title: Half-lives of plasma membrane Na(+)/H(+) exchangers NHE1-3: plasma membrane NHE2 has a rapid rate of degradation.
abstract: The Na(+)/H(+) exchangers NHE2 and NHE3 are involved in epithelial Na(+) and HCO absorption. To increase insights into the functions of NHE2 vs. NHE3, we compared their cellular processing with each other and with the housekeeping isoform NHE1. Using biotinylated exchanger, we determined that the half-life of plasma membrane NHE2 was short (3 h) compared with that of NHE1 (24 h) and NHE3 (14 h) in both PS120 fibroblasts and Caco-2 cells. NHE2 transport and plasma membrane levels were reduced by 3 h of Brefeldin A treatment, whereas NHE1 was unaffected. NHE2 was degraded by the lysosomes but not proteosomes, as demonstrated by increasing levels of endocytosed NHE2 protein after inhibition of the lysosomes, but not with proteosome inhibition. Unlike that of NHE3, basal NHE2 transport activity was not affected by phosphatidylinositol 3-kinase inhibition and did not appear to be localized in the juxtanuclear recycling endosome. Therefore, for NHE2, protein degradation and/or protein synthesis probably play important roles in its basal and regulated states. These results suggest fundamental differences in the cellular processing and trafficking of NHE2 and NHE3. These differences may underlie the specialized roles that these exchangers play in epithelial cells.
authors.affiliation: Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Cavet
authors.forename: S
authors.initials: S
authors.lastname: Akhter
authors.forename: R
authors.initials: R
authors.lastname: Murtazina
authors.forename: F
authors.initials: F
authors.lastname: Sanchez de Medina
authors.forename: C M
authors.initials: CM
authors.lastname: Tse
authors.forename: M
authors.initials: M
authors.lastname: Donowitz
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D019921:Biotinylation; D020126:Brefeldin A / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D020033:Protein Isoforms / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000502:physiology*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D009097:Multienzyme Complexes; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors; C081517:SLC9A2 protein, human; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D020126:Brefeldin A; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000077191:Wortmannin