SPoC bypass through Cdc5-independent constitutive recruitment of the Hippo-like Cdc15 kinase is consistent with this hypothesis (Vannini et al, 2021). In addition, it is possible that other SPB receptors for Cdc5 –like Spc72– would contribute to the adaptation response via their roles in the sequential and asymmetric recruitment of SPB components to the organelle (Matellán et al, 2020).…”

Editorial to Summarize the Papers Published in the Special Issue “10th Anniversary of Cells—Advances in Cell Cycle”

“…Therefore, most cancer drugs are designed to specifically target mitotic cells. The next two research articles published in this Special Issue focused on the mitotic phase of the cell cycle [ 2 , 3 ].…”

“…Vannini et al, studied the regulation of the mitotic exit in the budding yeast Saccharomyces cerevisiae [ 3 ]. The mitotic exit is critical for the successful completion of a cell division cycle.…”

“…In this research, a collaborative team led by Dr. Seshan identified a hyperactive allele of NUD1, nud1-A308T, that recruits Cdc15 to SPBs in all stages of the cell cycle in a CDC5-independent manner. They further showed that nud1-A308T leads to the early recruitment of Dbf2-Mob1 during metaphase [ 3 ]. Their findings highlight the importance of scaffold regulation in signaling pathways to prevent improper activation.…”