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D-type cyclin-dependent kinase activity in mammalian cells
H Matsushime1, D E Quelle, S A Shurtleff
1Department of Genetics, University of Tokyo, Japan.
Molecular and Cellular Biology
|March 1, 1994
Summary
D-type cyclin-dependent kinase (CDK) activities, particularly those involving CDK4, were detected in mammalian cells. These kinases phosphorylate the retinoblastoma protein (pRb) and are regulated by cell cycle progression and serum stimulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- D-type cyclin-dependent kinase (CDK) activities were previously undetected in mammalian cells.
- Understanding the role of D-type cyclins and their partners in cell cycle regulation is crucial.
Purpose of the Study:
- To detect and characterize D-type cyclin-dependent kinase activities in mammalian cells.
- To investigate the regulation of these kinase activities during cell cycle progression.
Main Methods:
- Immune complex kinase assays using antibodies against cyclins D1, D2, D3, and CDK4.
- Analysis of kinase activity in rodent fibroblasts, mouse macrophages, and myeloid cells.
- Overexpression studies in engineered rodent fibroblasts.
Main Results:
- D-type cyclin-dependent kinase activities were detected, primarily associated with CDK4, readily phosphorylating retinoblastoma protein (pRb).
- Cyclin D1-CDK4 kinase activity emerged in mid-G1, peaked near the G1/S transition, and lagged behind cyclin induction.
- Activity remained dependent on serum stimulation even with enforced cyclin and CDK4 overproduction, suggesting regulation by upstream factors.
Conclusions:
- Mammalian cells possess D-type cyclin-dependent kinase activities, mainly mediated by CDK4-cyclin D complexes.
- The assembly of active cyclin D-CDK4 complexes and their kinase activity are tightly regulated by cell cycle entry and serum stimulation.
- Upstream regulators are essential for governing the formation of active D-type cyclin-CDK complexes.