Publications by authors named "Accalia Fu"

19 Publications

  • Page 1 of 1

Glucose metabolism and pyruvate carboxylase enhance glutathione synthesis and restrict oxidative stress in pancreatic islets.

Cell Rep 2021 Nov;37(8):110037

Department of Cancer Biology, Dana-Farber Cancer Institute, 450 Brookline Ave., Boston, MA 02115, USA; Department of Medical Oncology, Dana-Farber Cancer Institute, Boston 02115, MA, USA; Department of Medicine, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA. Electronic address:

Glucose metabolism modulates the islet β cell responses to diabetogenic stress, including inflammation. Here, we probed the metabolic mechanisms that underlie the protective effect of glucose in inflammation by interrogating the metabolite profiles of primary islets from human donors and identified de novo glutathione synthesis as a prominent glucose-driven pro-survival pathway. We find that pyruvate carboxylase is required for glutathione synthesis in islets and promotes their antioxidant capacity to counter inflammation and nitrosative stress. Loss- and gain-of-function studies indicate that pyruvate carboxylase is necessary and sufficient to mediate the metabolic input from glucose into glutathione synthesis and the oxidative stress response. Altered redox metabolism and cellular capacity to replenish glutathione pools are relevant in multiple pathologies beyond obesity and diabetes. Our findings reveal a direct interplay between glucose metabolism and glutathione biosynthesis via pyruvate carboxylase. This metabolic axis may also have implications in other settings where sustaining glutathione is essential.
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http://dx.doi.org/10.1016/j.celrep.2021.110037DOI Listing
November 2021

UCP1 governs liver extracellular succinate and inflammatory pathogenesis.

Nat Metab 2021 05 17;3(5):604-617. Epub 2021 May 17.

Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA.

Non-alcoholic fatty liver disease (NAFLD), the most prevalent liver pathology worldwide, is intimately linked with obesity and type 2 diabetes. Liver inflammation is a hallmark of NAFLD and is thought to contribute to tissue fibrosis and disease pathogenesis. Uncoupling protein 1 (UCP1) is exclusively expressed in brown and beige adipocytes, and has been extensively studied for its capacity to elevate thermogenesis and reverse obesity. Here we identify an endocrine pathway regulated by UCP1 that antagonizes liver inflammation and pathology, independent of effects on obesity. We show that, without UCP1, brown and beige fat exhibit a diminished capacity to clear succinate from the circulation. Moreover, UCP1KO mice exhibit elevated extracellular succinate in liver tissue that drives inflammation through ligation of its cognate receptor succinate receptor 1 (SUCNR1) in liver-resident stellate cell and macrophage populations. Conversely, increasing brown and beige adipocyte content in mice antagonizes SUCNR1-dependent inflammatory signalling in the liver. We show that this UCP1-succinate-SUCNR1 axis is necessary to regulate liver immune cell infiltration and pathology, and systemic glucose intolerance in an obesogenic environment. As such, the therapeutic use of brown and beige adipocytes and UCP1 extends beyond thermogenesis and may be leveraged to antagonize NAFLD and SUCNR1-dependent liver inflammation.
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http://dx.doi.org/10.1038/s42255-021-00389-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8207988PMC
May 2021

CRISPR-engineered human brown-like adipocytes prevent diet-induced obesity and ameliorate metabolic syndrome in mice.

Sci Transl Med 2020 08;12(558)

Section on Integrative Physiology and Metabolism, Joslin Diabetes Center, Harvard Medical School, Boston, MA 02215, USA.

Brown and brown-like beige/brite adipocytes dissipate energy and have been proposed as therapeutic targets to combat metabolic disorders. However, the therapeutic effects of cell-based therapy in humans remain unclear. Here, we created human brown-like (HUMBLE) cells by engineering human white preadipocytes using CRISPR-Cas9-SAM-gRNA to activate endogenous uncoupling protein 1 expression. Obese mice that received HUMBLE cell transplants showed a sustained improvement in glucose tolerance and insulin sensitivity, as well as increased energy expenditure. Mechanistically, increased arginine/nitric oxide (NO) metabolism in HUMBLE adipocytes promoted the production of NO that was carried by -nitrosothiols and nitrite in red blood cells to activate endogenous brown fat and improved glucose homeostasis in recipient animals. Together, these data demonstrate the utility of using CRISPR-Cas9 technology to engineer human white adipocytes to display brown fat-like phenotypes and may open up cell-based therapeutic opportunities to combat obesity and diabetes.
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http://dx.doi.org/10.1126/scitranslmed.aaz8664DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7704293PMC
August 2020

Glucose-dependent partitioning of arginine to the urea cycle protects β-cells from inflammation.

Nat Metab 2020 05 11;2(5):432-446. Epub 2020 May 11.

Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA.

Chronic inflammation is linked to diverse disease processes, but the intrinsic mechanisms that determine cellular sensitivity to inflammation are incompletely understood. Here, we show the contribution of glucose metabolism to inflammation-induced changes in the survival of pancreatic islet β-cells. Using metabolomic, biochemical and functional analyses, we investigate the protective versus non-protective effects of glucose in the presence of pro-inflammatory cytokines. When protective, glucose metabolism augments anaplerotic input into the TCA cycle via pyruvate carboxylase (PC) activity, leading to increased aspartate levels. This metabolic mechanism supports the argininosuccinate shunt, which fuels ureagenesis from arginine and conversely diminishes arginine utilization for production of nitric oxide (NO), a chief mediator of inflammatory cytotoxicity. Activation of the PC-urea cycle axis is sufficient to suppress NO synthesis and shield cells from death in the context of inflammation and other stress paradigms. Overall, these studies uncover a previously unappreciated link between glucose metabolism and arginine-utilizing pathways via PC-directed ureagenesis as a protective mechanism.
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http://dx.doi.org/10.1038/s42255-020-0199-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7568475PMC
May 2020

Hydrocarbon-Stitched Peptide Agonists of Glucagon-Like Peptide-1 Receptor.

ACS Chem Biol 2020 06 27;15(6):1340-1348. Epub 2020 May 27.

Department of Pediatric Oncology, Dana-Farber Cancer Institute, 450 Brookline Avenue, Boston, Massachusetts 02215, United States.

Glucagon-like peptide 1 (GLP-1) is a natural peptide agonist of the GLP-1 receptor (GLP-1R) found on pancreatic β-cells. Engagement of the receptor stimulates insulin release in a glucose-dependent fashion and increases β-cell mass, two ideal features for pharmacologic management of type 2 diabetes. Thus, intensive efforts have focused on developing GLP-1-based peptide agonists of GLP-1R for therapeutic application. A primary challenge has been the naturally short half-life of GLP-1 due to its rapid proteolytic degradation . Whereas mutagenesis and lipidation strategies have yielded clinical agents, we developed an alternative approach to preserving the structure and function of GLP-1 by all-hydrocarbon , + 7 stitching. This particular "stitch" is especially well-suited for reinforcing and protecting the structural fidelity of GLP-1. Lead constructs demonstrate striking proteolytic stability and potent biological activity . Thus, we report a facile approach to generating alternative GLP-1R agonists for glycemic control.
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http://dx.doi.org/10.1021/acschembio.0c00308DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7366314PMC
June 2020

Grasping for aspartate in tumour metabolism.

Nat Cell Biol 2018 07;20(7):738-739

Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.

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http://dx.doi.org/10.1038/s41556-018-0137-9DOI Listing
July 2018

High-throughput Functional Genomics Identifies Regulators of Primary Human Beta Cell Proliferation.

J Biol Chem 2016 Feb 6;291(9):4614-25. Epub 2016 Jan 6.

the Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, the Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada

The expansion of cells for regenerative therapy will require the genetic dissection of complex regulatory mechanisms governing the proliferation of non-transformed human cells. Here, we report the development of a high-throughput RNAi screening strategy specifically for use in primary cells and demonstrate that silencing the cell cycle-dependent kinase inhibitors CDKN2C/p18 or CDKN1A/p21 facilitates cell cycle entry of quiescent adult human pancreatic beta cells. This work identifies p18 and p21 as novel targets for promoting proliferation of human beta cells and demonstrates the promise of functional genetic screens for dissecting therapeutically relevant state changes in primary human cells.
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http://dx.doi.org/10.1074/jbc.M115.683912DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4813485PMC
February 2016

A Northern contaminant mixture impairs pancreas function in obese and lean JCR rats and inhibits insulin secretion in MIN6 cells.

Toxicology 2015 Aug 9;334:81-93. Epub 2015 Jun 9.

Regulatory Toxicology Research Division, Bureau of Chemical Safety, Food Directorate, Health Canada, 251 Sir Frederick Banting Driveway, Ottawa, Ontario K1A 0K9, Canada. Electronic address:

Rates of obesity and diabetes mellitus of Arctic populations are increasing due to multiple reasons including a departure from traditional lifestyles and alcohol consumption patterns. These populations are also exposed to a variety of anthropogenic contaminants through consumption of contaminated country foods. We have previously shown that a Northern contaminant mixture (NCM), containing 22 organic and inorganic contaminants found in the blood of Canadian Arctic populations, induces endothelial cell dysfunction and exacerbates development of non-alcoholic fatty liver disease in experimental models. In order to determine if these contaminants affect pancreas function and physiology and if obesity and alcohol can influence contaminant toxicity and the development of diabetes, lean and obese JCR rats were orally treated with NCM at 0 (vehicle), 1.6 or 16mg/kg BW for four weeks in the presence or absence of 10% (v/v) alcohol. NCM treatment altered islet morphology, increased iron deposit in pancreas, and reduced circulating and pancreatic insulin levels and circulating glucagon levels as a result of direct islet injury with β and α cell loss with or without exposure to alcohol. Studies conducted with cultured mouse insulin-secreting (MIN6) β cells further demonstrated that NCM inhibited insulin release and induced cell death through oxidative stress and mitochondrial dysfunction. 2,3,4,6-Tetrabromophenol, a minor component of the NCM, alone also inhibited insulin release from MIN6 cells after 10min of exposure. These results suggest that Northern contaminants may contribute to pancreatic dysfunction, and possibly development of diabetes, in some of the highly exposed Arctic populations. The implications and relevance of these findings to Northern populations remains to be confirmed through epidemiological studies.
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http://dx.doi.org/10.1016/j.tox.2015.06.001DOI Listing
August 2015

LKB1 couples glucose metabolism to insulin secretion in mice.

Diabetologia 2015 Jul 16;58(7):1513-22. Epub 2015 Apr 16.

Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, K1H 8L1, Canada.

Aims/hypothesis: Precise regulation of insulin secretion by the pancreatic beta cell is essential for the maintenance of glucose homeostasis. Insulin secretory activity is initiated by the stepwise breakdown of ambient glucose to increase cellular ATP via glycolysis and mitochondrial respiration. Knockout of Lkb1, the gene encoding liver kinase B1 (LKB1) from the beta cell in mice enhances insulin secretory activity by an undefined mechanism. Here, we sought to determine the molecular basis for how deletion of Lkb1 promotes insulin secretion.

Methods: To explore the role of LKB1 on individual steps in the insulin secretion pathway, we used mitochondrial functional analyses, electrophysiology and metabolic tracing coupled with by gas chromatography and mass spectrometry.

Results: Beta cells lacking LKB1 surprisingly display impaired mitochondrial metabolism and lower ATP levels following glucose stimulation, yet compensate for this by upregulating both uptake and synthesis of glutamine, leading to increased production of citrate. Furthermore, under low glucose conditions, Lkb1(-/-) beta cells fail to inhibit acetyl-CoA carboxylase 1 (ACC1), the rate-limiting enzyme in lipid synthesis, and consequently accumulate NEFA and display increased membrane excitability.

Conclusions/interpretation: Taken together, our data show that LKB1 plays a critical role in coupling glucose metabolism to insulin secretion, and factors in addition to ATP act as coupling intermediates between feeding cues and secretion. Our data suggest that beta cells lacking LKB1 could be used as a system to identify additional molecular events that connect metabolism to cellular excitation in the insulin secretion pathway.
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http://dx.doi.org/10.1007/s00125-015-3579-7DOI Listing
July 2015

Phospho-BAD BH3 mimicry protects β cells and restores functional β cell mass in diabetes.

Cell Rep 2015 Feb 29;10(4):497-504. Epub 2015 Jan 29.

Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. Electronic address:

Strategies that simultaneously enhance the survival and glucose responsiveness of insulin-producing β cells will greatly augment β cell replacement therapies in type 1 diabetes (T1D). We show that genetic and pharmacologic mimetics of the phosphorylated BCL-2 homology 3 (BH3) domain of BAD impart β-cell-autonomous protective effects in the face of stress stimuli relevant to β cell demise in T1D. Importantly, these benefits translate into improved engraftment of donor islets in transplanted diabetic mice, increased β cell viability in islet grafts, restoration of insulin release, and diabetes reversal. Survival of β cells in this setting is not merely due to the inability of phospho-BAD to suppress prosurvival BCL-2 proteins but requires its activation of the glucose-metabolizing enzyme glucokinase. Thus, BAD phospho-BH3 mimetics may prove useful in the restoration of functional β cell mass in diabetes.
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http://dx.doi.org/10.1016/j.celrep.2014.12.056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991214PMC
February 2015

Role of the SIK2-p35-PJA2 complex in pancreatic β-cell functional compensation.

Nat Cell Biol 2014 Mar;16(3):234-44

Energy sensing by the AMP-activated protein kinase (AMPK) is of fundamental importance in cell biology. In the pancreatic β-cell, AMPK is a central regulator of insulin secretion. The capacity of the β-cell to increase insulin output is a critical compensatory mechanism in prediabetes, yet its molecular underpinnings are unclear. Here we delineate a complex consisting of the AMPK-related kinase SIK2, the CDK5 activator CDK5R1 (also known as p35) and the E3 ligase PJA2 essential for β-cell functional compensation. Following glucose stimulation, SIK2 phosphorylates p35 at Ser 91, to trigger its ubiquitylation by PJA2 and promote insulin secretion. Furthermore, SIK2 accumulates in β-cells in models of metabolic syndrome to permit compensatory secretion; in contrast, β-cell knockout of SIK2 leads to accumulation of p35 and impaired secretion. This work demonstrates that the SIK2-p35-PJA2 complex is essential for glucose homeostasis and provides a link between p35-CDK5 and the AMPK family in excitable cells.
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http://dx.doi.org/10.1038/ncb2919DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107453PMC
March 2014

CRTC2 is required for β-cell function and proliferation.

Endocrinology 2013 Jul 15;154(7):2308-17. Epub 2013 May 15.

Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada.

Previous work in insulinoma cell lines has established that calcineurin plays a critical role in the activation of cAMP-responsive element binding protein (Creb), a key transcription factor required for β-cell function and survival, by dephosphorylating the Creb coactivator Creb-regulated transcription coactivator (Crtc)2 at 2 regulatory sites, Ser171 and Ser275. Here, we report that Crtc2 is essential both for glucose-stimulated insulin secretion and cell survival in the β-cell. Endogenous Crtc2 activation is achieved via increasing glucose levels to the physiological feeding range, indicating that Crtc2 is a sensor that couples ambient glucose concentrations to Creb activity in the β-cell. Immunosuppressant drugs such as cyclosporin A and tacrolimus that target the protein phosphatase calcineurin are commonly administered after organ transplantation. Chronic use is associated with reduced insulin secretion and new onset diabetes, suggestive of pancreatic β-cell dysfunction. Importantly, we show that overexpression of a Crtc2 mutant rendered constitutively active by introduction of nonphosphorylatable alanine residues at Ser171 and Ser275 permits Creb target gene activation under conditions when calcineurin is inhibited. Taken together, these data suggest that promoting Crtc2-Creb activity is required for β-cell function and proliferation and promoting this pathway could ameliorate symptoms of new onset diabetes after transplantation.
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http://dx.doi.org/10.1210/en.2012-2088DOI Listing
July 2013

Glutathionylation state of uncoupling protein-2 and the control of glucose-stimulated insulin secretion.

J Biol Chem 2012 Nov 3;287(47):39673-85. Epub 2012 Oct 3.

Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5.

The role of reactive oxygen species (ROS) in glucose-stimulated insulin release remains controversial because ROS have been shown to both amplify and impede insulin release. In regard to preventing insulin release, ROS activates uncoupling protein-2 (UCP2), a mitochondrial inner membrane protein that negatively regulates glucose-stimulated insulin secretion (GSIS) by uncoupling oxidative phosphorylation. With our recent discovery that the UCP2-mediated proton leak is modulated by reversible glutathionylation, a process responsive to small changes in ROS levels, we resolved to determine whether glutathionylation is required for UCP2 regulation of GSIS. Using Min6 cells and pancreatic islets, we demonstrate that induction of glutathionylation not only deactivates UCP2-mediated proton leak but also enhances GSIS. Conversely, an increase in mitochondrial matrix ROS was found to deglutathionylate and activate UCP2 leak and impede GSIS. Glucose metabolism also decreased the total amount of cellular glutathionylated proteins and increased the cellular glutathione redox ratio (GSH/GSSG). Intriguingly, the provision of extracellular ROS (H(2)O(2), 10 μM) amplified GSIS and also activated UCP2. Collectively, our findings indicate that the glutathionylation status of UCP2 contributes to the regulation of GSIS, and different cellular sites and inducers of ROS can have opposing effects on GSIS, perhaps explaining some of the controversy surrounding the role of ROS in GSIS.
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http://dx.doi.org/10.1074/jbc.M112.393538DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3501076PMC
November 2012

Role of AMPK in pancreatic beta cell function.

Mol Cell Endocrinol 2013 Feb 3;366(2):127-34. Epub 2012 Jul 3.

Children's Hospital of Eastern Ontario Research Institute, Ottawa, Canada.

Pharmacological activation of AMP activated kinase (AMPK) by metformin has proven to be a beneficial therapeutic approach for the treatment of type II diabetes. Despite improved glucose regulation achieved by administration of small molecule activators of AMPK, the potential negative impact of enhanced AMPK activity on insulin secretion by the pancreatic beta cell is an important consideration. In this review, we discuss our current understanding of the role of AMPK in central functions of the pancreatic beta cell, including glucose-stimulated insulin secretion (GSIS), proliferation, and survival. In addition we discuss the controversy surrounding the role of AMPK in insulin secretion, underscoring the merits and caveats of methods used to date.
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http://dx.doi.org/10.1016/j.mce.2012.06.020DOI Listing
February 2013

Regulation of the CREB coactivator TORC by the dual leucine zipper kinase at different levels.

Cell Signal 2011 Feb 19;23(2):344-53. Epub 2010 Oct 19.

Department of Pharmacology, University of Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany.

CREB is a ubiquitously expressed transcription factor regulating gene expression via binding to a CRE DNA element. Previous work showed that the dual leucine zipper kinase (DLK) reduced CREB-dependent gene transcription at least in part via inhibition of the coactivator CBP. Here we demonstrate that DLK also inhibits CREB activity by affecting the interaction of CREB with its second coactivator TORC. DLK acted on TORC-dependent transcription by distinct mechanisms. An interaction between DLK and all three TORC isoforms was demonstrated by in vitro protein-protein interaction assays and in cells by coimmunoprecipitation that required the N-terminus of TORC and the leucine zipper of dimerized DLK. Overexpressed DLK induced the phosphorylation of TORC2 and TORC1 on Ser-171 and 167, respectively and on additional residues. Since a kinase-dead DLK mutant did not prevent the nuclear localization of TORC and did not reduce TORC transcriptional activity to the same extent as wild-type DLK, we suggest that DLK-induced phosphorylation of TORC contributes to DLK's inhibitory action. Both the interaction with and the phosphorylation of TORC by DLK might account for the reduced recruitment of TORC to a CRE containing promoter as revealed by chromatin immunoprecipitation assay. These results show for the first time the inhibition of TORC function by a mitogen-activated kinase. Given the dependence on TORC in CREB-directed gene transcription, DLK and its downstream kinases thus contribute to the finely tuned regulation of CREB-dependent effects.
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http://dx.doi.org/10.1016/j.cellsig.2010.10.001DOI Listing
February 2011

Depletion of intranuclear rodlets in mouse models of diabetes.

Endocr Pathol 2010 Dec;21(4):230-5

Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario, Canada.

Intranuclear rodlets (INRs) are structures present within the nuclei of human insulin-secreting beta cells of the endocrine pancreas. Their physiological significance, and whether they are altered in disease, is unknown. In the present study, the proportion of pancreatic beta cells containing INRs was examined in mouse models of type II diabetes and in a model with improved beta cell function. To gain insights into the molecular regulators of INR formation, mice with a conditional adult beta cell-specific knockout of the serine/threonine protein kinase Lkb1 (Lkb1 adult beta cell knockout (LABKO) mice) were studied. To investigate INR changes in a pathophysiological context, beta cell INRs were examined in two models of human metabolic syndrome: (1) mice maintained on a high-fat diet and (2) leptin-deficient ob/ob mice. The proportion of beta cells containing INRs was significantly reduced in LABKO mice. This reduction was not mediated by two key downstream effectors of Lkb1, mTor and Mark2. High-fat diet regimen reduced beta cell INR frequency by more than 40%, and leptin-deficient ob/ob mice exhibited a dramatically (19-fold) reduced INR frequency relative to wild-type mice. Taken together, our results support the view that INR formation in pancreatic beta cells is a dynamic and regulated process. The substantial depletion of beta cell INRs in LABKO and diabetic mice suggests their relationship to beta cell function and potential involvement in diabetes pathogenesis.
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http://dx.doi.org/10.1007/s12022-010-9136-5DOI Listing
December 2010

Loss of Lkb1 in adult beta cells increases beta cell mass and enhances glucose tolerance in mice.

