title: Endosomal acidification by Na+/H+ exchanger NHE5 regulates TrkA cell-surface targeting and NGF-induced PI3K signaling.
abstract: To facilitate polarized vesicular trafficking and signal transduction, neuronal endosomes have evolved sophisticated mechanisms for pH homeostasis. NHE5 is a member of the Na(+)/H(+) exchanger family and is abundantly expressed in neurons and associates with recycling endosomes. Here we show that NHE5 potently acidifies recycling endosomes in PC12 cells. NHE5 depletion by plasmid-based short hairpin RNA significantly reduces cell surface abundance of TrkA, an effect similar to that observed after treatment with the V-ATPase inhibitor bafilomycin. A series of cell-surface biotinylation experiments suggests that anterograde trafficking of TrkA from recycling endosomes to plasma membrane is the likeliest target affected by NHE5 depletion. NHE5 knockdown reduces phosphorylation of Akt and Erk1/2 and impairs neurite outgrowth in response to nerve growth factor (NGF) treatment. Of interest, although both phosphoinositide 3-kinase-Akt and Erk signaling are activated by NGF-TrkA, NGF-induced Akt-phosphorylation appears to be more sensitively affected by perturbed endosomal pH. Furthermore, NHE5 depletion in rat cortical neurons in primary culture also inhibits neurite formation. These results collectively suggest that endosomal pH modulates trafficking of Trk-family receptor tyrosine kinases, neurotrophin signaling, and possibly neuronal differentiation.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Graham H
authors.initials: GH
authors.lastname: Diering
authors.forename: Yuka
authors.initials: Y
authors.lastname: Numata
authors.forename: Steven
authors.initials: S
authors.lastname: Fan
authors.forename: John
authors.initials: J
authors.lastname: Church
authors.forename: Masayuki
authors.initials: M
authors.lastname: Numata
mesh_terms: D000143:Acids / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000196:embryology; D011992:Endosomes / Q000737:chemistry / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008856:Microscopy, Fluorescence; D020932:Nerve Growth Factor / Q000494:pharmacology*; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D020917:Receptor, trkA / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D000143:Acids; D017923:Sodium-Hydrogen Exchangers; C117561:sodium-hydrogen exchanger 5; D020932:Nerve Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D020917:Receptor, trkA; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases