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cAMP differentially regulates expression of mRNA encoding IL-1 alpha and IL-1 beta in murine peritoneal macrophages
Y Ohmori1, G Strassman, T A Hamilton
1Research Institute, Cleveland Clinic Foundation, OH 44195-5069.
Abstract:
The influence of PGE2 and the consequent rise in intracellular cAMP on LPS-induced IL-1 alpha and IL-1 beta mRNA levels has been examined in murine peritoneal macrophages. As has been previously reported, neither PGE2 nor dibutyryl cAMP modulated the levels of LPS-induced IL-1 alpha mRNA. In contrast, the levels of IL-1 beta mRNA were markedly potentiated (greater than 10 fold) under the same experimental conditions. This effect was due to elevation of intracellular cAMP because other agents known to elevate cAMP levels (e.g., cholera toxin, forskolin, 1-isomethyl-3-isobutylxanthine) had the same selective effect on IL-1 beta mRNA levels. PGE2 and dBcAMP not only potentiated LPS-induced IL-1 beta mRNA levels but were also able to stimulate modest accumulation of IL-1 beta mRNA in the absence of LPS. Although measurement of IL-1 activity by bioassay suggested that dBcAMP and PGE2 could suppress LPS-induced IL-1 expression, levels of IL-1 protein, determined by radioreceptor assay, were markedly elevated. cAMP did not appreciably alter the stability of either IL-1 alpha or IL-1 beta mRNA. Instead dBcAMP independently stimulated the transcriptional activity of the IL-1 beta gene. In concert the results demonstrate that cAMP can modulate the response of mononuclear phagocytes to LPS in a complex pattern; gene expression may be unaltered, suppressed, or potentiated and will thereby affect both the quality and magnitude of the ensuing inflammatory response.
Insights
Elevated cyclic AMP (cAMP) selectively potentiates Interleukin-1 beta (IL-1 beta) mRNA in macrophages stimulated by lipopolysaccharide (LPS). This cAMP-mediated effect enhances IL-1 beta gene transcription, influencing inflammatory responses.
Area of Science:
- Immunology
- Molecular Biology
- Cellular Signaling
Background:
- Lipopolysaccharide (LPS) triggers inflammatory responses in macrophages.
- Interleukin-1 (IL-1) alpha and IL-1 beta are key inflammatory cytokines.
- Prostaglandin E2 (PGE2) and cyclic adenosine monophosphate (cAMP) are known modulators of cellular processes.
Purpose of the Study:
- To investigate the influence of PGE2 and intracellular cAMP on LPS-induced IL-1 alpha and IL-1 beta mRNA levels in murine peritoneal macrophages.
- To determine the specific mechanisms by which cAMP affects IL-1 gene expression.
- To understand the impact of these modulations on the overall inflammatory response.
Main Methods:
- Murine peritoneal macrophages were treated with LPS, PGE2, and dibutyryl cAMP (dBcAMP).
- mRNA levels for IL-1 alpha and IL-1 beta were quantified.
- Other cAMP-elevating agents like cholera toxin and forskolin were used.
- Transcriptional activity and mRNA stability were assessed.
- IL-1 protein levels were measured using radioreceptor assay.
Main Results:
- PGE2 and dBcAMP did not affect LPS-induced IL-1 alpha mRNA levels.
- IL-1 beta mRNA levels were significantly potentiated (over 10-fold) by PGE2 and dBcAMP.
- Other cAMP-elevating agents showed a similar selective potentiation of IL-1 beta mRNA.
- dBcAMP and PGE2 stimulated IL-1 beta mRNA accumulation even without LPS.
- While bioassays suggested suppression, radioreceptor assays showed elevated IL-1 protein levels.
- cAMP did not alter mRNA stability but stimulated IL-1 beta gene transcription.
Conclusions:
- Intracellular cAMP selectively potentiates LPS-induced IL-1 beta mRNA levels in macrophages.
- cAMP-mediated potentiation of IL-1 beta is primarily due to increased gene transcription.
- These findings highlight the complex, gene-specific modulation of macrophage responses to LPS by cAMP.
- The modulation of IL-1 gene expression by cAMP significantly impacts the quality and magnitude of inflammatory responses.