Related Experiment Video
Updated: Jul 3, 2026
Analysis of Cell Cycle Position in Mammalian Cells
Published on: January 21, 2012
CDK redundancy guarantees cell cycle progression in Rb-negative tumor cells independently of their p16 status
Marta Santamariña1, Gonzalo Hernández, Juan Zalvide
1Department of Physiology, School of Medicine, University of Santiago de Compostela, Spain.
Abstract:
A high percentage of tumor cells bear mutations in the Rb tumor suppressor gene. They have high levels of the cdk inhibitor p16(ink4a) and no cyclin D/cdk4-6 complexes. Although p16 is known not to arrest the proliferation of Rb-negative cells, it is not known whether its presence affects how their cycle progresses, how E2F-dependent transcription is modulated, and whether and how Rb-related proteins are inactivated. We have assessed the relevance of p16(ink4a) for cell cycle progression of these cells. Using SaOS2 osteosarcoma cells as a model, we find that downregulation of p16(ink4a) by RNAi and reconstitution of active cyclin D/cdk4 complexes does not affect progression of the cycle of these cells or expression of E2F-dependent genes. Rb-negative tumor cells can functionally inactivate Rb-related proteins in G(1)/S transition independently of their p16(ink4a) status. Furthermore, Rb-negative tumor cells do not arrest when cdk1, cdk2 or cdk3 are inhibited by RNAi, independently of their p16(ink4a) status, and combined inhibition of these cdks is also not enough to arrest their cell cycle. However, cell cycle progression of Rb-negative tumor cells is sensitive to complete cdk inhibition, as it is arrested by the chemical cdk inhibitor roscovitine and the biological cdk inhibitor p27. These results suggest that, despite their lack of cyclin D-containing complexes, Rb-negative tumor cells, like normal untransformed cells, take advantage of the high degree of redundancy of cdks for their cell cycle progression.
Insights
Rb-negative tumor cells with high p16INK4a levels can still progress through the cell cycle. This suggests redundancy in cyclin-dependent kinases (CDKs) allows Rb-negative cells to bypass cell cycle arrest mechanisms.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Many tumor cells lack functional Retinoblastoma (Rb) tumor suppressor protein.
- These Rb-negative cells often exhibit high levels of the CDK inhibitor p16INK4a.
- The impact of p16INK4a on cell cycle progression and gene transcription in Rb-negative cells remains unclear.
Purpose of the Study:
- To investigate the role of p16INK4a in the cell cycle progression of Rb-negative tumor cells.
- To determine how p16INK4a influences E2F-dependent transcription and Rb-related protein inactivation.
- To assess the sensitivity of Rb-negative cells to CDK inhibition.
Main Methods:
- Utilized SaOS2 osteosarcoma cells (Rb-negative) as a model system.
- Employed RNA interference (RNAi) to downregulate p16INK4a.
- Reconstituted active cyclin D/CDK4 complexes.
- Inhibited specific CDKs (CDK1, CDK2, CDK3) using RNAi.
- Assessed cell cycle progression, E2F-dependent gene expression, and response to chemical CDK inhibitors (roscovitine) and biological inhibitors (p27).
Main Results:
- Downregulation of p16INK4a and reconstitution of cyclin D/CDK4 complexes did not alter cell cycle progression or E2F-dependent gene expression in Rb-negative cells.
- Rb-negative cells inactivated Rb-related proteins during G1/S transition independently of p16INK4a status.
- Inhibition of individual CDKs (CDK1, CDK2, CDK3) did not arrest Rb-negative cells, even when combined.
- Complete CDK inhibition using roscovitine or p27 effectively arrested Rb-negative cell cycle progression.
Conclusions:
- Rb-negative tumor cells possess mechanisms to inactivate Rb-related proteins and progress through the cell cycle, irrespective of p16INK4a levels.
- These cells exhibit functional redundancy in CDK activity, allowing them to bypass specific inhibitory signals.
- Cell cycle progression in Rb-negative cells is ultimately dependent on overall CDK activity, highlighting a potential therapeutic vulnerability.
More Related Videos
10:33Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors
Published on: October 26, 2015
12:02Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols
Published on: June 6, 2017
Related Concept Videos
02:34Inhibition of Cdk Activity
02:34Inhibition of CDK Activity
01:23Negative Regulator Molecules
01:20The Retinoblastoma Gene
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,...
02:36DNA Damage can Stall the Cell Cycle
02:36DNA Damage Can Stall the Cell Cycle