Stimulation of insulin secretion and associated nuclear accumulation of iPLA2β in INS-1 insulinoma cells

2002 ◽  
Vol 282 (4) ◽  
pp. E820-E833 ◽  
Author(s):  
Zhongmin Ma ◽  
Sheng Zhang ◽  
John Turk ◽  
Sasanka Ramanadham
Keyword(s):  
Insulin Secretion ◽  
Enzymatic Activity ◽  
Cytosolic Calcium ◽  
Nuclear Accumulation ◽  
Nuclear Fraction ◽  
Β Cells ◽  
Β Protein ◽  
Specific Enzymatic Activity ◽  
Insulinoma Cells ◽  
Stimulation Of

Accumulating evidence suggests that the cytosolic calcium-independent phospholipase A2 (iPLA2β) manifests a signaling role in insulin-secreting (INS-1) β-cells. Earlier, we reported that insulin-secretory responses to cAMP-elevating agents are amplified in iPLA2β-overexpressing INS-1 cells (Ma Z, Ramanadham S, Bohrer A, Wohltmann M, Zhang S, and Turk J. J Biol Chem276: 13198–13208, 2001). Here, immunofluorescence, immunoaffinity, and enzymatic activity analyses are used to examine distribution of iPLA2β in stimulated INS-1 cells in greater detail. Overexpression of iPLA2β in INS-1 cells leads to increased accumulation of iPLA2β in the nuclear fraction. Increasing glucose concentrations alone results in modest increases in insulin secretion, relative to parental cells, and in nuclear accumulation of the iPLA2β protein. In contrast, cAMP-elevating agents induce robust increases in insulin secretion and in time-dependent nuclear accumulation of iPLA2β fluorescence, which is reflected by increases in nuclear iPLA2β protein content and specific enzymatic activity. The stimulated effects are significantly attenuated in the presence of cell-permeable inhibitors of protein phosphorylation and glycosylation. These findings suggest that conditions that amplify insulin secretion promote translocation of β-cell iPLA2β to the nuclei, where it may serve a crucial signaling role.

scholarly journals Deficiency of VCP-Interacting Membrane Selenoprotein (VIMP) Leads to G1 Cell Cycle Arrest and Cell Death in MIN6 Insulinoma Cells

2018 ◽  
Vol 51 (5) ◽  
pp. 2185-2197 ◽  
Author(s):  
Lili Men ◽  
Juan Sun ◽  
Decheng Ren
Keyword(s):  
Cell Cycle ◽  
Cell Death ◽  
Insulin Secretion ◽  
Cell Apoptosis ◽  
Β Cells ◽  
Β Cell ◽  
Cycle Arrest ◽  
G1 Cell Cycle Arrest ◽  
Insulinoma Cells

Background/Aims: VCP-interacting membrane selenoprotein (VIMP), an ER resident selenoprotein, is highly expressed in β-cells, however, the role of VIMP in β-cells has not been characterized. In this study, we studied the relationship between VIMP deficiency and β-cell survival in MIN6 insulinoma cells. Methods: To determine the role of VIMP in β-cells, lentiviral VIMP shRNAs were used to knock down (KD) expression of VIMP in MIN6 cells. Cell death was quantified by propidium iodide (PI) staining followed by flow cytometric analyses using a FACS Caliber and FlowJo software. Cell apoptosis and proliferation were determined by TUNEL assay and Ki67 staining, respectively. Cell cycle was analyzed after PI staining. Results: The results show that 1) VIMP suppression induces β-cell apoptosis, which is associated with a decrease in Bcl-xL, and the β-cell apoptosis induced by VIMP suppression can be inhibited by overexpression of Bcl-xL; 2) VIMP knockdown (KD) decreases cell proliferation and G1 cell cycle arrest by accumulating p27 and decreasing E2F1; 3) VIMP KD suppresses unfolded protein response (UPR) activation by regulating the IRE1α and PERK pathways; 4) VIMP KD increases insulin secretion. Conclusion: These results suggest that VIMP may function as a novel regulator to modulate β-cell survival, proliferation, cell cycle, UPR and insulin secretion in MIN6 cells.

