title: Inhibition of Chk1 by activated PKB/Akt.
abstract: We have shown recently that DNA damage effector kinase Chk1 is phosphorylated in vitro by protein kinase B/Akt (PKB/Akt) on serine 280. Activation of Chk1 by DNA damage in vivo is suppressed in presence of activated PKB. In this study we show that Chk1 is phosphorylated by PKB in vivo, and that increased phosphorylation by PKB on serine 280 correlates with impairment of Chk1 activation by DNA damage. Our results indicate a likely mechanism for the negative effects that phosphorylation of serine 280 has on activation of Chk1. The Chk1 protein phosphorylated by PKB on serine 280 does not enter into protein complexes after replication arrest. Moreover, Chk1 phosphorylated by PKB fails to undergo activating phosphorylation on serine 345 by ATM/ATR. Phosphorylation by ATM/ATR and association with other checkpoint proteins are essential steps in activation of Chk1. Inhibition of these steps provides a plausible explanation for the observed attenuation of Chk1 activation by activated PKB after DNA damage.
authors.affiliation: Cancer Research Institute, University of California San Francisco, 94115, USA.
authors.forename: Frank W
authors.initials: FW
authors.lastname: King
authors.forename: Jennifer
authors.initials: J
authors.lastname: Skeen
authors.forename: Nissim
authors.initials: N
authors.lastname: Hay
authors.forename: Emma
authors.initials: E
authors.lastname: Shtivelman
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D006801:Humans; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine / Q000378:metabolism; D025521:Tumor Suppressor Proteins
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D012694:Serine; D011494:Protein Kinases; C494918:AKT1 protein, human; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt