Isoform specificity of Na-K-ATPase-mediated ouabain signaling

Dept. of Physiology and Pharmacology, Univ. of Toledo College of Medicine, 3035 Arlington Ave., Toledo, OH 43614-5804, USA.
American journal of physiology. Renal physiology (Impact Factor: 3.3). 05/2008; 294(4):F859-66. DOI: 10.1152/ajprenal.00089.2007
Source: PubMed

ABSTRACT The ion transporter Na-K-ATPase functions as a cell signal transducer that mediates ouabain-induced activation of protein kinases, such as ERK. While Na-K-ATPase composed of the alpha(1)-polypeptide is involved in cell signaling, the role of other alpha-isoforms (alpha(2), alpha(3), and alpha(4)) in transmitting ouabain effects is unknown. We have explored this using baculovirus-directed expression of Na-K-ATPase polypeptides in insect cells and ERK phosphorylation as an indicator of ouabain-induced signaling. Ouabain addition to Sf-9 cells coexpressing Na-K-ATPase alpha(1)- and beta(1)-isoforms stimulated ERK phosphorylation. In contrast, expression of the alpha(1)- and beta(1)-polypeptides alone resulted in no effect, indicating that the alphabeta-complex is necessary for Na-K-ATPase signaling. Moreover, the ouabain effect was sensitive to genistein, suggesting that Na-K-ATPase-mediated tyrosine kinase activation is a critical event in the intracellular cascade leading to ERK phosphorylation. In addition, the Na-K-ATPases alpha(3)beta(1)- and alpha(4)beta(1)-isozymes, but not alpha(2)beta(1), responded to ouabain treatment. In agreement with the differences in ouabain affinity of the alpha-polypeptides, alpha(1)beta(1) required 100- to 1,000-fold more ouabain to signal than did alpha(4)beta(1) and alpha(3)beta(1), respectively. These results confirm the role of the Na-K-ATPase in ouabain signal transduction, show that there are important isoform-specific differences in Na-K-ATPase signaling, and demonstrate the suitability of the baculovirus expression system for studying Na-K-ATPase-mediated ouabain effects.

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