Direct effect of parathyroid hormone on insulin secretion from pancreatic islets

1990 ◽  
Vol 258 (6) ◽  
pp. E975-E984 ◽  
Author(s):  
G. Z. Fadda ◽  
M. Akmal ◽  
L. G. Lipson ◽  
S. G. Massry
Keyword(s):  
Insulin Secretion ◽  
Parathyroid Hormone ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Direct Effect ◽  
Indirect Evidence ◽  
Cytosolic Calcium ◽  
Dependent Manner ◽  
Stimulation Of

Indirect evidence indicates that parathyroid hormone (PTH) interacts with pancreatic islets and modulates their insulin secretion. This property of PTH has been implicated in the genesis of impaired insulin release in chronic renal failure. We examined the direct effect of PTH-(1-84) and PTH-(1-34) on insulin release using in vitro static incubation and dynamic perifusion of pancreatic islets from normal rats. Both moieties of the hormone stimulated in a dose-dependent manner glucose-induced insulin release but higher doses inhibited glucose-induced insulin release. This action of PTH was modulated by the calcium concentration in the media. The stimulatory effect of PTH was abolished by its inactivation and blocked by its antagonist [Tyr-34]bPTH-(7-34)NH2. PTH also augmented phorbol ester (TPA)-induced insulin release, stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation by pancreatic islets, and significantly increased (+50 +/- 2.7%, P less than 0.01) their cytosolic calcium. Verapamil inhibited the stimulatory effect of PTH on insulin release. The data show that 1) pancreatic islets are a PTH target and may have PTH receptors, 2) stimulation of glucose-induced insulin release by PTH is mediated by a rise in cytosolic calcium, 3) stimulation of cAMP production by PTH and a potential indirect activation of protein kinase C by PTH may also contribute to the stimulatory effect on glucose-induced insulin release, and 4) this action of PTH requires calcium in incubation or perifusion media.

scholarly journals Molecular Regulations and Functions of the Transient Receptor Potential Channels of the Islets of Langerhans and Insulinoma Cells

Cells ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 685 ◽  
Author(s):  
Md. Shahidul Islam
Keyword(s):  
Insulin Secretion ◽  
Electrical Activity ◽  
Islets Of Langerhans ◽  
Transient Receptor Potential ◽  
Trp Channels ◽  
Receptor Potential ◽  
Transient Receptor Potential Channels ◽  
Β Cells ◽  
Transient Receptor ◽  
Insulinoma Cells

Insulin secretion from the β-cells of the islets of Langerhans is triggered mainly by nutrients such as glucose, and incretin hormones such as glucagon-like peptide-1 (GLP-1). The mechanisms of the stimulus-secretion coupling involve the participation of the key enzymes that metabolize the nutrients, and numerous ion channels that mediate the electrical activity. Several members of the transient receptor potential (TRP) channels participate in the processes that mediate the electrical activities and Ca2+ oscillations in these cells. Human β-cells express TRPC1, TRPM2, TRPM3, TRPM4, TRPM7, TRPP1, TRPML1, and TRPML3 channels. Some of these channels have been reported to mediate background depolarizing currents, store-operated Ca2+ entry (SOCE), electrical activity, Ca2+ oscillations, gene transcription, cell-death, and insulin secretion in response to stimulation by glucose and GLP1. Different channels of the TRP family are regulated by one or more of the following mechanisms: activation of G protein-coupled receptors, the filling state of the endoplasmic reticulum Ca2+ store, heat, oxidative stress, or some second messengers. This review briefly compiles our current knowledge about the molecular mechanisms of regulations, and functions of the TRP channels in the β-cells, the α-cells, and some insulinoma cell lines.

scholarly journals Secretagogin affects insulin secretion in pancreatic β-cells by regulating actin dynamics and focal adhesion

2016 ◽  
Vol 473 (12) ◽  
pp. 1791-1803 ◽  
Author(s):  
Seo-Yun Yang ◽  
Jae-Jin Lee ◽  
Jin-Hee Lee ◽  
Kyungeun Lee ◽  
Seung Hoon Oh ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Focal Adhesion ◽  
Underlying Mechanism ◽  
Neuroendocrine Cells ◽  
Actin Dynamics ◽  
Second Phase ◽  
Dependent Manner ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulinoma Cells

Secretagogin (SCGN), a Ca2+-binding protein having six EF-hands, is selectively expressed in pancreatic β-cells and neuroendocrine cells. Previous studies suggested that SCGN enhances insulin secretion by functioning as a Ca2+-sensor protein, but the underlying mechanism has not been elucidated. The present study explored the mechanism by which SCGN enhances glucose-induced insulin secretion in NIT-1 insulinoma cells. To determine whether SCGN influences the first or second phase of insulin secretion, we examined how SCGN affects the kinetics of insulin secretion in NIT-1 cells. We found that silencing SCGN suppressed the second phase of insulin secretion induced by glucose and H2O2, but not the first phase induced by KCl stimulation. Recruitment of insulin granules in the second phase of insulin secretion was significantly impaired by knocking down SCGN in NIT-1 cells. In addition, we found that SCGN interacts with the actin cytoskeleton in the plasma membrane and regulates actin remodelling in a glucose-dependent manner. Since actin dynamics are known to regulate focal adhesion, a critical step in the second phase of insulin secretion, we examined the effect of silencing SCGN on focal adhesion molecules, including FAK (focal adhesion kinase) and paxillin, and the cell survival molecules ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt. We found that glucose- and H2O2-induced activation of FAK, paxillin, ERK1/2 and Akt was significantly blocked by silencing SCGN. We conclude that SCGN controls glucose-stimulated insulin secretion and thus may be useful in the therapy of Type 2 diabetes.

Potentiation of insulin secretion by phorbol esters is mediated by PKC-α and nPKC isoforms

2002 ◽  
Vol 283 (5) ◽  
pp. E880-E888 ◽  
Author(s):  
Gordon C. Yaney ◽  
Jamison M. Fairbanks ◽  
Jude T. Deeney ◽  
Helen M. Korchak ◽  
Keith Tornheim ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Membrane Potential ◽  
Phorbol Esters ◽  
Myristate Acetate ◽  
Β Cells ◽  
Kinase C ◽  
Pkc Isoforms ◽  
Enhanced Secretion ◽  
Intracellular Ca ◽  
Stimulation Of

Culturing clonal β-cells (HIT-T15) overnight in the presence of phorbol ester [phorbol myristate acetate (PMA)] enhanced insulin secretion while causing downregulation of some protein kinase C (PKC) isoforms and most PKC activity. We show here that this enhanced secretion required the retention of PMA in the cell. Hence, it could not be because of long-lived phosphorylation of cellular substrates by the isoforms that were downregulated, namely PKC-α, -βII, and -ε, but could be because of the continued activation of the two remaining diacylglycerol-sensitive isoforms δ and μ. The enhanced secretion did not involve changes in glucose metabolism, cell membrane potential, or intracellular Ca2+handling, suggesting a distal effect. PMA washout caused the loss of the enhanced response, but secretion was then stimulated by acute readdition of PMA or bombesin. The magnitude of this restimulation appeared dependent on the mass of PKC-α, which was rapidly resynthesized during PMA washout. Therefore, stimulation of insulin secretion by PMA, and presumably by endogenous diacylglycerol, involves the activation of PKC isoforms δ and/or μ, and also PKC-α.

Studies of the mechanism of amino acid-induced stimulation of insulin secretion from clonal pancreatic β-cells

2000 ◽  
Vol 28 (5) ◽  
pp. A196-A196
Author(s):  
A. Shine ◽  
N. H. Mc Clenaghan ◽  
P. Flatt ◽  
JPG Malthouse ◽  
C. Hewage ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Amino Acid ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Stimulation Of

Inhibition of connexin 36 hemichannels by glucose contributes to the stimulation of insulin secretion

2014 ◽  
Vol 306 (12) ◽  
pp. E1354-E1366 ◽  
Author(s):  
Javier Pizarro-Delgado ◽  
Ilaria Fasciani ◽  
Ana Temperan ◽  
María Romero ◽  
Daniel González-Nieto ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Gap Junction ◽  
Atp Release ◽  
Sugar Metabolism ◽  
Atp Content ◽  
Wild Type ◽  
Β Cells ◽  
Gap Junction Channels ◽  
Connexin 36 ◽  
Stimulation Of

The existence of functional connexin36 ( Cx36) hemichannels in β-cells was investigated in pancreatic islets of rat and wild-type ( Cx36+/+), monoallelic ( Cx36+/−), and biallelic ( Cx36−/−) knockout mice. Hemichannel opening by KCl depolarization was studied by measuring ATP release and changes of intracellular ATP (ADP). Cx36+/+ islets lost ATP after depolarization with 70 mM KCl at 5 mM glucose; ATP loss was prevented by 8 and 20 mM glucose or 50 μM mefloquine (connexin inhibitor). ATP content was higher in Cx36−/− than Cx36+/+ islets and was not decreased by KCl depolarization; Cx36+/− islets showed values between that of control and homozygous islets. Five minimolar extracellular ATP increased ATP content and ATP/ADP ratio and induced a biphasic insulin secretion in depolarized Cx36+/+ and Cx36+/− but not Cx36−/− islets. Cx36 hemichannels expressed in oocytes opened upon depolarization of membrane potential, and their activation was inhibited by mefloquine and glucose (IC50 ∼8 mM). It is postulated that glucose-induced inhibition of Cx36 hemichannels in islet β-cells might avoid depolarization-induced ATP loss, allowing an optimum increase of the ATP/ADP ratio by sugar metabolism and a biphasic stimulation of insulin secretion. Gradual suppression of glucose-induced insulin release in Cx36+/− and Cx36−/− islets confirms that Cx36 gap junction channels are necessary for a full secretory stimulation and might account for the glucose intolerance observed in mice with defective Cx36 expression. Mefloquine targeting of Cx36 on both gap junctions and hemichannels also suppresses glucose-stimulated secretion. By contrast, glucose stimulation of insulin secretion requires Cx36 hemichannels' closure but keeping gap junction channels opened.

