To allow for normal gas exchange at birth, the ion transport functions of the lung must change dramatically as the fetus transits into postnatal life. Late in gestation, as the fetus approaches birth, the lung changes from a chloride secreting to a sodium-absorbing organ. This results in the net resorption of salt and water from the alveolar airspace and prepares the fetus for the successful transition to the postnatal period in which the alveolus is dry and normal gas exchange takes place. This resorptive process occurs through the active transport of sodium via the basolateral Na, K-ATPase (sodium pump) and the passive transport of sodium, primarily through the apical amiloride-sensitive sodium channel. During late gestation, glucocorticoids influence the expression of the Na, K-ATPase gene in a manner that is dependent on the gestational age at the time of glucocorticoid administration, and the duration and dose of glucocorticoid therapy. The major effect of glucocorticoids is on the beta1 subunit, demonstrating a concomitant increase in gene expression, protein levels and activity as measured by wet to dry weights. Glucocorticoids regulate the Na, K-ATPase both transcriptionally and translationally depending on cell type. We found that glucocorticoids increase Na, K-ATPase gene expression via transcriptional regulation in fetal and adult lung epithelial cells, however, the regulatory elements and specific transcription factors involved in this upregulation remain unknown. Although the Na, K-ATPase beta1 promoter contains partial glucocorticoid receptor elements (GRE), few of these elements are classical GRE. In addition, upregulation by glucocorticoids occurs over hours, suggesting regulation may be through a unique delayed primary response that involves secondary proteins. The main objective of this grant is to extend our previous studies of pump transcriptional regulation by glucocorticoids and explore in vitro mapping of DNA regulatory elements and transcription factor identification that are critical for Na, K-ATPase beta1 regulation comparing fetal to adult lung epithelial cells. I have chosen to study the Na, K-ATPase beta1, since: 1) glucocorticoids increase beta1 protein levels concomitant to increased mRNA levels; 2) the Na, K-ATPase beta1 subunit is the rate limiting subunit in lung epithelial cells; and 3) the Na, K-ATPase beta1 subunit is necessary for the assembly of alpha-beta heterodimers and plasma membrane targeting.
