title: Protease-activated receptor-1 in human lung fibroblasts mediates a negative feedback downregulation via prostaglandin E2.
abstract: Among the four protease-activated receptors (PARs), PAR-1 plays an important role in normal lung functioning and in the development of lung diseases, including fibrosis. We compared the expression and functional activity of PARs in normal and fibrotic human lung fibroblasts. Both normal and fibrotic cells express PAR-1, -2, and -3, with PAR-2 showing the lowest level. There was no significant difference between normal and fibrotic fibroblasts in expression levels of PAR-1 and PAR-3, whereas a fourfold higher expression level of PAR-2 was observed in fibrotic cells compared with normal cells. Ca(2+) imaging studies revealed apparently only PAR-1-induced Ca(2+) signaling in lung fibroblasts. PAR-1 agonists, thrombin and synthetic activating peptide, induced concentration-dependent Ca(2+) mobilization with EC(50) values of 5 nM and 1 microM, respectively. The neutrophil protease cathepsin G produced a transient Ca(2+) response followed by disabling PAR-1, whereas elastase did not affect Ca(2+) level. PAR-1 activation by thrombin or receptor-activating peptide downregulated expression of all three PARs in lung fibroblasts, with maximal effect at 3-6 h, whereas expression returned toward basal level after 24 h. Furthermore, PAR-1 agonists dose dependently increased PGE(2) secretion from lung fibroblasts and induction of cyclooxygenase-2 expression. We then found that PGE(2) downregulated expression of all three PARs. The effect of PGE(2) was continuously growing with time. Furthermore, PGE(2) exerts its effect through the EP2 receptor that was confirmed using the selective EP2 agonist butaprost. This novel autocrine feedback mechanism of PGE(2) in lung fibroblasts seems to be an important regulator in lung physiology and pathology.
authors.affiliation: Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Institut für Neurobiochemie, Leipziger Strasse 44, D-39120 Magdeburg, Germany.
authors.forename: Elena
authors.initials: E
authors.lastname: Sokolova
authors.forename: Zoryana
authors.initials: Z
authors.lastname: Grishina
authors.forename: Frank
authors.initials: F
authors.lastname: Bühling
authors.forename: Tobias
authors.initials: T
authors.lastname: Welte
authors.forename: Georg
authors.initials: G
authors.lastname: Reiser
mesh_terms: D002118:Calcium / Q000378:metabolism; D056649:Cathepsin G; D002403:Cathepsins / Q000494:pharmacology; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000096:biosynthesis / Q000378:metabolism*; D015536:Down-Regulation; D025461:Feedback, Physiological / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D019272:Leukocyte Elastase / Q000494:pharmacology; D008565:Membrane Proteins; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism; D011658:Pulmonary Fibrosis / Q000378:metabolism* / Q000503:physiopathology; D044463:Receptor, PAR-1 / Q000235:genetics / Q000378:metabolism*; D044464:Receptor, PAR-2 / Q000235:genetics / Q000378:metabolism; D018179:Receptors, Thrombin / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000494:pharmacology; D013820:Thermolysin / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; C105295:protease-activated receptor 3; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D019272:Leukocyte Elastase; D013820:Thermolysin; D015232:Dinoprostone; D002118:Calcium