During lung injury, alveolar epithelial fluid and electrolyte transport are fundamental in resorbing edema fluid and restoring gas exchange. Type II alveolar epithelial cells absorb sodium from their luminal surface using an apical sodium channel and a basolateral Na.K-ATPase. Using hyperoxia as a model for injury (>959% O2 for 48 hr), we demonstrated that the steady state level of Na,K-ATPase α1 and β1 subunit mRNA is increased in both type II cells and MDCK cells without a change in mRNA stability. We hypothesized that the increase in mRNA was due to an increase in transcription. To assess transcription. MDCK cells were transfected with [il subunit promoter-reporter constructs in normoxic and hyperoxic conditions. The promoter-reporter construct of the l subunit consisted of 817 base pairs of the β l promoter plus 151 base pairs of exon I linked to a luciferase gene. In the presence of hyperoxia. relative luciferase activity increased l .9 fold compared to normoxia. Transfection with 5' deletion constructs located the area of hyperoxia regulation to a 61 bp region between-41 and-102. DNase I footprinting of the coding strand identifies a footprint at -61 to -67 with surrounding hypersensitive sites. In conclusion, the increase in Na,K-ATPase beta subunit mRNA steady stale level during hyperoxia is due to an increase in transcription and is probably acting through a regulatory region at approximately -61 bp. CW:NIH-K08HUM1 14-01, DI: A1A-H.
|Original language||English (US)|
|State||Published - Dec 1 1996|