Cell Metab 2009 Oct;10(4):285-95

Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada.

The Lkb1 tumor suppressor exerts its biological effects through phosphorylation and consequent activation of the AMP kinase (AMPK) family. Extensive genetic and biochemical evidence supports a role for Lkb1 in cell cycle arrest, establishment of cell polarity, and cellular energy metabolism. However, the role of Lkb1 and the AMPK family in beta cell function in vivo has not been established. We generated conditional knockout mice with a deletion of the Lkb1 gene in the beta cell compartment of pancreatic islets; these mice display improved glucose tolerance and protection against diet-induced hyperglycemia. Lkb1(-/-) beta cells are hypertrophic because of elevated mTOR activity; they also proliferate more and secrete more insulin in response to glucose. These data indicate that inhibiting Lkb1 activity in beta cells may facilitate beta cell expansion and glucose tolerance in vivo.
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http://dx.doi.org/10.1016/j.cmet.2009.08.008DOI Listing
October 2009

Using kinomics to delineate signaling pathways: control of CRTC2/TORC2 by the AMPK family.

Cell Cycle 2008 Dec 21;7(24):3823-8. Epub 2008 Dec 21.

Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, Ontario, Canada.

The classical role of AMP-activated protein kinase (AMPK) as an energy status sensor is expanding to include other members of the AMPK family. Recent genetic and cell biological evidence points to a role for MAP/microtubule affinity-regulating kinase 2 (MARK2/EMK/Par1b) in the regulation of metabolic events as well as in the control of CREB-dependent transcription activated by glucose in pancreatic islet beta cells. We have recently developed an in vitro kinase screening platform to identify novel kinase:substrate pairs, the building blocks of signal transduction pathways. Application of this technology led us to identify MARK2 as the kinase that targets a novel glucose-regulated phosphorylation site on Transducer of Regulated CREB Activity 2 (TORC2, referred to as CREB-Regulated Transcriptional Coactivator 2, or CRTC2), a transcriptional coactivator essential for CREB activity in beta cells. We discuss these recent developments and suggest a model whereby members of the AMPK family integrate numerous signals to coordinate energy metabolism and cellular polarity with gene expression to regulate cell function/proliferation.
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http://dx.doi.org/10.4161/cc.7.24.7241DOI Listing
December 2008

Glucose controls CREB activity in islet cells via regulated phosphorylation of TORC2.

Proc Natl Acad Sci U S A 2008 Jul 14;105(29):10161-6. Epub 2008 Jul 14.

Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON, Canada.

CREB is a cAMP- and calcium-responsive transcriptional activator that is required for islet beta cell proliferation and survival. Glucose and incretin hormones elicit beta cell insulin secretion and promote synergistic CREB activity by inducing the nuclear relocalization of TORC2 (also known as Crtc2), a coactivator for CREB. In islet cells under basal conditions when CREB activity is low, TORC2 is phosphorylated and sequestered in the cytoplasm by 14-3-3 proteins. In response to feeding stimuli, TORC2 is dephosphorylated, enters the nucleus, and binds to CREB located at target gene promoters. The dephosphorylation of TORC2 at Ser-171 in response to cAMP is insufficient to account for the dynamics of TORC2 localization and CREB activity in islet cells. Here, we identify Ser-275 of TORC2 as a 14-3-3 binding site that is phosphorylated under low glucose conditions and which becomes dephosphorylated by calcineurin in response to glucose influx. Dephosphorylation of Ser-275 is essential for both glucose and cAMP-mediated activation of CREB in beta cells and islets. Using a cell-based screen of 180 human protein kinases, we identified MARK2, a member of the AMPK family of Ser/Thr kinases, as a Ser-275 kinase that blocks TORC2:CREB activity. Taken together, these data provide the mechanistic underpinning for how cAMP and glucose cooperatively promote a transcriptional program critical for islet cell survival, and identifies MARK2 as a potential target for diabetes treatment.
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http://dx.doi.org/10.1073/pnas.0800796105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2481316PMC
July 2008
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