1,721,027 research outputs found
Role of peroxisome proliferator - Activated receptor-gamma in the glucose-sensing apparatus of liver and beta-cells
No full textType 2 diabetes develops in the context of both insulin resistance and beta-cell failure. Thiazolidinediones are a class of antidiabetic agents that are known to improve insulin sensitivity in various animal models of diabetes. The improved insulin sensitivity may be achieved either by systemic insulin sensitization or by direct action of peroxisome proliferator-activated receptor (PPAR)-gamma on the transcription of genes involved in glucose disposal. Evidence supporting the direct action of PPAR-gamma on glucose metabolism is observed in the genes involved in insulin-stimulated glucose disposal. We already showed that GLUT2 and beta-glucokinase were directly activated by PPAR-gamma. Recently, we have identified and characterized the functional PPAR response element in the GLUT2 and liver type glucokinase (LGK) promoter of the liver. It is well known that adipose tissue plays a crucial role in antidiabetic action of PPAR-gamma. In addition, PPAR-gamma can directly affect liver and pancreatic beta-cells to improve glucose homeostasis. Diabetes 53 (Suppl. 1):S60-S65, 2004
Peripheral Serotonin: a New Player in Systemic Energy Homeostasis
No full textWhole body energy balance is achieved through the coordinated regulation of energy intake and energy expenditure in various tissues including liver, muscle and adipose tissues. A positive energy imbalance by excessive energy intake or insufficient energy expenditure results in obesity and related metabolic diseases. Although there have been many obesity treatment trials aimed at the reduction of energy intake, these strategies have achieved only limited success because of their associated adverse effects. An ancient neurotransmitter, serotonin is among those traditional pharmacological targets for anti-obesity treatment because it exhibits strong anorectic effect in the brain. However, recent studies suggest the new functions of peripheral serotonin in energy homeostasis ranging from the endocrine regulation by gut-derived serotonin to the autocrine/paracrine regulation by adipocyte-derived serotonin. Here, we discuss the role of serotonin in the regulation of energy homeostasis and introduce peripheral serotonin as a possible target for anti- obesity treatment
Functional role of serotonin in insulin secretion under diet induced insulin resistant state
No full textIdentification of transacting factors responsible for the tissue-specific expression of human glucose transporter type 2 isoform gene - Cooperative role of hepatocyte nuclear factors 1 alpha and 3 beta
No full textWe investigated transacting factors binding to the cis-element important in tissue-specific expression of the human glucose transporter type 2 isoform (GLUT2) gene. By transient transfection assay, we determined that the 227-base pair fragment upstream of the ATG start site contained promoter activity and that the region from +87 to +132 (site C) was responsible for tissue-specific expression. DNase I footprinting and electrophoretic mobility shift assay indicated that site C contained one binding site for hepatocyte nuclear factor 1 (HNF1) and two binding sites for HNF3 The mutations at positions +101 and +103, which are considered to be critical in binding HNF1 and HNF3, resulted in a 53% decrease in promoter activity, whereas the mutation of the proximal HNF3 binding site (+115 and +117) reduced promoter activity by 28%. The mutations of these four sites resulted in marked decrease (70%) in promoter activity as well as diminished bindings of HNF1 and HNF3, A to G mutation, which causes conversion of the HNF1 and HNF3 binding sequence to the NF-Y binding site, resulted in a 22% decrease in promoter activity. We identified that both HNF1 and HNF3 function as transcriptional activators in GLUTS gene expression. Coexpression of the pGL+74 (+74 to +301) construct with the HNF1 alpha and HNF3 beta expression vectors in NIH 3T3 cells showed the synergistic effect on GLUTS promoter activity compared with the expression of HNF1 alpha, HNF3 beta, or a combination of HNF1 beta and HNF3 beta. These data suggest that HNF1 alpha and HNF3 beta may be the most important players in the tissue-specific expression of the human GLUTS gene
HNF1 and/or HNF3 may contribute to the tissue specific expression of glucokinase gene
No full textA possible role of hepatocyte nuclear factor 1 (HNF1) or HNF3, a predominant trans-acting factors of hepatic or pancreatic p-cells, was examined on the tissue specific interdependent expression of glucokinase (GK) in liver, H4IIE, HepG2, HIT-T15 and MIN6 cell line. The tissues or cell lines known to express GK showed abundant levels of HNF1 and HNF3 mRNA as observed in liver, H4IIE, HepG2, HIT-T15 and MIN6 cells, whereas they were not detected in brain, heart, NIH 3T3, HeLa cells. The promoter of glucokinase contains several HNF3 consensus sequences and are well conserved in human, mouse and rat. Transfection of the glucokinase promotor linked with luciferase reporter to liver or pancreatic beta cell lines showed high interacting activities with HNF1 and HNF3, whereas minimal activities were detected in the cells expressing very low levels of HNFs. The binding of HNF1 or HNF3 to the GK promoter genes was confirmed by electrophoretic mobility shift assay (EMSA). From these data, we propose that the expression of HNF1 and/or HNF3 may, in part, contribute to the tissue specific expression of GK
Ectopic serotonin production in β-cell specific transgenic mice
No full textGenetically modified mice have been widely used in the field of beta-cell research. However, analysis of results gathered using genetically modified organisms should be interpreted carefully as the results may be confounded by several factors. Here, we showed the ectopic serotonin (5-HT) production in beta-cells of RIP-Cre(Mgn), MIP-GFP, and MIP-Cre/ERT mice. These mice contained a human growth hormone (hGH) cassette to enhance transgene expression and hGH expression and Stat5 phosphorylation were detected in pancreatic islets of these mice. The expression level of tryptophan hydroxylase 1 (Tph1) was upregulated in pancreatic islets of transgenic mice with an hGH cassette but not in transgenic mice without an hGH cassette. Ectopic 5-HT production was not observed in beta-cell-specific prolactin receptor (Prlr) knockout mice or Stat5 knockout mice crossed with RIP-Cre(Mgn). We further confirmed that 5-HT production in beta-cells of several transgenic mice was induced by hGH expression followed by the activation of the Prlr-Stat5-Tph1 pathway. These findings indicate that results obtained using transgenic mice containing the hGH cassette should be interpreted with care. (C) 2017 Elsevier Inc. All rights reserved.
