Differential roles for checkpoint kinases in DNA damage-dependent degradation of the Cdc25A protein phosphatase.
In response to DNA damage, cells activate a signaling pathway that promotes cell cycle arrest and degradation of the cell cycle regulator Cdc25A. Cdc25A degradation occurs via the SCFbeta-TRCP pathway and phosphorylation of Ser-76. Previous work indicates that the checkpoint kinase Checkpoint kinase 1 (Chk1) is capable of phosphorylating Ser-76 in Cdc25A, thereby promoting its degradation. In contrast, other experiments involving overexpression of dominant Chk2 mutant proteins point to a role for Chk2 in Cdc25A degradation. However, loss-of-function studies that implicate Chk2 in Cdc25A turnover are lacking, and there is no evidence that Chk2 is capable of phosphorylating Ser-76 in Cdc25A despite the finding that Chk1 and Chk2 sometimes share overlapping primary specificity. We find that although Chk2 can phosphorylate many of the same sites in Cdc25A that Chk1 phosphorylates, albeit with reduced efficiency, Chk2 is unable to efficiently phosphorylate Ser-76. Consistent with this, Chk2, unlike Chk1, is unable to support SCFbeta-TRCP-mediated ubiquitination of Cdc25A in vitro. In CHK2(-/-) HCT116 cells, the kinetics of Cdc25A degradation in response to ionizing radiation is comparable with that seen in HCT116 cells containing Chk2, indicating that Chk2 is not generally required for timely DNA damage-dependent Cdc25A turnover. In contrast, depletion of Chk1 by RNA interference in CHK2(-/-) cells leads to Cdc25A stabilization in response to ionizing radiation. These data support the idea that Chk1 is the primary signal transducer linking activation of the ATM/ATR kinases to Cdc25A destruction in response to ionizing radiation.
Jin
Jianping
J
Department of Pathology, Harvard Medical School, Boston Massachusetts 02115, USA.
Ang
Xiaolu L
XL
Ye
Xin
X
Livingstone
Mark
M
Harper
J Wade
JW
D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D004249:DNA Damage / Q000235:genetics / Q000528:radiation effects*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006801:Humans; D010766:Phosphorylation / Q000528:radiation effects; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011839:Radiation, Ionizing; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics / Q000378:metabolism; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D044844:beta-Transducin Repeat-Containing Proteins; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases