Exocytosis in mast cells by basic secretagogues: evidence for direct activation of GTP-binding proteins.
Histamine release induced by the introduction of a nonhydrolyzable analogue of GTP, GTP-gamma-S, into ATP-permeabilized mast cells, is associated with phosphoinositide breakdown, as evidenced by the production of phosphatidic acid (PA) in a neomycin-sensitive process. The dependency of both PA formation and histamine secretion on GTP-gamma-S concentrations is bell shaped. Whereas concentrations of up to 0.1 mM GTP-gamma-S stimulate both processes, at higher concentrations the cells' responsiveness is inhibited. At a concentration of 1 mM, GTP-gamma-S self-inhibits both PA formation and histamine secretion. Inhibition of secretion can, however, be overcome by the basic secretagogues compound 48/80 and mastoparan that in suboptimal doses synergize with 1 mM GTP-gamma-S to potentiate secretion. Secretion under these conditions is not accompanied by PA formation and is resistant both to depletion of Ca2+ from internal stores and to pertussis toxin (PtX) treatment. In addition, 48/80, like mastoparan, is capable of directly stimulating the GTPase activity of G-proteins in a cell-free system. Together, our results are consistent with a model in which the continuous activation of a phosphoinositide-hydrolyzing phospholipase C (PLC) by a stimulatory G-protein suffices to trigger histamine secretion. Basic secretagogues of mast cells, such as compound 48/80 and mastoparan, are capable of inducing secretion in a mechanism that bypasses PLC by directly activating a G-protein that is presumably located downstream from PLC (GE). Thereby, these secretagogues induce histamine secretion in a receptor-independent manner.
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
M
M
Aridor
L M
LM
Traub
R
R
Sagi-Eisenberg
D000255:Adenosine Triphosphate; D000818:Animals; D001921:Brain / Q000201:enzymology; D002463:Cell Membrane Permeability; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006636:Histamine Release / Q000187:drug effects / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins; D008297:Male; D008407:Mast Cells / Q000378:metabolism*; D008566:Membranes / Q000201:enzymology; D010455:Peptides; D037342:Pertussis Toxin; D010712:Phosphatidic Acids / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013873:Thionucleotides / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010712:Phosphatidic Acids; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003189:p-Methoxy-N-methylphenethylamine; C037500:mastoparan; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins