title: Phospholipase A2 in alveolar type II epithelial cells: biochemical and immunologic characterization.
abstract: The enzyme phospholipase A2 (PLA2) catalyzes phospholipid hydrolysis and is thought to play important roles in surfactant synthesis and in the generation of lipid mediators, including eicosanoids and platelet-activating factor. This study sought to characterize PLA2 in rat type II pneumocytes by biochemical and immunologic means. Type II cells were found to contain an alkaline-active, Ca(2+)-dependent PLA2 activity predominantly localized to cytosol fraction. This activity preferred phospholipids containing arachidonate in the sn-2 position and phosphatidylethanolamine (PE) over phosphatidylcholine (PC); it was active at physiologically relevant Ca2+ concentrations and was resistant to dithiothreitol. These biochemical features were suggestive of a high-molecular-weight form of PLA2, and immunoblot analysis of type II cell extracts indeed detected a 97-kDa protein corresponding to a high-molecular-weight PLA2, but no low-molecular-weight pancreatic-type enzyme. Human A549 cells, which share certain features with type II cells, contained a similar PLA2 activity and immunoreactive protein. By contrast, whole rat lung cytosol contained both a 97-kDa PLA2 and a 14-kDa pancreatic-type PLA2, but its activity was typical of the latter in that it lacked sn-2 specificity for arachidonate and was inhibited by dithiothreitol. These results indicate that rat type II as well as human A549 epithelial cells contain a high-molecular-weight PLA2, for which mounting evidence suggests an important role in physiological and pathophysiological situations.
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor.
authors.forename: G R
authors.initials: GR
authors.lastname: Neagos
authors.forename: A
authors.initials: A
authors.lastname: Feyssa
authors.forename: M
authors.initials: M
authors.lastname: Peters-Golden
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004847:Epithelial Cells; D004848:Epithelium / Q000201:enzymology; D006801:Humans; D015151:Immunoblotting; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology; D008297:Male; D010641:Phenotype; D010741:Phospholipases A / Q000032:analysis*; D054467:Phospholipases A2; D011650:Pulmonary Alveoli / Q000166:cytology* / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions; D014407:Tumor Cells, Cultured
chemical_list: D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium; D004229:Dithiothreitol