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Failure to inactivate CDK activity is responsible for the enhanced apoptotic response in U937 cells mediated by

Jinniu Deng1, Jianfeng Zhou, Fankai Meng

  • 1Department of Hematology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030.

Journal of Huazhong University of Science and Technology. Medical Sciences = Hua Zhong Ke Ji Da Xue Xue Bao. Yi Xue Ying De Wen Ban = Huazhong Keji Daxue Xuebao. Yixue Yingdewen Ban
|March 28, 2003
PubMed

Insights

Silencing the ATM gene enhances apoptosis by maintaining active cyclin-dependent kinase (CDK) activity. This leads to increased cell death in response to irradiation and chemotherapy, highlighting CDK as a key molecular mechanism.

Area of Science:

  • Cell Biology
  • Molecular Oncology
  • Cancer Research

Background:

  • The ATM gene plays a critical role in DNA damage response and cell cycle regulation.
  • ATM deficiency can lead to altered cellular responses to genotoxic stress, including apoptosis.
  • Understanding the molecular mechanisms underlying ATM-mediated apoptosis is crucial for cancer therapy.

Purpose of the Study:

  • To identify the molecular factors responsible for the enhanced apoptotic response in U937 cells with silenced ATM gene.
  • To investigate the role of cyclin-dependent kinase (CDK) activity and CDC25 proteins in ATM-deficient apoptosis.
  • To elucidate the signaling pathways linking ATM silencing to increased radiosensitivity and chemosensitivity.

Main Methods:

  • Utilized U937 cell mutants (ATM-negative and wild-type) as a model system.
  • Assessed apoptosis by measuring free nucleosome concentrations.
  • Employed Western blot to quantify specific protein levels (CDC25A, B, C; p34cdc2) and phosphorylation states.
  • Used RT-PCR to determine CDC25 transcript levels.

Main Results:

  • ATM-silenced cells (U937-ASPI3K) showed enhanced apoptosis upon irradiation, independent of protein synthesis.
  • Inhibition of protein phosphatases or CDK abolished this enhancement, indicating the involvement of phosphorylation/dephosphorylation and CDK activity.
  • Irradiation failed to inactivate p34cdc2 in ATM-silenced cells due to sustained nuclear CDC25 protein levels.
  • Active p34cdc2 and CDK2 were identified as key executors of apoptosis in the absence of ATM.

Conclusions:

  • Aberrantly activated CDK activity is the central molecular mechanism driving enhanced apoptosis in ATM-deficient cells.
  • Silencing the ATM gene prevents the inactivation of p34cdc2 after irradiation by maintaining CDC25 protein levels.
  • Active CDK activity acts as a critical executioner of apoptosis, contributing to increased sensitivity to irradiation and chemotherapy agents.

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