Munc 18-1 and granuphilin collaborate during insulin granule exocytosis

Traffic. 2008 May;9(5):813-32. doi: 10.1111/j.1600-0854.2008.00709.x. Epub 2008 Jan 19.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / metabolism
  • Autophagy
  • Cell Line
  • Doxycycline / metabolism
  • Exocytosis / physiology*
  • Glucose / metabolism
  • Humans
  • Insulin / metabolism*
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / metabolism*
  • Munc18 Proteins / genetics
  • Munc18 Proteins / metabolism*
  • RNA Interference
  • Rats
  • Secretory Vesicles / chemistry
  • Secretory Vesicles / metabolism*
  • Synaptosomal-Associated Protein 25 / metabolism
  • Syntaxin 1 / metabolism
  • Vacuoles / metabolism
  • Vesicle-Associated Membrane Protein 2 / metabolism
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism*

Substances

  • Anti-Bacterial Agents
  • Insulin
  • Munc18 Proteins
  • SYTL4 protein, human
  • Synaptosomal-Associated Protein 25
  • Syntaxin 1
  • Vesicle-Associated Membrane Protein 2
  • Vesicular Transport Proteins
  • Glucose
  • Doxycycline