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Differential utilization of Ras signaling pathways by macrophage colony-stimulating factor (CSF) and
1Divisions of Endocrinology and Metabolism and Cellular and Molecular Medicine, Department of Medicine, University of California, San Diego, La Jolla, California 92093-0651, USA.
Abstract:
Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) independently stimulate the proliferation and differentiation of macrophages from bone marrow progenitor cells. Although the GM-CSF and M-CSF receptors are unrelated, both couple to Ras-dependent signal transduction pathways, suggesting that these pathways might account for common actions of GM-CSF and M-CSF on the expression of macrophage-specific genes. To test this hypothesis, we have investigated the mechanisms by which GM-CSF and M-CSF regulate the expression of the macrophage scavenger receptor A (SR-A) gene. We demonstrate that induction of the SR-A gene by M-CSF is dependent on AP-1 and cooperating Ets domain transcription factors that bind to sites in an M-CSF-dependent enhancer located 4.1 to 4.5 kb upstream of the transcriptional start site. In contrast, regulation by GM-CSF requires a separate enhancer located 4.5 to 4.8 kb upstream of the transcriptional start site that confers both immediate-early and sustained transcriptional responses. Results of a combination of DNA binding experiments and functional assays suggest that immediate transcriptional responses are mediated by DNA binding proteins that are constitutively bound to the GM-CSF enhancer and are activated by Ras. At 12 to 24 h after GM-CSF treatment, the GM-CSF enhancer becomes further occupied by additional DNA binding proteins that may contribute to sustained transcriptional responses. In concert, these studies indicate that GM-CSF and M-CSF differentially utilize Ras-dependent signal transduction pathways to regulate scavenger receptor gene expression, consistent with the distinct functional properties of M-CSF- and GM-CSF-derived macrophages.
Insights
Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) differentially regulate scavenger receptor A (SR-A) gene expression. These distinct pathways highlight differences in M-CSF- and GM-CSF-derived macrophages.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) are key regulators of macrophage proliferation and differentiation.
- Both factors activate Ras-dependent signaling pathways, suggesting a common mechanism for regulating macrophage-specific gene expression.
Purpose of the Study:
- To investigate the distinct molecular mechanisms by which GM-CSF and M-CSF regulate the expression of the macrophage scavenger receptor A (SR-A) gene.
- To determine how these differential signaling pathways contribute to the unique functions of macrophages derived from each factor.
Main Methods:
- Analysis of gene regulation using DNA binding experiments and functional assays.
- Identification of specific enhancer elements and transcription factors involved in SR-A gene induction.
- Comparison of transcriptional responses to GM-CSF and M-CSF over time.
Main Results:
- M-CSF induction of SR-A gene expression depends on AP-1 and Ets transcription factors binding to an upstream enhancer.
- GM-CSF regulation involves a separate upstream enhancer, mediating both immediate-early and sustained transcriptional responses.
- Ras activation is crucial for immediate transcriptional responses to GM-CSF, while sustained responses involve additional DNA-binding proteins.
Conclusions:
- GM-CSF and M-CSF utilize distinct Ras-dependent signaling pathways to control SR-A gene expression.
- These differential regulatory mechanisms contribute to the distinct functional characteristics of macrophages generated by GM-CSF and M-CSF.