Munc 18-1 and granuphilin collaborate during insulin granule exocytosis.
Munc 18-1 is a member of the Sec/Munc family of syntaxin-binding proteins known to bind to the plasma membrane Q-SNARE syntaxin1 and whose precise role in regulated exocytosis remains controversial. Here, we show that Munc 18-1 plays a positive role in regulated insulin secretion from pancreatic beta cells. Munc 18-1 depletion caused a loss in the secretory capacity of both transiently transfected INS 1E cells and a stable clone with tetracycline-regulated Munc 18-1 RNA interference. In addition, Munc 18-1-depleted cells exhibited defective docking of insulin granules to the plasma membrane and accumulated insulin in the trans Golgi network. Furthermore, glucose stimulation after Munc 18-1 depletion resulted in the rapid formation of autophagosomes. In contrast, overexpression of Munc 18-1 had no effect on insulin secretion. Although there was no detectable interaction between Munc 18-1 and Munc-18-interacting protein 1 or calcium/calmodulin-dependent serine protein kinase, Munc 18-1 associated with the granular protein granuphilin. This association was regulated by glucose and was required for the specific interaction of insulin granules with syntaxin1. We conclude that Munc 18-1 and granuphilin collaborate in the docking of insulin granules to the plasma membrane in an initial fusion-incompetent state, with Munc 18-1 subsequently playing a positive role in a later stage of insulin granule exocytosis.
Tomas
Alejandra
A
Department of Genetic Medicine and Development, University of Geneva Medical School, 1211 Geneva 4, Switzerland. alejandra.tomascatala@medecine.unige.ch
Meda
Paolo
P
Regazzi
Romano
R
Pessin
Jeffrey E
JE
Halban
Philippe A
PA
D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism; D001343:Autophagy; D002460:Cell Line; D004318:Doxycycline / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D051381:Rats; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism; D050827:Syntaxin 1 / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D007328:Insulin; D051938:Munc18 Proteins; C512779:SYTL4 protein, human; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D050988:Vesicle-Associated Membrane Protein 2; D033921:Vesicular Transport Proteins; D005947:Glucose; D004318:Doxycycline