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Concept
Cyclin B
Résumé
Cyclin B is a member of the cyclin family. Cyclin B is a mitotic cyclin. The amount of cyclin B (which binds to Cdk1) and the activity of the cyclin B-Cdk complex rise through the cell cycle until mitosis, where they fall abruptly due to degradation of cyclin B (Cdk1 is constitutively present). The complex of Cdk and cyclin B is called maturation promoting factor or mitosis promoting factor (MPF).
Cyclin B is necessary for the progression of the cells into and out of M phase of the cell cycle.
At the end of S phase the phosphatase cdc25c dephosphorylates tyrosine15 and this activates the cyclin B/CDK1 complex. Upon activation the complex is shuttled to the nucleus where it serves to trigger for entry into mitosis. However, if DNA damage is detected alternative proteins are activated which results in the inhibitory phosphorylation of cdc25c and therefore cyclinB/CDK1 is not activated. In order for the cell to progress out of mitosis, the degradation of cyclin B is necessary.
The cyclin B/CDK1 complex also interacts with a variety of other key proteins and pathways which regulate cell growth and progression of mitosis. Cross-talk between many of these pathways links cyclin B levels indirectly to induction of apoptosis. The cyclin B/CDK1 complex plays a critical role in the expression of the survival signal survivin. Survivin is necessary for proper creation of the mitotic spindle which strongly affects cell viability, therefore when cyclin B levels are disrupted cells experience difficulty polarizing. A decrease in survivin levels and the associated mitotic disarray triggers apoptosis via caspase 3 mediated pathway.
Cyclin B plays an integral role in many types of cancer. Hyperplasia (uncontrolled cell growth) is one of the hallmarks of cancer. Because cyclin B is necessary for cells to enter mitosis and therefore necessary for cell division, cyclin B levels are often de-regulated in tumors. When cyclin B levels are elevated, cells can enter M phase prematurely and strict control over cell division is lost, which is a favorable condition for cancer development.
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Cyclin-dependent kinase 1
Cyclin-dependent kinase 1 also known as CDK1 or cell division cycle protein 2 homolog is a highly conserved protein that functions as a serine/threonine protein kinase, and is a key player in cell cycle regulation. It has been highly studied in the budding yeast S. cerevisiae, and the fission yeast S. pombe, where it is encoded by genes cdc28 and cdc2, respectively. With its cyclin partners, Cdk1 forms complexes that phosphorylate a variety of target substrates (over 75 have been identified in budding yeast); phosphorylation of these proteins leads to cell cycle progression.
Kinase dépendante des cyclines
vignette|350px|Schéma du cycle cellulaire. Cercle extérieur: I=Interphase, M=Mitose; cercle intérieur: M=Mitose et cytocinèse; G1=Phase G1; S=Phase S; G2=Phase G2. La durée de la mitose par rapport aux autres phases du cycle cellulaire est exagérée dans ce diagramme Les kinases dépendantes des cyclines (en anglais, cyclin-dependent kinase ou CDK) sont une famille de protéines kinases qui jouent un rôle majeur dans la régulation du cycle cellulaire.
Cyclin A
Cyclin A is a member of the cyclin family, a group of proteins that function in regulating progression through the cell cycle. The stages that a cell passes through that culminate in its division and replication are collectively known as the cell cycle Since the successful division and replication of a cell is essential for its survival, the cell cycle is tightly regulated by several components to ensure the efficient and error-free progression through the cell cycle.