TY - JOUR
T1 - Half-lives of plasma membrane Na+/H+ exchangers NHE1-3
T2 - Plasma membrane NHE2 has a rapid rate of degradation
AU - Cavet, Megan E.
AU - Akhter, Shafinaz
AU - Murtazina, Rakhilya
AU - De Medina, Fermin Sanchez
AU - Chung-Ming, T. S.E.
AU - Donowitz, Mark
PY - 2001
Y1 - 2001
N2 - The Na+/H+ exchangers NHE2 and NHE3 are involved in epithelial Na+ and HCO3- 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.
AB - The Na+/H+ exchangers NHE2 and NHE3 are involved in epithelial Na+ and HCO3- 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.
KW - Caco-2 cells
KW - Lysosomes
KW - Sodium absorption
KW - Trafficking
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U2 - 10.1152/ajpcell.2001.281.6.c2039
DO - 10.1152/ajpcell.2001.281.6.c2039
M3 - Article
C2 - 11698263
AN - SCOPUS:0035658769
SN - 0363-6143
VL - 281
SP - C2039-C2048
JO - American Journal of Physiology - Cell Physiology
JF - American Journal of Physiology - Cell Physiology
IS - 6 50-6
ER -