Display Settings:

Format

Send to:

Choose Destination
We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
DNA Repair (Amst). 2006 May 10;5(5):575-90. Epub 2006 Mar 29.

DNA-PK phosphorylates histone H2AX during apoptotic DNA fragmentation in mammalian cells.

Author information

  • 1Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Road, NC-7.206, Dallas, TX 75390, USA.

Abstract

The phosphorylation of histone H2AX at serine 139 is one of the earliest responses of mammalian cells to ionizing radiation-induced DNA breaks. DNA breaks are also generated during the terminal stages of apoptosis when chromosomal DNA is cleaved into oligonucleosomal pieces. Apoptotic DNA fragmentation and the consequent chromatin condensation are important for efficient clearing of genomic DNA and nucleosomes and for protecting the organism from auto-immmunization and oncogenic transformation. In this study, we demonstrate that H2AX is phosphorylated during apoptotic DNA fragmentation in mouse, Chinese hamster ovary, and human cells. We have previously shown that ataxia telangiectasia mutated kinase (ATM) is primarily responsible for H2AX phosphorylation in murine cells in response to ionizing radiation. Interestingly, we find here that DNA-dependent protein kinase (DNA-PK) is solely responsible for H2AX phosphorylation during apoptosis while ATM is dispensable for the process. Moreover, the kinase activity of DNA-PKcs (catalytic subunit of DNA-PK) is specifically required for the induction of gammaH2AX. We further show that DNA-PKcs is robustly activated in apoptotic cells, as evidenced by autophosphorylation at serine 2056, before it is inactivated by cleavage. In contrast, ATM is degraded well before DNA fragmentation and gammaH2AX induction resulting in the predominance of DNA-PK during the later stages of apoptosis. Finally, we show that DNA-PKcs autophosphorylation and gammaH2AX induction occur only in apoptotic nuclei with characteristic chromatin condensation but not in non-apoptotic nuclei from the same culture establishing the most direct link between DNA fragmentation, DNA-PKcs activation, and H2AX phosphorylation. It is well established that DNA-PK is inactivated by cleavage late in apoptosis in order to forestall DNA repair. Our results demonstrate, for the first time, that DNA-PK is actually activated in late apoptotic cells and is able to initiate an early step in the DNA-damage response, namely H2AX phosphorylation, before it is inactivated by proteolysis.

PMID:
16567133
[PubMed - indexed for MEDLINE]
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Elsevier Science
    Loading ...
    Write to the Help Desk