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Ca2+-independent insulin exocytosis induced by alpha-latrotoxin requires latrophilin, a G protein-coupled receptor

Published inEMBO journal, vol. 17, no. 3, p. 648-657
Publication date1998
Abstract

alpha-Latrotoxin (alpha-LTX) induces exocytosis of small synaptic vesicles (SSVs) in neuronal cells both by a calcium-independent mechanism and by opening cation-permeable pores. Since the basic molecular events regulating exocytosis in neurons and endocrine cells may be similar, we have used the exocytosis of insulin-containing large dense core vesicles (LDCVs) as a model system. In primary pancreatic beta-cells and in the derived cell lines INS-1 and MIN6, alpha-LTX increased insulin release in the absence of extracellular calcium, but the insulin-secreting cell lines HIT-T15 and RINm5F were unresponsive. alpha-LTX did not alter membrane potential or cytosolic calcium, and its stimulatory effect on exocytosis was still observed in pre-permeabilized INS-1 cells kept at 0.1 microM Ca2+. Consequently, pore formation or ion fluxes induced by alpha-LTX could be excluded. The Ca2+-independent alpha-LTX-binding protein, latrophilin, is a novel member of the secretin family of G protein-coupled receptors (GPCR). Sensitivity to alpha-LTX correlated with expression of latrophilin, but not with synaptotagmin I or neurexin Ialpha expression. Moreover, transient expression of latrophilin in HIT-T15 cells conferred alpha-LTX-induced exocytosis. Our results indicate that direct stimulation of exocytosis by a GPCR mediates the Ca2+-independent effects of alpha-LTX in the absence of altered ion fluxes. Therefore, direct regulation by receptor-activated heterotrimeric G proteins constitutes an important feature of the endocrine exocytosis of insulin-containing LDCVs and may also apply to SSV exocytosis in neurons.

Keywords
  • Animals
  • Bacterial Toxins/pharmacology
  • Calcium/pharmacology
  • Calcium-Binding Proteins
  • Cell Line
  • Cell Membrane/drug effects/physiology
  • Cell Membrane Permeability/drug effects
  • Cytosol/chemistry/drug effects
  • Exocytosis/drug effects/physiology
  • GTP-Binding Proteins/metabolism
  • Gene Expression
  • Glycoproteins
  • Hemolysin Proteins/pharmacology
  • Insulin/secretion
  • Islets of Langerhans/metabolism/secretion
  • Membrane Glycoproteins/genetics
  • Membrane Potentials/drug effects
  • Nerve Tissue Proteins/genetics
  • Neuropeptides
  • Protein Binding
  • Receptors, Cell Surface/metabolism
  • Receptors, Peptide/genetics/metabolism
  • Spider Venoms/chemistry/metabolism/pharmacology
  • Staphylococcus aureus/chemistry
  • Synaptotagmin I
  • Synaptotagmins
Citation (ISO format)
LANG, Jochen et al. Ca<sup>2+</sup>-independent insulin exocytosis induced by alpha-latrotoxin requires latrophilin, a G protein-coupled receptor. In: EMBO journal, 1998, vol. 17, n° 3, p. 648–657. doi: 10.1093/emboj/17.3.648
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Article (Published version)
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Identifiers
ISSN of the journal0261-4189
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