PBP 10 (RhoB-Glu-Arg-Leu-Phe-Glc-Val-Lys-Glc-Arg-Arg) is a 10-aa-long rhodamine-linked and membrane-permeable peptide inhibitor. It is highly specific for FPR2 and has no inhibitory function on FPR1. And it derived from a phosphatidylinositol 4,5-bisphosphate-binding sequence in the cytoskeletal protein gelsolin.
Research has shown that the activity of PBP 10 may depend on its ability to pass through the membrane, to disassemble actin filament structures and FPR2-mediated cellular responses. The membrane permeability is important to the cellular effects. The neutrophil activity induced by a cell-permeable peptide (a pepducin) derived from the third intracellular loop of FPR2 was dose-dependently inhibited by PBP10, which suggested similarities between the PBP10-sensitive pathway and the pathway triggered by pepducin.
The A549 cell pretreated with FPR2 antagonist PBP10 prevented IAV- induced ERK activation after 5 minutes of binding but not thereafter. Therefore, PBP10 delayed IAV-FPR2 recognition, which led to impaired early ERK activation. In the absence of the ERK pathway inhibitor U0126, cell treatment with PBP10 alone decreased virus production in A/PR/8/34 virus-infected cells. The cell treatment with U0126 alone also showed the antiviral activity as expected. Nevertheless, the difference in viral replication between untreated and PBP10-treated cells was eliminated, in the presence of U0126. Thus, PBP10 blocked viral replication through FPR2-induced ERK activation.
Pharmacokinetics and metabolism
Experiments have showed that there was no increased binding/association of the PBP10 peptide related to the receptor exposure. The amount of peptide bound is represented by a MFI value of ∼200 when interacting with the stable transfectant expressing FPR1 (210 ± 80 [mean ± SD], n = 9). And the amount of peptide bound is represented by a MFI value of ∼150 when interacting with cells expressing FPR2 (160 ± 60 [mean ± SD], n = 9) (as measured by FACS analysis). An inhibitor/agonist molar ratio of 5:10 is needed to achieve full functional inhibition of the PBP10 peptide. However, in order to inhibit binding, a higher molar ratio is required. In the presence of such concentrations, PBP10 displaced some of the binding of neutrophils to a specific FPR2 agonist peptide (Cy5-WKYMVM), but binding of a specific FPR1 agonist (FITC-fNLPNTL) was also affected. At a molar ratio of 100 (100 nM PBP10 and 1 nM agonist peptide), the binding of FPR2-specific agonist would be reduced by ∼30% (31 ± 18% [mean ± SD], n = 5), and the binding of FPR1-specific agonist would also be reduced by ∼15% (17 ± 14% [mean ± SD], n = 4).
1. Forsman, H., Andréasson, E., Karlsson, J., Boulay, F., Rabiet, M. J., & Dahlgren, C. (2012). Structural characterization and inhibitory profile of formyl peptide receptor 2 selective peptides descending from a PIP2-binding domain of gelsolin. The Journal of Immunology, 1101616.
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