YAP and AP-1 Cooperate to Initiate Pancreatic Cancer Development from Ductal Cells in Mice
No full textThe development of pancreatic cancer is heavily dependent upon the aberrant activation of KRAS signaling. Among the downstream targets of KRAS, the effectors of the Hippo pathway YAP and TAZ (YAP/TAZ) are crucial during cancer initiation and progression. However, little is known about the cell type-specific effects of YAP/TAZ on the development of pancreatic cancer. Here we clarify the unique consequences of YAP/TAZ activation in the ductal cell population of the pancreas by generating mice with pancreatic duct cell-specific, inducible knockouts of Lats1 and Lats2, the main kinases upstream of YAP/TAZ. Oncogenic activation of YAP by deletion of Lats1/2 in ductal cells led to the rapid transformation of the pancreas, which was accompanied by a robust increase in the expression of YAP and AP-1 target genes. Pharmacologic inhibition of AP-1 activity induced death in Lats1/2 knockout organoids and attenuated YAP-dependent transformation of the pancreas in vivo. Both YAP and AP-1 were activated during the development of KRAS-dependent cancer in mice and human patients with pancreatic ductal adenocarcinoma, suggesting that this signaling hub represents an important mediator of pancreatic cancer development and progression. Collectively, these data define a YAP-dependent mechanism of pancreatic cancer cell development and suggest that inhibition of AP-1 can suppress this development. Significance: A pancreatic ductal cell-specific knockout mouse model featuring constitutively active YAP allows for the study of YAP-dependent transformation of the pancreas and for screening pharmacologically active inhibitors.
Analysis of polymorphism of the GLUT2 promoter in NIDDM patients and its functional consequence to the promoter activity
No full textGlucose transporter type 2 (GLUT2), along with glucokinase, has been implicated to participate in glucose-induced insulin secretion in pancreatic beta-cells. Recently, several sequence variations in the promoter of GLUT2 have been identified in patients with non-insulin dependent diabetes mellitus (NIDDM), but the functional effects of these polymorphisms on promoter activity have not previously been studied. We compared the incidence of sequence variations in the GLUT2 promoter in 100 normal subjects and 100 NIDDM patients. Sequencing of the promoter region (-294 to +301) revealed that an A-->G variant at position -44 was found in 45 of 100 NIDDM patients, but only in 23 of 100 normal subjects. In addition, -269 A-->C and +103 A-->G mutations were identified in a single diabetic patient. Electrophoretic mobility shift assays using double-stranded oligonucleotide containing -44A as a probe showed a clearly shifted band of DNA-protein. To examine whether the sequence variation at position -44 affects the promoter activity, we carried out in vitro transfection experiments. Site-specific mutagenesis at position -44 region from A to C, T or G resulted in reductions of CAT activity by 52.3%, 63.8%, and 63.6%, respectively. The -269 A-->C and +103 A-->G mutations also decreased the promoter activity. These results suggest that polymorphisms at positions -269, -44, or +103 may affect GLUT2 gene transcription, possibly associated with reduced expression of the GLUT2 gene in NIDDM patients
Identification and functional characterization of the peroxisomal proliferator response element in rat GLUT2 promoter
No full textWe identified the peroxisomal proliferator response element (PPRE) in the +68/+89 region of the rat GLUT2 gene. To identify whether the putative PPRE in the GLUTS gene (GLUT2-PPRE) is functional, GLUTS promoter-luciferase reporter constructs were transfected into CV-1 cells. Promoter activities were increased by coexpression of peroxisomal proliferator-activated receptor (PPAR)-gamma, retinoid X receptor (RXR)-alpha, and treatment of their ligands; troglitazone and g-cis retinoic acid potentiated the transactivational effects, Introduction of mutations in GLUT2-PPBE resulted in loss of transactivational effects of the PPAR-gamma/RXR-alpha heterodimer, Electrophoretic mobility shift assay using nuclear extracts of CV-1 cells, which were transfected with various combinations of PPARs or RXR-alpha expression plasmids, revealed that heterodimers of PPAR-gamma and RXR-alpha preferentially bound to GLUT2-PPRE. In HIT-T15 cells, promoter activity of the mt GLUTS gene was increased by troglitazone and g-cis retinoic acid, and mutations of GLUT2-PPRE resulted in reduction of promoter activity. In addition, we observed increased GLUTS transcription by troglitazone and 9-cis retinoic acid in isolated rat primary islets, These results suggested that the GLUT2-PPRE is functional and plays a significant role in gene expression of GLUTS in pancreatic beta-cells. This is the first report; identifying PPRE in a gene involved in glucose homeostasis, linking the effect; of troglitazone on the regulation of insulin secretion
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