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p34cdc2 is physically associated with and phosphorylated by a cdc2-specific tyrosine kinase
D K Ferris1, G A White, D J Kelvin
1Biological Carcinogenesis and Development Program, Program Resources, Inc./DynCorp, Frederick, Maryland.
Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|July 1, 1991
Summary
A specific tyrosine kinase phosphorylates the cell cycle regulator p34cdc2 at tyrosine 15. This interaction, involving cyclin B-associated cdc2, occurs in the cytosol and is crucial for regulating kinase activity.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The yeast cdc2 gene's mammalian homologue encodes p34cdc2, a serine/threonine kinase and subunit of M phase-promoting factor.
- p34cdc2 is a major tyrosine-phosphorylated protein in HeLa cells, with phosphotyrosine content linked to cell cycle regulation and kinase activity.
Purpose of the Study:
- To investigate the specific tyrosine kinase responsible for phosphorylating p34cdc2.
- To elucidate the site and conditions of p34cdc2 tyrosine phosphorylation and its association with other kinases.
Main Methods:
- In vitro kinase assays to study the phosphorylation of p34cdc2 by a specific tyrosine kinase.
- Analysis of p34cdc2 phosphorylation site (tyrosine 15) and its association with cyclin B.
- Fractionation of cellular compartments (cytosolic vs. nuclear) to compare p34cdc2 phosphorylation states.
Main Results:
- p34cdc2 is physically associated with and phosphorylated in vitro by a specific tyrosine kinase at tyrosine 15, mirroring in vivo phosphorylation.
- The association occurs in the cytosol and involves cyclin B-associated p34cdc2.
- Cytosolic p34cdc2 is predominantly hypophosphorylated, while nuclear p34cdc2 is hyperphosphorylated.
- The identified tyrosine kinase is a 67-kilodalton protein, distinct from known kinases like src, abl, and fms.
Conclusions:
- A novel, specific tyrosine kinase regulates p34cdc2 activity through tyrosine phosphorylation at residue 15.
- This regulation is compartmentalized, with distinct phosphorylation states in the cytosol and nucleus.
- The findings identify a new player in cell cycle control and kinase regulation.