GAP-43 controls the availability of secretory chromaffin granules for regulated exocytosis by stimulating a granule-associated G0.
Besides having a role in signal transduction, heterotrimeric G proteins may also be involved in membrane trafficking events as suggested by their presence in specific intracellular compartments. In chromaffin cells, G alpha 0 is associated with secretory organelles, and its activation inhibits exocytosis. Although plasma membrane-bound G proteins are activated by cell-surface receptors, the intracellular proteins controlling organelle-associated G proteins are currently unknown. GAP-43, a neuronal protein enriched in axonal growth cones and presynaptic terminals, is one possible candidate since it can directly stimulate purified G0. We have investigated the interaction of adrenal medullary GAP-43 with chromaffin granule-associated G0 and its effect on catecholamine secretion. Cytosolic and depalmitoylated membrane-extracted GAP-43 were found to stimulate guanine nucleotide binding and exchange activity in chromaffin granule membranes. In permeabilized chromaffin cells, both forms of GAP-43 blocked calcium-dependent exocytosis, and this effect was inhibited by specific antibodies against G alpha 0. A synthetic peptide corresponding to the GAP-43 domain that interacts with G0 inhibited catecholamine secretion. This effect could be selectively reversed by the COOH-terminal peptide of G alpha 0. These results indicate that GAP-43 may be an endogenous pseudoreceptor for the secretory granule-bound form of G0 and can thereby control calcium-regulated exocytosis in chromaffin cells.
Vitale
N
N
Institut National de la Santé et de la Recherche Médicale, U-338 Biologie de la Communication Cellulaire, Strasbourg, France.
Deloulme
J C
JC
Thiersé
D
D
Aunis
D
D
Bader
M F
MF
D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D002837:Chromaffin Granules / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects; D019922:GAP-43 Protein; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006133:Growth Substances / Q000378:metabolism / Q000494:pharmacology; D006706:Homeostasis; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology; D010455:Peptides; D013373:Substance P / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology
D019922:GAP-43 Protein; D006133:Growth Substances; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D010455:Peptides; D014862:Wasp Venoms; D013373:Substance P; C037500:mastoparan; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D009638:Norepinephrine