Pancreatic Islet Expression of the Homeobox Factor STF-1 Relies on an E-box Motif That Binds USF

Sharma, Seema; Leonard, Janet L.; Lee, Soon; Chapman, Harold D.; Leiter, Edward H.; Montminy, Marc

doi:10.1074/jbc.271.4.2294

Cited by 80 publications

(80 citation statements)

References 32 publications

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“…The luciferase-reporter plasmid DNA containing the CEB mutation within the rat insulin I gene promoter was created by mutation of the CEB box from Ϫ128 TG-TAAT Ϫ133 to Ϫ128 CTCGGC Ϫ133 using oligonucleotide-directed mutagenesis (39). The luciferase plasmid containing 190 bp of the promoter of IDX-1 (Ϫ190IDX-LUC) was a gift from Dr. Marc Montminy (The Salk Institute, La Jolla, CA) and has been described previously (40). The luciferase reporter construct containing the proximal 180 bp of the promoter sequence of the human islet sulfonylurea receptor (Ϫ180SUR-LUC) 3 was a gift from Dr. Jorge Ferrer (Harvard Medical School, Boston, MA).…”

Section: Methodsmentioning

confidence: 99%

Pancreatic β-Cell-specific Repression of Insulin Gene Transcription by CCAAT/Enhancer-binding Protein β

Lu¹,

Seufert²,

Habener

1997

Journal of Biological Chemistry

120

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Chronic exposure of ␤-cells to supraphysiologic glucose concentrations results in decreased insulin gene transcription. Here we identify the basic leucine zipper transcription factor, CCAAT/enhancer-binding protein ␤ (C/EBP␤), as a repressor of insulin gene transcription in conditions of supraphysiological glucose levels. C/EBP␤ is expressed in primary rat islets. Moreover, after exposure to high glucose concentrations the ␤-cell lines HIT-T15 and INS-1 express increased levels of C/ EBP␤. The rat insulin I gene promoter contains a consensus binding motif for C/EBP␤ (CEB box) that binds C/EBP␤. In non-␤-cells C/EBP␤ stimulates the activity of the rat insulin I gene promoter through the CEB box. Paradoxically, in ␤-cells C/EBP␤ inhibits transcription, directed by the promoter of the rat insulin I gene by direct protein-protein interaction with a heptad leucine repeat sequence within activation domain 2 of the basic helix-loop-helix transcription factor E47. This interaction leads to the inhibition of both dimerization and DNA binding of E47 to the E-elements of the insulin promoter, thereby reducing functionally the transactivation potential of E47 on insulin gene transcription. We suggest that the induction of C/EBP␤ in pancreatic ␤-cells by chronically elevated glucose levels may contribute to the impaired insulin secretion in severe type II diabetes mellitus.Insulin is a hormone essential for the control of mammalian glucose homeostasis and is produced predominantly in pancreatic ␤-cells of adult animals (1). The expression of the insulin gene occurs to a large extent at the level of transcription. Control elements residing in the 5Ј 350-base pair sequence flanking exon 1 of the rat insulin I gene are sufficient to direct ␤-cell-specific expression (2) (Fig. 1A). Arrays of A and E elements 1 (Far-FLAT, Nir-P1) constitute symmetrical enhansons that cooperatively account for Ͼ90% of the transcriptional activity of the insulin gene promoter (3). The E elements are recognition motifs for transcription factors in the basic helixloop-helix (bHLH) 2 family, such as E12 and E47, which activate the insulin promoter in close synergism with A element binding homeobox transcription factors, such as IDX-1.Chronic hyperglycemia may contribute to the pancreatic ␤-cell dysfunction observed in patients with type II diabetes, a phenomenon attributed to the concept of glucose toxicity (4). Studies using in vivo animal models and in vitro ␤-cell lines have demonstrated that a reduction of insulin gene transcription by glucose toxicity is associated with the loss of transactivator proteins such as IDX-1/IPF-1/STF-1 and RIPE3b1-binding protein (5-10). Because insulin gene transcription is both positively and negatively regulated, we sought to identify repressors that might also mediate the effects of glucose toxicity on insulin gene transcription. In this report we describe CCAAT/enhancer binding protein-␤ (C/EBP␤) as a glucoseinduced repressor of insulin gene transcription.C/EBPs are a family of transcription factors that regulate...

