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

Abstract

Saccharomyces cerevisiae cell division ends with destruction of a septum deposited during cytokinesis; this must occur only after the structure's construction is complete. Genes involved in septum destruction are induced by the transcription factor Ace2, which is activated by the kinase Cbk1, an Ndr/LATS-related protein that functions in a system related to metazoan hippo pathways. Phosphorylation of a conserved hydrophobic motif (HM) site regulates Cbk1; at peak levels in late mitosis we found that approximately 3% of Cbk1 carries this modification. HM site phosphorylation prior to mitotic exit occurs in response to activation of the FEAR (Cdc fourteen early anaphase release) pathway. However, HM site phosphorylation is not sufficient for Cbk1 to act on Ace2: the kinase is also negatively regulated prior to cytokinesis, likely by cyclin-dependent kinase (CDK) phosphorylation. Cbk1 cannot phosphorylate Ace2 until after mitotic exit network (MEN)-initiated release of the phosphatase Cdc14. Treatment of Cbk1 with Cdc14 in vitro does not increase its intrinsic enzymatic activity, but Cdc14 is required for Cbk1 function in vivo. Thus, we propose that Cdc14 coordinates cell separation with mitotic exit via FEAR-initiated phosphorylation of the Cbk1 HM site and MEN-activated reversal of mitotic CDK phosphorylations that block both Cbk1 and Ace2 function.

Protein kinase Ypk1 phosphorylates regulatory proteins Orm1 and Orm2 to control sphingolipid homeostasis in Saccharomyces cerevisiae

“…This mode of regulation appears to be unique to those AGC kinases under TORC2 control because, by contrast, mammalian p70 S6K and yeast Sch9 absolutely require modification by TORC1 for their activity (27,32). Likewise, activity and function of yeast Cbk1 (an AGC kinase of the Ndr/LATS subfamily) is completely dependent on phosphorylation of its hydrophobophobic motif by a distinct complex containing the kinase Kic1 (34,35).…”

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

“…Intriguingly, Cdc14p is further required for the functionality of the LATS/ NDR kinase Cbk1p (the second LATS/NDR kinase in budding yeast) [43]. Weiss and colleagues showed recently that Cdc14 is essential for Cbk1 function in vivo, even though Cdc14p does not influence Cbk1p in vitro [43]. Since Cbk1 mainly functions in the G1-phase of the cell cycle [44][45][46], these findings suggest that the MEN can even play a role beyond mitotic exit and cytokinesis.…”

“…Cdc14p may also directly regulate Boi1, Boi2, Chs1, Shs1 and other mitotic factors to facilitate cytokinesis [33], however, the direct regulation of these proteins by Cdc14p is yet to be established. Intriguingly, Cdc14p is further required for the functionality of the LATS/ NDR kinase Cbk1p (the second LATS/NDR kinase in budding yeast) [43]. Weiss and colleagues showed recently that Cdc14 is essential for Cbk1 function in vivo, even though Cdc14p does not influence Cbk1p in vitro [43].…”

Mechanisms of cytokinesis in budding yeast

“…All these upstream components are required for Cbk1 activation as well as its daughter nucleus-restricted localization [Nelson et al, 2003]. Cbk1 activation also depends on MEN [Brace et al, 2011]. Direct phosphorylation by Cbk1 activates Ace2, which initiates and then maintains the asymmetric localization of Ace2 in the daughter nucleus [Mazanka et al, 2008].…”