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Changes in regulatory phosphorylation of Cdc25C Ser287 and Wee1 Ser549 during normal cell cycle progression and checkpoint arrests
Journal article   Open access

Changes in regulatory phosphorylation of Cdc25C Ser287 and Wee1 Ser549 during normal cell cycle progression and checkpoint arrests

Jennifer S Stanford and Joan V Ruderman
Molecular biology of the cell, v 16(12), pp 5749-5760
Dec 2005
PMID: 16195348
url
https://doi.org/10.1091/mbc.E05-06-0541View
Published, Version of Record (VoR) Open

Abstract

Cyclic AMP-Dependent Protein Kinases - metabolism Phosphorylation Protein-Tyrosine Kinases - metabolism Xenopus laevis Cell Cycle Proteins - metabolism Male Cell Nucleus - ultrastructure Phosphoserine - metabolism Ovum - cytology Animals Cell Cycle - physiology Female Xenopus Proteins - metabolism Ovum - ultrastructure Spermatozoa - cytology Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors Spermatozoa - ultrastructure cdc25 Phosphatases - metabolism
Entry into mitosis is catalyzed by cdc2 kinase. Previous work identified the cdc2-activating phosphatase cdc25C and the cdc2-inhibitory kinase wee1 as targets of the incomplete replication-induced kinase Chk1. Further work led to the model that checkpoint kinases block mitotic entry by inhibiting cdc25C through phosphorylation on Ser287 and activating wee1 through phosphorylation on Ser549. However, almost all conclusions underlying this idea were drawn from work using recombinant proteins. Here, we report that in the early Xenopus egg cell cycles, phosphorylation of endogenous cdc25C Ser287 is normally high during interphase and shows no obvious increase after checkpoint activation. By contrast, endogenous wee1 Ser549 phosphorylation is low during interphase and increases after activation of either the DNA damage or replication checkpoints; this is accompanied by a slight increase in wee1 kinase activity. Blocking mitotic entry by adding the catalytic subunit of PKA also results in increased wee1 Ser549 phosphorylation and maintenance of cdc25C Ser287 phosphorylation. These results argue that in response to checkpoint activation, endogenous wee1 is indeed a critical responder that functions by repressing the cdc2-cdc25C positive feedback loop. Surprisingly, endogenous wee1 Ser549 phosphorylation is highest during mitosis just after the peak of cdc2 activity. Treatments that block inactivation of cdc2 result in further increases in wee1 Ser549 phosphorylation, suggesting a previously unsuspected role for wee1 in mitosis.

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Cell Biology
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