Cyclin B1

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Cyclin B1 is a protein that in humans is encoded by the CCNB1 gene. It is a regulatory protein involved in mitosis, the process that leads to the division of a cell into two daughter cells. Cyclin B1 belongs to the cyclin family, a group of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes.

Function

Cyclin B1 plays a critical role in controlling the cell cycle at the G2/M transition. It forms a complex with CDK1 (also known as CDC2), and this complex is necessary for the initiation of mitosis. The activity of the cyclin B1-CDK1 complex is regulated by several mechanisms, including the synthesis and degradation of cyclin B1, phosphorylation, and dephosphorylation. The activation of this complex leads to the phosphorylation of various proteins involved in chromosome condensation, nuclear envelope breakdown, and the formation of the mitotic spindle, which are essential steps in mitosis.

Regulation

The levels of cyclin B1 begin to rise during the S phase of the cell cycle, peak in the G2 phase, and rapidly decrease as cells exit mitosis. The destruction of cyclin B1 is mediated by the anaphase-promoting complex (APC/C), an E3 ubiquitin ligase that targets cyclin B1 for degradation by the proteasome. This degradation is crucial for the exit from mitosis and the completion of the cell cycle.

Clinical Significance

Abnormal expression of cyclin B1 has been associated with various cancers, including breast cancer, colorectal cancer, and lung cancer. Overexpression of cyclin B1 can lead to uncontrolled cell proliferation, a hallmark of cancer. Therefore, cyclin B1 is considered a potential target for cancer therapy, and efforts are underway to develop drugs that can modulate its activity.

See Also

• Cyclin
• Cell cycle
• Mitosis
• Cyclin-dependent kinase