The M Phase Kinase Greatwall (Gwl) Promotes Inactivation of PP2A/B55δ, a Phosphatase Directed Against CDK Phosphosites |
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| Authors: | Priscila V Castilho Byron C Williams Satoru Mochida Yong Zhao Michael L Goldberg |
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| Institution: | *Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; and ;‡Cancer Research UK, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom |
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| Abstract: | 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 B55δ regulatory subunit. Gwl is activated during M phase by Cdk1/cyclin B (MPF), but once activated, Gwl promotes PP2A/B55δ inhibition with no further requirement for MPF. In the absence of Gwl, PP2A/B55δ remains active even when MPF levels are high. The removal of PP2A/B55δ 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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