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Updated: Apr 28, 2026
A Macrophage Reporter Cell Assay to Examine Toll-Like Receptor-Mediated NF-kB/AP-1 Signaling on Adsorbed Protein Layers on Polymeric Surfaces
Published on: January 7, 2020
Phosphoproteome profiling of the macrophage response to different toll-like receptor ligands identifies differences
Virginie Sjoelund1, Margery Smelkinson, Aleksandra Nita-Lazar
1Laboratory of Systems Biology, and §Research Technology Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Bethesda, Maryland 20892, United States.
Abstract:
Toll-like receptors (TLRs) are among the first sensors that detect infection and drive immune response. Macrophages encountering a pathogen are usually stimulated not by one TLR, but by a combination of TLRs engaged by distinct microbe ligands. To understand the integrated signaling under complex conditions, we investigated the differences in the phosphoprotein signaling cascades triggered by TLR2, TLR4, and TLR7 ligands using a single responding cell population. We performed a global, quantitative, early poststimulation kinetic analysis of the mouse macrophage phosphoproteome using stable isotope labeling with amino acids coupled to phosphopeptide enrichment and high-resolution mass spectrometry. For each TLR ligand, we found marked elevation of phosphorylation of cytoskeleton components, GTPases of the Rho family, and phospholipase C signaling pathway proteins. Phosphorylation of proteins involved in phagocytosis was only seen in response to TLR2 and TLR4 but not to TLR7 activation. Changes in the phosphorylation of proteins involved in endocytosis were delayed in response to TLR2 as compared to TLR4 ligands. These findings reveal that the phosphoproteomic response to stimulation of distinct TLRs varies both in the major modification targets and the phosphorylation dynamics. These results advance the understanding of how macrophages sense and respond to a diverse set of TLR stimuli.
Insights
Macrophages utilize Toll-like receptors (TLRs) to detect pathogens. This study reveals distinct phosphoprotein signaling cascades activated by TLR2, TLR4, and TLR7 ligands, impacting cytoskeleton and phagocytosis pathways.
Area of Science:
- Immunology
- Cell Biology
- Proteomics
Background:
- Toll-like receptors (TLRs) are crucial for innate immunity, sensing microbial components.
- Macrophages integrate signals from multiple TLRs during infection.
- Understanding differential TLR signaling is key to deciphering immune responses.
Purpose of the Study:
- To investigate and compare the phosphoprotein signaling cascades triggered by TLR2, TLR4, and TLR7 ligands in macrophages.
- To analyze the kinetic differences in these signaling pathways.
Main Methods:
- Quantitative phosphoproteomics using stable isotope labeling and mass spectrometry.
- Kinetic analysis of early post-stimulation signaling events in mouse macrophages.
- Global analysis of protein phosphorylation changes.
Main Results:
- TLR2, TLR4, and TLR7 ligand stimulation induced distinct phosphorylation patterns.
- Cytoskeleton, Rho GTPases, and phospholipase C pathway proteins showed elevated phosphorylation across all tested TLRs.
- Phagocytosis-related protein phosphorylation was specific to TLR2 and TLR4 activation.
- Endocytosis-related protein phosphorylation dynamics differed between TLR2 and TLR4 stimulation.
Conclusions:
- Distinct TLR stimulation elicits unique phosphoproteomic responses in macrophages.
- TLR signaling pathways exhibit variations in targeted proteins and temporal dynamics.
- These findings enhance the understanding of macrophage sensing and response to diverse microbial stimuli.
