Direct control of exocytosis by receptor-mediated activation of the heterotrimeric GTPases Gi and G(o) or by the expression of their active G alpha subunits.
The exocytotic release of potent hormones is a tightly controlled process. Its direct regulation without the involvement of second messengers would ensure rapid signal processing. In streptolysin O-permeabilized insulin-secreting cells, a preparation allowing dialysis of cytosolic macromolecules, activation of alpha 2-adrenergic receptors caused pertussis toxin-sensitive inhibition of calcium-induced exocytosis. This inhibition was mimicked very efficiently by the use of specific receptor-mimetic peptides, indicating the involvement of Gi and, to a lesser extent, of G(o). The regulation was exerted beyond the ATP-dependent step of exocytosis. In addition, low nanomolar amounts of pre-activated Gi/G(o) directly inhibited exocytosis. As transient overexpression of constitutively active mutants of G alpha i1, G alpha i2, G alpha i3 and G alpha o2 but not of G alpha o1 reproduced this regulation, the G alpha subunit alone is sufficient to induce inhibition. These results define exocytosis as an effector for heterotrimeric G-proteins and delineate the properties of the transduction pathway.
Lang
J
J
Division de Biochimie Clinique, Université de Genève, Switzerland.
Nishimoto
I
I
Okamoto
T
T
Regazzi
R
R
Kiraly
C
C
Weller
U
U
Wollheim
C B
CB
D000255:Adenosine Triphosphate / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D002096:C-Peptide / Q000032:analysis; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability; D004789:Enzyme Activation; D004837:Epinephrine / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism; D037342:Pertussis Toxin; D051381:Rats; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013301:Streptolysins; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001426:Bacterial Proteins; D002096:C-Peptide; D007328:Insulin; D010455:Peptides; D017527:Receptor, IGF Type 2; D018341:Receptors, Adrenergic, alpha-2; D013301:Streptolysins; D010566:Virulence Factors, Bordetella; C025964:streptolysin O; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium; D004837:Epinephrine