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DNA damage-induced G2-M checkpoint activation by histone H2AX and 53BP1
Oscar Fernandez-Capetillo1, Hua-Tang Chen, Arkady Celeste
1Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Abstract:
Activation of the ataxia telangiectasia mutated (ATM) kinase triggers diverse cellular responses to ionizing radiation (IR), including the initiation of cell cycle checkpoints. Histone H2AX, p53 binding-protein 1 (53BP1) and Chk2 are targets of ATM-mediated phosphorylation, but little is known about their roles in signalling the presence of DNA damage. Here, we show that mice lacking either H2AX or 53BP1, but not Chk2, manifest a G2-M checkpoint defect close to that observed in ATM(-/-) cells after exposure to low, but not high, doses of IR. Moreover, H2AX regulates the ability of 53BP1 to efficiently accumulate into IR-induced foci. We propose that at threshold levels of DNA damage, H2AX-mediated concentration of 53BP1 at double-strand breaks is essential for the amplification of signals that might otherwise be insufficient to prevent entry of damaged cells into mitosis.
Insights
Histone H2AX and p53 binding-protein 1 (53BP1) are crucial for DNA damage signaling after low-dose ionizing radiation (IR). Their interaction ensures proper cell cycle arrest, preventing mitosis with damaged DNA.
Area of Science:
- Molecular Biology
- Cellular Biology
- Radiation Biology
Background:
- The ataxia telangiectasia mutated (ATM) kinase is activated by ionizing radiation (IR) and initiates cellular responses, including cell cycle checkpoints.
- Key ATM targets include Histone H2AX, p53 binding-protein 1 (53BP1), and Chk2, but their precise roles in DNA damage signaling are not fully understood.
Purpose of the Study:
- To investigate the roles of H2AX, 53BP1, and Chk2 in DNA damage signaling and cell cycle checkpoint control following ionizing radiation exposure.
- To elucidate the relationship between H2AX and 53BP1 in the accumulation of DNA damage response foci.
Main Methods:
- Analysis of G2-M checkpoint function in mice deficient in H2AX, 53BP1, or Chk2 after exposure to varying doses of IR.
- Microscopic examination of IR-induced foci formation in the absence of H2AX.
Main Results:
- Mice lacking H2AX or 53BP1 exhibited a G2-M checkpoint defect similar to ATM-deficient cells upon low-dose IR exposure, but not high-dose IR.
- H2AX deficiency impaired the efficient accumulation of 53BP1 into IR-induced foci.
- Chk2 deficiency did not result in a significant G2-M checkpoint defect.
Conclusions:
- H2AX and 53BP1 play essential roles in the G2-M checkpoint response to low levels of DNA damage induced by IR.
- H2AX facilitates 53BP1 recruitment to double-strand breaks, amplifying the DNA damage signal.
- This H2AX-dependent amplification of 53BP1 is critical for preventing mitotic entry in cells with sub-threshold DNA damage.