title: Autoregulatory mechanisms of phosphorylation of checkpoint kinase 1.
abstract: Checkpoint kinase 1 (Chk1), a serine/threonine protein kinase, is centrally involved in cell-cycle checkpoints and cellular response to DNA damage. Phosphorylation of Chk1 at 2 Ser/Gln (SQ) sites, Ser-317 and Ser-345, by the upstream kinase ATR is critical for checkpoint activation. However, the precise molecular mechanisms controlling Chk1 phosphorylation and subsequent checkpoint activation are not well understood. Here, we report unique autoregulatory mechanisms that control protein phosphorylation of human Chk1, as well as checkpoint activation and cell viability. Phosphorylation of Ser-317 is required, but not sufficient, for maximal phosphorylation at Ser-345. The N-terminal kinase domain of Chk1 prevents Chk1 phosphorylation at the C-terminus by ATR in the absence of DNA damage. Loss of the inhibitory effect imposed by the N-terminus causes constitutive phosphorylation of Chk1 by ATR under normal growth conditions, which in turn triggers artificial checkpoints that suppress the S-phase progression. Furthermore, two point mutations were identified that rendered Chk1 constitutively active, and expression of the constitutively active mutant form of Chk1 inhibited cancer cell proliferation. Our findings therefore reveal unique regulatory mechanisms of Chk1 phosphorylation and suggest that expression of constitutively active Chk1 may represent a novel strategy to suppress tumor growth. Cancer Res; 72(15); 3786-94. ©2012 AACR.
authors.affiliation: Department of Pharmacology, Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Jingna
authors.initials: J
authors.lastname: Wang
authors.forename: Xiangzi
authors.initials: X
authors.lastname: Han
authors.forename: Youwei
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D020134:Catalytic Domain / Q000235:genetics; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D000071877:Checkpoint Kinase 1; D057809:HEK293 Cells; D006367:HeLa Cells; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D010766:Phosphorylation / Q000235:genetics; D017354:Point Mutation / Q000502:physiology; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology; D012694:Serine / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D012694:Serine; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases