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Repression of IL-4-induced gene expression by IFN-gamma requires Stat1 activation
C Venkataraman1, S Leung, A Salvekar
1Tularik, Inc., South San Francisco, CA 94080, USA.
Journal of Immunology (Baltimore, Md. : 1950)
|April 14, 1999
Summary
Interferon-gamma (IFN-gamma) inhibits Interleukin-4 (IL-4) induced IgE production by repressing gene transcription. This repression is mediated by Signal Transducer and Activator of Transcription 1 (Stat1) and Silencer of Cytokine Signaling-1 (SOCS-1).
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Interferon-gamma (IFN-gamma) antagonizes many Interleukin-4 (IL-4) mediated physiological responses.
- IL-4 plays a crucial role in IgE production, and IFN-gamma inhibits this process.
- The mechanism of IFN-gamma's inhibitory effect on IL-4 signaling is not fully understood.
Purpose of the Study:
- To elucidate the molecular mechanisms by which IFN-gamma inhibits IL-4-induced IgE production.
- To investigate the role of Signal Transducer and Activator of Transcription (Stat) proteins and other signaling molecules in this inhibitory pathway.
- To determine if Silencer of Cytokine Signaling-1 (SOCS-1) is involved in IFN-gamma's repression of IL-4 signaling.
Main Methods:
- Reporter gene assays using the germline epsilon promoter to assess transcriptional repression.
- Cellular experiments using lymphoid and nonlymphoid cell lines, including Stat1-deficient U3A cells.
- Analysis of Stat6 phosphorylation, nuclear translocation, and DNA binding.
- Investigation of gene expression changes, specifically SOCS-1, following IFN-gamma and IL-4 stimulation.
- Overexpression studies of Stat1 isoforms and SOCS-1.
Main Results:
- IFN-gamma-mediated repression of IL-4-induced transcription was observed and localized to the IL-4 response element of the germline epsilon promoter.
- The inhibitory effect requires prolonged IFN-gamma treatment and the transcription activation function of Stat1.
- IFN-gamma stimulation leads to decreased IL-4-induced Stat6 tyrosine phosphorylation, nuclear translocation, and DNA binding.
- IFN-gamma specifically up-regulates SOCS-1 expression, which in turn inhibits IL-4-induced Stat6 phosphorylation and transcription.
- Repression was restored in Stat1-deficient cells upon Stat1alpha but not Stat1beta overexpression.
Conclusions:
- IFN-gamma inhibits IL-4-induced IgE production primarily at the transcriptional level.
- The mechanism involves Stat1-dependent repression, independent of direct DNA binding competition.
- SOCS-1 plays a significant role in mediating IFN-gamma's inhibitory effects on IL-4 signaling by blocking Stat6 activation.
- These findings provide insights into the cross-regulation of cytokine signaling pathways in immune responses.