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The Ser-Thr kinase mammalian target of rapamycin (mTOR) controls cell growth and metabolism by stimulating glycolysis and synthesis of proteins and lipids. To further understand the central role of mTOR in cell physiology, we used quantitative phosphoproteomics to identify substrates or downstream effectors of the two mTOR complexes. mTOR controlled the phosphorylation of 335 proteins, including CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase). CAD catalyzes the first three steps in de novo pyrimidine synthesis. mTORC1 indirectly phosphorylated CAD-S1859 through S6 kinase (S6K). CAD-S1859 phosphorylation promoted CAD oligomerization and thereby stimulated de novo synthesis of pyrimidines and progression through S phase of the cell cycle in mammalian cells. Thus, mTORC1 also stimulates the synthesis of nucleotides to control cell proliferation.

The liver is a key metabolic organ that controls whole-body physiology in response to nutrient availability. Mammalian target of rapamycin (mTOR) is a nutrient-activated kinase and central controller of growth and metabolism that is negatively regulated by the tumor suppressor tuberous sclerosis complex 1 (TSC1). To investigate the role of hepatic mTOR complex 1 (mTORC1) in whole-body physiology, we generated liver-specific Tsc1 (L- Tsc1 KO) knockout mice. L- Tsc1 KO mice displayed reduced locomotor activity, body temperature, and hepatic triglyceride content in a rapamycin-sensitive manner. Ectopic activation of mTORC1 also caused depletion of hepatic and plasma glutamine, leading to peroxisome proliferator–activated receptor γ coactivator-1α (PGC-1α)–dependent fibroblast growth factor 21 (FGF21) expression in the liver. Injection of glutamine or knockdown of PGC-1α or FGF21 in the liver suppressed the behavioral and metabolic defects due to mTORC1 activation. Thus, mTORC1 in the liver controls whole-body physiology through PGC-1α and FGF21. Finally, mTORC1 signaling correlated with FGF21 expression in human liver tumors, suggesting that treatment of glutamine-addicted cancers with mTOR inhibitors might have beneficial effects at both the tumor and whole-body level.

Glucagon-Like Peptide-1 Protects β-Cells Against Apoptosis by Increasing the Activity of an Igf-2/Igf-1 Receptor Autocrine Loop Marion Cornu 1 , Jiang-Yan Yang 2 , Evrim Jaccard 2 , Carine Poussin 1 , Christian Widmann 2 and Bernard Thorens 1 1 Department of Physiology and Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland; 2 Department of Physiology and Department of Cellular Biology and Morphology, Biology and Medicine Faculty, University of Lausanne, Lausanne, Switzerland. Corresponding author: Bernard Thorens, bernard.thorens{at}unil.ch . Abstract OBJECTIVE The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect β-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect. RESEARCH DESIGN AND METHODS We performed comparative transcriptomic analysis of islets from control and GipR −/− ;Glp-1-R −/− mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis. RESULTS We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1–induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary β-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1–induced protection against apoptosis. CONCLUSIONS An IGF-2/IGF-1 receptor autocrine loop operates in β-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1–induced protection against apoptosis. These findings may lead to novel ways of preventing β-cell loss in the pathogenesis of diabetes. Footnotes The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received January 13, 2009. Accepted April 20, 2009. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details. © 2009 by the American Diabetes Association.

Exendin-4 Protects β-Cells From Interleukin-1β–Induced Apoptosis by Interfering With the c-Jun NH 2 -Terminal Kinase Pathway Mourad Ferdaoussi 1 2 , Saida Abdelli 1 2 , Jiang-Yan Yang 2 3 , Marion Cornu 3 4 , Guy Niederhauser 1 2 , Dimitri Favre 1 2 , Christian Widmann 2 3 , Romano Regazzi 2 , Bernard Thorens 3 4 , Gérard Waeber 1 and Amar Abderrahmani 1 2 1 Service of Internal Medicine, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland 2 Department of Cellular Biology and Morphology, University of Lausanne, Lausanne, Switzerland 3 Department of Physiology, University of Lausanne, Lausanne, Switzerland 4 Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland Corresponding author: Dr. Amar Abderrahmani, Privat-Docent, Department of Cellular Biology and Morphology, Rue du Bugnon 9, 1005 Lausanne, Switzerland. E-mail: amar.abderrahmani{at}unil.ch Abstract OBJECTIVE— The pro-inflammatory cytokine interleukin-1β (IL-1β) generates pancreatic β-cells apoptosis mainly through activation of the c-Jun NH 2 -terminal kinase (JNK) pathway. This study was designed to investigate whether the long-acting agonist of the hormone glucagon-like peptide 1 (GLP-1) receptor exendin-4 (ex-4), which mediates protective effects against cytokine-induced β-cell apoptosis, could interfere with the JNK pathway. RESEARCH DESIGN AND METHODS— Isolated human, rat, and mouse islets and the rat insulin-secreting INS-1E cells were incubated with ex-4 in the presence or absence of IL-1β. JNK activity was assessed by solid-phase JNK kinase assay and quantification of c-Jun expression. Cell apoptosis was determined by scoring cells displaying pycnotic nuclei. RESULTS— Ex-4 inhibited induction of the JNK pathway elicited by IL-1β. This effect was mimicked with the use of cAMP-raising agents isobutylmethylxanthine and forskolin and required activation of the protein kinase A. Inhibition of the JNK pathway by ex-4 or IBMX and forskolin was concomitant with a rise in the levels of islet-brain 1 (IB1), a potent blocker of the stress-induced JNK pathway. In fact, ex-4 as well as IBMX and forskolin induced expression of IB1 at the promoter level through cAMP response element binding transcription factor 1. Suppression of IB1 levels with the use of RNA interference strategy impaired the protective effects of ex-4 against apoptosis induced by IL-1β. CONCLUSIONS— The data establish the requirement of IB1 in the protective action of ex-4 against apoptosis elicited by IL-1β and highlight the GLP-1 mimetics as new potent inhibitors of the JNK signaling induced by cytokines. Footnotes Published ahead of print at http://diabetes.diabetesjournals.org on 5 February 2008. DOI: 10.2337/db07-1214. ChIP, chromatin immunoprecipitation; CRE, cAMP response element; CREB, CRE–binding protein; EMSA, electromobility shift assay; ex-4, exendin-4; GFP, green fluorescent protein; GLP-1, glucagon-like peptide 1; GLP-1R, GLP-1 receptor; GST, glutathione S-transferase; HES-1, hairy and enhancer of split-1; IB1, islet-brain 1; IBMX, isobutylmethylxanthine; ICER, inducible cAMP early repressor; IL, interleukin; JBD, c-Jun NH 2 -terminal kinase binding domain; JNK, c-Jun NH 2 -terminal kinase; JNKi, JBD of IB1; MAPK, mitogen-activated protein kinase; PI 3-kinase, phosphatidylinositol 3-kinase; PKA, protein kinase A; PKB, protein kinase B; RNAi, RNA interference; shIB1, target-specific shRNA directed against IB1; shRNA, short hairpin RNA; siRNA, small interfering RNA. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Accepted January 30, 2008. Received August 29, 2007. DIABETES

Decreased expression of histidine phosphatase LHPP, a novel tumour suppressor, results in increased global histidine phosphorylation and hepatocellular carcinoma. A role for histidine phosphatase in tumour suppression Histidine phosphorylation is a poorly understood process involved in the post-translational modification of proteins. Michael Hall and colleagues have identified LHPP as a histidine phosphatase and provide evidence that it functions as a tumour suppressor in liver tumours. They find that patients with hepatocellular carcinoma and low levels of LHPP have reduced overall survival. Histidine phosphorylation, the so-called hidden phosphoproteome, is a poorly characterized post-translational modification of proteins 1 , 2 . Here we describe a role of histidine phosphorylation in tumorigenesis. Proteomic analysis of 12 tumours from an mTOR-driven hepatocellular carcinoma mouse model revealed that NME1 and NME2, the only known mammalian histidine kinases, were upregulated. Conversely, expression of the putative histidine phosphatase LHPP was downregulated specifically in the tumours. We demonstrate that LHPP is indeed a protein histidine phosphatase. Consistent with these observations, global histidine phosphorylation was significantly upregulated in the liver tumours. Sustained, hepatic expression of LHPP in the hepatocellular carcinoma mouse model reduced tumour burden and prevented the loss of liver function. Finally, in patients with hepatocellular carcinoma, low expression of LHPP correlated with increased tumour severity and reduced overall survival. Thus, LHPP is a protein histidine phosphatase and tumour suppressor, suggesting that deregulated histidine phosphorylation is oncogenic.

Dedifferentiation of insulin-secreting β cells in the islets of Langerhans has been proposed to be a major mechanism of β-cell dysfunction. Whether dedifferentiated β cells can be targeted by pharmacological intervention for diabetes remission, and ways in which this could be accomplished, are unknown as yet. Here we report the use of streptozotocin-induced diabetes to study β-cell dedifferentiation in mice. Single-cell RNA sequencing (scRNA-seq) of islets identified markers and pathways associated with β-cell dedifferentiation and dysfunction. Single and combinatorial pharmacology further show that insulin treatment triggers insulin receptor pathway activation in β cells and restores maturation and function for diabetes remission. Additional β-cell selective delivery of oestrogen by Glucagon-like peptide-1 (GLP-1–oestrogen conjugate) decreases daily insulin requirements by 60%, triggers oestrogen-specific activation of the endoplasmic-reticulum-associated protein degradation system, and further increases β-cell survival and regeneration. GLP-1–oestrogen also protects human β cells against cytokine-induced dysfunction. This study not only describes mechanisms of β-cell dedifferentiation and regeneration, but also reveals pharmacological entry points to target dedifferentiated β cells for diabetes remission. β-cell dedifferentiation has emerged as a contributing mechanism in type 1 and type 2 diabetes development. Here Sachs et al. show that a pharmacological treatment that combines insulin and a GLP-1–oestrogen conjugate reverses dedifferentiation, and improves β-cell function and hyperglycaemia in diabetic mice.

