Exendin-4 regulates GLUT2 expression via the CaMKK/CaMKIV pathway in a pancreatic β-cell line.
The GLUT2 glucose transporter plays an important role in glucose-induced insulin secretion in pancreatic β-cells by catalyzing the uptake of glucose into the cell. In this study, we investigated whether exendin-4, a long-acting agonist of glucagon-like peptide-1, mediates stimulatory effects on GLUT2 gene expression through the Ca²+/calmodulin (CaM)-dependent protein kinase IV (CaMKIV) cascade. GLUT2 expression was examined by real-time polymerase chain reaction, Western blot analysis, and a reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. An increased expression level of GLUT2 protein was noted in response to increasing concentrations of exendin-4, with maximal induction at 10 nmol/L. Real-time polymerase chain reaction analysis similarly revealed a significant increase in the amount of GLUT2 messenger RNA by 10 nmol/L exendin-4. Exendin-4 also stimulated GLUT2 promoter activity in response to increasing exendin-4 concentrations, but failed to do so in the presence of STO-609, a CaMKK inhibitor. We also investigated the effect of the constitutively active form of CaMKK (CaMKKc) on GLUT2 promoter activity. The result is consistent with the observations that CaMKKc/CaMKIV enhanced or up-regulated GLUT2 promoter activity in INS-1 cells. Furthermore, exendin-4 induction of GLUT2 protein expression was significantly suppressed in the cells knocking down the CaMKIV. In summary, activation of the CaMKK/CaMKIV cascade might be required for exendin-4-induced GLUT2 gene transcription, indicating that exendin-4 plays an important role in insulin secretion in pancreatic β-cells.
Chen
Ke
K
Division of Endocrinology and Metabolism, Department of Internal Medicine, Faculty of Medicine, Kagawa University, 1750-1 Ikenobe Miki-CHO, Kagawa 761-0793, Japan.
Yu
Xiao
X
Murao
Koji
K
Imachi
Hitomi
H
Li
Junhua
J
Muraoka
Tomie
T
Masugata
Hisashi
H
Zhang
Guo-Xing
GX
Kobayashi
Ryoji
R
Ishida
Toshihiko
T
Tokumitsu
Hiroshi
H
D000818:Animals; D015153:Blotting, Western; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000077270:Exenatide; D017930:Genes, Reporter; D051273:Glucose Transporter Type 2 / Q000096:biosynthesis* / Q000235:genetics; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000201:enzymology / Q000378:metabolism*; D008156:Luciferases / Q000235:genetics; D010455:Peptides / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection; D014688:Venoms / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D051273:Glucose Transporter Type 2; D007004:Hypoglycemic Agents; D010455:Peptides; D034741:RNA, Small Interfering; C495683:Slc2a2 protein, rat; D014688:Venoms; D000077270:Exenatide; D008156:Luciferases; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4