β-adrenergic agonists regulate Na-K-ATPase via p70^S6k

We have recently reported that the β-adrenergic agonist isoproterenol regulates the alveolar epithelial cell Na-K-ATPase via MAPK/extracellular signal-regulated kinase and rapamycin-sensitive pathways. Here we report that isoproterenol phosphorylated the protein S6 kinase (p70^S6k) in alveolar epithelial cells, which was inhibited by both rapamycin and the MEK1/2 inhibitor U-0126. In alveolar epithelial cells transfected with a p70 ^S6k dominant negative construct, isoproterenol did not increase Na-K-ATPase total protein expression, whereas in cells transfected with a rapamycin-resistant mutant, the isoproterenol-mediated increase in Na-K-ATPase was not prevented by rapamycin. Accordingly, we provide here first evidence that isoproterenol regulates Na-K-ATPase via p70^S6k in alveolar epithelial cells.