Related Experiment Video

Updated: Jul 15, 2026

Inducible and Reversible Dominant-negative (DN) Protein Inhibition
08:35

Inducible and Reversible Dominant-negative (DN) Protein Inhibition

Published on: January 7, 2019

p21(Waf1/Cip1/Sdi1) mediates retinoblastoma protein degradation

E V Broude1, M E Swift, C Vivo

  • 1Cancer Center, Ordway Research Institute, Albany, NY 12208, USA.

Oncogene
|May 9, 2007
PubMed

Insights

The protein p21, induced by DNA damage, not only dephosphorylates but also depletes the retinoblastoma protein (Rb). This dual action of p21 suggests a negative feedback loop regulating cell-cycle arrest.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • The G1 checkpoint in mammalian cells, crucial for preventing DNA replication errors, involves p53-mediated upregulation of p21(Waf1) (CDKN1A).
  • p21 inhibits cyclin-dependent kinases (CDKs) CDK2 and CDK4/6, leading to retinoblastoma protein (Rb) dephosphorylation and activation.

Purpose of the Study:

  • To investigate the role of p21 in regulating Rb stability and function beyond its canonical CDK inhibitory activity.
  • To elucidate the mechanism by which p21 influences Rb levels during DNA damage-induced cell-cycle arrest.

Main Methods:

  • Ectopic expression of p21 in HT1080 fibrosarcoma cells.
  • Treatment with proteasome inhibitors.
  • Analysis of Rb dephosphorylation and depletion in response to p21 and other CDK inhibitors (p27, p16).
  • Assessment of Rb depletion in HT1080 and HCT116 cells following DNA damage.
  • Inhibition of p21 induction using short hairpin RNA and dominant-negative p53.

Main Results:

  • Ectopic p21 expression induced both dephosphorylation and depletion of Rb in a p53-independent manner, sensitive to proteasome inhibitors.
  • CDK inhibitor p27 also caused Rb dephosphorylation and depletion, whereas p16 induced only dephosphorylation.
  • Rb depletion was observed in HT1080 and HCT116 cells upon DNA damage, and this process was dependent on p21.
  • Inhibition of p21 induction or its expression reduced Rb depletion after DNA damage.

Conclusions:

  • p21 plays a dual role in regulating Rb: it activates Rb via dephosphorylation and inactivates it through proteasomal degradation.
  • This dual mechanism suggests a novel negative feedback pathway for p21 in controlling damage-induced cell-cycle arrest.
  • The findings highlight p21 as a key regulator of Rb stability, impacting cell-cycle control during DNA damage response.

More Related Videos

Analysis of Cell Cycle Position in Mammalian Cells12:19

Analysis of Cell Cycle Position in Mammalian Cells

Published on: January 21, 2012

Related Concept Videos

The Retinoblastoma Gene01:20

The Retinoblastoma Gene

Tumor suppressor genes are normal genes that can slow down cell division, repair DNA mistakes, or program the cells for apoptosis in case of irreparable damage. Hence, they play an essential role in preventing the proliferation of damaged cells.
The first-ever tumor suppressor gene called Rb was identified in retinoblastoma - a rare eye tumor in children. In inherited forms of the disease, a child inherits one defective copy of the Rb gene, which predisposes them to retinoblastoma. However,...
The Retinoblastoma Gene01:20

The Retinoblastoma Gene

Tumor suppressor genes are normal genes that can slow down cell division, repair DNA mistakes, or program the cells for apoptosis in case of irreparable damage. Hence, they play an essential role in preventing the proliferation of damaged cells.
The first-ever tumor suppressor gene called Rb was identified in retinoblastoma - a rare eye tumor in children. In inherited forms of the disease, a child inherits one defective copy of the Rb gene, which predisposes them to retinoblastoma. However,...
Negative Regulator Molecules01:23

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.
Inhibition of Cdk Activity02:34

Inhibition of Cdk Activity

The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...
Abnormal Proliferation02:23

Abnormal Proliferation

Under normal conditions, most adult cells remain in a non-proliferative state unless stimulated by internal or external factors to replace lost cells. Abnormal cell proliferation is a condition in which the cell's growth exceeds and is uncoordinated with normal cells. In such situations, cell division persists in the same excessive manner even after cessation of the stimuli, leading to persistent tumors. The tumor arises from the damaged cells that replicate to pass the damage to the daughter...
Anaphase Promoting Complex00:50

Anaphase Promoting Complex

The stepwise destruction of specific proteins is necessary for the progression and completion of the cell cycle. Such proteins are ubiquitinated by ubiquitin ligases and then subsequently destroyed by the proteasome. The SCF (Skp1/Cullin/F-box) and the anaphase-promoting complex (APC) are two important ubiquitin ligases involved in cell cycle progression. While SCF is active throughout the cell cycle, APC gets activated during metaphase to anaphase transition. Cdc20 or Cdh1 binds to APC and...