Overexpression of a Modified Human Malonyl-CoA Decarboxylase Blocks the Glucose-induced Increase in Malonyl-CoA Level but Has No Impact on Insulin Secretion in INS-1-derived (832/13) β-Cells

Mulder, Hindrik; Lu, Danhong; Finley, John K.; An, Jing; Cohen, Jonathan C.; Antinozzi, Peter A.; McGarry, Julie; Newgard, Christopher B.

doi:10.1074/jbc.m010364200

Cited by 84 publications

(97 citation statements)

References 26 publications

(47 reference statements)

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“…However, LC-CoA also stimulates K ATP channel activity in patch-clamped ␤-cells (44,45), an effect seemingly at odds with a role of LC-CoA as a glucose-derived stimulus/secretion coupling factor. Furthermore, prevention of the glucose-induced rise in malonyl-CoA levels by overexpression of malonyl-CoA decarboxylase has no impact on GSIS (33,46), a finding recently confirmed by the laboratory that developed the malonyl-CoA/LC-CoA hypothesis (47). Similarly, treatment of ␤-cells with Triacsin C, an inhibitor of LC-CoA synthetase, does not impair glucose responsiveness (33,46).…”

Section: Discussionsupporting

confidence: 50%

“…Furthermore, prevention of the glucose-induced rise in malonyl-CoA levels by overexpression of malonyl-CoA decarboxylase has no impact on GSIS (33,46), a finding recently confirmed by the laboratory that developed the malonyl-CoA/LC-CoA hypothesis (47). Similarly, treatment of ␤-cells with Triacsin C, an inhibitor of LC-CoA synthetase, does not impair glucose responsiveness (33,46). In a modification of the original hypothesis, it has recently been suggested that malonyl-CoA/ LC-CoA might be important for the potentiating effect of fatty acids on GSIS, since experiments with triacsin C and malonylCoA decarboxylase overexpression diminished this action of fatty acids in ␤-cell lines and rat islets (47), although different results were obtained by another laboratory with malonyl-CoA decarboxylase (46).…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, treatment of ␤-cells with Triacsin C, an inhibitor of LC-CoA synthetase, does not impair glucose responsiveness (33,46). In a modification of the original hypothesis, it has recently been suggested that malonyl-CoA/ LC-CoA might be important for the potentiating effect of fatty acids on GSIS, since experiments with triacsin C and malonylCoA decarboxylase overexpression diminished this action of fatty acids in ␤-cell lines and rat islets (47), although different results were obtained by another laboratory with malonyl-CoA decarboxylase (46). Overall, there is now a consistent lack of evidence for a direct role of malonyl-CoA in regulation of GSIS, whereas its potential role in lipid-mediated potentiation of GSIS remains an open question.…”

Section: Discussionmentioning

confidence: 99%

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The Mitochondrial Citrate/Isocitrate Carrier Plays a Regulatory Role in Glucose-stimulated Insulin Secretion

