Identification of Nipsnap1 as a novel auxiliary protein inhibiting TRPV6 activity
The transient receptor potential vanilloid channels 5 and 6 (TRPV5/6) are the most Ca2+-selective channels within the TRP superfamily of ion channels. These epithelial Ca2+ channels are regulated at different intra- and extracellular sites by the feedback response of Ca2+ itself, calciotropic hormones, and by TRPV5/6-associated proteins. In the present study, bioinformatics was used to search for novel TRPV5/6-associated genes. By including pull-down assays and functional analysis, Nipsnap1—a hitherto functionally uncharacterized globular protein—was identified as a novel factor involved in the regulation of TRPV6. Electrophysiological recordings revealed that Nipsnap1 abolishes TRPV6 currents. Subsequent biotinylation assays showed that TRPV6 plasma membrane expression did not change in the presence of Nipsnap1, suggesting that TRPV6 inhibition by Nipsnap1 is independently regulated from reduced cell surface channel expression. In addition, semi-quantitative reverse transcriptase PCR and immunohistochemical labeling of Nipsnap1 indicated that Nipsnap1 is expressed in mouse intestinal tissues—where TRPV6 is predominantly expressed—but that it does not co-localize with TRPV5 in the kidney. In conclusion, this study presents the first physiological function of Nipsnap1 as an associated protein inhibiting TRPV6 activity that possibly exerts its effect directly at the plasma membrane.
KeywordsTRPV5 TRPV6 Nipsnap1 Calcium homeostasis Bioinformatics
Nipsnap1 cDNA was kindly provided by Dr. P. Deen (Physiology, Nijmegen Centre for Molecular Life Sciences, Nijmegen, The Netherlands), and rabbit-anti-GFP antiserum was kindly provided by Dr. B. Wieringa (Cell Biology, Nijmegen Centre for Molecular Life Sciences, Nijmegen, The Netherlands). We thank Mr. J. Janssen for excellent technical assistance and Mr. M. Oti for providing the conserved co-expression database. This work was supported by the Dutch Organization of Scientific Research (NWO-ALW 814.02.001, NWO-ALW 805.09.042, NWO-ALW 816.02.003) and the European Union [5th project CIMES (QLK3-2002-02151), EURYI 2006 grant to JH].
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