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TNFalpha-mediated cell death is independent of cdc25A
G Krupitza1, M Grusch, K Braun
1Institute of Clinical Pathology, University of Vienna, Gene Environment Interaction, International Agency for Research on Cancer (IACR), F-69372 Lyon, Cedex 08, France.
Abstract:
Tumor necrosis factor (TNFs) have been shown to be synthesized by ovarian carcinomas, and may therefore affect tumor cells in an autocrine manner. Therefore, we investigated the effects of recombinant TNFs on ovarian carcinoma cells N.1 and examined expression of the proto-oncogenes c-myc and cdc25A which are known to play a prominent role in apoptosis. TNFalpha elicited apoptosis in N.1 cells within 72 h which was shown by typical morphological changes, DNA fragmentation and signature type cleavage of poly(ADP-ribose) polymerase into a 89 kDa proteolytic peptide. TNFalpha-induced apoptosis was accompanied by constitutive c-Myc expression, although the mRNA level of phosphatase cdc25A was suppressed within 24 h of TNFalpha treatment and the protein level decreased after 48 h. Cdc25A tyrosine phosphatase is an activator of the cdk2-cyclin E complex which allows for cell cycle progression. As expected, we found TNFalpha-mediated Cdc25A down-regulation to inhibit Cdk2 activity. Cdc25A suppression was related to TNFalpha-induced apoptosis but not to a TNFalpha-induced G0 arrest because cyclin D1 expression was unaffected and the gene gas6 (growth arrest specific 6) was not induced. Arresting cells by treatment with genistein prevented TNFalpha-triggered apoptosis and inhibited c-myc expression. TNFalpha-induced apoptosis is not accompanied by cell cycle arrest which may be due to constitutive c-Myc expression, although Cdc25A and Cdk2 activity is also down-regulated. High c-Myc and low Cdc25A activity might present conflicting signals to the cell cycle machinery which are incompatible with cell survival.
Insights
Tumor necrosis factor-alpha (TNFα) induces apoptosis in ovarian cancer cells by downregulating Cdc25A phosphatase, impacting cell cycle progression. Constitutive c-Myc expression contributes to this TNFα-induced cell death.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Ovarian carcinomas can synthesize tumor necrosis factors (TNFs), potentially influencing tumor cells via autocrine signaling.
- Proto-oncogenes c-myc and cdc25A are critical regulators of apoptosis and cell cycle progression.
Purpose of the Study:
- To investigate the effects of recombinant TNFs on ovarian carcinoma cells (N.1).
- To examine the expression of c-myc and cdc25A in response to TNFα treatment.
Main Methods:
- Treatment of N.1 ovarian carcinoma cells with TNFα.
- Analysis of apoptosis through morphological changes and DNA fragmentation.
- Assessment of c-myc and cdc25A mRNA and protein levels.
- Evaluation of Cdk2 activity and cell cycle markers (cyclin D1, gas6).
- Inhibition of TNFα-induced apoptosis using genistein.
Main Results:
- TNFα elicited apoptosis in N.1 cells within 72 hours, characterized by morphological changes and DNA fragmentation.
- TNFα-induced apoptosis correlated with constitutive c-Myc expression and suppressed cdc25A mRNA and protein levels.
- TNFα-mediated Cdc25A downregulation inhibited Cdk2 activity, but apoptosis was not linked to G0 arrest.
- Genistein treatment blocked TNFα-induced apoptosis and c-myc expression.
Conclusions:
- TNFα induces apoptosis in ovarian cancer cells through mechanisms involving c-Myc and Cdc25A.
- Downregulation of Cdc25A and Cdk2 activity, coupled with constitutive c-Myc expression, may create conflicting cell cycle signals leading to apoptosis.
- These findings highlight potential therapeutic targets in ovarian cancer treatment.