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Tumor necrosis factor-alpha affects LTR-controlled oncogene expression in transformed mouse fibroblasts at the
B Seliger1, G Stark, K Pfizenmaier
1Clinical Research Group, Max-Planck-Society, Göttingen, Federal Republic of Germany.
Abstract:
Potential mechanisms of TNF-alpha action on tumor cells have been investigated in a model of mouse fibroblasts transformed by distinct retroviral vectors carrying the v-mos, c-myc, and v-Ha-ras oncogene, respectively. Treatment of v-mos and c-myc transformed cells with murine rTNF-alpha in non-cytotoxic concentrations caused a strong inhibition of both proliferative capacity in monolayer culture and colony formation in soft agar. In contrast, v-Ha-ras transformed cells showed little sensitivity to TNF-alpha treatment. These changes in cell growth characteristics of v-mos and c-myc transformants was preceded by a selective reduction of oncogene-specific steady RNA levels, whereas no RNA down-regulation was observed for v-Ha-ras transformants. An unchanged transcriptional activity of the LTR-controlled v-mos and c-myc genes, but a decreased half-life of oncogene-specific mRNA suggests that TNF-alpha primarily affects stability of v-mos and c-myc RNA without influencing the activity of retroviral promoters. This is confirmed by an unchanged chloramphenicol acetyl transferase activity in TNF-treated LTR-chloramphenicol acetyl transferase transformants. Removal of TNF-alpha from cultures of reverted cells provoked a rapid retransformation, with full recovery of neoplastic growth characteristics 10 days after abrogation of TNF-alpha treatment. These data suggest that in cases of non-cytocidal action of TNF-alpha persistent suppression of tumor cell growth requires continuous TNF-alpha treatment.
Insights
Tumor necrosis factor-alpha (TNF-alpha) inhibits tumor cell growth by reducing oncogene RNA stability, not transcription. Continuous TNF-alpha treatment is required for sustained tumor suppression.
Area of Science:
- Oncology
- Molecular Biology
- Immunology
Background:
- Tumor necrosis factor-alpha (TNF-alpha) is a cytokine with known anti-tumor properties.
- The precise mechanisms by which TNF-alpha affects tumor cell growth are not fully understood.
- Understanding TNF-alpha's action is crucial for developing targeted cancer therapies.
Purpose of the Study:
- To investigate the molecular mechanisms of TNF-alpha's anti-tumor effects.
- To determine how TNF-alpha influences the expression of specific oncogenes in transformed cells.
- To assess the role of oncogene RNA stability in TNF-alpha-mediated growth inhibition.
Main Methods:
- Utilized a mouse fibroblast model transformed with v-mos, c-myc, and v-Ha-ras oncogenes.
- Treated transformed cells with non-cytotoxic concentrations of murine recombinant TNF-alpha (rTNF-alpha).
- Assessed cell proliferation, colony formation in soft agar, oncogene-specific RNA levels, mRNA half-life, and transcriptional activity.
Main Results:
- TNF-alpha significantly inhibited proliferation and soft agar colony formation in v-mos and c-myc transformed cells, but not v-Ha-ras transformed cells.
- TNF-alpha treatment led to reduced oncogene-specific RNA levels in sensitive cells.
- TNF-alpha decreased the half-life of v-mos and c-myc mRNA without affecting transcriptional activity or promoter function.
Conclusions:
- TNF-alpha primarily affects tumor cell growth by decreasing the stability of specific oncogene mRNAs.
- Continuous TNF-alpha exposure is necessary for sustained suppression of tumor cell proliferation.
- These findings highlight the importance of RNA stability in TNF-alpha's anti-cancer mechanisms.