The islet beta cell-enriched MafA activator is a key regulator of insulin gene transcription.
The islet-enriched MafA, PDX-1, and BETA2 activators contribute to both beta cell-specific and glucose-responsive insulin gene transcription. To investigate how these factors impart activation, their combined impact upon insulin enhancer-driven expression was first examined in non-beta cell line transfection assays. Individual expression of PDX-1 and BETA2 led to little or no activation, whereas MafA alone did so modestly. MafA together with PDX-1 or BETA2 produced synergistic activation, with even higher insulin promoter activity found when all three proteins were present. Stimulation was attenuated upon compromising either MafA transactivation or DNA-binding activity. MafA interacted with endogenous PDX-1 and BETA2 in coimmunoprecipitation and in vitro GST pull-down assays, suggesting that regulation involved direct binding. Dominant-negative acting and small interfering RNAs of MafA also profoundly reduced insulin promoter activity in beta cell lines. In addition, MafA was induced in parallel with insulin mRNA expression in glucose-stimulated rat islets. Insulin mRNA levels were also elevated in rat islets by adenoviral-mediated expression of MafA. Collectively, these results suggest that MafA plays a key role in coordinating and controlling the level of insulin gene expression in islet beta cells.
Zhao
Li
L
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Guo
Min
M
Matsuoka
Taka-Aki
TA
Hagman
Derek K
DK
Parazzoli
Susan D
SD
Poitout
Vincent
V
Stein
Roland
R
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins / Q000502:physiology; D005786:Gene Expression Regulation; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000378:metabolism*; D051473:Maf Transcription Factors, Large; D051258:MafB Transcription Factor; D009687:Nuclear Proteins / Q000502:physiology; D015513:Oncogene Proteins / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D007328:Insulin; D051473:Maf Transcription Factors, Large; D051258:MafB Transcription Factor; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C485159:MAFA protein, human; C490407:MAFB protein, human; C093970:NEUROD1 protein, human; C084010:pancreatic and duodenal homeobox 1 protein