Neomycin is a potent secretagogue of mast cells that directly activates a GTP-binding protein involved in exocytosis.
When loaded alongside GTP-gamma-S into ATP-permeabilized cells, neomycin, at concentrations below 1 mM, inhibits GTP-gamma-S-induced histamine secretion and phosphatidic acid formation (Cockcroft, S., and B. D. Gomperts, 1985. Nature (Lond.). 314: 534-536; Aridor, M., L. M. Traub, and R. Sagi-Eisenberg. 1990. J. Cell Biol. 111:909-917). However, at higher concentrations internally applied neomycin induces histamine secretion in a process that is: (a) dose dependent; (b) dependent on the internal application of GTP; (c) independent of phosphoinositide breakdown; and (d) inhibited by pertussis toxin (PtX) treatment. These results indicate that neomycin can stimulate histamine secretion in a mechanism that bypasses phospholipase C (PLC) activation and yet involves a PtX-sensitive GTP-binding protein (G protein). Unlike its dual effects, when internally applied, neomycin induces histamine secretion from intact mast cells in a dose-dependent manner. Half-maximal and maximal effects are obtained at 0.5 and 1 mM neomycin, respectively. This process is rapid (approximately 30 s), is independent of external Ca2+, and is associated with phosphatidic acid formation, implying that neomycin can activate histamine secretion by a mechanism similar to that utilized by other basic secretagogues of mast cells. Neomycin stimulates fourfold the GTPase activity of cholate-solubilized rat brain membranes in a PtX-inhibitable manner. In addition neomycin, as well as the basic secretagogues of mast cells, compound 48/80, and mastoparan, significantly reduce (by approximately 80%) the ADP ribosylation of PtX substrates present in rat brain membranes. Taken together these data suggest that neomycin can stimulate secretion from mast cells by directly activating G proteins that play a role in stimulus-secretion coupling. When internally applied, neomycin presumably stimulates secretion by activating a G protein that is located downstream to PLC. This G protein serves as a substrate for PtX.
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
M
M
Aridor
R
R
Sagi-Eisenberg
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000255:Adenosine Triphosphate; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D002463:Cell Membrane Permeability; D004789:Enzyme Activation / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects*; D020558:GTP Phosphohydrolases / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000187:drug effects*; D006636:Histamine Release / Q000187:drug effects; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism*; D008565:Membrane Proteins / Q000187:drug effects; D015394:Molecular Structure; D009355:Neomycin / Q000031:analogs & derivatives / Q000494:pharmacology*; D037342:Pertussis Toxin; D010712:Phosphatidic Acids / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D008565:Membrane Proteins; D010712:Phosphatidic Acids; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D009355:Neomycin