Mechanisms of mastoparan-stimulated surfactant secretion from isolated pulmonary alveolar type 2 cells.
Mastoparan, a tetradecapeptide component of wasp venom, is a potent activator of secretion in a variety of cell types, and has been shown to activate purified G-proteins reconstituted into phospholipid vesicles with a preferential activation of Gi over Gs (Higashijima, T., Uzu, S., Nakajima, T., and Ross, E. R. (1988) J. Biol. Chem. 263, 6491-6494). To identify the biochemical activities of mastoparan in a cellular system, we characterized the effects of mastoparan on signal transduction pathways in rat pulmonary alveolar type 2 epithelial cells, which synthesize and secrete pulmonary surfactant. Mastoparan inhibited adenylylcyclase activity in a manner that was dose-dependent (IC50 = 30 microM), but sensitive to neither guanine nucleotide nor pertussis toxin (PT). Mastoparan induced a PT-sensitive increase in cellular inositol trisphosphate and a rapid rise in cytosolic calcium released from intracellular stores; the time to onset of the calcium rise, but neither the rate nor the amplitude of the rise, were PT-sensitive. Mastoparan also caused a dose- (EC50 = 16 microM) and time-dependent activation of arachidonic acid release that was completely insensitive to pretreatment with PT. Secretion of pulmonary surfactant was increased by mastoparan approximately 8-fold over constitutive levels at 1 h with an EC50 = 20 microM, and mastoparan-stimulated secretion was partially sensitive to PT at late time points and to inhibitors of arachidonic acid metabolism, but not to the protein kinase C inhibitor H7. These findings are consistent with the activation of Gi proteins in type 2 cells by mastoparan, although the lack of predicted triphosphoguanine nucleotide and PT sensitivity for some activities indicates that mastoparan does not act in a manner strictly analogous to liganded receptors or that some activities are not mediated by activation of Gi. While mastoparan is a potent secretagogue in several cell types, its secretory activity appears to have only a limited dependence on the activation of Gi proteins in type 2 cells.
Joyce-Brady
M
M
Pulmonary Center, Boston University School of Medicine, Massachusetts 02118.
Rubins
J B
JB
Panchenko
M P
MP
Bernardo
J
J
Steele
M P
MP
Kolm
L
L
Simons
E R
ER
Dickey
B F
BF
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D008297:Male; D010455:Peptides; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology*
D001095:Arachidonic Acids; D006150:Guanine Nucleotides; D007295:Inositol Phosphates; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D011663:Pulmonary Surfactants; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; C037500:mastoparan; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010738:Type C Phospholipases; D002118:Calcium