TY - JOUR
T1 - γ-Glutamyl transpeptidase is a polarized alveolar epithelial membrane protein
AU - Ingbar, D. H.
AU - Hepler, K.
AU - Dowin, R.
AU - Jacobsen, E.
AU - Dunitz, J. M.
AU - Nici, L.
AU - Jamieson, J. D.
PY - 1995
Y1 - 1995
N2 - In many diseases the lung is injured by oxidants. γ-Glutamyl transpeptidase (GGT) is an ectoenzyme on the apical plasma membrane of many epithelial cells that protects against oxidants by replenishing intracellular glutathione. We sought to localize GGT within rat lungs in vivo and in cultured alveolar epithelial cells. In the adult rat lung, indirect immunofluorescence (IF) with a polyclonal antibody to triton-solubilized GGT revealed linear staining outlining the alveoli. Immunoelectron microscopy (IEM) localized the protein on the apical surface of the alveolar epithelial cells, but more densely on type I cells than type II cells, as well as on the apical surface of some ciliated bronchial cells. On Western blots of whole lung and isolated type II cell membrane proteins, the antibody predominantly recognized a broad protein band of 110-120 kDa, consistent with the uncleaved, glycosylated form of GGT. Over time in culture, isolated rat type II cells had increasing immunoreactivity on Western blots and indirect IF but decreasing enzyme activity. At 2 days in culture, confocal laser scanning microscopy demonstrated that GGT was polarized to the apical surface of nonconfluent type II cells. Thus GGT is a polarized apical membrane protein in type I and II cells, suggesting a role in the metabolic functions of these cells. The increased immunoreactive GGT of cultured type II cells is consistent with their acquisition of properties similar to type I cells, but the lack of correlation between immunoreactive protein and enzyme activity awaits explanation.
AB - In many diseases the lung is injured by oxidants. γ-Glutamyl transpeptidase (GGT) is an ectoenzyme on the apical plasma membrane of many epithelial cells that protects against oxidants by replenishing intracellular glutathione. We sought to localize GGT within rat lungs in vivo and in cultured alveolar epithelial cells. In the adult rat lung, indirect immunofluorescence (IF) with a polyclonal antibody to triton-solubilized GGT revealed linear staining outlining the alveoli. Immunoelectron microscopy (IEM) localized the protein on the apical surface of the alveolar epithelial cells, but more densely on type I cells than type II cells, as well as on the apical surface of some ciliated bronchial cells. On Western blots of whole lung and isolated type II cell membrane proteins, the antibody predominantly recognized a broad protein band of 110-120 kDa, consistent with the uncleaved, glycosylated form of GGT. Over time in culture, isolated rat type II cells had increasing immunoreactivity on Western blots and indirect IF but decreasing enzyme activity. At 2 days in culture, confocal laser scanning microscopy demonstrated that GGT was polarized to the apical surface of nonconfluent type II cells. Thus GGT is a polarized apical membrane protein in type I and II cells, suggesting a role in the metabolic functions of these cells. The increased immunoreactive GGT of cultured type II cells is consistent with their acquisition of properties similar to type I cells, but the lack of correlation between immunoreactive protein and enzyme activity awaits explanation.
KW - alveolar epithelium
KW - glutamyl transpeptidase
KW - oxidants
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U2 - 10.1152/ajplung.1995.269.2.l261
DO - 10.1152/ajplung.1995.269.2.l261
M3 - Article
C2 - 7653588
AN - SCOPUS:0029347134
SN - 1040-0605
VL - 269
SP - L261-L271
JO - American Journal of Physiology - Lung Cellular and Molecular Physiology
JF - American Journal of Physiology - Lung Cellular and Molecular Physiology
IS - 2 13-2
ER -