Type 2 diabetes (T2D) is a heterogenous disease, and conventionally, peripheral insulin resistance (IR) was thought to precede islet β-cell dysfunction, promoting progression from prediabetes T2D. New evidence suggests that T2D-lean individuals experience early dysfunction without significant IR. Regardless of the primary event (i.e., IR vs. dysfunction) contributes dysglycemia, early-onset oxidative damage mitochondrial in multiple metabolic tissues may be driver T2D onset progression....

The small Rho family GTPases Cdc42 and Rac1 have each been shown to function in insulin exocytosis are presumed actin remodeling granule mobilization. However, whether either GTPase is required for the mobilization phase of release (second phase) linked a common signaling pathway has remained unknown. Here we demonstrate that interfering RNA-mediated depletion from isolated islets results selective loss second release. Consistent with role this nutrient-dependent phase, activation was...

The p21-activated kinase PAK1 is implicated in tumorigenesis, and efforts to inhibit signaling as a means induce tumor cell apoptosis are underway. However, has also been positive effector of mechanisms clonal pancreatic beta cells skeletal myotubes that would be crucial maintaining glucose homeostasis vivo. Of relevance, human islets Type 2 diabetic donors contained ∼80% less protein compared with non-diabetics, implicating islet signaling/scaffolding functions. Mimicking this, from PAK1−/−...

Glucose-induced insulin exocytosis is coupled to associations between F-actin and SNARE proteins, although the nature function of these interactions remains unknown. Toward this end we show here that both Syntaxin 1A 4 associated with in MIN6 cells each interaction was rapidly transiently diminished by stimulation d-glucose. Of two isoforms, only capable interacting directly an vitro sedimentation assay, conferred N-terminal 39-112 residues 4. The fragment selective competitive inhibitory...

How the Sec1/Munc18–syntaxin complex might transition to form SNARE core remains unclear. Toward this, Munc18c tyrosine phosphorylation has been correlated with its dissociation from syntaxin 4. Using 3T3-L1 adipocytes subjected small interfering ribonucleic acid reduction of as a model impaired insulin-stimulated GLUT4 vesicle exocytosis, we found that coordinate expression Munc18c–wild type or select phosphomimetic mutants, but not phosphodefective restored suggesting requirement for at...

The disruption of Munc18c binding to syntaxin 4 impairs insulin-stimulated GLUT4 vesicle translocation in 3T3L1 adipocytes. To investigate the physiological function and requirement for regulation glucose homeostasis vivo, we used homologous recombination generate Munc18c-knockout (KO) mice. Homozygotic gene resulted early embryonic lethality, whereas heterozygous KO mice (Munc18c−/+) had normal viability. Munc18c−/+ displayed significantly decreased insulin sensitivity an tolerance test a...

The widely expressed Sec/Munc18 (SM) protein Munc18c is required for SNARE-mediated insulin granule exocytosis from islet beta cells and GLUT4 vesicle in skeletal muscle adipocytes. Although function known to involve binding the t-SNARE Syntaxin 4, a paucity of Munc18c-binding proteins has restricted elucidation mechanism by which it facilitates these events. Toward this end, we have identified double C2 domain Doc2β as new partner Munc18c. Unlike its granule/vesicle localization neuronal...

OBJECTIVE The Sec1/Munc18 protein Munc18c has been implicated in Syntaxin 4–mediated exocytosis events, although its purpose remained elusive. Given that 4 functions the second phase of glucose-stimulated insulin secretion (GSIS), we hypothesized would also be required and sought insight into possible mechanism(s) using islet β-cell as a model system. RESEARCH DESIGN AND METHODS Perifusion analyses isolated Munc18c- (−/+) or Munc18c-depleted (RNAi) mouse islets were used to assess biphasic...

Glucose-stimulated insulin secretion is mediated by syntaxin 4-based SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes and the Sec1/Munc18 Munc18c. Our laboratory recently reported that Munc18c-syntaxin 4 are further regulated competitive binding of double C2 domain Doc2beta to Munc18c, although underlying mechanism for this unknown. Because region Munc18c contained residue Tyr-219 becomes phosphorylated in response glucose stimulation, we hypothesized...

