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

EMBO J. 1995 Aug 1;14(15):3635-44.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / physiology
  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins
  • C-Peptide / analysis
  • Calcium / metabolism
  • Cell Line
  • Cell Membrane Permeability
  • Enzyme Activation
  • Epinephrine / pharmacology
  • Exocytosis / drug effects
  • Exocytosis / physiology*
  • GTP Phosphohydrolases / chemistry
  • GTP Phosphohydrolases / metabolism*
  • GTP-Binding Proteins / metabolism*
  • Humans
  • Insulin / metabolism
  • Insulin Secretion
  • Islets of Langerhans / metabolism
  • Molecular Sequence Data
  • Peptides / chemical synthesis
  • Peptides / metabolism
  • Pertussis Toxin
  • Rats
  • Receptor, IGF Type 2 / metabolism
  • Receptors, Adrenergic, alpha-2 / metabolism
  • Signal Transduction / physiology*
  • Streptolysins
  • Virulence Factors, Bordetella / pharmacology

Substances

  • Bacterial Proteins
  • C-Peptide
  • Insulin
  • Peptides
  • Receptor, IGF Type 2
  • Receptors, Adrenergic, alpha-2
  • Streptolysins
  • Virulence Factors, Bordetella
  • streptolysin O
  • Adenosine Triphosphate
  • Pertussis Toxin
  • GTP Phosphohydrolases
  • GTP-Binding Proteins
  • Calcium
  • Epinephrine