Prolactin regulatory element binding protein as a potential transcriptional factor for the insulin gene in response to glucose stimulation.
OBJECTIVE
Prolactin regulatory element binding (PREB) protein has been identified as a factor that regulates prolactin promoter activity in rat anterior pituitary. PREB is located not only in the anterior pituitary but also in pancreas; however its role in the pancreas is not known. We therefore examined the role of PREB in insulin gene expression.


METHODS
To analyse the effects of PREB on insulin gene transcription, we employed the luciferase reporter gene assay and electrophoretic mobility shift assay (EMSA). In cells expressing or knocked down for PREB, insulin expression and secretion were determined.


RESULTS
PREB was located mainly in nuclei of rat pancreatic beta cells and its cell line, INS-1. A nuclear extract of INS-1 cells contained material that was recognised by PREB antiserum. This nuclear extract also showed insulin promoter binding activity that was super-shifted by PREB antiserum in EMSA studies. In the INS-1 cells, co-expression of PREB and the insulin promoter induced activity of the latter. The addition of glucose to the cells increased PREB expression. Deletional analysis of the insulin promoter showed that A3, a glucose-responsive cis-element in the insulin promoter, mediated the transcriptional effect of PREB. In addition, synthesised PREB bound the A3 element by EMSA, while a mutant of this motif in the insulin promoter abrogated the effect of PREB. Cells expressing or knocked down for PREB exhibited increased or decreased insulin expression, respectively.


CONCLUSIONS
These results demonstrate that PREB may contribute to the regulation of insulin gene transcription and insulin secretion in response to glucose stimulation.
Ohtsuka
S
S
Division of Endocrinology and Metabolism, Department of Internal Medicine, Kagawa University, 1750-1, Miki-cho, Kita-gun, Kagawa, Japan.
Murao
K
K
Imachi
H
H
Cao
W M
WM
Yu
X
X
Li
J
J
Iwama
H
H
Wong
N C W
NC
Bancroft
C
C
Ishida
T
T
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism / Q000502:physiology*; D007328:Insulin / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D011401:Promoter Regions, Genetic; D051381:Rats; D017208:Rats, Wistar; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*
D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin; C485592:Preb protein, rat; D014157:Transcription Factors; D005947:Glucose