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IFN-gamma inhibits c-myc gene expression by impairing the splicing process in a colony-stimulating factor dependent
A Harel-Bellan1, A T Brini, W L Farrar
1Laboratory of Molecular Immunoregulation, National Cancer Institute, Frederick Cancer Research Facility, MD 21701.
Abstract:
Proliferation of NSF-60.8 cells, a CSF-dependent murine myeloid cell line, is strongly inhibited by murine IFN-gamma. Northern analysis of growth arrested, NSF-60.8 cells activated by addition of CSF in the presence or absence of IFN-gamma indicated that IFN-gamma inhibited the induction of c-myc mRNA steady state level by CSF. The effect was observed as early as 30 min after induction and the inhibition was complete after 20 h. IFN-gamma did not impair the transcriptional activation of c-myc gene, and it had only a slight destabilizing effect on the mature c-myc message. Study of the processing steps of c-myc mRNA precursor indicated that in the presence of IFN-gamma, a putative 3.6-kb splice intermediate accumulated instead of the mature message, suggesting that IFN-gamma inhibits the splicing of c-myc precursor.
Insights
Murine interferon-gamma (IFN-gamma) inhibits myeloid cell proliferation by blocking the induction of c-myc mRNA. This inhibition occurs at the splicing stage of c-myc precursor processing, not transcription.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- NSF-60.8 cells are a murine myeloid cell line dependent on colony-stimulating factor (CSF) for proliferation.
- Murine interferon-gamma (IFN-gamma) is known to inhibit the proliferation of these cells.
Purpose of the Study:
- To investigate the mechanism by which IFN-gamma inhibits CSF-induced c-myc mRNA induction in NSF-60.8 cells.
- To determine if IFN-gamma affects c-myc gene transcription, mRNA stability, or mRNA processing.
Main Methods:
- Northern blot analysis was used to examine c-myc mRNA steady-state levels.
- Analysis of c-myc precursor processing steps was performed.
Main Results:
- IFN-gamma significantly inhibited the CSF-induced increase in c-myc mRNA steady-state levels.
- IFN-gamma did not affect c-myc gene transcriptional activation or significantly destabilize mature c-myc mRNA.
- A 3.6-kb splice intermediate of c-myc mRNA precursor accumulated in the presence of IFN-gamma, while mature message formation was inhibited.
Conclusions:
- IFN-gamma inhibits CSF-induced c-myc mRNA production in NSF-60.8 cells.
- The primary mechanism of inhibition by IFN-gamma is the suppression of c-myc mRNA splicing, not transcriptional regulation or mRNA degradation.