Joseph

Jensen

Ilkayeva

et al. 2006

Journal of Biological Chemistry

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157

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Glucose-stimulated insulin secretion (GSIS) is mediated in part by glucose metabolism-driven increases in ATP/ADP ratio, but by-products of mitochondrial glucose metabolism also play an important role. Here we investigate the role of the mitochondrial citrate/isocitrate carrier (CIC) in regulation of GSIS. Inhibition of CIC activity in INS-1-derived 832/13 cells or primary rat islets by the substrate analogue 1,2,3-benzenetricarboxylate (BTC) resulted in potent inhibition of GSIS, involving both first and second phase secretion. A recombinant adenovirus containing a CIC-specific siRNA (Ad-siCIC) dose-dependently reduced CIC expression in 832/13 cells and caused parallel inhibitory effects on citrate accumulation in the cytosol. Ad-siCIC treatment did not affect glucose utilization, glucose oxidation, or ATP/ADP ratio but did inhibit glucose incorporation into fatty acids and glucose-induced increases in NADPH/NADP ؉ ratio relative to cells treated with a control siRNA virus (Ad-siControl). Ad-siCIC also inhibited GSIS in 832/13 cells, whereas overexpression of CIC enhanced GSIS and raised cytosolic citrate levels. In normal rat islets, Ad-siCIC treatment also suppressed CIC mRNA levels and inhibited GSIS. We conclude that export of citrate and/or isocitrate from the mitochondria to the cytosol is an important step in control of GSIS.The mechanism of glucose-stimulated insulin secretion (GSIS) 2 from pancreatic islet ␤-cells is not completely understood. One component of the signaling pathway involves glucose-induced increases in cytosolic ATP/ADP ratio, leading to closure of K ATP channels at the plasma membrane. K ATP channel closure results in membrane depolarization and activation of voltage-dependent Ca 2ϩ channels, increasing the concentration of cytosolic Ca 2ϩ (1-4). Elevation of cytosolic Ca 2ϩ promotes exocytosis of insulin-containing secretory granules (5). However, fluctuations in cytosolic Ca 2ϩ are not the only signal, because under conditions of clamped cytosolic Ca 2ϩ concentrations, glucose can still cause significant insulin secretion (6). This suggests that glucose generates signals/second messengers that are distinct from ATP and membrane depolarization for regulation of insulin secretion (7,8). Some of the suggested mitochondrial factors include glutamate, malonyl-CoA, longchain acyl-CoAs (LC-CoA), and/or NADPH (7-17).The production of malonyl-CoA, LC-CoA, and NADPH in the cytosol depends on the export of mitochondrial metabolites. NADPH can be produced via one of three pyruvate cycling pathways, the pyruvate/malate pathway, the pyruvate/citrate pathway, or the pyruvate/isocitrate pathway, via cytosolic NADP ϩ -dependent isoforms of malic enzyme (used in the pyruvate/malate and pyruvate/citrate pathways) or cytosolic, NADP ϩ -dependent isocitrate dehydrogenase (ICDc) (used in the pyruvate/isocitrate cycle) (18,19). Citrate emanating from mitochondrial metabolism can also be cleaved by ATP-citrate lyase to produce malonyl-CoA and LC-CoA (19). We and others have previously established that anap...

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Section: Discussionsupporting

confidence: 50%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The Mitochondrial Citrate/Isocitrate Carrier Plays a Regulatory Role in Glucose-stimulated Insulin Secretion

Joseph

Jensen

Ilkayeva

et al. 2006

Journal of Biological Chemistry

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157

215

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“…Human C-peptide (synthesized from a human proinsulin cDNA) is packaged in an identical fashion to mouse C-peptide and insulin in granules, but is immunologically distinct from mouse endogenous C-peptide and serves as a reporter from transfected cells. MIN6 cells cotransfected with pcDNA3 control DNA plus human pro- insulin DNA exhibited 160 Ϯ 5.2% (p Ͻ 0.005) of basal human C-peptide secretion in response to glucose, an appropriate increase in human C-peptide secretion in response to glucose in this assay system (55,56). In contrast, overexpression of Munc18c-WT or Munc18c-Y219F reduced glucose-stimulated secretion to 115 and 121% of the basal level, respectively (Fig.…”

Section: Tyr 219 Confers Glucose-induced Phosphorylation To Munc18c-bmentioning

confidence: 96%

The Stimulus-induced Tyrosine Phosphorylation of Munc18c Facilitates Vesicle Exocytosis

Thurmond

2006

Journal of Biological Chemistry

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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 in multiple cell types. Use of [ 32 P]orthophosphate incorporation, pervanadate treatment, and phosphotyrosine-specific antibodies demonstrated that Munc18c underwent tyrosine phosphorylation. Phosphorylation was apparent under basal conditions, but levels were significantly increased within 5 min of glucose stimulation in MIN6 beta cells. Tyrosine phosphorylation of Munc18c was also detected in 3T3L1 adipocytes and increased with insulin stimulation, suggesting that this may be a conserved mechanism. Syntaxin 4 binding to Munc18c decreased as Munc18c phosphorylation levels increased in pervanadate-treated cells, suggesting that phosphorylation dissociates the Munc18c-Syntaxin 4 complex. Munc18c phosphorylation was localized to the N-terminal 255 residues. Mutagenesis of one residue in this region, Y219F, significantly increased the affinity of Munc18c for Syntaxin 4, whereas mutation of three other candidate sites was without effect. Moreover, Munc18c-Y219F expression in MIN6 cells functionally inhibited glucose-stimulated SNARE complex formation and insulin granule exocytosis. These data support a novel and conserved mechanism for the dissociation of Munc18c-Syntaxin 4 complexes in a stimulus-dependent manner to facilitate the increase in Syntaxin 4-VAMP2 association and to promote vesicle/granule fusion.In the early 1990s, the discovery of soluble N-ethylmaleimidesensitive factor attachment protein receptor (SNARE) 2 proteins elucidated the molecular basis for synaptic vesicle exocytosis (1, 2). Vesicle exocytosis entails the pairing of a vesicle-associated membrane protein (VAMP) SNARE with a binary cognate receptor complex at the target membrane composed of SNAP-25/23 and syntaxin proteins (target SNAREs) to form the SNARE core complex (3-7). Shortly thereafter, SNARE protein complexes were identified and found to regulate secretory processes in many diverse cell types ranging from yeast and Caenorhabditis elegans to humans, which has led to the general concept that most types of regulated vesicle fusion occur by a common mechanism.Concurrent with the discovery of SNARE proteins was the discovery of the yeast Sec1 secretory protein, which was found to interact directly with the target SNARE syntaxin (8). Homologs in C. elegans (UNC-18), Drosophila melanogaster (ROP), and mammalian cells (Munc18a-c) were also identified (9 -13). Collectively, the Sec1 and Munc18 protein families are now referred to as "SM" proteins for Sec1 and Munc18. Munc18 proteins are ϳ66 -68 kDa in size and are soluble factors with no transmembrane domain (14). They are found localized to the cytosol and also to the plasma membrane through high affinity binding to their cognate syntaxin (15, 16). Munc18a (also known as Munc18-1/neural Sec1/rat brain Sec1) was demonstrated to interact with Syntaxin 1 in a manner mutually exclusive of the other...

