The intracellular Na(+)/H(+) exchanger NHE7 effects a Na(+)-coupled, but not K(+)-coupled proton-loading mechanism in endocytosis.
Vesicular H(+)-ATPases and ClC-chloride transporters are described to acidify intracellular compartments, which also express the highly conserved Na(+)/H(+) exchangers NHE6, NHE7, and NHE9. Mutations of these exchangers cause autism-spectrum disorders and neurodegeneration. NHE6, NHE7, and NHE9 are hypothesized to exchange cytosolic K(+) for H(+) and alkalinize vesicles, but this notion has remained untested in K(+) because their intracellular localization prevents functional measurements. Using proton-killing techniques, we selected a cell line that expresses wild-type NHE7 at the plasma membrane, enabling measurement of the exchanger's transport parameters. We found that NHE7 transports Li(+) and Na(+), but not K(+), is nonreversible in physiological conditions and is constitutively activated by cytosolic H(+). Therefore, NHE7 acts as a proton-loading transporter rather than a proton leak. NHE7 mediates an acidification of intracellular vesicles that is additive to that of V-ATPases and that accelerates endocytosis. This study reveals an unexpected function for vesicular Na(+)/H(+) exchangers and provides clues for understanding NHE-linked neurological disorders.
Université Nice-Sophia Antipolis, LP2M CNRS-UMR 7370, Faculté de Médecine, 28 Avenue de Valombrose, 06107 Nice, France.
Nina
N
Milosavljevic
Université Nice-Sophia Antipolis, LP2M CNRS-UMR 7370, Faculté de Médecine, 28 Avenue de Valombrose, 06107 Nice, France.
Michaël
M
Monet
Université Nice-Sophia Antipolis, LP2M CNRS-UMR 7370, Faculté de Médecine, 28 Avenue de Valombrose, 06107 Nice, France.
Isabelle
I
Léna
Université Nice-Sophia Antipolis, IPMC CNRS-UMR 7275, 660 Route des Lucioles Sophia Antipolis, 06560 Valbonne, France.
Frédéric
F
Brau
Université Nice-Sophia Antipolis, CCMA Faculté des Sciences Parc Valrose, 06108 Nice, France.
Sandra
S
Lacas-Gervais
Université Nice-Sophia Antipolis, IPMC CNRS-UMR 7275, 660 Route des Lucioles Sophia Antipolis, 06560 Valbonne, France.
Sylvain
S
Feliciangeli
Université Nice-Sophia Antipolis, LP2M CNRS-UMR 7370, Faculté de Médecine, 28 Avenue de Valombrose, 06107 Nice, France. Electronic address: laurent.counillon@unice.fr.
Laurent
L
Counillon
Université Nice-Sophia Antipolis, LP2M CNRS-UMR 7370, Faculté de Médecine, 28 Avenue de Valombrose, 06107 Nice, France.
Mallorie
M
Poët
D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007477:Ions / Q000737:chemistry; D008094:Lithium / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D011188:Potassium / Q000378:metabolism*; D011522:Protons; D034741:RNA, Small Interfering / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D007477:Ions; D011522:Protons; D034741:RNA, Small Interfering; C429538:SLC9A7 protein, human; D017923:Sodium-Hydrogen Exchangers; D008094:Lithium; D012964:Sodium; D011188:Potassium