The role of calcium/calmodulin-dependent protein kinase cascade in glucose upregulation of insulin gene expression.
A number of factors have been reported to affect insulin synthesis in beta-cells. Although glucose is the most important regulator of insulin gene expression in pancreatic beta-cells, the mechanisms whereby glucose stimulates insulin gene transcription in response to changes in glucose concentration have not been clarified yet. In this study, we examined the role of the Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaM-K) cascade in transcriptional activation of insulin. RT-PCR, Western blotting, and immunohistochemical staining analysis revealed that CaM-K kinase-alpha (CaM-KKalpha) and CaM-KIV were localized in rat pancreatic beta-cells and their cell line, INS-1. Exposure of INS-1 cells to 11.2 mmol/l glucose elicited an increase of insulin promoter activity as well as upregulation of CaM-KIV activity within 2 min after stimulation. We investigated the influence on insulin promoter activity of the constitutively active form (CaM-KIVc) or dominant-negative mutant (CaM-KIVdn) of CaM-KIV in transfected INS-1 cells. CaM-KIVc alone was sufficient, and the upstream kinase, CaM-KK, was enhanced to upregulate the insulin promoter activity in INS-1 cells. Furthermore, cotransfection of CaM-KIVdn suppressed to a significant degree the glucose-upregulated activity of the insulin promoter. Taken together, these results indicated that the CaM-KK/CaM-KIV cascade might play an important role in glucose-upregulated transcriptional activation of the insulin gene.
Yu
Xiao
X
First Department of Internal Medicine, Kagawa Medical University, 1750-1, Miki-cho, Kita-gun, Kagawa, 761-0793, Japan.
Murao
Koji
K
Sayo
Yoshitaka
Y
Imachi
Hitomi
H
Cao
Wen M
WM
Ohtsuka
Shouji
S
Niimi
Michio
M
Tokumitsu
Hiroshi
H
Inuzuka
Hiroyuki
H
Wong
Norman C W
NC
Kobayashi
Ryoji
R
Ishida
Toshihiko
T
D000818:Animals; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D015870:Gene Expression / Q000502:physiology; D005799:Genes, Dominant; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000502:physiology; D015854:Up-Regulation
D007328:Insulin; D007527:Isoenzymes; D017346:Protein Serine-Threonine Kinases; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517701:Camkk1 protein, rat; D005947:Glucose