Localization of a candidate surfactant convertase to type II cells, macrophages, and surfactant subfractions
Clark, H.; Allen, L.; Collins, E.; Barr, F.; Dobbs, L.; Putz, G.; Goerke, J.; Hawgood, S.
American Journal of Physiology 276(3): L452-L458
1999
ISSN/ISBN: 0002-9513 PMID: 10070109 Document Number: 510378
Pulmonary surfactant exists in the alveolus in several distinct subtypes that differ in their morphology, composition, and surface activity. Experiments by others have implicated a serine hydrolase in the production of the inactive small vesicular subtype of surfactant (N. J. Gross and R. M. Schultz. Biochim. Biophys. Acta 1044: 222-230, 1990). Our laboratory recently identified this enzyme in the rat as the serine carboxylesterase ES-2 [F. Barr, H. Clark, and S. Hawgood. Am. J. Physiol. 274 (Lung Cell. Mol. Physiol. 18): L404-L410, 1998]. In the present study, we determined the cellular sites of expression of ES-2 in rat lung using a digoxygenin-labeled ES-2 riboprobe. ES-2 mRNA was localized to type II cells and alveolar macrophages but not to Clara cells. Using a specific ES-2 antibody, we determined the protein distribution of ES-2 in the lung by immunohistochemistry, and it was found to be consistent with the sites of mRNA expression. Most of the ES-2 in rat bronchoalveolar lavage is in the surfactant-depleted supernatant, but ES-2 was also consistently localized to the small vesicular surfactant subfraction presumed to form as a consequence of conversion activity. These results are consistent with a role for endogenous lung ES-2 in surfactant metabolism. Reprinted by permission of the publisher.