German cockroach extract activates protease-activated receptor 2 in human airway epithelial cells

Background: The German cockroach has been reported to act as an allergen that might be associated with a protease reaction in asthma. However, the molecular identities of the antigens in German cockroach extract (GCE) with protease activity and the protease-activated receptors (PARs) that are activated by GCE in human airway epithelial cells have not been characterized. Objective: We investigated the direct effect of GCE on Ca²⁺ signaling in human airway epithelial cells and the type of PARs activated by GCE. Methods: The Ca²⁺-sensitive dye Fura2 was used to determine intracellular Ca²⁺ concentration ([Ca²⁺]_i) by means of spectrofluorometry. Results: GCE induced a baseline type of [Ca ²⁺]_i oscillations in a dose-dependent manner. The oscillations persisted for long periods of time In the absence of Ca ²⁺ entry across the plasma membrane, suggesting that the observed [Ca²⁺]_i increases were due to Ca²⁺ release from intracellular stores. Accordingly, after depleting endoplasmic reticulum Ca²⁺ with thapsigargin, an endoplasmic reticulum Ca²⁺ ATPase inhibitor, the GCE-mediated [Ca²⁺]_i signals were abolished. Whereas desensitization of PAR-1, PAR-3, and PAR-4 had no effect on GCE-mediated Ca²⁺ mobilization, no GCE-mediated [Ca ²⁺]_i increase was observed after desensitization of PAR-2. Conclusions: These results indicate that GCE has a direct effect on human airway epithelial cells, in particular generating [Ca²⁺]_i oscillations through Ca²⁺ release from thapsigargin-sensitive Ca ²⁺ stores through activation of PAR-2.