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A unique sorting nexin regulates trafficking of potassium channels via a PDZ domain interaction

Abstract

G protein–gated potassium (Kir3) channels are important for controlling neuronal excitability in the brain. Using a proteomics approach, we have identified a unique rodent intracellular protein, sorting nexin 27 (SNX27), which regulates the trafficking of Kir3 channels. Like most sorting nexins, SNX27 possesses a functional PX domain that selectively binds the membrane phospholipid phosphatidylinositol-3-phosphate (PI3P) and is important for trafficking to the early endosome. SNX27, however, is the only sorting nexin to contain a PDZ domain. This PDZ domain discriminates between channels with similar class I PDZ-binding motifs, associating with the C-terminal end of Kir3.3 and Kir3.2c (−ESKV), but not with that of Kir2.1 (−ESEI) or Kv1.4 (−ETDV). SNX27 promotes the endosomal movement of Kir3 channels, leading to reduced surface expression, increased degradation and smaller Kir3 potassium currents. The regulation of endosomal trafficking via sorting nexins reveals a previously unknown mechanism for controlling potassium channel surface expression.

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Figure 1: SNX27 associates with Kir3.3 channels.
Figure 2: SNX27-PDZ domain associates with Kir3.3 and Kir3.2c channels.
Figure 3: SNX27 contains a functional lipid-binding motif (PX domain) that colocalizes with Kir3.3 in the early endosome.
Figure 4: SNX27 regulates cell surface expression of Kir3.3 channels.
Figure 5: Downregulation of Kir3 channels by SNX27 requires lysosomal targeting and PDZ-binding motifs in Kir3.3.
Figure 6: Kir3.2c channels colocalize with SNX27 in the early endosomes, but show no change in cell surface expression.
Figure 7: Kir3.3 promotes downregulation of Kir3.2c channels by SNX27.
Figure 8: Overlapping expression of SNX27 and Kir3.3 mRNA in the brain.
Figure 9: Colocalization of SNX27b and Kir3 channels in hippocampal neurons.

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Acknowledgements

We thank C. Vandenberg and D. Leonoudakis for their invaluable advice for the proteomics study, D. Clapham for providing Kir3.3 and Kir3.4 cDNAs, M. Sheng for providing PSD-95 and Chapsyn-110 cDNAs, L. Jan and E. Cooper for providing Kv1.4 cDNA, I. Verma for the use of his confocal microscope, and C. Lüscher, M. Montminy and members of the Slesinger lab for reading versions of the manuscript. This work was made possible by financial support from the McKnight Endowment for Neuroscience (P.A.S.), the Hearst Foundation (P.A.S.) and the National Institute of Neurological Disorders and Stroke (NIH R01 NS37682, P.A.S.).

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M.-L.L., R.N. and P.A.S. were responsible for all cell biological and electrophysiological experiments, data interpretation and writing the manuscript. C.A. and J.T. assisted in preparing mutants and conducting in vitro protein binding assays. M.-L.L., I.M. and J.R.Y. (III) were responsible for conducting, interpreting, and writing-up the HPLC-MS-MS proteomics experiments. M.-L.L., C.M.A. and P.E.S. were responsible for conducting, interpreting, and writing-up the in situ experiments. P.A.S. supervised all of the experiments, including the design, data analysis and interpretation.

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Correspondence to Paul A Slesinger.

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Lunn, ML., Nassirpour, R., Arrabit, C. et al. A unique sorting nexin regulates trafficking of potassium channels via a PDZ domain interaction. Nat Neurosci 10, 1249–1259 (2007). https://doi.org/10.1038/nn1953

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