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Section: Methodsmentioning

confidence: 99%

Pancreatic β-Cell-specific Repression of Insulin Gene Transcription by CCAAT/Enhancer-binding Protein β

Lu¹,

Seufert²,

Habener

1997

Journal of Biological Chemistry

120

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“…These subregion sequences in mouse are located between Ϫ2761 to Ϫ2457 bp (area I), Ϫ2141 to Ϫ1923 bp (area II), and Ϫ1879 to Ϫ1600 bp (area III) and between Ϫ2839 to Ϫ2521 bp (area I), Ϫ2252 to Ϫ2023 bp (area II), and Ϫ1939 to Ϫ1664 bp (area III) in humans. The numbering is relative to the S1 transcription start site (21)). Point mutants within the HNF3␤ binding elements of the human and mouse area I and area II pTk constructs were generated using the Quik Change mutagenesis kit (Stratagene).…”

Section: Characterization Of 5ј-flanking Regions Of Human Andmentioning

confidence: 99%

“…1). An E-box element at Ϫ99 to Ϫ94 bp, which represents a upstream stimulatory factor regulatory site in the HSS3 region (21), is conserved within the mouse and human pdx-1 genes (data not shown).…”

Section: Conservation Of Hss1 Sequences Between Mouse Humanmentioning

confidence: 99%

“…The analysis of pdx-1-driven reporter constructs in transgenic mice has shown that the cis-acting elements mediating pancreas-and duodenumspecific expression are found within the 5Ј-flanking region of the gene (21,22). DNaseI and micrococcal nuclease studies performed on the endogenous mouse pdx-1 gene identified three nuclease hypersensitive sites (HSS), which are located approximately between nucleotides Ϫ2560 to Ϫ1880 (HSS1), Ϫ1330 to Ϫ800 (HSS2), and Ϫ260 to ϩ180 (HSS3) (22).…”

mentioning

confidence: 99%

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Pancreatic β Cell-specific Transcription of thepdx-1 Gene

Gerrish¹,

Gannon²,

Shih³

et al. 2000

Journal of Biological Chemistry

145

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To identify potential transactivators of pdx-1, we sequenced approximately 4.5 kilobases of the 5 promoter region of the human and chicken homologs, assuming that sequences conserved with the mouse gene would contain critical cis-regulatory elements. The sequences associated with hypersensitive site 1 (HSS1) represented the principal area of homology within which three conserved subdomains were apparent: area I (؊2694 to ؊2561 base pairs (bp)), area II (؊2139 to ؊1958 bp), and area III (؊1879 to ؊1799 bp). The identities between the mouse and chicken/human genes are very high, ranging from 78 to 89%, although only areas I and III are present within this region in chicken. Pancreatic ␤ cell-selective expression was shown to be controlled by mouse and human area I or area II, but not area III, from an analysis of pdx-1-driven reporter activity in transfected ␤-and non-␤ cells. Mutational and functional analyses of conserved hepatic nuclear factor 3 (HNF3)-like sites located within area I and area II demonstrated that activation by these regions was mediated by HNF3␤. To determine if a similar regulatory relationship might exist within the context of the endogenous gene, pdx-1 expression was measured in embryonic stem cells in which one or both alleles of HNF3␤ were inactivated. pdx-1 mRNA levels induced upon differentiation to embryoid bodies were down-regulated in homozygous null HNF3␤ cells. Together, these results suggest that the conserved sequences represented by areas I and II define the binding sites for factors such as HNF3␤, which control islet ␤ cell-selective expression of the pdx-1 gene.The PDX-1 homeodomain transcription factor is an essential regulator of pancreatic endocrine cell development and adult islet ␤ cell function. Pancreatic development in homozygous pdx-1 Ϫ/Ϫ mice is blocked at a very early stage (1-3), and endocrine cells in the rostral duodenum (3) and stomach (4) are also reduced or absent. The finding that a human born without a pancreas was homozygous for an inactivating mutation in pdx-1 (5) highlights the critical conserved role that this factor plays in pancreas formation in vertebrates.In the adult pancreas, PDX-1 is expressed at highest levels within islet ␤ cells (6). PDX-1 can specifically stimulate reporter gene expression from transfected constructs driven by promoter sequences from several genes that are normally transcribed selectively in ␤ cells, including insulin (7-11), glucokinase (12), islet amyloid polypeptide (13-16), and glucose transporter type 2 (GLUT2) 1 (17). The importance of PDX-1 in controlling the expression of genes required for the sensing and regulation of blood glucose levels suggested that an inactivating mutation within the protein would result in dysfunctional ␤ cells. Indeed, mice that are heterozygous mutant carriers of PDX-1 exhibit symptoms of glucose intolerance, suggesting a dosage effect on insulin expression and ␤ cell function (18,19). More significantly, humans with this condition are susceptible to a form of Type II (non-insulin-dependent)...

