Cycloheximide decreases α‐ENaC mRNA level in alveolar epithelial cells via an ERK and P38 pathway

The expression and activity of the epithelial sodium channel (ENaC) is tightly regulated in alveolar epithelial cells. Cycloheximide (Chx) at high concentration decreases ENaC mRNA suggesting the possible involvement of proteins with short half‐life in the regulation of α‐ENaC mRNA stability. To test this hypothesis, rat alveolar epithelial cells in primary culture were treated with Chx (0.1, 1.0, 8.8μM) for 6h and the α‐ENaC mRNA expression quantified by qPCR. Chx at concentration ineffective to inhibit protein synthesis (0.1, 1.0μM) induced a 50% decrease of α‐ENaC mRNA. The decrease was inhibited by ERK and P38 inhibitors. Western blots have confirmed that Chx activates ERK phosphorylation within 15 min. To test if transcription was involved in this process, we also studied the effect of actinomycin D and α‐amanitin. These transcription inhibitors increased the steady‐state level of α‐ENaC mRNA, but inhibited as well the effect of Chx on α‐ENaC mRNA. These results suggest that MAPK induction by Chx can modulate α‐ENaC mRNA steady‐state level and that transcription is important for this process. Supported by CCFF and CIHR.