Fiche publication
Date publication
mai 1994
Journal
The Biochemical journal
Auteurs
Membres identifiés du Cancéropôle Est :
Dr BADER Marie-France
,
Dr VITALE Nicolas
Tous les auteurs :
Vitale N, Thiersé D, Aunis D, Bader MF
Lien Pubmed
Résumé
We have previously described that mastoparan, an amphiphilic tetradecapeptide that activates heterotrimeric G-proteins, inhibits Ca(2+)-induced MgATP-dependent secretion from streptolysin-O-permeabilized chromaffin cells [Vitale, Mukai, Rouot, Thiersé, Aunis and Bader (1993) J. Biol. Chem. 268, 14715-14723]. Our observations suggest the involvement of an inhibitory G(o)-protein, possibly located on the membrane of secretory granules, in the final stages of the exocytotic pathway in chromaffin cells. Here, we demonstrate that mastoparan is also able to stimulate the Ca(2+)-dependent secretion of catecholamines in the absence of MgATP in the medium. This MgATP-independent secretion is totally blocked by tetanus toxin, a potent inhibitor of exocytosis in all neurosecretory cells so far investigated, suggesting that the mastoparan target is a component of the exocytotic machinery. Mas17, a mastoparan analogue inactive on G-proteins, had no effect on catecholamine secretion whereas both Mas7, a highly active analogue of mastoparan, and AlF4-, which selectively activates trimeric G-proteins, triggered MgATP-independent secretion. Non-hydrolysable GTP analogues (GTP[S] and p[NH]ppG) mimicked the dual effects of mastoparan on secretion: they inhibited exocytosis in the presence of MgATP and stimulated MgATP-independent secretion. The different potencies displayed by these two analogues suggest the involvement of two distinct G-proteins. Accordingly, the mastoparan-induced MgATP-independent secretion is highly sensitive to pertussis toxin (PTX) whereas the inhibition by mastoparan of secretion in the presence of MgATP is resistant to PTX treatment. When permeabilized cells were incubated with mastoparan, the release of arachidonic acid increased in a PTX-sensitive manner. 7,7-Dimethyl-5,8-eicosadienoic acid, a potent inhibitor of intracellular phospholipase A2, inhibited both the arachidonate release and the MgATP-independent catecholamine secretion evoked by mastoparan. In contrast, neomycin, an inhibitor of phospholipase C, had no significant effect on either the release of arachidonic acid or the secretion of catecholamines provoked by mastoparan. We conclude that two distinct heterotrimeric G-proteins act in series in the exocytotic pathway in chromaffin cells: one controls an ATP-dependent priming step through an effector pathway that remains to be determined, and the second is involved in a late Ca(2+)-dependent step which does not require MgATP but possibly involves the generation of arachidonic acid.
Mots clés
Adenosine Triphosphate, metabolism, Adrenal Glands, cytology, Animals, Arachidonic Acid, metabolism, Calcium, pharmacology, Catecholamines, secretion, Cattle, Cells, Cultured, Chromaffin Granules, Exocytosis, Fatty Acids, Unsaturated, pharmacology, GTP-Binding Proteins, metabolism, Guanosine Triphosphate, metabolism, Neomycin, pharmacology, Peptides, Pertussis Toxin, Phospholipases A, antagonists & inhibitors, Phospholipases A2, Type C Phospholipases, antagonists & inhibitors, Virulence Factors, Bordetella, pharmacology, Wasp Venoms, pharmacology
Référence
Biochem. J.. 1994 May;300 ( Pt 1):217-27
