Dexamethasone increases airway epithelial cell neutral endopeptidase by enhancing transcription and new protein synthesis

Abstract

Neutral endopeptidase (NEP; also known as EC 3.4.24. 11, CALLA) is a widely distributed membrane-bound enzyme that hydrolyzes many biologically important endogenous peptides. To evaluate the influence of glucocorticoids on airway epithelial cell NEP expression, we used the human airway epithelial cell line Calu-1. Cells, grown to confluency in Dulbecco's modified Eagle medium with 10% fetal bovine serum and penicillin-streptomycin, were incubated with different concentrations of dexamethasone or vehicle alone in the presence or absence of actinomycin D or cycloheximide for planned times. NEP activity was assayed at the end of treatment employing reverse-phase, high-pressure liquid chromatography. In some experiments, changes in NEP-specific mRNAs in the presence or absence of dexamethasone and/or the inhibitors were also evaluated by Northern blot analysis. We found that dexamethasone increased Calu-1 NEP activity in a dose- and time-dependent manner. Northern blot analysis indicated that NEP-specific mRNAs were also increased by dexamethasone. Furthermore, neither actinomycin D nor cycloheximide inhibited the increases in NEP activity and NEP-specific mRNAs caused by dexamethasone stimulation. We speculate, therefore, that dexamethasone increases NEP expression of these airway epithelial cells by enhancing transcription and new protein synthesis.