title: The sodium/proton exchanger NHE8 regulates late endosomal morphology and function.
abstract: The pH and lumenal environment of intracellular organelles is considered essential for protein sorting and trafficking through the cell. We provide the first evidence that a mammalian NHE sodium (potassium)/proton exchanger, NHE8, plays a key role in the control of protein trafficking and endosome morphology. At steady state, the majority of epitope-tagged NHE8 was found in the trans-Golgi network of HeLa M-cells, but a proportion was also localized to multivesicular bodies (MVBs). Depletion of NHE8 in HeLa M-cells with siRNA resulted in the perturbation of MVB protein sorting, as shown by an increase in epidermal growth factor degradation. Additionally, NHE8-depleted cells displayed striking perinuclear clustering of endosomes and lysosomes, and there was a ninefold increase in the cellular volume taken up by LAMP1/LBPA-positive, dense MVBs. Our data points to a role for the ion exchange activity of NHE8 being required to maintain endosome morphology, as overexpression of a nonfunctional point mutant protein (NHE8 E225Q) resulted in phenotypes similar to those seen after siRNA depletion of endogenous NHE8. Interestingly, we found that depletion of NHE8, despite its function as a sodium (potassium)/proton antiporter, did not affect the overall pH inside dense MVBs.
authors: Institute for Structural and Molecular Biology, Division of Biosciences, University College London, London, United Kingdom.
authors: Scott P
authors: SP
authors: Lawrence
authors: Nicholas A
authors: NA
authors: Bright
authors: J Paul
authors: JP
authors: Luzio
authors: Katherine
authors: K
authors: Bowers
mesh_terms: D002451:Cell Compartmentation; D015536:Down-Regulation; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D004815:Epidermal Growth Factor / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000378:metabolism; D057146:Multivesicular Bodies / Q000378:metabolism / Q000648:ultrastructure; D050505:Mutant Proteins / Q000378:metabolism; D053140:Organelle Shape / Q000502:physiology*; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D000939:Epitopes; D050505:Mutant Proteins; D034741:RNA, Small Interfering; C486775:SLC9A8 protein, human; D017923:Sodium-Hydrogen Exchangers; D004815:Epidermal Growth Factor