Cyclin D

Definition

Cyclin D is a regulatory protein that plays a crucial role in controlling the cell cycle, specifically in the transition from the G1 phase to the S phase. It acts by activating cyclin-dependent kinases (CDKs), which are essential for driving the cell through key checkpoints in the cell cycle, responding to growth signals and regulating cellular proliferation.

5 Must Know Facts For Your Next Test

1. Cyclin D levels fluctuate throughout the cell cycle, rising during the G1 phase and falling as the cell transitions into S phase.
2. Cyclin D specifically binds to CDK4 and CDK6, forming a complex that phosphorylates target proteins to promote cell cycle progression.
3. Overexpression of cyclin D can lead to uncontrolled cell proliferation and is often associated with various types of cancer.
4. The activity of cyclin D is regulated by external growth factors and internal signaling pathways, making it crucial for cellular responses to environmental cues.
5. Dysregulation of cyclin D expression or activity can result in failure of the cell cycle checkpoints, contributing to tumorigenesis.

Review Questions

• How does cyclin D influence the transition between different phases of the cell cycle?
  • Cyclin D is essential for transitioning from the G1 phase to the S phase of the cell cycle. It activates CDK4 and CDK6, which then phosphorylate target proteins that allow the cell to progress toward DNA synthesis. This regulation is critical for ensuring that cells only replicate when they are adequately prepared, responding effectively to both internal signals and external growth factors.
• Discuss the implications of cyclin D overexpression in relation to cancer development.
  • Overexpression of cyclin D can lead to uncontrolled cell division, as it pushes cells through checkpoints without proper regulation. This can result in genomic instability, allowing mutations and other alterations that contribute to cancer progression. As cyclin D plays a pivotal role in promoting cellular proliferation, its dysregulation is commonly linked with various cancers, making it a potential target for therapeutic intervention.
• Evaluate the relationship between cyclin D activity and cellular responses to growth signals, particularly in the context of gene regulation mechanisms involved in cancer.
  • Cyclin D's activity is intricately connected to how cells respond to growth signals, functioning as a key mediator between external stimuli and internal cell cycle progression. When growth factors bind to their receptors, they activate signaling pathways that lead to increased cyclin D expression. This process illustrates a gene regulation mechanism where proper modulation of cyclin D is vital for maintaining normal cellular functions. In cancer, aberrant signaling can lead to excessive cyclin D levels, overriding checkpoint controls and promoting tumorigenesis.

Related terms

Cyclin-dependent kinase (CDK): A family of protein kinases that are activated by binding to cyclins and play a significant role in regulating the cell cycle.

Cell cycle checkpoint: Regulatory points in the cell cycle where the cell assesses whether it is ready to proceed with division or needs to halt due to errors or damage.

Oncogene: A gene that has the potential to cause cancer when mutated or expressed at high levels, often involved in promoting cell growth and division.