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Updated: Jul 6, 2026
Induction and Validation of Cellular Senescence in Primary Human Cells
Published on: June 20, 2018
Triggering senescence programs suppresses Chk1 kinase and sensitizes cells to genotoxic stresses
Vladimir L Gabai1, Cornelia O'Callaghan-Sunol, Le Meng
1Department of Biochemistry, Boston University Medical School, Boston, MA 02118, USA.
Abstract:
Depletion of the major heat shock protein Hsp72 leads to activation of the senescence program in a variety of tumor cell lines via both p53-dependent and p53-independent pathways. Here, we found that the Hsp72-depleted cells show defect in phosphorylation and activation of the protein kinase Chk1 by genotoxic stresses, such as UVC irradiation or camptothecin. Under these conditions, phosphorylation of Rad17 was also suppressed, whereas phosphorylation of p53 at Ser(15) was not affected, indicating a specific defect in phosphorylation of a subset of the ATR kinase substrates. Similarly, suppression of Chk1 activation was seen when senescence signaling was triggered by direct stimulation of p53, depletion of Cdc2, or overexpression of the cell cycle inhibitors p21 or p16. Thus, defect in Chk1 activation was not a consequence of the chaperone imbalance, but rather a downstream effect of activation of the senescence signaling. Inhibition of Chk1 was associated with inefficient inter-S phase checkpoint, as Hsp72 depleted cells failed to halt cell cycle progression upon UVC irradiation. Accordingly, sensitivity of cells to genotoxic stimuli after Hsp72 depletion was significantly enhanced. Thus, activation of the senescence signaling causes a defect in the DNA damage response manifested in increased sensitivity to genotoxic stresses.
Insights
Depleting heat shock protein 72 (Hsp72) activates cell senescence, impairing the DNA damage response. This leads to defective Chk1 activation and increased sensitivity to genotoxic stress.
Area of Science:
- Cellular senescence
- DNA damage response
- Protein kinase regulation
Background:
- Heat shock protein 72 (Hsp72) depletion triggers senescence via p53-dependent and -independent pathways.
- The senescence program impacts various cellular functions, including stress response mechanisms.
Purpose of the Study:
- To investigate the effect of Hsp72 depletion on DNA damage response pathways, specifically focusing on Chk1 activation.
- To determine if Chk1 activation defects are a direct consequence of chaperone imbalance or downstream of senescence signaling.
Main Methods:
- Utilized genotoxic stresses (UVC irradiation, camptothecin) in Hsp72-depleted tumor cell lines.
- Assessed phosphorylation and activation of key proteins including Chk1, Rad17, and p53.
- Investigated Chk1 activation under various senescence-inducing conditions (p53 stimulation, Cdc2 depletion, p21/p16 overexpression).
Main Results:
- Hsp72-depleted cells exhibited defects in Chk1 and Rad17 phosphorylation following genotoxic stress.
- p53 phosphorylation at Ser(15) remained unaffected, indicating a specific ATR substrate defect.
- Chk1 activation was suppressed when senescence was induced by p53 stimulation, Cdc2 depletion, or p21/p16 overexpression.
- Hsp72-depleted cells showed inefficient inter-S phase checkpoint control and increased sensitivity to genotoxic agents.
Conclusions:
- Defects in Chk1 activation are a downstream consequence of senescence signaling, not chaperone imbalance.
- Senescence activation impairs the DNA damage response by inhibiting Chk1, leading to increased genotoxic sensitivity.
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