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Protein phosphatases and cell division cycle control
M Yanagida1, N Kinoshita, E M Stone
1Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Abstract:
Fission yeast has at least ten protein phosphatase genes that appear to play distinct roles in cell cycle control. Because of functional overlap, a clear lethal phenotype can be obtained only after multiple genetic alterations. Cells that have lost the protein phosphatase 1 (PP1)-like dis2/sds21 phosphatase activities prematurely enter mitosis and remain in a defective mitotic state with high H1 kinase activity and without sister chromatid disjunction. The same phenotype can be obtained in the presence of hydroxyurea. Overexpression of PP1-like phosphatase, on the other hand, delays the entry into mitosis. Cells that have lost PP2A-like ppa2 phosphatase activity also prematurely enter mitosis with a reduction in cell size. This semi-wee phenotype is enhanced in delta ppa2 mutants treated with the phosphatase inhibitor, okadaic acid. Genetic interactions between ppa2 and mitotic regulators suggest that ppa1/ppa2 phosphatase may directly or indirectly inhibit p34cdc2/cyclin kinase. Thus both PP1- and PP2A-like phosphatases in fission yeast may negatively regulate entry into mitosis. The major property of the dis2/sds21 mutant which is distinct from those of the ppa2/ppa1 mutant is its failure to inactivate the p34cdc2/cyclin complex after entry into mitosis. A novel phosphatase regulator encoded by sds22+ binds to dis2 phosphatase and controls the substrate specificity which appears to become essential in the progression from metaphase to anaphase.
Insights
Fission yeast protein phosphatases PP1 and PP2A regulate entry into mitosis. Loss of these phosphatases causes premature mitosis, while their overexpression delays it, highlighting their crucial cell cycle control roles.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Fission yeast possesses multiple protein phosphatase genes involved in cell cycle control.
- Functional overlap necessitates multiple genetic alterations to observe clear phenotypes.
- Protein phosphatases PP1 and PP2A play critical roles in regulating mitotic entry and progression.
Purpose of the Study:
- To investigate the roles of protein phosphatase 1 (PP1)-like dis2/sds21 and PP2A-like ppa2 in fission yeast cell cycle control.
- To elucidate the mechanisms by which these phosphatases regulate entry into and progression through mitosis.
- To identify novel regulators of phosphatase activity in mitosis.
Main Methods:
- Genetic analysis of fission yeast mutants lacking specific protein phosphatase activities (dis2/sds21, ppa2).
- Phenotypic analysis including cell cycle progression, H1 kinase activity, and sister chromatid disjunction.
- Investigating the effects of hydroxyurea and okadaic acid on mutant phenotypes.
- Examining genetic interactions with known mitotic regulators.
- Characterizing the interaction between dis2 phosphatase and its novel regulator Sds22+.
Main Results:
- Loss of PP1-like dis2/sds21 or PP2A-like ppa2 activity leads to premature entry into mitosis.
- PP1/PP2A phosphatases negatively regulate entry into mitosis, potentially by inhibiting p34cdc2/cyclin kinase.
- Disruption of PP1-like activity prevents inactivation of the p34cdc2/cyclin complex post-mitotic entry.
- Overexpression of PP1-like phosphatases delays mitotic entry.
- A novel regulator, Sds22+, binds dis2 phosphatase and is essential for metaphase-anaphase progression.
Conclusions:
- Both PP1- and PP2A-like phosphatases are essential negative regulators of mitotic entry in fission yeast.
- Dis2/sds21 and ppa2/ppa1 phosphatases have distinct roles in mitotic progression, particularly in the inactivation of the p34cdc2/cyclin complex.
- The Sds22+ protein is a novel regulator that modulates dis2 phosphatase activity and substrate specificity, crucial for anaphase.
- These findings deepen the understanding of cell cycle control mechanisms mediated by protein phosphatases.