Regulation of Na-K-ATPase gene expression by hyperoxia in MDCK cells

Na-K-ATPase plays a central role in a variety of physiological processes, including ion transport and regulation of cell volume. Our previous data showed that hyperoxia increased the expression of Na-K-ATPase α₁ and β₁ mRNA in lung type II cells. We similarly show that hyperoxia (≤95% O₂ for 24-48 h) increased steady-state mRNA levels in both Na-K- ATPase subunits in Madin-Darby canine kidney (MDCK) cells. The mechanism of gene regulation by hyperoxia was assessed. Stability of the Na-K-ATPase mRNA levels of both subunits was unchanged in hyperoxia-exposed MDCK cells. To determine whether gene transcription was augmented by hyperoxia, MDCK cells were transfected with a β₁-subunit promoter-reporter construct. Transfection with the wild-type promoter (β₁-817) revealed a 1.9 ± 0.2- fold increase in promoter activity. Transfection with 5' deletion constructs identified a 61-base pair (bp) region between -102 and -41 that was necessary for this increase in promoter activity by hyperoxia. Incorporation of this 61-bp region into a minimal promoter (mouse mammary tumor virus) similarly increased promoter activity 2.3-fold in the presence of hyperoxia. This increase in promoter activity was not seen when MDCK cells were incubated with various concentrations of hydrogen peroxide. In summary, hyperoxia increased Na-K-ATPase β₁-subunit mRNA steady-state level due to increased transcription in MDCK cells. A region necessary for this hyperoxic effect on β₁ transcription is located between base pairs -102 and -41 on the promoter.