[The relationship between ATM gene silence inducing apoptosis susceptibility and abnormal CDK activity].
OBJECTIVE
To explore the molecular elements responsible for the enhanced apoptotic susceptibility in U937 cells mediated by silencing atactic telangiectasis mutation (ATM) gene.


METHODS
Two U937 cell mutants, U937-ASPI3K (ATM gene negative) and U937-pZEOSV2 (+) (ATM gene positive) were used as a cell model system. Apoptosis was examined by measuring free nucleosome concentrations in U937 cells. Western blotting was employed to measure nuclear protein abundances of cdc25A, cdc25B, cdc25C, total p34cdc2, p34cdc2 (Thr161) or p34cdc2 (Thr14, Tyr15). RT-PCR was used to estimate cdc25 transcript levels.


RESULTS
U937-ASPI3K exhibited an enhanced apoptotic susceptibility to lower dosage of irradiation, which could not be blocked by protein synthesis inhibitor. Protein serine-theronine phosphatase inhibitor or cyclin-dependent kinase (CDK) inhibitors could abolish the enhancement. Upon irradiation, p34cdc2 in U937-pZEOSV2 (+) was in an inactive state owing to phosphorylation of Thr 14 and Tyr15, which was associated with a dramatic decrease of nuclear cdc25A, cdc25B and cdc25C poteins. In contrast, p34cdc2 in U937-ASPI3K was in an active state owing to the low phosphorylation of Thr14 and Tyr15, which was associated with constant nuclear cdc25A, cdc25B and cdc25C protein abundance before and after irradiation. The responsive decrease of nuclear cdc25 proteins occurred at the post-transcription level.


CONCLUSIONS
Silencing ATM gene blocks the irradiation induced responsive decrease of nuclear cdc25 proteins, resulting in an abnormal activation p34cdc2 is the critical molecular mechanism for the enhanced apoptotic responses.
Zhou
Jian-feng
JF
Tongji Hospital, Tongji Medical College of Huazhong University of Science & Technology, Wuhan 430030, China.
Tang
Yi
Y
Liu
Wen-li
WL
Sun
Han-ying
HY
Hu
Jun-bo
JB
Gong
Jian-ping
JP
D017209:Apoptosis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020868:Gene Silencing / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D008387:Marine Toxins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D025521:Tumor Suppressor Proteins; D020298:U937 Cells; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D009687:Nuclear Proteins; D010080:Oxazoles; D011500:Protein Synthesis Inhibitors; D025521:Tumor Suppressor Proteins; C059041:calyculin A; D003513:Cycloheximide; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; D018844:Cyclin-Dependent Kinases; D010749:Phosphoprotein Phosphatases; C517004:CDC25A protein, human; C517008:CDC25B protein, human; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases