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B-cell translocation gene 2 positively regulates GLP-1-stimulated insulin secretion via induction of PDX-1 in pancreatic β-cells.

Hwang SL, Kwon O, Kim SG, Lee IK, Kim YD - Exp. Mol. Med. (2013)

Bottom Line: Notably, adenovirus-mediated overexpression of BTG2 significantly elevated insulin secretion, as well as insulin and PDX-1 gene expression.Physical interaction studies showed that BTG2 is associated with increased PDX-1 occupancy on the insulin gene promoter via a direct interaction with PDX-1.Finally, we revealed that Ex-4 and GLP-1 significantly elevated insulin secretion via upregulation of the BTG2-PDX-1 axis in pancreatic islets, and this phenomenon was abolished by endogenous BTG2 knockdown.

View Article: PubMed Central - PubMed

Affiliation: College of Pharmacy, Yeungnam University, Gyeongsan, Republic of Korea.

ABSTRACT
Glucagon-like peptide-1 (GLP-1) is a potent glucoincretin hormone and an important agent for the treatment of type 2 diabetes. Here we demonstrate that B-cell translocation gene 2 (BTG2) is a crucial regulator in GLP-1-induced insulin gene expression and insulin secretion via upregulation of pancreatic duodenal homeobox-1 (PDX-1) in pancreatic β-cells. GLP-1 treatment significantly increased BTG2, PDX-1 and insulin gene expression in pancreatic β-cells. Notably, adenovirus-mediated overexpression of BTG2 significantly elevated insulin secretion, as well as insulin and PDX-1 gene expression. Physical interaction studies showed that BTG2 is associated with increased PDX-1 occupancy on the insulin gene promoter via a direct interaction with PDX-1. Exendin-4 (Ex-4), a GLP-1 agonist, and GLP-1 in pancreatic β-cells increased insulin secretion through the BTG2-PDX-1-insulin pathway, which was blocked by endogenous BTG2 knockdown using a BTG2 small interfering RNA knockdown system. Finally, we revealed that Ex-4 and GLP-1 significantly elevated insulin secretion via upregulation of the BTG2-PDX-1 axis in pancreatic islets, and this phenomenon was abolished by endogenous BTG2 knockdown. Collectively, our current study provides a novel molecular mechanism by which GLP-1 positively regulates insulin gene expression via BTG2, suggesting that BTG2 has a key function in insulin secretion in pancreatic β-cells.

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Ex-4 increases insulin gene expression via BTG2 induction. (a and b) C57BL/6 mice were injected intraperitoneally with Ex-4 (20 μg kg−1 of body weight) for 7 days, and pancreatic islets were obtained for protein extracts to perform western blot analysis with various antibodies (a) and total RNA isolation for northern blot analysis using BTG2, PDX-1 and insulin probes (b). Protein and mRNA expression were normalized to β-actin and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) level, respectively. (c) Pancreatic islets were transfected with BTG2 siRNA (si BTG2) and Scrambled siRNA (si Scram) for 36 h. After knockdown for 36 h, insulin secretion was performed from pancreatic islets and treated with or without GLP-1 (10 nℳ) and Ex-4 (100 nℳ) using a radioimmunoassay kit. All mice were separated into experimental groups (n=4–6 mice per group). *P<0.05 and **P<0.05 compared with untreated control and GLP-1- and Ex-4-treated cells.
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fig5: Ex-4 increases insulin gene expression via BTG2 induction. (a and b) C57BL/6 mice were injected intraperitoneally with Ex-4 (20 μg kg−1 of body weight) for 7 days, and pancreatic islets were obtained for protein extracts to perform western blot analysis with various antibodies (a) and total RNA isolation for northern blot analysis using BTG2, PDX-1 and insulin probes (b). Protein and mRNA expression were normalized to β-actin and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) level, respectively. (c) Pancreatic islets were transfected with BTG2 siRNA (si BTG2) and Scrambled siRNA (si Scram) for 36 h. After knockdown for 36 h, insulin secretion was performed from pancreatic islets and treated with or without GLP-1 (10 nℳ) and Ex-4 (100 nℳ) using a radioimmunoassay kit. All mice were separated into experimental groups (n=4–6 mice per group). *P<0.05 and **P<0.05 compared with untreated control and GLP-1- and Ex-4-treated cells.

Mentions: Previous studies have shown that GLP-1 and Ex-4, a GLP-1 agonist, elevate insulin gene expression and subsequently increase insulin secretion in rodent and human subjects.4, 8, 28, 29 On the basis of these findings, we confirmed the biological relevance between Ex-4-mediated insulin gene expression and BTG2 in animal experiments. In agreement with in vitro experiments, Ex-4 treatment significantly increased protein production and mRNA levels of BTG2 and PDX-1, and subsequently elevated insulin gene expression in pancreatic islets (Figures 5a and b). Taken together, these findings suggest that Ex-4 has an important function in the regulation of the PDX-1–insulin pathway via BTG2 induction in pancreatic islets. Finally, we confirmed the crucial role of BTG2 on Ex-4- and GLP-1-stimulated insulin secretion in pancreatic islets. As expected, Ex-4 and GLP-1 significantly elevated insulin secretion, consistent with the previous results (Figures 4c and d), and this stimulation was markedly abolished by BTG2 knockdown (Figure 5c). Overall, these results suggest that BTG2 has an important role in the positive regulation of Ex-4-stimulated insulin secretion in pancreatic islets.


