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This Article Full Text Full Text (PDF) All Versions of this Article: 296/5/F1118    most recent 90492.2008v1 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 PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Reining, S. C. Articles by Hernando, N. Search for Related Content PubMed PubMed Citation Articles by Reining, S. C. Articles by Hernando, N.

GABARAP deficiency modulates expression of NaPi-IIa in renal brush-border membranes

¹Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland; ²Department of Internal Medicine and ³Charles and Jane Pak Center of Mineral Metabolism, University of Texas Southwestern Medical Center, Dallas, Texas; and ⁴Department of Neurochemistry, Max Planck Institute for Brain Research, Frankfurt am Main, Germany

Submitted 14 August 2008 ; accepted in final form 13 February 2009

Renal reabsorption of inorganic phosphate (P_i) is mainly mediated by the Na⁺-dependent P_i-cotransporter NaPi-IIa that is expressed in the brush-border membrane (BBM) of renal proximal tubules. Regulation and apical expression of NaPi-IIa are known to depend on a network of interacting proteins. Most of the interacting partners identified so far associate with the COOH-terminal PDZ-binding motif (TRL) of NaPi-IIa. In this study GABA_A receptor-associated protein (GABARAP) was identified as a novel interacting partner of NaPi-IIa applying a membrane yeast-two-hybrid system (MYTH 2.0) to screen a mouse kidney library with the TRL-truncated cotransporter as bait. GABARAP mRNA and protein are present in renal tubules, and the interaction of NaPi-IIa and GABARAP was confirmed by using glutathione S-transferase pulldowns from BBM and coimmunoprecipitations from transfected HEK293 cells. Amino acids 36–68 of GABARAP were identified as the determinant for the described interaction. The in vivo effects of this interaction were studied in a murine model. GABARAP^–/– mice have reduced urinary excretion of P_i, higher Na⁺-dependent ³²P_i uptake in BBM vesicles, and increased expression of NaPi-IIa in renal BBM compared with GABARAP^+/+ mice. The expression of Na⁺/H⁺ exchanger regulatory factor (NHERF)1, an important scaffold for the apical expression of NaPi-IIa, is also increased in GABARAP^–/– mice. The absence of GABARAP does not interfere with the regulation of the cotransporter by either parathyroid hormone or acute changes of dietary P_i content.

epithelial transport; renal proximal tubules; phosphate homeostasis