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Tumor necrosis factor alpha transcription in macrophages is attenuated by an autocrine factor that preferentially
M Baer1, A Dillner, R C Schwartz
1Advanced BioScience Laboratories-Basic Research Program, SAIC Frederick, MD 21707-1201, USA.
Abstract:
Macrophages are a major source of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha), which are expressed during conditions of inflammation, infection, or injury. We identified an activity secreted by a macrophage tumor cell line that negatively regulates bacterial lipopolysaccharide (LPS)-induced expression of TNF-alpha. This activity, termed TNF-alpha-inhibiting factor (TIF), suppressed the induction of TNF-alpha expression in macrophages, whereas induction of three other proinflammatory cytokines (interleukin-1beta [IL-1beta], IL-6, and monocyte chemoattractant protein 1) was accelerated or enhanced. A similar or identical inhibitory activity was secreted by IC-21 macrophages following LPS stimulation. Inhibition of TNF-alpha expression by macrophage conditioned medium was associated with selective induction of the NF-kappaB p50 subunit. Hyperinduction of p50 occurred with delayed kinetics in LPS-stimulated macrophages but not in fibroblasts. Overexpression of p50 blocked LPS-induced transcription from a TNF-alpha promoter reporter construct, showing that this transcription factor is an inhibitor of the TNF-alpha gene. Repression of the TNF-alpha promoter by TIF required a distal region that includes three NF-kappaB binding sites with preferential affinity for p50 homodimers. Thus, the selective repression of the TNF-alpha promoter by TIF may be explained by the specific binding of inhibitory p50 homodimers. We propose that TIF serves as a negative autocrine signal to attenuate TNF-alpha expression in activated macrophages. TIF is distinct from the known TNF-alpha-inhibiting factors IL-4, IL-10, and transforming growth factor beta and may represent a novel cytokine.
Insights
Researchers discovered a novel TNF-alpha-inhibiting factor (TIF) secreted by macrophages. TIF selectively suppresses tumor necrosis factor alpha (TNF-alpha) while enhancing other inflammatory cytokines, offering new insights into immune regulation.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Macrophages are key producers of proinflammatory cytokines like TNF-alpha during inflammation and infection.
- Dysregulated TNF-alpha contributes to inflammatory conditions.
- Understanding the regulation of TNF-alpha is crucial for developing targeted therapies.
Purpose of the Study:
- To identify and characterize novel factors that regulate TNF-alpha expression in macrophages.
- To elucidate the mechanism by which TNF-alpha production is controlled at the molecular level.
- To investigate the role of specific transcription factors in TNF-alpha gene regulation.
Main Methods:
- Macrophage cell lines were cultured and stimulated with bacterial lipopolysaccharide (LPS).
- Secreted factors in conditioned media were analyzed for their effects on cytokine expression.
- NF-kappaB subunit expression and DNA binding activity were assessed.
- Reporter gene assays were used to evaluate promoter activity and transcription factor function.
Main Results:
- A novel TNF-alpha-inhibiting factor (TIF) was identified in macrophage-conditioned medium.
- TIF selectively suppressed LPS-induced TNF-alpha expression but enhanced IL-1beta, IL-6, and MCP-1.
- TIF activity correlated with the selective induction of the NF-kappaB p50 subunit.
- Overexpression of p50 inhibited TNF-alpha promoter activity, dependent on NF-kappaB binding sites.
Conclusions:
- TIF acts as a negative autocrine signal to attenuate TNF-alpha expression in activated macrophages.
- The inhibitory mechanism involves the specific binding of p50 homodimers to the TNF-alpha promoter.
- TIF represents a novel cytokine distinct from known inhibitors like IL-4, IL-10, and TGF-beta.