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Mol Biol Cell. 2009 Nov;20(22):4777-89. doi: 10.1091/mbc.E09-07-0643. Epub 2009 Sep 30.

The M phase kinase Greatwall (Gwl) promotes inactivation of PP2A/B55delta, a phosphatase directed against CDK phosphosites.

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Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.


We have previously shown that Greatwall kinase (Gwl) is required for M phase entry and maintenance in Xenopus egg extracts. Here, we demonstrate that Gwl plays a crucial role in a novel biochemical pathway that inactivates, specifically during M phase, "antimitotic" phosphatases directed against phosphorylations catalyzed by cyclin-dependent kinases (CDKs). A major component of this phosphatase activity is heterotrimeric PP2A containing the B55delta regulatory subunit. Gwl is activated during M phase by Cdk1/cyclin B (MPF), but once activated, Gwl promotes PP2A/B55delta inhibition with no further requirement for MPF. In the absence of Gwl, PP2A/B55delta remains active even when MPF levels are high. The removal of PP2A/B55delta corrects the inability of Gwl-depleted extracts to enter M phase. These findings support the hypothesis that M phase requires not only high levels of MPF function, but also the suppression, through a Gwl-dependent mechanism, of phosphatase(s) that would otherwise remove MPF-driven phosphorylations.

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