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This Article Full Text Full Text (PDF) All Versions of this Article: 297/1/F36    most recent 90559.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sindic, A. Articles by Miller, R. T. PubMed PubMed Citation Articles by Sindic, A. Articles by Miller, R. T.

MUPP1 complexes renal K⁺ channels to alter cell surface expression and whole cell currents

¹Department of Physiology and Biophysics, Case Western Reserve University, Cleveland; ²Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota; ³Department of Medicine, Case Western Reserve University, Cleveland; ⁴Louis Stokes Veteran Affairs Medical Center, Cleveland; ⁵University School, Cleveland; and ⁶Rammelkamp Center for Research and Education, MetroHealth System Campus, Cleveland, Ohio

Submitted 17 September 2008 ; accepted in final form 2 May 2009

We previously found that the Ca²⁺-sensing receptor (CaR) interacts with and inactivates the inwardly rectifying K⁺ channel Kir4.2 that is expressed in the kidney cortex and that has a COOH-terminal PDZ domain. To identify potential scaffolding proteins that could organize a macromolecular signaling complex involving the CaR and Kir4.2, we used yeast two-hybrid cloning with the COOH-terminal 125 amino acids (AA) of Kir4.2 as bait to screen a human kidney cDNA library. We identified two independent partial cDNAs corresponding to the COOH-terminal 900 AA of MUPP1, a protein containing 13 PDZ binding domains that is expressed in the kidney in tight junctions and lateral borders of epithelial cells. When expressed in human embryonic kidney (HEK)-293 cells, Kir4.2 coimmunoprecipitates reciprocally with MUPP1 but not with a Kir4.2 construct lacking the four COOH-terminal amino acids, Kir5.1, or the CaR. MUPP1 and Kir4.2 coimmunoprecipitate reciprocally from rat kidney cortex extracts. Coexpression of MUPP1 with Kir4.2 in HEK-293 cells leads to reduced cell surface expression of Kir4.2 as assessed by cell surface biotinylation. Coexpression of MUPP1 and Kir4.2 in Xenopus oocytes results in reduced whole cell currents compared with expression of Kir4.2 alone, whereas expression of Kir4.2PDZ results in minimal currents and is not affected by coexpression with MUPP1. Immunofluorescence studies of oocytes demonstrate that MUPP1 reduces Kir4.2 membrane localization. These results indicate that Kir4.2 interacts selectively with MUPP1 to affect its cell surface expression. Thus MUPP1 and Kir4.2 may participate in a protein complex in the nephron that could regulate transport of K⁺ as well as other ions.

PDZ binding proteins; potassium transport; calcium sensing; Xenopus oocyte expression