TGF‐β regulates Na,K‐ATPase activity by changing the regulatory subunit stoichiometry of the Na,K‐ATPase complex

Abstract

The Na,K-ATPase regulates ion transport and fluid balance in the lung, generating the driving force for alveolar fluid clearance (AFC). TGF-β is a mediator of acute lung injury (ALI), and impacts AFC. We hypothesized that TGF-β influences Na,K-ATPase function by controlling subunit expression and stoichiometry. The ATP1B1 subunit regulates Na,K-ATPase cell-surface density. Quantitative PCR analysis revealed ATP1B1 downregulation in lungs from ALI patients and in TGF-β-treated A549 cells. Moreover, biotinylation and 86Rb+ uptake assays revealed TGF-β depleted cell-surface Na,K-ATPase, and reduced Na,K-ATPase activity in A549 cells and primary mouse alveolar type II cells. In silico and dual-luciferase reporter analyses of ATP1B1 promoter detected number of putative TGF-β responding elements. However, siRNA experiments revealed that downregulation of ATP1B1 expression does not rely on conventional TGF-β-associated transcriptional regulation. Conversely, epigenetic mechanisms of class I HDAC action is involved in the regulation of ATP1B1 expression by TGF-β. Together, these data suggest that TGF-β impacts Na,K-ATPase function by regulating subunit expression in lung epithelium. German Research Foundation