Mechanisms of mastoparan-stimulated surfactant secretion from isolated pulmonary alveolar type 2 cells

M. Joyce-Brady, J. B. Rubins, M. P. Panchenko, J. Bernardo, M. P. Steele, L. Kolm, E. R. Simons, B. F. Dickey

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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 G(i) over G(s) (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 adenylycyclase activity in a manner that was dose-dependent (IC50 = 30 μM), 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 μM) 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 μM, 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 G(i) 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 G(i). While mastoparan is a potent secretagogue in several cell types, its secretory activity appears to have only a limited dependence on the activation of G(i) proteins in type 2 cells.

Original languageEnglish (US)
Pages (from-to)6859-6865
Number of pages7
JournalJournal of Biological Chemistry
Issue number11
StatePublished - 1991


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