Gelsolin associates with the N terminus of syntaxin 4 to regulate insulin granule exocytosis

Mol Endocrinol. 2012 Jan;26(1):128-41. doi: 10.1210/me.2011-1112. Epub 2011 Nov 22.

Abstract

The plasma membrane soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) protein syntaxin (Syn)4 is required for biphasic insulin secretion, although how it regulates each phase remains unclear. In a screen to identify new Syn4-interacting factors, the calcium-activated F-actin-severing protein gelsolin was revealed. Gelsolin has been previously implicated as a positive effector of insulin secretion, although a molecular mechanism to underlie this function is lacking. Toward this, our in vitro binding studies showed the Syn4-gelsolin interaction to be direct and mediated by the N-terminal Ha domain (amino acid residues 39-70) of Syn4. Syn4-gelsolin complexes formed under basal conditions and dissociated upon acute glucose or KCl stimulation; nifedipine blocked dissociation. The dissociating action of secretagogues could be mimicked by expression of the N-terminal Ha domain of Syn4 fused to green fluorescent protein (GFP) (GFP-39-70). Furthermore, GFP-39-70 expression in isolated mouse islet and clonal MIN6 β-cells initiated insulin release in the absence of appropriate stimuli. Consistent with this, the inhibitory GFP-39-70 peptide also initiated Syn4 activation in the absence of stimuli. Moreover, although MIN6 β-cells expressing the GFP-39-70 peptide maintained normal calcium influx in response to KCl, KCl-stimulated insulin secretion and the triggering pathway of insulin secretion were significantly impaired. Taken together, these data support a mechanistic model for gelsolin's role in insulin exocytosis: gelsolin clamps unsolicited soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE)-regulated exocytosis through direct association with Syn4 in the absence of appropriate stimuli, which is relieved upon stimulus-induced calcium influx to activate gelsolin and induce its dissociation from Syn4 to facilitate insulin exocytosis.

Publication types

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

MeSH terms

  • Animals
  • Biological Transport
  • Calcium / metabolism
  • Cell Line
  • Cell Membrane / metabolism
  • Exocytosis*
  • Gelsolin / metabolism*
  • Glucose / pharmacology
  • Green Fluorescent Proteins
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / metabolism*
  • Mice
  • Nifedipine / pharmacology
  • Potassium Chloride / pharmacology
  • Qa-SNARE Proteins / metabolism*
  • SNARE Proteins / metabolism
  • Secretory Vesicles / metabolism*

Substances

  • Gelsolin
  • Insulin
  • Qa-SNARE Proteins
  • SNARE Proteins
  • Green Fluorescent Proteins
  • Potassium Chloride
  • Nifedipine
  • Glucose
  • Calcium