Insulin gene expression is regulated by DNA methylation.
BACKGROUND
Insulin is a critical component of metabolic control, and as such, insulin gene expression has been the focus of extensive study. DNA sequences that regulate transcription of the insulin gene and the majority of regulatory factors have already been identified. However, only recently have other components of insulin gene expression been investigated, and in this study we examine the role of DNA methylation in the regulation of mouse and human insulin gene expression.


RESULTS
Genomic DNA samples from several tissues were bisulfite-treated and sequenced which revealed that cytosine-guanosine dinucleotide (CpG) sites in both the mouse Ins2 and human INS promoters are uniquely demethylated in insulin-producing pancreatic beta cells. Methylation of these CpG sites suppressed insulin promoter-driven reporter gene activity by almost 90% and specific methylation of the CpG site in the cAMP responsive element (CRE) in the promoter alone suppressed insulin promoter activity by 50%. Methylation did not directly inhibit factor binding to the CRE in vitro, but inhibited ATF2 and CREB binding in vivo and conversely increased the binding of methyl CpG binding protein 2 (MeCP2). Examination of the Ins2 gene in mouse embryonic stem cell cultures revealed that it is fully methylated and becomes demethylated as the cells differentiate into insulin-expressing cells in vitro.


CONCLUSIONS
Our findings suggest that insulin promoter CpG demethylation may play a crucial role in beta cell maturation and tissue-specific insulin gene expression.
Kuroda
Akio
A
Department of Diabetes, Endocrinology, & Metabolism, Research Institute of City of Hope, Duarte, California, United States of America.
Rauch
Tibor A
TA
Todorov
Ivan
I
Ku
Hsun Teresa
HT
Al-Abdullah
Ismail H
IH
Kandeel
Fouad
F
Mullen
Yoko
Y
Pfeifer
Gerd P
GP
Ferreri
Kevin
K
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D018899:CpG Islands; D019175:DNA Methylation; D017931:DNA Primers / Q000737:chemistry; D053595:Embryonic Stem Cells / Q000166:cytology; D044127:Epigenesis, Genetic; D005786:Gene Expression Regulation; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology; D051379:Mice; D008954:Models, Biological; D008957:Models, Genetic; D011401:Promoter Regions, Genetic; D015533:Transcriptional Activation
D017931:DNA Primers; D007328:Insulin