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Thrombin receptor activation inhibits monocyte spreading by induction of ET(B) receptor-coupled nitric oxide release
1Department of Biology, Queens College and Graduate School, City University of New York, Flushing 11367, USA.
Abstract:
The effect of thrombin receptor activation on monocyte conformation was evaluated using the human monocyte cell line, THP-1, and the thrombin mimetic peptide, Trap-14. Treatment of THP-1 cells with Trap-14 induced rapid rounding of ameboid cells adherent to fibronectin-coated slides, whereas cell rounding was abrogated in the presence of the nitric oxide synthase inhibitor, NG-nitro-L-arginine or the endothelin B receptor antagonist, BQ-788. Endothelin-1 (ET-1) levels in the culture supernatant increased markedly within minutes of Trap-14 exposure with a concomitant loss in cellular ET-1 immunoreactivity. Importantly, loss of ET-1 immunoreactivity was blocked by pretreatment with the vesicle translocation inhibitor, nocodazole. Trap-14 potently induced the release of NO from THP-1 cells, whereas NO release was ablated by preincubation with BQ-788. These data demonstrate that thrombin receptor activation may inhibit cellular spreading as a result of autocrine ET-1 release and subsequent endothelin B receptor-dependent NO production, and suggest that initial exposure of inflammatory cells to thrombin may limit cellular activation and recruitment.
Insights
Thrombin receptor activation causes monocytes to round via endothelin-1 release and nitric oxide production. This process may limit inflammatory cell activation and recruitment.
Area of Science:
- Immunology
- Cell Biology
Background:
- Monocyte conformation and activation are critical in inflammatory responses.
- Thrombin signaling plays a role in regulating immune cell behavior.
Purpose of the Study:
- To investigate the impact of thrombin receptor activation on monocyte conformation.
- To elucidate the molecular mechanisms underlying thrombin-induced changes in monocyte morphology.
Main Methods:
- Utilized the human monocyte cell line THP-1 and the thrombin mimetic peptide Trap-14.
- Assessed cell rounding, nitric oxide synthase (NOS) inhibition, endothelin B receptor antagonism, and endothelin-1 (ET-1) levels.
- Employed immunofluorescence and vesicle translocation inhibitors.
Main Results:
- Trap-14 induced rapid monocyte rounding, which was blocked by NOS and endothelin B receptor inhibitors.
- Thrombin receptor activation led to increased supernatant ET-1 and decreased cellular ET-1 immunoreactivity.
- Trap-14 stimulated nitric oxide (NO) release, dependent on endothelin B receptor signaling.
Conclusions:
- Thrombin receptor activation inhibits monocyte spreading through autocrine ET-1 release and endothelin B receptor-mediated NO production.
- Initial thrombin exposure may limit inflammatory cell activation and recruitment, suggesting a regulatory role in inflammation.