scholarly journals Oxytocin signal contributes to the adaptative growth of islets during gestation

2021 ◽  
Author(s):  
Ping Gu ◽  
Yuege Lin ◽  
Qi Wan ◽  
Dongming Su ◽  
Qun Shu
Keyword(s):  
Insulin Secretion ◽  
Pregnant Women ◽  
Cell Function ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Cell Adaptation ◽  
Β Cell Function ◽  
Insulinoma Cells

Background: Increased insulin production and secretion by pancreatic β-cells are important for ensuring the high insulin demand during gestation. However, the underlying mechanism of β-cell adaptation during gestation or in gestational diabetes mellitus (GDM) remains unclear. Oxytocin is an important physiological hormone in gestation and delivery, and it also contributes to the maintenance of β-cell function. The aim of this study was to investigate the role of oxytocin in β-cell adaptation during pregnancy. Methods: The relationship between the blood oxytocin level and pancreatic β-cell function in patients with GDM and healthy pregnant women was investigated. Gestating and non-gestating mice were used to evaluate the in vivo effect of oxytocin signal on β-cells during pregnancy. In vitro experiments were performed on INS-1 insulinoma cells. Results: The blood oxytocin levels were lower in patients with GDM than in healthy pregnant women and were associated with impaired pancreatic β-cell function. Acute administration of oxytocin increased insulin secretion in both gestating and non-gestating mice. A three-week oxytocin treatment promoted the proliferation of pancreatic β-cells and increased the β-cell mass in gestating but not non-gestating mice. Antagonism of oxytocin receptors by atosiban impaired insulin secretion and induced GDM in gestating but not non-gestating mice. Oxytocin enhanced glucose-stimulated insulin secretion, activated the mitogen-activated protein kinase pathway, and promoted cell proliferation in INS-1 cells. Conclusions: These findings provide strong evidence that oxytocin is needed for β-cell adaptation during pregnancy to maintain β-cell function, and lack of oxytocin could be associated with the risk of GDM.

scholarly journals Chronic fructose renders pancreatic β-cells hyper-responsive to glucose-stimulated insulin secretion through extracellular ATP signaling

2019 ◽  
Vol 317 (1) ◽  
pp. E25-E41 ◽  
Author(s):  
Clarissa Bartley ◽  
Thierry Brun ◽  
Lucie Oberhauser ◽  
Mariagrazia Grimaldi ◽  
Filippo Molica ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Atp Release ◽  
Extracellular Atp ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Cellular Mechanisms ◽  
Kinase Activation ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells ◽  
Atp Signaling

Fructose is widely used as a sweetener in processed food and is also associated with metabolic disorders, such as obesity. However, the underlying cellular mechanisms remain unclear, in particular, regarding the pancreatic β-cell. Here, we investigated the effects of chronic exposure to fructose on the function of insulinoma cells and isolated mouse and human pancreatic islets. Although fructose per se did not acutely stimulate insulin exocytosis, our data show that chronic fructose rendered rodent and human β-cells hyper-responsive to intermediate physiological glucose concentrations. Fructose exposure reduced intracellular ATP levels without affecting mitochondrial function, induced AMP-activated protein kinase activation, and favored ATP release from the β-cells upon acute glucose stimulation. The resulting increase in extracellular ATP, mediated by pannexin1 (Panx1) channels, activated the calcium-mobilizer P2Y purinergic receptors. Immunodetection revealed the presence of both Panx1 channels and P2Y1 receptors in β-cells. Addition of an ectonucleotidase inhibitor or P2Y1 agonists to naïve β-cells potentiated insulin secretion stimulated by intermediate glucose, mimicking the fructose treatment. Conversely, the P2Y1 antagonist and Panx1 inhibitor reversed the effects of fructose, as confirmed using Panx1-null islets and by the clearance of extracellular ATP by apyrase. These results reveal an important function of ATP signaling in pancreatic β-cells mediating fructose-induced hyper-responsiveness.

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