Exendin-4 regulates glucokinase expression by CaMKK/CaMKIV pathway in pancreatic β-cell line

K. Murao, J. Li, H. Imachi, T. Muraoka, H. Masugata, G. X. Zhang, R. Kobayashi, T. Ishida, Hiroshi Tokumitsu

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Aim: Glucokinase (GK) in pancreatic β cells is thought to be involved in insulin secretion and glucose homeostasis. This study investigates whether the long-acting agonist of the glucagon-like peptide 1, namely exendin-4, mediates stimulatory effects on GK gene expression through the Ca2+/calmodulin (CaM)-dependent protein kinase (CaMK) cascade. Methods: : GK expression was examined by real-time PCR, western blot analysis and reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. CaMKIV activity was assessed by detection of activation loop phosphorylation (Thr196) of CaMKIV. We investigated the effect of the constitutively active form (CaMKIVc) of CaMKIV on GK promoter activity. Results: Increased expression level of GK protein was noted in response to rising concentrations of exendin-4 with maximum induction at 10 nM. Real-time PCR analysis showed a significant increase in the amount of GK mRNA in response to rising concentrations of exendin-4. Exendin-4 also stimulated GK promoter activity but failed to do so in the presence of STO-609, a CaMKK inhibitor. This result is consistent with the observations that the upregulation of CaMKIV phosphorylation (at Thr196) peaked after 15 min of exposure to exendin-4 and that CaMKIVc enhanced or upregulated GK promoter activity in INS-1 cells. Furthermore, STO-609 significantly suppressed the exendin-4 - upregulated the expression of the GK protein. Conclusion: Activation of the CaMKK/CaMKIV cascade might be required for exendin-4-induced GK gene transcription, indicating that exendin-4 plays an important role in insulin secretion in pancreatic β cells.

Original languageEnglish
Pages (from-to)939-946
Number of pages8
JournalDiabetes, Obesity and Metabolism
Volume11
Issue number10
DOIs
Publication statusPublished - Oct 2009
Externally publishedYes

Fingerprint

Calcium-Calmodulin-Dependent Protein Kinase Kinase
Glucokinase
Cell Line
Insulin
Real-Time Polymerase Chain Reaction
Phosphorylation
exenatide
Calcium-Calmodulin-Dependent Protein Kinases
Glucagon-Like Peptide 1
Reporter Genes

Keywords

  • CaMKK/CaMKIV
  • Exendin-4
  • GLP-1
  • Glucokinase

ASJC Scopus subject areas

  • Internal Medicine
  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

Exendin-4 regulates glucokinase expression by CaMKK/CaMKIV pathway in pancreatic β-cell line. / Murao, K.; Li, J.; Imachi, H.; Muraoka, T.; Masugata, H.; Zhang, G. X.; Kobayashi, R.; Ishida, T.; Tokumitsu, Hiroshi.

In: Diabetes, Obesity and Metabolism, Vol. 11, No. 10, 10.2009, p. 939-946.

Research output: Contribution to journalArticle

Murao, K, Li, J, Imachi, H, Muraoka, T, Masugata, H, Zhang, GX, Kobayashi, R, Ishida, T & Tokumitsu, H 2009, 'Exendin-4 regulates glucokinase expression by CaMKK/CaMKIV pathway in pancreatic β-cell line', Diabetes, Obesity and Metabolism, vol. 11, no. 10, pp. 939-946. https://doi.org/10.1111/j.1463-1326.2009.01067.x
Murao, K. ; Li, J. ; Imachi, H. ; Muraoka, T. ; Masugata, H. ; Zhang, G. X. ; Kobayashi, R. ; Ishida, T. ; Tokumitsu, Hiroshi. / Exendin-4 regulates glucokinase expression by CaMKK/CaMKIV pathway in pancreatic β-cell line. In: Diabetes, Obesity and Metabolism. 2009 ; Vol. 11, No. 10. pp. 939-946.
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AU - Murao, K.

AU - Li, J.

AU - Imachi, H.

AU - Muraoka, T.

AU - Masugata, H.

AU - Zhang, G. X.

AU - Kobayashi, R.

AU - Ishida, T.

AU - Tokumitsu, Hiroshi

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N2 - Aim: Glucokinase (GK) in pancreatic β cells is thought to be involved in insulin secretion and glucose homeostasis. This study investigates whether the long-acting agonist of the glucagon-like peptide 1, namely exendin-4, mediates stimulatory effects on GK gene expression through the Ca2+/calmodulin (CaM)-dependent protein kinase (CaMK) cascade. Methods: : GK expression was examined by real-time PCR, western blot analysis and reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. CaMKIV activity was assessed by detection of activation loop phosphorylation (Thr196) of CaMKIV. We investigated the effect of the constitutively active form (CaMKIVc) of CaMKIV on GK promoter activity. Results: Increased expression level of GK protein was noted in response to rising concentrations of exendin-4 with maximum induction at 10 nM. Real-time PCR analysis showed a significant increase in the amount of GK mRNA in response to rising concentrations of exendin-4. Exendin-4 also stimulated GK promoter activity but failed to do so in the presence of STO-609, a CaMKK inhibitor. This result is consistent with the observations that the upregulation of CaMKIV phosphorylation (at Thr196) peaked after 15 min of exposure to exendin-4 and that CaMKIVc enhanced or upregulated GK promoter activity in INS-1 cells. Furthermore, STO-609 significantly suppressed the exendin-4 - upregulated the expression of the GK protein. Conclusion: Activation of the CaMKK/CaMKIV cascade might be required for exendin-4-induced GK gene transcription, indicating that exendin-4 plays an important role in insulin secretion in pancreatic β cells.

AB - Aim: Glucokinase (GK) in pancreatic β cells is thought to be involved in insulin secretion and glucose homeostasis. This study investigates whether the long-acting agonist of the glucagon-like peptide 1, namely exendin-4, mediates stimulatory effects on GK gene expression through the Ca2+/calmodulin (CaM)-dependent protein kinase (CaMK) cascade. Methods: : GK expression was examined by real-time PCR, western blot analysis and reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. CaMKIV activity was assessed by detection of activation loop phosphorylation (Thr196) of CaMKIV. We investigated the effect of the constitutively active form (CaMKIVc) of CaMKIV on GK promoter activity. Results: Increased expression level of GK protein was noted in response to rising concentrations of exendin-4 with maximum induction at 10 nM. Real-time PCR analysis showed a significant increase in the amount of GK mRNA in response to rising concentrations of exendin-4. Exendin-4 also stimulated GK promoter activity but failed to do so in the presence of STO-609, a CaMKK inhibitor. This result is consistent with the observations that the upregulation of CaMKIV phosphorylation (at Thr196) peaked after 15 min of exposure to exendin-4 and that CaMKIVc enhanced or upregulated GK promoter activity in INS-1 cells. Furthermore, STO-609 significantly suppressed the exendin-4 - upregulated the expression of the GK protein. Conclusion: Activation of the CaMKK/CaMKIV cascade might be required for exendin-4-induced GK gene transcription, indicating that exendin-4 plays an important role in insulin secretion in pancreatic β cells.

KW - CaMKK/CaMKIV

KW - Exendin-4

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KW - Glucokinase

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