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“…However, the kinetics of insulin release and of proinsulin biosynthesis, and the metabolic signals mediating these processes, are not identical [3,8]. In fact, the role of various glycolytic and TCA cycle intermediates in glucose-stimulated insulin secretion is controversial [7,[9][10][11][12][13][14][15][16], and even less is known about the metabolic signals for glucose-stimulated insulin production. A previous report by Alarcon et al suggested that succinate is the key signal for glucose stimulation of preproinsulin mRNA translation [3].…”

Section: Introductionmentioning

confidence: 99%

Mitochondrial regulation of insulin production in rat pancreatic islets

Leibowitz

Khaldi²,

Shauer

et al. 2005

Diabetologia

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Aims/hypothesis: The study was designed to identify the key metabolic signals of glucose-stimulated proinsulin gene transcription and translation, focusing on the mechanism of succinate stimulation of insulin production. Methods: Wistar rat islets were incubated in 3.3 mmol/l glucose with and without esters of different mitochondrial metabolites or with 16.7 mmol/l glucose. Proinsulin biosynthesis was analysed by tritiated leucine incorporation into newly synthesised proinsulin. Preproinsulin gene transcription was evaluated following transduction with adenoviral vectors expressing the luciferase reporter gene under the control of the rat I preproinsulin promoter. Steady-state preproinsulin mRNA was determined using relative quantitative PCR. The mitochondrial membrane potential was measured by microspectrofluorimetry using rhodamine-123. Results: Succinic acid monomethyl ester, but not other mitochondrial metabolites, stimulated preproinsulin gene transcription and translation. Similarly to glucose, succinate increased specific preproinsulin gene transcription and biosynthesis. The inhibitor of succinate dehydrogenase (SDH), 3-nitropropionate, abolished glucose-and succinate-stimulated mitochondrial membrane hyperpolarisation and proinsulin biosynthesis, indicating that stimulation of proinsulin translation depends on SDH activity. Partial inhibition of SDH activity by exposure to fumaric acid monomethyl ester abolished the stimulation of preproinsulin gene transcription, but only partially inhibited the stimulation of proinsulin biosynthesis by glucose and succinate, suggesting that SDH activity is particularly important for the transcriptional response to glucose. Conclusions/interpretation: Succinate is a key metabolic mediator of glucose-stimulated preproinsulin gene transcription and translation. Moreover, succinate stimulation of insulin production depends on its metabolism via SDH. The differential effect of fumarate on preproinsulin gene transcription and translation suggests that these processes have different sensitivities to metabolic signals.

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Overexpression of a Modified Human Malonyl-CoA Decarboxylase Blocks the Glucose-induced Increase in Malonyl-CoA Level but Has No Impact on Insulin Secretion in INS-1-derived (832/13) β-Cells

Cited by 84 publications

References 26 publications

The Mitochondrial Citrate/Isocitrate Carrier Plays a Regulatory Role in Glucose-stimulated Insulin Secretion

The Mitochondrial Citrate/Isocitrate Carrier Plays a Regulatory Role in Glucose-stimulated Insulin Secretion

The Stimulus-induced Tyrosine Phosphorylation of Munc18c Facilitates Vesicle Exocytosis

Mitochondrial regulation of insulin production in rat pancreatic islets

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