Phosphorylation of histone H2A.X by DNA-dependent protein kinase is not affected by core histone acetylation, but it alters nucleosome stability and histone H1 binding.
Phosphorylation of the C-terminal end of histone H2A.X is the most characterized histone post-translational modification in DNA double-stranded breaks (DSB). DNA-dependent protein kinase (DNA-PK) is one of the three phosphatidylinositol 3 kinase-like family of kinase members that is known to phosphorylate histone H2A.X during DNA DSB repair. There is a growing body of evidence supporting a role for histone acetylation in DNA DSB repair, but the mechanism or the causative relation remains largely unknown. Using bacterially expressed recombinant mutants and stably and transiently transfected cell lines, we find that DNA-PK can phosphorylate Thr-136 in addition to Ser-139 both in vitro and in vivo. Furthermore, the phosphorylation reaction is not inhibited by the presence of H1, which in itself is a substrate of the reaction. We also show that, in contrast to previous reports, the ability of the enzyme to phosphorylate these residues is not affected by the extent of acetylation of the core histones. In vitro assembled nucleosomes and HeLa S3 native oligonucleosomes consisting of non-acetylated and acetylated histones are equally phosphorylated by DNA-PK. We demonstrate that the apparent differences in the extent of phosphorylation previously observed can be accounted for by the differential chromatin solubility under the MgCl(2) concentrations required for the phosphorylation reaction in vitro. Finally, we show that although H2A.X does not affect nucleosome conformation, it has a de-stabilizing effect that is enhanced by the DNA-PK-mediated phosphorylation and results in an impaired histone H1 binding.
Li
Andra
A
Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8W 3P6, Canada.
Yu
Yaping
Y
Lee
Sheng-Chun
SC
Ishibashi
Toyotaka
T
Lees-Miller
Susan P
SP
Ausió
Juan
J
D000818:Animals; D004247:DNA / Q000737:chemistry; D051747:DNA-Activated Protein Kinase / Q000737:chemistry*; D006367:HeLa Cells; D006657:Histones / Q000737:chemistry*; D006801:Humans; D051379:Mice; D009707:Nucleosomes / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012694:Serine / Q000737:chemistry; D013912:Threonine / Q000737:chemistry; D014162:Transfection
D006657:Histones; D009707:Nucleosomes; D013912:Threonine; D012694:Serine; D004247:DNA; D051747:DNA-Activated Protein Kinase