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“…The proximal region of Pdx1 promoter consists of an islet-specific expression consensus E-box motif, which predominantly binds the upstream transcription factor [27]. Site-specific acetylation or deacetylation of nucleosomal histones H3 and H4 is central to the switch between permissive and repressive chromatin structure and thus activation or repression of transcription [28].…”

mentioning

confidence: 99%

Molecular mechanisms for hyperinsulinaemia induced by overproduction of selenium-dependent glutathione peroxidase-1 in mice

et al. 2008

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Aims/hypothesis We previously observed hyperglycaemia, hyperinsulinaemia, insulin resistance and obesity in Gpx1-overexpressing mice (OE). Here we determined whether these phenotypes were eliminated by diet restriction, subsequently testing whether hyperinsulinaemia was a primary effect of Gpx1 overexpression and caused by dysregulation of pancreatic duodenal homeobox 1 (PDX1) and uncoupling protein-2 (UCP2) in islets. Methods First, 24 male OE and wild-type (WT) mice (2 months old) were given 3 g (diet-restricted) or 5 g (fullfed) feed per day for 4 months to compare their glucose metabolism. Thereafter, several mechanistic experiments were conducted with pancreas and islets of the two genotypes (2 or 6 months old) to assay for beta cell mass, reactive oxygen species (ROS) levels, mitochondrial membrane potential (Δ= m ) and expression profiles of regulatory proteins. A functional assay of islets was also performed. Results Diet restriction eliminated obesity but not hyperinsulinaemia in OE mice. These mice had greater pancreatic beta cell mass (more than twofold) and pancreatic insulin content (40%) than the WT, along with an enhanced Δ= m and glucose-stimulated insulin secretion in islets. With diminished ROS production, the OE islets displayed hyperacetylation of H3 and H4 histone in the Pdx1 promoter, elevated PDX1 and decreased UCP2. Conclusions/interpretation Overproduction of the major antioxidant enzyme, glutathione peroxidase 1, caused seemingly beneficial changes in pancreatic PDX1 and UCP2, but eventually led to chronic hyperinsulinaemia by dysregulating islet insulin production and secretion.

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Pancreatic Islet Expression of the Homeobox Factor STF-1 Relies on an E-box Motif That Binds USF

Cited by 80 publications

References 32 publications

Pancreatic β-Cell-specific Repression of Insulin Gene Transcription by CCAAT/Enhancer-binding Protein β

Pancreatic β-Cell-specific Repression of Insulin Gene Transcription by CCAAT/Enhancer-binding Protein β

Pancreatic β Cell-specific Transcription of thepdx-1 Gene

Molecular mechanisms for hyperinsulinaemia induced by overproduction of selenium-dependent glutathione peroxidase-1 in mice

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