Dexamethasone responsive element in the rat Na, K-ATPase β 1 gene coding region

Abstract

The Na, K-ATPase plays an essential role in active alveolar epithelial fluid resorption. In fetal and adult alveolar epithelial cells, glucocorticoids (GC) increase Na, K-ATPase activity, mRNA levels, and transcription rate of the β 1 subunit. In this study, we describe a glucocorticoid responsive element (GRE) in the coding region of the rat Na, K-ATPase β 1 gene in a rat lung epithelial cell line. Transient transfection experiments with the β 1 subunit coding region with or without the 5′ and 3′ untranslated regions demonstrated responsiveness to dexamethasone induction and also identified a GRE at +434 in exon IV. The +434 GRE conferred dexamethasone responsiveness in a heterologous thymidine kinase promoter irrespective of its orientation to the β 1 promoter. Transcriptional upregulation by dexamethasone was abolished in +434 mutants. Electrophoretic mobility shift assays (EMSA) demonstrated specific binding of nuclear proteins to the +434 GRE and the presence of the GC receptor. This specific binding was inhibited by a GRE previously described in the rat Na, K-ATPase β 1 gene at −631. In conclusion, we identified a GRE at +434 in the exon IV of the rat Na, K-ATPase β 1 gene.