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Nuclear integration of JAK/STAT and Ras/AP-1 signaling by CBP and p300
1Division of Endocrinology and Metabolism, University of California at San Diego, La Jolla 92093-0651, USA.
Abstract:
We report that interferon gamma (IFN-gamma) inhibits transcription of the macrophage scavenger receptor gene by antagonizing the Ras-dependent activities of AP-1 and cooperating ets domain transcription factors, apparently as a result of competition between AP-1/ets factors and activated STAT1 for limiting amounts of CBP and p300. Consistent with this model, STAT1 alpha interacts directly with CBP in cells, and microinjection of anti-CBP and anti-p300 antibodies blocks transcriptional responses to IFN-gamma. Cells lacking STAT1 fail to inhibit AP-1/ets activity, and overexpression of CBP both potentiates IFN-gamma-dependent transcription and relieves AP-1/ets repression. Thus, CBP and p300 integrate both positive and negative effects of IFN-gamma on gene expression by serving as essential coactivators of STAT1 alpha, modulating gene-specific responses to simultaneous activation of two or more signal transduction pathways.
Insights
Interferon gamma (IFN-gamma) inhibits macrophage scavenger receptor gene transcription by interfering with AP-1 and Ets factors. This occurs via competition for coactivators CBP and p300 with STAT1, impacting gene expression pathways.
Area of Science:
- Molecular Biology
- Immunology
- Gene Regulation
Background:
- Interferon gamma (IFN-gamma) is a key cytokine involved in immune responses.
- Gene transcription is tightly regulated by various signaling pathways and transcription factors.
- Macrophage scavenger receptors play roles in lipid metabolism and immune cell function.
Purpose of the Study:
- To elucidate the molecular mechanism by which IFN-gamma inhibits macrophage scavenger receptor gene transcription.
- To investigate the role of transcription factors AP-1, Ets, STAT1, and coactivators CBP/p300 in IFN-gamma signaling.
- To understand how multiple signaling pathways are integrated to modulate gene expression.
Main Methods:
- Reporter gene assays to measure transcriptional activity.
- Co-immunoprecipitation to study protein-protein interactions.
- Western blotting to detect protein levels.
- Microinjection of antibodies to block protein function.
- Gene silencing or overexpression studies to assess factor roles.
Main Results:
- IFN-gamma inhibits AP-1 and Ets-dependent transcription of the macrophage scavenger receptor gene.
- This inhibition is mediated by competition between AP-1/Ets factors and STAT1 for limited CBP and p300 coactivators.
- STAT1 directly interacts with CBP, and blocking CBP/p300 function inhibits IFN-gamma responses.
- STAT1-deficient cells do not show inhibition of AP-1/Ets activity by IFN-gamma.
- Overexpression of CBP enhances IFN-gamma transcription and relieves AP-1/Ets repression.
Conclusions:
- CBP and p300 act as essential coactivators for STAT1 alpha in IFN-gamma signaling.
- These coactivators integrate positive and negative regulatory effects of IFN-gamma on gene expression.
- CBP/p300 play a crucial role in modulating gene-specific responses to the simultaneous activation of multiple signal transduction pathways.