Greatwall Phosphorylates an Inhibitor of Protein Phosphatase 2Α That Is Essential for Mitosis

概要

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Entry into mitosis in eukaryotes requires the activity of Cyclin-dependent kinase1 (CDK1). CDK1 is opposed by protein phosphatases in two ways: they inhibitits activation by dephosphorylating the protein kinases Wee1 and Myt1 and theprotein phosphatase Cdc25 (key regulators of Cdk1) and they also antagonize itsown phosphorylation of downstream targets. A particular form of proteinphosphatase 2A (PP2A) containing a B55δ subunit is the major proteinphosphatase that acts on model CDK substrates in Xenopus egg extracts and hasanti-mitotic activity. The activity of PP2A-B55δ is high in interphase and low inmitosis, exactly opposite to that of CDK1. We report that inhibition of PP2A-B55δ　results from a small protein known as α-Endosulfine (Ensa), which isphosphorylated in mitosis by the protein kinase Greatwall (Gwl). This convertsEnsa into a potent and specific inhibitor of PP2A-B55δ. This pathway representsa new element in the control of mitosis.
2010-12-17