RB

Definition

RB, or retinoblastoma protein, is a crucial tumor suppressor that plays a significant role in regulating the cell cycle. It controls the transition from the G1 phase to the S phase, preventing excessive cell growth and division. When functional, RB binds to and inhibits transcription factors that promote cell cycle progression, ensuring that cells do not proliferate uncontrollably, which is a key aspect of cancer development.

5 Must Know Facts For Your Next Test

1. RB is often mutated or inactivated in various cancers, leading to uncontrolled cellular proliferation.
2. The active form of RB is unphosphorylated, allowing it to bind to E2F transcription factors and inhibit genes required for DNA synthesis.
3. Loss of RB function can lead to retinoblastoma, a rare eye cancer primarily affecting children.
4. RB also interacts with other proteins involved in cell cycle regulation, highlighting its role as a central hub in cancer pathways.
5. The pathway involving RB is frequently disrupted by viral oncoproteins from viruses such as HPV and SV40, which target RB to promote cell division.

Review Questions

• How does RB function as a tumor suppressor in regulating the cell cycle?
  • RB functions as a tumor suppressor by binding to E2F transcription factors when it is unphosphorylated. This binding inhibits the expression of genes necessary for transitioning from the G1 phase to the S phase of the cell cycle. By preventing this transition, RB ensures that cells do not progress through the cycle without proper growth signals or checkpoints being met, thus controlling excessive proliferation that could lead to cancer.
• What are the consequences of mutations in the RB gene on cellular proliferation?
  • Mutations in the RB gene can lead to its inactivation, resulting in a loss of its regulatory control over the cell cycle. This disruption allows cells to progress uncontrollably through the G1 phase into the S phase without appropriate checks. As a result, these cells can undergo unregulated division and contribute to tumor formation. The connection between mutated RB and various cancers underscores its vital role in maintaining normal cellular proliferation.
• Evaluate the implications of viral interactions with RB on cancer development.
  • Viral interactions with RB proteins significantly impact cancer development by hijacking normal cellular mechanisms. Certain viruses, like HPV and SV40, produce oncoproteins that bind to and inactivate RB. This action disrupts the normal regulation of the cell cycle, allowing infected cells to bypass growth controls and proliferate unchecked. The evaluation of these interactions highlights not only the role of RB in tumor suppression but also how viral oncogenesis can contribute to malignancy.

Related terms

Tumor Suppressor Genes: Genes that help prevent uncontrolled cell growth by regulating cell division and repairing DNA damage.

Cell Cycle: The series of phases that a cell goes through as it grows and divides, including G1, S, G2, and M phases.

Phosphorylation: A biochemical process where a phosphate group is added to a protein, often modifying its function and activity, which is critical in regulating RB's activity.