Related Experiment Video
Updated: Aug 5, 2026
Analysis of Cell Cycle Position in Mammalian Cells
Published on: January 21, 2012
p53 down-regulates CHK1 through p21 and the retinoblastoma protein
V Gottifredi1, O Karni-Schmidt, S S Shieh
1Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Abstract:
Both fission yeast and mammalian cells require the function of the checkpoint kinase CHK1 for G2 arrest after DNA damage. The tumor suppressor p53, a well-studied stress response factor, has also been shown to play a role in DNA damage G2 arrest, although in a manner that is probably independent of CHK1. p53, however, can be phosphorylated and regulated by both CHK1 as well as another checkpoint kinase, hCds1 (also called CHK2). It was therefore of interest to determine whether reciprocally, p53 affects either CHK1 or CHK2. We found that induction of p53 either by diverse stress signals or ectopically using a tetracycline-regulated promoter causes a marked reduction in CHK1 protein levels. CHK1 downregulation by p53 occurs as a result of reduced CHK1 RNA accumulation, indicating that repression occurs at the level of transcription. Repression of CHK1 by p53 requires p21, since p21 alone is sufficient for this to occur and cells lacking p21 cannot downregulate CHK1. Interestingly, pRB is also required for CHK1 downregulation, suggesting the possible involvement of E2F-dependent transcription in the regulation of CHK1. Our results identify a new repression target of p53 and suggest that p53 and CHK1 play interdependent and complementary roles in regulating both the arrest and resumption of G2 after DNA damage.
Insights
The tumor suppressor p53 reduces levels of checkpoint kinase CHK1 by decreasing its RNA accumulation, a process requiring p21 and pRB. This reveals interdependent roles for p53 and CHK1 in DNA damage response.
Area of Science:
- Cellular biology
- Molecular biology
- Genetics
Background:
- Checkpoint kinase CHK1 is essential for G2 arrest in response to DNA damage in both yeast and mammalian cells.
- The tumor suppressor p53 also contributes to G2 arrest, potentially independently of CHK1.
- p53 can be regulated by CHK1 and CHK2, prompting an investigation into whether p53 reciprocally affects these kinases.
Purpose of the Study:
- To investigate the reciprocal effect of p53 on checkpoint kinases CHK1 and CHK2.
- To elucidate the mechanism by which p53 influences CHK1 and CHK2 levels.
- To understand the functional relationship between p53 and CHK1 in DNA damage response pathways.
Main Methods:
- Induction of p53 using various stress signals and a tetracycline-regulated promoter.
- Analysis of CHK1 protein and RNA levels following p53 induction.
- Assessment of the roles of p21 and pRB in p53-mediated CHK1 downregulation.
- Investigation of potential involvement of E2F-dependent transcription.
Main Results:
- Induction of p53 leads to a significant reduction in CHK1 protein levels.
- p53-mediated CHK1 downregulation occurs at the transcriptional level, evidenced by reduced CHK1 RNA.
- The repression of CHK1 by p53 is dependent on p21, as p21 alone is sufficient and its absence prevents downregulation.
- pRB is also required for CHK1 downregulation, suggesting a link to E2F-dependent transcription.
Conclusions:
- p53 acts as a repressor of CHK1, targeting it at the transcriptional level.
- p53-mediated repression of CHK1 requires both p21 and pRB.
- These findings highlight interdependent and complementary roles for p53 and CHK1 in regulating G2 arrest and cell cycle progression after DNA damage.
Related Concept Videos
01:23Negative Regulator Molecules
02:36DNA Damage can Stall the Cell Cycle
02:34Inhibition of Cdk Activity
02:23Abnormal Proliferation
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