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

Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois

Submitted 8 September 2006 ; accepted in final form 22 February 2007

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 ₂- or 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 ₁-isoform. However, inclusion of butyrate in the growth medium leads to upregulation of overexpressed ₁- or ₂-subunits and to their appearance at the apical surface. The ₂-isoform expressed in MDCK cells does not assemble into ₁₂ 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.

Madin-Darby canine kidney cells; apical localization; sodium pump subunits

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