Related Experiment Videos

MDM2 promotes p21waf1/cip1 proteasomal turnover independently of ubiquitylation

Yetao Jin1, Hunjoo Lee, Shelya X Zeng

  • 1Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.

The EMBO Journal
|November 25, 2003
PubMed

Insights

MDM2 directly degrades the CDK inhibitor p21waf1/cip1 via a ubiquitin-independent pathway. This process reduces p21waf1/cip1 stability, inhibiting cell growth arrest in cancer cells lacking p53.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • p21waf1/cip1 is a key cyclin-dependent kinase (CDK) inhibitor regulating cell cycle progression.
  • The degradation of p21waf1/cip1 is crucial for cell cycle control, but the underlying mechanisms are not fully elucidated.
  • MDM2 is known as an E3 ubiquitin ligase and a negative regulator of p53.

Purpose of the Study:

  • To investigate the role of MDM2 in the degradation of p21waf1/cip1.
  • To determine if MDM2 mediates p21waf1/cip1 degradation through a ubiquitin-independent pathway.
  • To elucidate the functional consequences of MDM2-mediated p21waf1/cip1 degradation on cell growth.

Main Methods:

  • Utilized p53-null cells and p53-null/Rb-null cells.
  • Employed overexpression of wild-type and mutant MDM2 (ring finger-deleted, NLS-deleted, p21waf1/cip1-binding-defective).
  • Applied proteasome inhibitors (MG132, lactacystin) and siRNA against MDM2.
  • Performed in vitro and in-cell binding assays.
  • Assessed protein half-life and degradation of lysine-free mutants.

Main Results:

  • MDM2 overexpression reduced p21waf1/cip1 levels without ubiquitylation or affecting its mRNA.
  • MDM2-mediated degradation was reversed by proteasome inhibitors, p19arf, and MDM2 siRNA.
  • p21waf1/cip1 directly bound to MDM2, and a binding-defective MDM2 mutant failed to degrade p21waf1/cip1.
  • MDM2 significantly shortened the half-life of p21waf1/cip1 and promoted degradation of its lysine-free mutant.
  • MDM2 suppressed p21waf1/cip1-induced cell growth arrest in p53-deficient cells.

Conclusions:

  • MDM2 directly mediates the degradation of p21waf1/cip1 through a ubiquitin-independent proteolytic pathway.
  • This interaction reduces p21waf1/cip1 stability, thereby inhibiting its cell cycle regulatory functions.
  • MDM2 acts as a direct negative regulator of p21waf1/cip1 stability and function, independent of p53.

Related Concept Videos

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...
5.0K
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...
3.3K
Regulated Protein Degradation02:58

Regulated Protein Degradation

It is vital to regulate the activity of enzymatic as well as non-enzymatic proteins inside the cell. This can be achieved either through creating a balance between their rate of synthesis and degradation or regulating the intrinsic activity of the protein. Both these regulation mechanisms play an essential role in the normal functioning of cells.
Protein degradation plays two important roles in the cells. It helps to protect cells from misfolded or damaged proteins before they lead to a...
8.6K
Covalently Linked Protein Regulators02:04

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
These groups modify specific amino acids in a protein....
8.5K
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...
5.5K
The Proteasome01:13

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...
1.5K