Related Experiment Video

Updated: Aug 14, 2026

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
12:26

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

Published on: May 3, 2018

Negative regulation of TSC1-TSC2 by mammalian D-type cyclins

Sima J Zacharek1, Yue Xiong, Stuart D Shumway

  • 1Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, 27599, USA.

Cancer Research
|December 17, 2005
PubMed

Insights

Mammalian D-type cyclins regulate cell growth by interacting with the TSC1-TSC2 complex. This interaction affects cell size, suggesting a role beyond the cell cycle

Area of Science:

  • Cell biology
  • Molecular oncology
  • Cell cycle regulation

Background:

  • Cyclin-dependent kinases (CDKs) drive the metazoan cell cycle, with cyclin D- and cyclin E-CDKs regulating progression through G1 phase via pRb phosphorylation.
  • While cyclin D-CDKs are known to influence cell cycle entry, their roles in Rb-independent pathways and cell growth remain less understood.
  • The tuberous sclerosis complex (TSC) proteins, TSC1 and TSC2, negatively regulate cell growth by inhibiting mTOR signaling.

Purpose of the Study:

  • To investigate potential non-pRb substrates and Rb-independent pathways regulated by cyclin D.
  • To determine if cyclin D interacts with and regulates the TSC1-TSC2 complex.
  • To elucidate the role of D-type cyclins in cell growth control.

Main Methods:

  • Co-immunoprecipitation to identify cyclin D binding partners.
  • Western blotting to assess protein phosphorylation and detection levels (TSC1, TSC2, 4E-BP1, S6K1).
  • Cell culture experiments involving ectopic expression of cyclin D1, CDK4/6, mutant cyclin D1, INK4 inhibitors, and catalytically inactive CDK6.
  • Cell size measurements following ectopic expression of relevant proteins.

Main Results:

  • The tumor suppressor TSC2 was identified as a cyclin D binding protein.
  • Coexpression of cyclin D1-CDK4/6 increased TSC1 and TSC2 phosphorylation, decreased their detection, and promoted phosphorylation of mTOR substrates 4E-BP1 and S6K1.
  • Ectopic cyclin D1 expression rescued cell size reduction caused by TSC1-TSC2 expression.
  • Down-regulation of TSC proteins occurred even with a cyclin D1 mutant unable to bind CDK4/6 or when coexpressed with INK4 inhibitors or inactive CDK6, suggesting CDK-independent regulation.

Conclusions:

  • Mammalian D-type cyclins bind to and negatively regulate the TSC1-TSC2 complex.
  • Cyclin D-mediated regulation of TSC1-TSC2 impacts cell growth and cell size control.
  • These findings reveal a novel role for D-type cyclins in cell growth regulation, potentially independent of their canonical cell cycle functions.

More Related Videos

Studying Proteolysis of Cyclin B at the Single Cell Level in Whole Cell Populations10:54

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

Published on: September 17, 2012

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols12:02

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols

Published on: June 6, 2017

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...
Positive Regulator Molecules02:39

Positive Regulator Molecules

Mitotic cell division results in daughter cells that exactly resemble the parent cell. However, errors in the DNA replication or distribution of genetic material may lead to genetic mutations that may be passed down to every new cell formed from the resulting abnormal cell. Propagation of such mutant cells is restricted through checkpoint mechanisms present at different stages of the cell cycle. These checkpoints involve regulator molecules that either promote or demote cell cycle events.
Positive Regulator Molecules01:45

Positive Regulator Molecules

To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.
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...
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.