Dbf2–Mob1 drives relocalization of protein phosphatase Cdc14 to the cytoplasm during exit from mitosis

Abstract

Exit from mitosis is characterized by a precipitous decline in cyclin-dependent kinase (Cdk) activity, dissolution of mitotic structures, and cytokinesis. In Saccharomyces cerevisiae, mitotic exit is driven by a protein phosphatase, Cdc14, which is in part responsible for counteracting Cdk activity. Throughout interphase, Cdc14 is sequestered in the nucleolus, but successful anaphase activates the mitotic exit network (MEN), which triggers dispersal of Cdc14 throughout the cell by a mechanism that has remained unknown. In this study, we show that a MEN component, protein kinase Dbf2–Mob1, promotes transfer of Cdc14 to the cytoplasm and consequent exit from mitosis by direct phosphorylation of Cdc14 on serine and threonine residues adjacent to a nuclear localization signal (NLS), thereby abrogating its NLS activity. Our results define a mechanism by which the MEN promotes exit from mitosis.

Mitotic Exit and Separation of Mother and Daughter Cells

“…In vitro studies showed that Dbf2 is basophilic, preferring to phosphorylate serine or threonine residues that are three residues C-terminal to arginine (R-X-X-[S/T]) (Mah et al 2005). This short consensus motif, which is shared by other basophilic kinases, has been borne out for several in vivo substrates (Mohl et al 2009;Oh et al 2012).…”

“…Mob1-Dbf2/Cdc14 release positive feedback loop: In vitro and in vivo studies indicate that Mob1-Dbf2 directly drives cytoplasmic accumulation of Cdc14 by phosphorylating it at sites near its C-terminal nuclear localization sequence (NLS) (Mohl et al 2009). This inhibits the NLS's function, shifting Cdc14's distribution from the nucleus to the cytoplasm and thus allowing it to remove CDK phosphorylations on cytoplasmic proteins.…”

Hippo signalling in the G2/M cell cycle phase: Lessons learned from the yeast MEN and SIN pathways

“…Initially, it was unclear how the Mob1p/Dbf2p complex transmitted the signal to Cdc14p. However, Mohl et al (2009) recently showed that the Mob1p/Dbf2p complex can directly phosphorylate Cdc14p, an event that is sufficient to trigger the relocalisation of Cdc14p at the end of mitosis [34]. To sum up, activation of the Tem1p/Cdc15/Mob1p/Dbf2p/Cdc14p cascade results in CDK1 inactivation, which enables mitotic exit.…”

Mitotic Exit Control of the Saccharomyces cerevisiae Ndr/LATS Kinase Cbk1 Regulates Daughter Cell Separation after Cytokinesis

“…We previously demonstrated that Cbk1 is a hyperphosphorylated protein, and we proposed a model in which this phosphorylation inhibits Cbk1's function in vivo (29). One important function of the MEN is to reverse the phosphorylations performed by the mitotic cyclin-dependent kinase Cdc28/Cdk1 (39,46,67). Thus, at the cdc15-2 arrest, mitotic CDK phosphorylations may persist and might contribute to the inhibition of Cbk1.…”

“…The MEN, initiated by activation of the GTPase Tem1, activates a signaling cascade of kinases, including Cdc15 and Dbf2/Mob1 (3,6,25,39,53,66). Dbf2/Mob1 phosphorylates Cdc14 to inactivate its nuclear localization signal (NLS), promoting release of Cdc14 into the cytoplasm (46). Cytoplasmic Cdc14 dephosphorylates CDK targets to promote mitotic exit and the final events of cell division (7,61,67).…”