ADP ribosylation of type II pulmonary epithelial cell G proteins.
Secretion of pulmonary surfactant by type II pulmonary epithelial cells (T2P) is regulated by receptor-mediated mechanisms. In other systems, coupling of receptor-linked signals to intracellular events involves guanine nucleotide-binding proteins (G proteins), but the specific role of G proteins in T2P signaling pathways is poorly defined. The present studies begin to address the role of G proteins in transmembrane signaling in these pneumocytes. Membrane preparations from purified T2Ps demonstrated ADP ribosylation of specific substrates by pertussis, cholera, and botulinum toxins (PT, CT, and BT, respectively). Toxin-dependent T2P substrate labeling from 32P-labeled NAD was dependent on time and membrane protein concentration. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography showed ADP ribosylation of membrane substrates of the following molecular masses: PT, 40/41 kDa; CT, 47/51 kDa; BT, 22 kDa. BT-dependent ADP ribosylation of a 22-kDa cytosolic substrate was also observed. Pretreatment of cultured T2P with the individual toxins led to ADP ribosylation of their respective specific substrates in a time-dependent fashion. In cells pretreated with PT or CT, substrates for the complimentary toxins remained available for subsequent ADP ribosylation in vitro. This result supports the specificity of the toxin effects. Basal secretion of the major phospholipid of pulmonary surfactant, disaturated phosphatidylcholine (DSPC) was unaffected in T2P treated with PT, but was stimulated in cells exposed to CT or BT. Neither CT nor BT altered release of lactate dehydrogenase. In cells treated with AMP or with isoproterenol DSPC secretion was stimulated six- to eightfold; preexposure of the cells to CT reduced the response to either agonist by 70%.(ABSTRACT TRUNCATED AT 250 WORDS)
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Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey 17033.
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D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008168:Lung / Q000502:physiology*; D008297:Male; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D009243:NAD / Q000378:metabolism*; D037342:Pertussis Toxin; D011663:Pulmonary Surfactants / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction / Q000187:drug effects; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D008565:Membrane Proteins; D011663:Pulmonary Surfactants; D010566:Virulence Factors, Bordetella; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D006165:Guanylyl Imidodiphosphate; D002772:Cholera Toxin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D007545:Isoproterenol