Upregulation of rat Ccnd1 gene by exendin-4 in pancreatic beta cell line INS-1: interaction of early growth response-1 with cis-regulatory element

Kang, Jung-Hoon; Kim, M.-J.; Ko, Seung Hyun; Jeong, In‐Kyung; Koh, Kyung-Hee; Rhie, Duck-Joo; Yoon, Shin Hee; Hahn, Sang June; Jo, Yang-Hyeok

doi:10.1007/s00125-006-0179-6

Cited by 28 publications

(20 citation statements)

References 37 publications

(50 reference statements)

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“…Reductions in Egr-1 expression levels diminish the proliferation rates of clonal insulin-producing cells (36). Furthermore, exendin-4 augments the expression levels of the cell cycle regulator cyclin D1 by increasing the binding of Egr-1 to the cyclin D1 promoter (60). These findings are concordant with the identification of multiple cell cycle regulators and growth factors as targets of Egr-1-mediated transcription in other cell types (61,62).…”

Section: Discussionsupporting

confidence: 74%

Regulation of Pancreas Duodenum Homeobox-1 Expression by Early Growth Response-1

Eto

Kaur

Thomas

2007

Journal of Biological Chemistry

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The homeodomain transcription factor pancreas duodenum homeobox-1 (PDX-1) is a key regulator of pancreatic ␤-cell development, function, and survival. Deficits in PDX-1 expression result in insulin deficiency and hyperglycemia. We previously found that the glucose-responsive transcription factor early growth response-1 (Egr-1) activates the insulin promoter in part by increasing expression levels of PDX-1. We now report that Egr-1 binds and activates multiple regulatory sites within the pdx-1 promoter. We identified consensus Egr-1 recognition sequences within proximal and distal regions of the mouse pdx-1 promoter and demonstrated specific binding of Egr-1 by chromatin immunoprecipitation and electrophoretic mobility shift assays. Overexpression of Egr-1 increased transcriptional activation of the ؊4500 proximal pdx-1 promoter and of the highly conserved regulatory Areas I, II, and III. Mutagenesis of a specific Egr-1 binding site within Area III substantially decreased Egr-1-mediated activation. Egr-1 increased the transcriptional activation of Areas I and II, despite the absence of Egr-1 recognition sequences within this promoter segment, suggesting that Egr-1 also can regulate the pdx-1 promoter indirectly. Egr-1 increased, and a dominant-negative Egr-1 mutant repressed, the transcriptional activation of distal pdx-1 promoter sequences. Mutagenesis of a specific Egr-1 binding site within regulatory Area IV reduced basal and Egr-1-mediated transcriptional activation. Our data indicate that Egr-1 regulates expression of PDX-1 in pancreatic ␤-cells by both direct and indirect activation of the pdx-1 promoter. We propose that Egr-1 expression levels may act as a sensor in pancreatic ␤-cells to translate extracellular signals into changes in PDX-1 expression levels and pancreatic ␤-cell function.The homeodomain transcription factor pancreas duodenum homeobox-1 (PDX-1) 2 is an essential regulator of the development of the pancreas in the embryo and of insulin production and glucose homeostasis in the adult. Homozygous disruption of the pdx-1/ipf-1 gene in mice or humans prevents normal pancreas development and leads to a phenotype of pancreatic agenesis (1-4). PDX-1 functions in later developmental stages to regulate the generation, function, and survival of insulinproducing pancreatic ␤-cells (5-10). PDX-1 mediates the adaptive responsiveness of pancreatic ␤-cells to changes in extracellular glucose concentrations through the regulation of expression levels of glucose sensors, such as glucose transporter-2 and glucokinase, and through the activation of glucoseresponsive enhancers within the insulin promoter, in conjunction with other transcriptional regulators (11). PDX-1 also functions downstream of the insulin signaling pathway in the regulation of pancreatic ␤-cell mass (12, 13). Deficits in PDX-1 expression levels in mice result in reduced insulin secretion, accelerated ␤-cell apoptosis, and insulin-deficient diabetes (5, 7-10). The appropriate regulation of PDX-1 expression is of clinical importance, as illu...

