Related Experiment Video

Updated: Aug 8, 2026

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations
10:54

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations

Published on: September 17, 2012

Ras promotes p21(Waf1/Cip1) protein stability via a cyclin D1-imposed block in proteasome-mediated degradation

Mathew L Coleman1, Christopher J Marshall, Michael F Olson

  • 1Cancer Research UK Centre for Cell and Molecular Biology, The Institute of Cancer Research, 237 Fulham Rd, London SW3 6JB, UK.

The EMBO Journal
|May 3, 2003
PubMed

Insights

Ras stabilizes p21 protein levels by inhibiting its degradation via the proteasome. This Ras-induced stabilization relies on cyclin D1, which blocks p21 binding to the proteasome complex.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Oncology

Background:

  • Ras oncoproteins are frequently activated in human cancers.
  • Ras signaling pathways, including Raf/MEK/ERK, influence cell cycle regulators.
  • Previous studies indicated acute Raf/MEK/ERK activation increases p21(Waf1/Cip1) (p21) via transcription.

Purpose of the Study:

  • To investigate the mechanism of p21 accumulation in Ras-transformed cells.
  • To determine if p21 induction by Ras occurs transcriptionally or post-translationally.
  • To elucidate the role of cyclin D1 in Ras-mediated p21 stabilization.

Main Methods:

  • Analysis of p21 protein levels and half-life in Ras-transformed murine fibroblasts.
  • Investigation of proteasome-mediated degradation pathways.
  • RNA interference (RNAi) for cyclin D1 knock-down.
  • In vitro binding assays with purified 20S proteasome complexes.

Main Results:

  • Chronic Ras activation leads to p21 stabilization by inhibiting proteasome-mediated degradation, increasing its half-life.
  • Ras-induced p21 stabilization is dependent on cyclin D1 expression.
  • Cyclin D1 directly inhibits p21 degradation by the 20S proteasome in vitro by preventing p21 binding to the C8alpha subunit.

Conclusions:

  • Ras stabilizes p21 protein primarily through a post-translational mechanism involving inhibition of proteasomal degradation.
  • Ras promotes the formation of p21-cyclin D1 complexes, which are critical for preventing p21 degradation.
  • This mechanism highlights a novel role for cyclin D1 in regulating p21 stability downstream of Ras signaling.

More Related Videos

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay12:26

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay

Published on: May 3, 2018

Purification of Ubiquitinated p53 Proteins from Mammalian Cells10:55

Purification of Ubiquitinated p53 Proteins from Mammalian Cells

Published on: March 21, 2022

Related Concept Videos

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...
DNA Damage Can Stall the Cell Cycle02:36

DNA Damage Can Stall the Cell Cycle

In response to DNA damage, cells can pause the cell cycle to assess and repair the breaks. However, the cell must check the DNA at certain critical stages during the cell cycle. If the cell cycle pauses before DNA replication, the cells will contain twice the amount of DNA. On the other hand, if cells arrest after DNA replication but before mitosis, they will contain four times the normal amount of DNA. With a host of specialized proteins at their disposal,cells must use the right protein at...
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...