Munc18-1 Regulates First-phase Insulin Release by Promoting Granule Docking to Multiple Syntaxin Isoforms

Oh, Eunjin; Kalwat, Michael A.; Kim, Min Jung; Verhage, Matthijs; Thurmond, Debbie C.

doi:10.1074/jbc.m112.361501

Cited by 69 publications

(80 citation statements)

References 62 publications

(66 reference statements)

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“…Further studies are required to explore other as yet undefined mechanisms by which Syn-4 mediates the recruitment and exocytosis of newcomer SGs. Taken together, our results raise the possibility that fusion machinery induced by Munc18c-Syn-4 interactions might be redundant to Munc18a-Syn-1A in mediating exocytosis of pre-docked SGs [32], and to Munc18b-Syn-3 in mediating newcomer SGs [5]. This in turn suggests that restoring Syn-4 (and/or Munc18c) into islets in type 2 diabetes [15] might be a preferred strategy by which to rescue the deficient biphasic GSIS.…”

Section: Discussionmentioning

confidence: 58%

Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells

et al. 2015

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Aims/hypothesis Of the four exocytotic syntaxins (Syns), much is now known about the role of Syn-1A (pre-docked secretory granules [SGs]) and Syn-3 (newcomer SGs) in insulin exocytosis. Some work was reported on Syn-4's role in biphasic glucose-stimulated insulin secretion (GSIS), but its precise role in insulin SG exocytosis remains unclear. In this paper we examine this role in human beta cells. Methods Endogenous function of Syn-4 in human islets was assessed by knocking down its expression with lentiviral single hairpin RNA (lenti-shRNA)-RFP. Biphasic GSIS was determined by islet perifusion assay. Single-cell analysis of exocytosis of red fluorescent protein (RFP)-positive beta cells (exhibiting near-total depletion of Syn-4) was by patch clamp capacitance measurements (Cm) and total internal reflection fluorescence microscopy (TIRFM), the latter to further assess single SG behaviour. Co-immunoprecipitations were conducted on INS-1 cells to assess exocytotic complexes. Results Syn-4 knockdown (KD) of 77% in human islets caused a concomitant reduction in cognate Munc18c expression (46%) without affecting expression of other exocytotic proteins; this resulted in reduction of GSIS in the first phase (by 42%) and the second phase (by 40%). Cm of RFP-tagged Syn-4-KD beta cells showed severe inhibition in the readily releasable pool (by 71%) and mobilisation from reserve pools (by 63%). TIRFM showed that Syn-4-KD-induced inhibition of first-phase GSIS was attributed to reduction in exocytosis of both pre-docked and newcomer SGs (which undergo minimal residence or docking time at the plasma membrane before fusion). Second-phase inhibition was attributed to reduction in newcomer SGs. Stx-4 co-immunoprecipitated Munc18c, VAMP2 and VAMP8, suggesting that these exocytotic complexes may be involved in exocytosis of pre-docked and newcomer SGs. Conclusions/interpretation Syn-4 is involved in distinct molecular machineries that influence exocytosis of both predocked and newcomer SGs in a manner functionally redundant to Syn-1A and Syn-3, respectively; this underlies Syn-4's role in mediating portions of first-phase and second-phase GSIS.

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Section: Discussionmentioning

confidence: 58%

Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells

et al. 2015

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“…In synaptic vesicles, a much studied model, this fusion is mediated by the SNARE protein VAMP2 (also called synaptobrevin2 (Syb2)) anchored in the outer leaf of the vesicle membrane interacting in a zipperlike fashion with syntaxin1a (Syx1a) and SNAP25 anchored in the target plasma membrane (68,(71)(72)(73)(74)(75). These proteins are also found in the beta cell (68,(77)(78)(79)(80)(81)(82)(83).…”

Section: Discussionmentioning

confidence: 99%

Characterization of Phospholipids in Insulin Secretory Granules and Mitochondria in Pancreatic Beta Cells and Their Changes with Glucose Stimulation

MacDonald

Ade

Ntambi

et al. 2015

Journal of Biological Chemistry

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Background: Phospholipids in insulin granules were characterized. Results: Phosphatidylserine and phospholipids with unsaturated or short fatty acids were concentrated in granules and increased with glucose stimulation. Conclusion: Phosphatidylserine enhances the interaction between proteins in granules and plasma membranes. Unsaturated and short FA increase the fluidity and curvature of lipid bilayers. Significance: Fusion of granules to PM and insulin exocytosis is enhanced.

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“…Although Munc18-1 was originally thought to be neuron-specific, its expression in other cell types, including mast cells, has been noted (41,56). In neurons, Munc18-1 is crucial for many of the steps leading to exocytosis (57), some but not all of which can be rescued by Munc18-2 expression (58), suggesting that although Munc18 homologs show some redundancy a degree of specificity is maintained.…”

Section: Discussionmentioning

confidence: 99%

Syntaxin binding mechanism and disease-causing mutations in Munc18-2

Hackmann

Graham

Ehl³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Significance Understanding the molecular mechanisms that control secretion from cytotoxic T lymphocytes (CTL) and natural killer (NK) cells is the key for understanding how these cells destroy virally infected and tumourigenic cells. Precisely how mutations in Munc18-2 and syntaxin 11 (Stx11) give rise to loss of CTL and NK function and severe immunodeficiency is poorly understood. In this study we present a crystal structure of human Munc18-2 and analyze the disease-causing mutations. Our findings reveal a mechanism that allows Munc18-2 to selectively bind Stx11 and identify potential surrogate binding partners, which could restore Munc18-Stx function upon IL-2 activation.

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Munc18-1 Regulates First-phase Insulin Release by Promoting Granule Docking to Multiple Syntaxin Isoforms

Cited by 69 publications

References 62 publications

Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells

Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells

Characterization of Phospholipids in Insulin Secretory Granules and Mitochondria in Pancreatic Beta Cells and Their Changes with Glucose Stimulation

Syntaxin binding mechanism and disease-causing mutations in Munc18-2

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