B-cell translocation gene 2 positively regulates GLP-1-stimulated insulin secretion via induction of PDX-1 in pancreatic β-cells.

Hwang SL, Kwon O, Kim SG, Lee IK, Kim YD - Exp. Mol. Med. (2013)

Ex-4 increases insulin gene expression via BTG2 induction. (a and b) C57BL/6 mice were injected intraperitoneally with Ex-4 (20 μg kg−1 of body weight) for 7 days, and pancreatic islets were obtained for protein extracts to perform western blot analysis with various antibodies (a) and total RNA isolation for northern blot analysis using BTG2, PDX-1 and insulin probes (b). Protein and mRNA expression were normalized to β-actin and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) level, respectively. (c) Pancreatic islets were transfected with BTG2 siRNA (si BTG2) and Scrambled siRNA (si Scram) for 36 h. After knockdown for 36 h, insulin secretion was performed from pancreatic islets and treated with or without GLP-1 (10 nℳ) and Ex-4 (100 nℳ) using a radioimmunoassay kit. All mice were separated into experimental groups (n=4–6 mice per group). *P<0.05 and **P<0.05 compared with untreated control and GLP-1- and Ex-4-treated cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3674408&req=5

fig5: Ex-4 increases insulin gene expression via BTG2 induction. (a and b) C57BL/6 mice were injected intraperitoneally with Ex-4 (20 μg kg−1 of body weight) for 7 days, and pancreatic islets were obtained for protein extracts to perform western blot analysis with various antibodies (a) and total RNA isolation for northern blot analysis using BTG2, PDX-1 and insulin probes (b). Protein and mRNA expression were normalized to β-actin and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) level, respectively. (c) Pancreatic islets were transfected with BTG2 siRNA (si BTG2) and Scrambled siRNA (si Scram) for 36 h. After knockdown for 36 h, insulin secretion was performed from pancreatic islets and treated with or without GLP-1 (10 nℳ) and Ex-4 (100 nℳ) using a radioimmunoassay kit. All mice were separated into experimental groups (n=4–6 mice per group). *P<0.05 and **P<0.05 compared with untreated control and GLP-1- and Ex-4-treated cells.
Mentions: Previous studies have shown that GLP-1 and Ex-4, a GLP-1 agonist, elevate insulin gene expression and subsequently increase insulin secretion in rodent and human subjects.4, 8, 28, 29 On the basis of these findings, we confirmed the biological relevance between Ex-4-mediated insulin gene expression and BTG2 in animal experiments. In agreement with in vitro experiments, Ex-4 treatment significantly increased protein production and mRNA levels of BTG2 and PDX-1, and subsequently elevated insulin gene expression in pancreatic islets (Figures 5a and b). Taken together, these findings suggest that Ex-4 has an important function in the regulation of the PDX-1–insulin pathway via BTG2 induction in pancreatic islets. Finally, we confirmed the crucial role of BTG2 on Ex-4- and GLP-1-stimulated insulin secretion in pancreatic islets. As expected, Ex-4 and GLP-1 significantly elevated insulin secretion, consistent with the previous results (Figures 4c and d), and this stimulation was markedly abolished by BTG2 knockdown (Figure 5c). Overall, these results suggest that BTG2 has an important role in the positive regulation of Ex-4-stimulated insulin secretion in pancreatic islets.

Bottom Line: Notably, adenovirus-mediated overexpression of BTG2 significantly elevated insulin secretion, as well as insulin and PDX-1 gene expression.Physical interaction studies showed that BTG2 is associated with increased PDX-1 occupancy on the insulin gene promoter via a direct interaction with PDX-1.Finally, we revealed that Ex-4 and GLP-1 significantly elevated insulin secretion via upregulation of the BTG2-PDX-1 axis in pancreatic islets, and this phenomenon was abolished by endogenous BTG2 knockdown.

View Article: PubMed Central - PubMed

Affiliation: College of Pharmacy, Yeungnam University, Gyeongsan, Republic of Korea.

ABSTRACT
Glucagon-like peptide-1 (GLP-1) is a potent glucoincretin hormone and an important agent for the treatment of type 2 diabetes. Here we demonstrate that B-cell translocation gene 2 (BTG2) is a crucial regulator in GLP-1-induced insulin gene expression and insulin secretion via upregulation of pancreatic duodenal homeobox-1 (PDX-1) in pancreatic β-cells. GLP-1 treatment significantly increased BTG2, PDX-1 and insulin gene expression in pancreatic β-cells. Notably, adenovirus-mediated overexpression of BTG2 significantly elevated insulin secretion, as well as insulin and PDX-1 gene expression. Physical interaction studies showed that BTG2 is associated with increased PDX-1 occupancy on the insulin gene promoter via a direct interaction with PDX-1. Exendin-4 (Ex-4), a GLP-1 agonist, and GLP-1 in pancreatic β-cells increased insulin secretion through the BTG2-PDX-1-insulin pathway, which was blocked by endogenous BTG2 knockdown using a BTG2 small interfering RNA knockdown system. Finally, we revealed that Ex-4 and GLP-1 significantly elevated insulin secretion via upregulation of the BTG2-PDX-1 axis in pancreatic islets, and this phenomenon was abolished by endogenous BTG2 knockdown. Collectively, our current study provides a novel molecular mechanism by which GLP-1 positively regulates insulin gene expression via BTG2, suggesting that BTG2 has a key function in insulin secretion in pancreatic β-cells.

Show MeSH
Related in: MedlinePlus