Related Experiment Video

Updated: Aug 24, 2026

Analysis of Cell Cycle Position in Mammalian Cells
12:19

Analysis of Cell Cycle Position in Mammalian Cells

Published on: January 21, 2012

Docking-dependent regulation of the Rb tumor suppressor protein by Cdk4

Maura Wallace1, Kathryn L Ball

  • 1CRUK Laboratories, University of Dundee Medical School, Dundee DD1 9SY, United Kingdom.

Molecular and Cellular Biology
|June 1, 2004
PubMed

Insights

Cyclin D1-Cdk4 kinase activity requires substrate docking. A novel Cdk4 docking motif in the Rb protein is essential for phosphorylation, cell cycle progression, and inhibiting apoptosis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Cyclin D1-Cdk4 (a protein kinase complex) phosphorylates target proteins, a process crucial for cell cycle regulation.
  • Efficient phosphorylation by cyclin D1-Cdk4 requires not only kinase activity but also substrate docking at a distinct site.
  • The retinoblastoma protein (Rb) is a key regulator of cell cycle progression and is targeted by cyclin D1-Cdk4.

Purpose of the Study:

  • To identify and characterize a novel Cdk4 docking motif within the Rb protein.
  • To investigate the role of this docking motif in Cdk4-mediated Rb phosphorylation and functional regulation.
  • To explore the impact of Cdk4 docking on Rb's growth-suppressive activity and its role in apoptosis.

Main Methods:

  • Site-directed mutagenesis and deletion analysis to create Rb mutants lacking the Cdk4 docking motif.
  • In vitro kinase assays using full-length Rb, Rb fragments, and synthetic peptides.
  • Cell-based assays to assess Rb phosphorylation, cell cycle progression, colony formation, and apoptosis.
  • Biochemical assays to determine the effect of Cdk4-Rb docking on Rb cleavage during apoptosis.

Main Results:

  • A 19-amino acid C-terminal motif in Rb was identified as essential for Cdk4 binding and docking.
  • Mutation or deletion of this motif abolished Cdk4-dependent phosphorylation of Rb in vitro and in cells.
  • Rb mutants with altered docking sites retained growth suppressor activity but were resistant to cyclin D1-Cdk4 inactivation.
  • Cdk4 binding to its Rb docking site inhibited Rb cleavage in response to apoptotic stimuli.

Conclusions:

  • The Cdk4 docking motif in Rb is critical for efficient Cdk4-mediated phosphorylation and functional inactivation.
  • This motif plays a key role in regulating Rb's tumor suppressor activity and promoting cell survival.
  • Cdk4 docking provides specificity to kinase activity and contributes to the regulation of apoptosis through Rb stabilization.

More Related Videos

Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors10:33

Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors

Published on: October 26, 2015

Related Concept Videos

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...
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...
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.
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,...
mTOR Signaling and Cancer Progression03:03

mTOR Signaling and Cancer Progression

The mammalian target of rapamycin or mTOR protein was discovered in 1994 due to its direct interaction with rapamycin. The protein gets its name from a yeast homolog called TOR. The mTOR protein complex in mammalian cells plays a major role in balancing anabolic processes such as the synthesis of proteins, lipids, and nucleotides and catabolic processes, such as autophagy in response to environmental cues, such as availability of nutrients and growth factors.
The mTOR pathway or the...
PI3K/mTOR/AKT Signaling Pathway01:22

PI3K/mTOR/AKT Signaling Pathway

The mammalian target of rapamycin  (mTOR) is a serine/threonine kinase that regulates growth, proliferation, and cell survival in response to hormones, growth factors, or nutrient availability. This kinase exists in two structurally and functionally distinct forms: mTOR complex 1  (mTORC1) and mTOR complex 2  (mTORC2). The first form (mTORC1) is composed of a rapamycin-sensitive Raptor and proline-rich Akt substrate, PRAS40. In contrast,  mTORC2 consists of a rapamycin-insensitive companion...