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Reversible tyrosine phosphorylation of cdc2: dephosphorylation accompanies activation during entry into mitosis
A O Morla1, G Draetta, D Beach
1Department of Biology, University of California, La Jolla, San Diego 92093.
Abstract:
Tyrosine phosphorylation of cdc2 is regulated in the cell cycle of mouse 3T3 fibroblasts. Phosphotyrosine in cdc2 is detectable at the onset of DNA synthesis and becomes maximal in the G2 phase of the cell cycle. Quantitative tyrosine dephosphorylation of cdc2 occurs during entry into mitosis and no phosphotyrosine is detected during the G1 phase of the cell cycle. While increasing tyrosine phosphorylation of cdc2 correlates with the formation of a cdc2/p62 complex, the tyrosine phosphorylated cdc2 is inactive as a histone H1 kinase. cdc2 is fully dephosphorylated in its most active mitotic form, yet specific tyrosine dephosphorylation of interphase cdc2 in vitro is insufficient to activate the kinase. In vivo inhibition of tyrosine dephosphorylation by exposure of cells to a phosphatase inhibitor is associated with G2 arrest, which is reversible upon the removal of the phosphatase inhibitor. Tyrosine dephosphorylation of cdc2 may be one of a number of obligatory steps in the mitotic activation of the kinase.
Insights
Cell cycle regulation involves tyrosine phosphorylation of cdc2 kinase. Dephosphorylation of cdc2 is crucial for mitotic activation, highlighting its role in cell cycle progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cdc2 kinase activity is tightly regulated during the cell cycle.
- Tyrosine phosphorylation plays a role in modulating cdc2 activity.
Purpose of the Study:
- To investigate the role of tyrosine phosphorylation and dephosphorylation of cdc2 in the cell cycle of mouse 3T3 fibroblasts.
- To determine the relationship between cdc2 phosphorylation status and its kinase activity.
Main Methods:
- Analysis of cdc2 tyrosine phosphorylation levels across different cell cycle phases.
- Assay of histone H1 kinase activity of cdc2.
- Inhibition of tyrosine dephosphorylation using phosphatase inhibitors.
Main Results:
- Tyrosine phosphorylation of cdc2 increases during the G1 to G2 phases and decreases during mitosis.
- Tyrosine-phosphorylated cdc2 is inactive as a histone H1 kinase.
- Inhibition of tyrosine dephosphorylation leads to G2 cell cycle arrest.
Conclusions:
- Tyrosine dephosphorylation of cdc2 is an essential step for its activation during mitosis.
- Cdc2 regulation involves dynamic changes in tyrosine phosphorylation status throughout the cell cycle.
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