Analysis of Proteinase-activated Receptor 2 and TLR4 Signal Transduction
Bibliographic record
Abstract
Proteinase-activated receptor 2 (PAR2), a seven-transmembrane G protein-coupled receptor, is activated at inflammatory sites by proteolytic cleavage of its extracellular N terminus by trypsin-like enzymes, exposing a tethered, receptor-activating ligand. Synthetic agonist peptides (AP) that share the tethered ligand sequence also activate PAR2, often measured by Ca2+ release. PAR2 contributes to inflammation through activation of NF-kappaB-regulated genes; however, the mechanism by which this occurs is unknown. Overexpression of human PAR2 in HEK293T cells resulted in concentration-dependent, PAR2 AP-inducible NF-kappaB reporter activation that was protein synthesis-independent, yet blocked by inhibitors that uncouple Gi proteins or sequester intracellular Ca2+. Because previous studies described synergistic PAR2- and TLR4-mediated cytokine production, we hypothesized that PAR2 and TLR4 might interact at the level of signaling. In the absence of TLR4, PAR2-induced NF-kappaB activity was inhibited by dominant negative (DN)-TRIF or DN-TRAM constructs, but not by DN-MyD88, findings confirmed using cell-permeable, adapter-specific BB loop blocking peptides. Co-expression of TLR4/MD-2/CD14 with PAR2 in HEK293T cells led to a synergistic increase in AP-induced NF-kappaB signaling that was MyD88-dependent and required a functional TLR4, despite the fact that AP exhibited no TLR4 agonist activity. Co-immunoprecipitation of PAR2 and TLR4 revealed a physical association that was AP-dependent. The response to AP or lipopolysaccharide was significantly diminished in TLR4(-/-) and PAR2(-/-) macrophages, respectively, and SW620 colonic epithelial cells exhibited synergistic responses to co-stimulation with AP and lipopolysaccharide. Our data suggest a unique interaction between two distinct innate immune response receptors and support a novel paradigm of receptor cooperativity in inflammatory responses.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".