Selective basolateral localization of overexpressed Na-K-ATPase 1- and 2- subunits is disrupted by butryate treatment of MDCK cells

Laughery MD, Clifford RJ, Chi Y, Kaplan JH. Selective basolateral localization of overexpressed Na-K-ATPase 1and 2-subunits is disrupted by butryate treatment of MDCK cells. Am J Physiol Renal Physiol 292: F1718–F1725, 2007. First published March 6, 2007; doi:10.1152/ajprenal.00360.2006.—The exclusive basolateral localization of the Na-K-ATPase in kidney epithelium is a critical aspect of nephron function. It has been suggested that mislocalized delivery of the Na-K-ATPase to the apical surface in autosomal dominant polycystic kidney disease (ADPKD) is due to the inappropriate expression of an alternative isoform of the -subunit, the 2-isoform. It has been reported that heterologous expression of this 2-isoform in Madin-Darby canine kidney (MDCK) cells results in apical delivery of the Na-K-ATPase. We created a MDCK cell line containing a tetracycline-inducible promoter and expressed either myc-tagged 2or flag-tagged 1-subunits to study the surface localization of these -subunit isoforms in polarized monolayers. We find that the 2-isoform is targeted to the basolateral surface of the plasma membrane in a polarization pattern indistinguishable from the 1isoform. However, inclusion of butyrate in the growth medium leads to upregulation of overexpressed 1or 2-subunits and to their appearance at the apical surface. The 2-isoform expressed in MDCK cells does not assemble into 1 2 heterodimers with the endogenous 1. Our findings demonstrate that expression of the 2-isoform does not lead to apical localization of the Na-K-ATPase in MDCK cells and provides evidence for an unexpected effect of butyrate on the trafficking of Na pump subunits.