Pregnancy and obesity are frequently associated with diminished insulin sensitivity, which is normally compensated for by an expansion of the functional β cell mass that prevents chronic hyperglycemia and development of diabetes mellitus. The molecular basis underlying compensatory β cell mass expansion is largely unknown. We found in rodents that β cell mass expansion during pregnancy and obesity is associated with changes in the expression of several islet microRNAs, including miR-338-3p. In isolated pancreatic islets, we recapitulated the decreased miR-338-3p level observed in gestation and obesity by activating the G protein-coupled estrogen receptor GPR30 and the glucagon-like peptide 1 (GLP1) receptor. Blockade of miR-338-3p in β cells using specific anti-miR molecules mimicked gene expression changes occurring during β cell mass expansion and resulted in increased proliferation and improved survival both in vitro and in vivo. These findings point to a major role for miR-338-3p in compensatory β cell mass expansion occurring under different insulin resistance states.

To establish the role of the transcription factor Pax4 in pancreatic islet expansion and survival in response to physiological stress and its impact on glucose metabolism, we generated transgenic mice conditionally and selectively overexpressing Pax4 or a diabetes-linked mutant variant (Pax4R129W) in β-cells. Glucose homeostasis and β-cell death and proliferation were assessed in Pax4- or Pax4R129W-overexpressing transgenic animals challenged with or without streptozotocin. Isolated transgenic islets were also exposed to cytokines, and apoptosis was evaluated by DNA fragmentation or cytochrome C release. The expression profiles of proliferation and apoptotic genes and β-cell markers were studied by immunohistochemistry and quantitative RT-PCR. Pax4 but not Pax4R129W protected animals against streptozotocin-induced hyperglycemia and isolated islets from cytokine-mediated β-cell apoptosis. Cytochrome C release was abrogated in Pax4 islets treated with cytokines. Interleukin-1β transcript levels were suppressed in Pax4 islets, whereas they were increased along with NOS2 in Pax4R129W islets. Bcl-2, Cdk4, and c-myc expression levels were increased in Pax4 islets while MafA, insulin, and GLUT2 transcript levels were suppressed in both animal models. Long-term Pax4 expression promoted proliferation of a Pdx1-positive cell subpopulation while impeding insulin secretion. Suppression of Pax4 rescued this defect with a concomitant increase in pancreatic insulin content. Pax4 protects adult islets from stress-induced apoptosis by suppressing selective nuclear factor-κB target genes while increasing Bcl-2 levels. Furthermore, it promotes dedifferentiation and proliferation of β-cells through MafA repression, with a concomitant increase in Cdk4 and c-myc expression.

Pregnancy and obesity are frequently associated with diminished insulin sensitivity, which is normally compensated for by an expansion of the functional β cell mass that prevents chronic hyperglycemia and development of diabetes mellitus. The molecular basis underlying compensatory β cell mass expansion is largely unknown. We found in ents that β cell mass expansion during pregnancy and obesity is associated with changes in the expression of several islet microRNAs, including miR-338-3p. In isolated pancreatic islets, we recapitulated the decreased miR-338-3p level observed in gestation and obesity by activating the G protein-coupled estrogen receptor GPR30 and the glucagon-like peptide 1 (GLP1) receptor. Blockade of miR-338-3p in β cells using specific anti-miR molecules mimicked gene expression changes occurring during13 cell mass expansion and resulted in increased proliferation and improved survival both in vitro and in vivo. These findings point to a major role for miR-338-3p in compensatory0 cell mass expansion occurring under different insulin resistance states.

Pregnancy and obesity are frequently associated with diminished insulin sensitivity, which is normally compensated for by an expansion of the functional β cell mass that prevents chronic hyperglycemia and development of diabetes mellitus. The molecular basis underlying compensatory β cell mass expansion is largely unknown. We found in rodents that β cell mass expansion during pregnancy and obesity is associated with changes in the expression of several islet micro RNAs, including miR-338-3p. In isolated pancreatic islets, we recapitulated the decreased miR-338-3p level observed in gestation and obesity by activating the G protein-coupled estrogen receptor GPR30 and the glucagon-like peptide 1 (GLP1) receptor. Blockade of miR-338-3p in β cells using specific anti-miR molecules mimicked gene expression changes occurring during β cell mass expansion and resulted in increased proliferation and improved survival both in vitro and in vivo. These findings point to a major role for miR-338-3p in compensatory β cell mass expansion occurring under different insulin resistance states. [PUBLICATION ABSTRACT]