| Project/Area Number |
11660328
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied molecular and cellular biology
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| Research Institution | Tokyo University of Agriculture |
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Principal Investigator |
CHIBAZAKURA taku Tokyo Univ. Agriculture, Fac. Applied Bio-Science, Assoc. Professor, 応用生物科学部, 助教授 (30227334)
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| Project Period (FY) |
1999 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2001: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2000: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1999: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Keywords | mammalian cell culture / cell cycle / cyclin A / cyclin-dependent kinase (CDK) / M / G1 transition / protein degradation / CDK inhibitor / P107 / サイクリン依存性キナーゼ(CDK) |
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| Research Abstract |
Destruction of cyclin A during mitotic (M) phase depends on a destruction box (D box) which is conserved among A- and B-type cyclins. We have constructed a D-box mutant of human cyclin A and investigated its fate and function during the cell cycle in mouse fibroblasts. When expressed at a nearly physiological level, this D-box mutant was stabilized during the mitosis and subsequent entry into G1 phase but did not interfere the progression of M-to-G1 transition. Thus the destruction of cyclin A is not essential for the M-to-G1 transition. Even though the D-box mutant of cyclin A was stable, we found its associated cyclin-dependent kinase (CDK) activity was downregulated at the conclusion of mitosis. The stabilized cyclin A-associated CDK activity was also repressed during the M-to-G1 transition in fibroblasts derived from mice nullizygous for CDK inhibitors p21 and/or p27, indicating that neither p21 nor p27 is essential for the repression. In addition, phosphoamino acid analyses strongly suggested that CDKs associated with the D-box mutant cyclin A are not inactivated by phosphorylation at tyrosines during the M-to-G1 transition. We found that an Rb-family tumor suppressor p107 binds to the D-box mutant cyclin A at the early G1 phase when both p21 and p27 are missing, and that the stabilized cyclin A-associated CDK activity is deprepressed in p21-/-p27-/-p107-/- fibroblasts. These results suggest that p21 and p27 function as primary inhibitors and p107 serves as a secondary inhibitor in the downregulation of the stabilized cyclin A-associated CDK during the M-to-G1 transition. This alternative downregulation pathway might be a "fail-safe" mechanism which maintains normal progression through the cell cycle independent of the cyclin destruction pathway.
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