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Section: Discussionsupporting

confidence: 74%

Regulation of Pancreas Duodenum Homeobox-1 Expression by Early Growth Response-1

Eto

Kaur

Thomas

2007

Journal of Biological Chemistry

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“…Exendin-4 suppressed Rb through two complementary mechanisms: downregulation of Rb mRNA and increased Rb phosphorylation. While Rb hyperphosphorylation may be driven through exendin 4-dependent induction of cyclin D1 [34], the mechanism by which this GLP-1R agonist inhibits Rb mRNA is yet to be established. The predominant Rb family member expressed in cycling cells, p107, showed a limited role in adult beta cell cycle control.…”

Section: Discussionmentioning

confidence: 99%

Rb and p107 are required for alpha cell survival, beta cell cycle control and glucagon-like peptide-1 action

Cai

Luk

et al. 2014

Diabetologia

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Aims/hypothesis Diabetes mellitus is characterised by beta cell loss and alpha cell expansion. Analogues of glucagonlike peptide-1 (GLP-1) are used therapeutically to antagonise these processes; thus, we hypothesised that the related cell cycle regulators retinoblastoma protein (Rb) and p107 were involved in GLP-1 action. Methods We used small interfering RNA and adenoviruses to manipulate Rb and p107 expression in insulinoma and alpha-TC cell lines. In vivo we examined pancreas-specific Rb knockout, whole-body p107 knockout and Rb/p107 doubleknockout mice.Results Rb, but not p107, was downregulated in response to the GLP-1 analogue, exendin-4, in both alpha and beta cells. Intriguingly, this resulted in opposite outcomes of cell cycle arrest in alpha cells but proliferation in beta cells. Overexpression of Rb in alpha and beta cells abolished or attenuated the effects of exendin-4 supporting the important role of Rb in GLP-1 modulation of cell cycling. Similarly, in vivo, Rb, but not p107, deficiency was required for the beta cell proliferative response to exendin-4. Consistent with this finding, Rb, but not p107, was suppressed in islets from humans with diabetes, suggesting the importance of Rb regulation for the compensatory proliferation that occurs under insulin resistant conditions. Finally, while p107 alone did not have an essential role in islet homeostasis, when combined with Rb deletion, its absence potentiated apoptosis of both alpha and beta cells resulting in glucose intolerance and diminished islet mass with ageing. Conclusions/interpretation We found a central role of Rb in the dual effects of GLP-1 in alpha and beta cells. Our findings highlight unique contributions of individual Rb family members to islet cell proliferation and survival.

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“…Total RNA isolation and the method for Northern blot analysis were described previously [Kang et al, 2006;Kim et al, 2008]. RNA samples (10 mg) were fractionated in a 1% formaldehyde agarose gel and transferred onto a Hybond-N nylon membrane.…”

Section: Northern Blot Analysismentioning

confidence: 99%

Quercetin‐induced upregulation of human GCLC gene is mediated by cis‐regulatory element for early growth response protein‐1 (EGR1) in INS‐1 beta‐cells

Kang

Chang

Jang

et al. 2009

J of Cellular Biochemistry

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The catalytic subunit of gamma-glutamylcysteine ligase (GCLC) catalyses the rate-limiting step in the de novo synthesis of glutathione (GSH), which is involved in maintaining intracellular redox balance. GSH is especially important for antioxidant defense system since beta-cells show intrinsically low expression of antioxidant enzymes. In the present study, we investigated the regulatory mechanisms by which quercetin, a flavonoid, induces the expression of the GCLC gene in rat pancreatic beta-cell line INS-1. Promoter study found that the proximal GC-rich region (from -90 to -34) of the GCLC promoter contained the quercetin-responsive cis-element(s). The quercetin-responsive region contains consensus DNA binding site for early growth response 1 (EGR1) at -67 (5'-CGCCTCCGC-3') which overlaps with a putative Sp1 binding site. Electrophoretic mobility shift assay showed that an oligonucleotide containing the EGR1 site was bound to nuclear factors EGR1, Sp1, and Sp3. In the promoter analysis, mutation of EGR1 site significantly reduced the quercetin response, whereas mutation of Sp1 site decreased only the basal activity of the GCLC promoter. Additionally, the transient overexpression of EGR1 significantly increased basal activity of the GCLC promoter. Finally, we showed that quercetin potently induced both EGR1 mRNA and its protein levels without affecting the expression of Sp1 and Sp3 proteins. Therefore, we concluded that EGR1 was bound to GC-rich region of the GCLC gene promoter, which was prerequisite for the transactivation of the GCLC gene by quercetin.

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Upregulation of rat Ccnd1 gene by exendin-4 in pancreatic beta cell line INS-1: interaction of early growth response-1 with cis-regulatory element

Cited by 28 publications

References 37 publications

Regulation of Pancreas Duodenum Homeobox-1 Expression by Early Growth Response-1

Regulation of Pancreas Duodenum Homeobox-1 Expression by Early Growth Response-1

Rb and p107 are required for alpha cell survival, beta cell cycle control and glucagon-like peptide-1 action

Quercetin‐induced upregulation of human GCLC gene is mediated by cis‐regulatory element for early growth response protein‐1 (EGR1) in INS‐1 beta‐cells

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