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Lookup NU author(s): Dr Radka Philipova, Emeritus Professor Michael Whitaker
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The human tyrosine phosphatase (p54(cdc25-c)) is activated by phosphorylation at mitosis entry. The phosphorylated p54(cdc25-c) in turn activates the p34-cyclin B protein kinase and triggers mitosis. Although the active p34-cyclin B protein kinase can itself phosphorylate and activate p54(cdc25-c), we have investigated the possibility that other kinases may initially trigger the phosphorylation and activation of p54(cdc25-c). We have examined the effects of the calcium/calmodulin-dependent protein kinase (CaM kinase II) on p54(cdc25-c). Our in vitro experiments show that CaM kinase II can phosphorylate p54(cdc25-c) and increase its phosphatase activity by 2.5- 3 fold. Treatment of a synchronous population of HeLa cells with KN-93 (a water-soluble inhibitor of CaM kinase II) or the microinjection of AC3-I (a specific peptide inhibitor of CaM kinase II) results in a cell cycle block in G2 phase. In the KN-93-arrested cells, p54(cdc25-c) is not phosphorylated, p34(cdc2) remains tyrosine phosphorylated, and there is no increase in histone H1 kinase activity. Our data suggest that a calcium-calmodulin- dependent step may be involved in the initial activation of p54(cdc25-c).
Author(s): Patel R, Holt M, Philipova R, Moss S, Schulman H, Hidaka H, Whitaker M
Publication type: Article
Publication status: Published
Journal: Journal of Biological Chemistry
Year: 1999
Volume: 274
Issue: 12
Pages: 7958-7968
Print publication date: 19/03/1999
ISSN (print): 0021-9258
ISSN (electronic):
Publisher: American Society for Biochemistry and Molecular Biology, Inc.
URL: http://dx.doi.org/10.1074/jbc.274.12.7958
DOI: 10.1074/jbc.274.12.7958
PubMed id: 10075693
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