Exocytosis of intracellular vesicles, such as insulin granules, is carried out by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) and Sec1/Munc18 (SM) proteins. An additional regulatory protein, Doc2b (double C2 domain), has recently been implicated in exocytosis from clonal β-cells 3T3-L1 adipocytes. Here, we investigated the role secretion, sensitivity, maintenance whole-body glucose homeostasis. heterozygous (Doc2b(+/-)) homozygous (Doc2b(-/-)) knockout mice...

Evidence suggests that dysfunctional β-cell insulin release precedes type 1 and 2 diabetes (T1D T2D, respectively) enhancing the efficiency of from pancreatic islet β-cells may delay/prevent these diseases. We took advantage rare opportunity to test this paradigm using islets human diabetic individuals.Insulin capacity is limited by abundance fusogenic soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Because enrichment Syntaxin 4, a plasma membrane...

Stimulus-induced tyrosine phosphorylation of Munc18c was investigated as a potential regulatory mechanism by which the Munc18c-Syntaxin 4 complex can be dissociated in response to divergent stimuli multiple cell types. Use [(32)P]orthophosphate incorporation, pervanadate treatment, and phosphotyrosine-specific antibodies demonstrated that underwent phosphorylation. Phosphorylation apparent under basal conditions, but levels were significantly increased within 5 min glucose stimulation MIN6...

Second-phase insulin release requires the sustained mobilization of granules from internal storage pools to cell surface for fusion with plasma membrane. However, detailed mechanisms underlying this process remain largely unknown. GTP-loading small GTPase Cdc42 is first glucose-specific activation step in process, although how glucose triggers entirely In a directed candidate screen guanine nucleotide exchange factors (GEFs), which directly activate GTPases, Cool-1/βPix was identified...

Abstract Mitochondrial dysfunction is implicated in skeletal muscle insulin resistance. Syntaxin 4 (STX4) levels are reduced human diabetic muscle, and global transgenic enrichment of STX4 expression improves sensitivity mice. Here, we show that muscle-specific (skmSTX4tg) mice reverses established resistance mitochondrial function the context diabetogenic stress. Specifically, skmSTX4tg reversed caused by high-fat diet (HFD) without altering body weight or food consumption. Electron...

The Drosophila raf (D-raf) gene promoter contains a recognition consensus sequence for STAT (D-STAT). By band mobility shift assay, we detected factor binding to the D-STAT-recognition in extracts of cultured cells treated with vanadate peroxide. UV-cross-linking analyses suggested size be almost same as that D-STAT. Furthermore, activity was increased cotransfected HOP and D-STAT expression plasmids. These results strongly suggest binds D-raf promoter. Transient luciferase assay using...

Skeletal muscle accounts for ~80% of insulin-stimulated glucose uptake. The Group I p21–activated kinase 1 (PAK1) is required the non-canonical GLUT4 vesicle translocation in skeletal cells. We found that abundances PAK1 protein and its downstream effector muscle, ARPC1B, are significantly reduced humans with type 2 diabetes, compared to non-diabetic controls, making a candidate regulator homeostasis. Although whole-body knockout mice exhibit intolerance insulin resistant, contribution...

Defects in soluble NSF attachment protein receptor (SNARE)-mediated granule exocytosis occur islet beta cells, adipocytes, and/or skeletal muscle cells correlate with increased susceptibility to insulin resistance and diabetes. The serine/threonine kinase WNK1 (with no K (lysine)) has recently been implicated is expressed all three of these cell types. To search for substrates related exocytosis, we conducted a two-hybrid screen, which yielded Munc18c. Munc18c known be key regulator...

Previous studies have shown that dexamethasone, a synthetic glucocorticoid, can induce G1 arrest, however, genistein, natural isoflavonoid phytoestrogen, induces G2/M arrest in the cell cycle progression various cancer lines. A block of checkpoint by dexamethasone and genistein correlates with selective induction cyclin-dependent kinase (Cdk) inhibitor p21WAF1/CIP1 tumor suppressor p53-independent manner abolishment Cdk2 phosphorylation. In present study, effects (both singly combined) on...