title: Phosphorylation of threonine 68 promotes oligomerization and autophosphorylation of the Chk2 protein kinase via the forkhead-associated domain.
abstract: Phosphorylation of Thr-68 by the ataxia telangiectasia-mutated is necessary for efficient activation of Chk2 when cells are exposed to ionizing radiation. By an unknown mechanism, this initial event promotes additional autophosphorylation events including modifications of Thr-383 and Thr-387, two amino acid residues located within the activation loop segment within the Chk2 catalytic domain. Chk2 and related kinases possess one or more Forkhead-associated (FHA) domains that are phosphopeptide-binding modules believed to be crucial for their checkpoint control activities. We show that the Chk2 FHA domain is dispensable for Thr-68 phosphorylation but necessary for efficient autophosphorylation in response to ionizing radiation. Phosphorylation of Thr-68 promotes oligomerization of Chk2 by serving as a specific ligand for the FHA domain of another Chk2 molecule. In addition, Chk2 phosphorylates its own FHA domain, and this modification reduces its affinity for Thr-68-phosphorylated Chk2. Thus, activation of Chk2 in irradiated cells may occur through oligomerization of Chk2 via binding of the Thr-68-phosphorylated region of one Chk2 to the FHA domain of another. Oligomerization of Chk2 may therefore increase the efficiency of trans-autophosphorylation resulting in the release of active Chk2 monomers that proceed to enforce checkpoint control in irradiated cells.
authors.affiliation: Department of Hematology/Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Joon-Young
authors.initials: JY
authors.lastname: Ahn
authors.forename: Xianghong
authors.initials: X
authors.lastname: Li
authors.forename: Heather L
authors.initials: HL
authors.lastname: Davis
authors.forename: Christine E
authors.initials: CE
authors.lastname: Canman
mesh_terms: D000595:Amino Acid Sequence; D064447:Checkpoint Kinase 2; D051858:Forkhead Transcription Factors; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry* / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D013912:Threonine / Q000737:chemistry*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D051858:Forkhead Transcription Factors; D008024:Ligands; D009687:Nuclear Proteins; D010455:Peptides; D011994:Recombinant Proteins; D014157:Transcription Factors; D013912:Threonine; D005982:Glutathione Transferase; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases