Gamma-glutamyl transpeptidase is a polarized alveolar epithelial membrane protein. Ingbar, David H., Kristin Hepler, Richard Dowin, Eric Jacobsen, Jordan M. Dunitz, Linda Nici, and James D. Jamieson. Department of Medicine, University of Minnesota, Minneapolis, MN; Departments of Medicine and Cell Biology, Yale University School of Medicine, New Haven, CT and Department of Medicine, Brown University, Providence, R.I.
APStracts 2:0063L, 1995.
In many diseases the lung is injured by oxidants. Gamma-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 kD, 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 immunofluorescence, but decreasing enzyme activity. At two 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 imunoreactive protein and enzyme activity awaits explanation. 

Received 10 January 1993; accepted in final form 25 January 1995.
APS Manuscript Number L213-3.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.