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 Ca(2+) signaling in human airway epithelial cells and the type of PARs activated by GCE.

METHODS

The Ca(2+)-sensitive dye Fura2 was used to determine intracellular Ca(2+) concentration (Ca(2+)) by means of spectrofluorometry.

RESULTS

GCE induced a baseline type of Ca(2+) 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 Ca(2+) increases were due to Ca(2+) release from intracellular stores. Accordingly, after depleting endoplasmic reticulum Ca(2+) with thapsigargin, an endoplasmic reticulum Ca(2+) ATPase inhibitor, the GCE-mediated Ca(2+) signals were abolished. Whereas desensitization of PAR-1, PAR-3, and PAR-4 had no effect on GCE-mediated Ca(2+) mobilization, no GCE-mediated Ca(2+) 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 Ca(2+) oscillations through Ca(2+) release from thapsigargin-sensitive Ca(2+) stores through activation of PAR-2.