The Sodium/Proton Exchanger NHE8 Regulates Late Endosomal Morphology and Function |
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| Authors: | Scott P. Lawrence Nicholas A. Bright J. Paul Luzio Katherine Bowers |
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| Affiliation: | *Institute for Structural and Molecular Biology, Division of Biosciences, University College London, London, WC1E 6BT, United Kingdom; and ;†Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke''s Hospital, Cambridge, CB2 0XY, United Kingdom |
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| 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. |
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