title: SNAP-25 is expressed in islets of Langerhans and is involved in insulin release.
abstract: SNAP-25 is known as a neuron specific molecule involved in the fusion of small synaptic vesicles with the presynaptic plasma membrane. By immunolocalization and Western blot analysis, it is now shown that SNAP-25 is also expressed in pancreatic endocrine cells. Botulinum neurotoxins (BoNT) A and E were used to study the role of SNAP-25 in insulin secretion. These neurotoxins inhibit transmitter release by cleaving SNAP-25 in neurons. Cells from a pancreatic B cell line (HIT) and primary rat islet cells were permeabilized with streptolysin-O to allow toxin entry. SNAP-25 was cleaved by BoNT/A and BoNT/E, resulting in a molecular mass shift of approximately 1 and 3 kD, respectively. Cleavage was accompanied by an inhibition of Ca(++)-stimulated insulin release in both cell types. In HIT cells, a concentration of 30-40 nM BoNT/E gave maximal inhibition of stimulated insulin secretion of approximately 60%, coinciding with essentially complete cleavage of SNAP-25. Half maximal effects in terms of cleavage and inhibition of insulin release were obtained at a concentration of 5-10 nM. The A type toxin showed maximal and half-maximal effects at concentrations of 4 and 2 nM, respectively. In conclusion, the results suggest a role for SNAP-25 in fusion of dense core secretory granules with the plasma membrane in an endocrine cell type- the pancreatic B cell.
authors.affiliation: Laboratoires de Recherche Louis Jeantet, Centre Médical Universitaire, Geneva, Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Sadoul
authors.forename: J
authors.initials: J
authors.lastname: Lang
authors.forename: C
authors.initials: C
authors.lastname: Montecucco
authors.forename: U
authors.initials: U
authors.lastname: Weller
authors.forename: R
authors.initials: R
authors.lastname: Regazzi
authors.forename: S
authors.initials: S
authors.lastname: Catsicas
authors.forename: C B
authors.initials: CB
authors.lastname: Wollheim
authors.forename: P A
authors.initials: PA
authors.lastname: Halban
mesh_terms: D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000187:drug effects; D051381:Rats; D050825:Synaptosomal-Associated Protein 25
chemical_list: D007328:Insulin; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D001905:Botulinum Toxins; D002118:Calcium