31 Zhao, L. Guo, M. Matsuoka, T. A. Hagman, D. K. Parazzoli, S. D. Poitout, V. Stein, R. 2005 J Biol Chem 280 12 11887-94 Mar 25 0021-9258 (Print) 15665000 DNA-Binding Proteins/physiology Basic Helix-Loop-Helix Transcription Factors *Transcription, Genetic Transcription Factors/physiology Trans-Activators/*physiology Oncogene Proteins/physiology Nuclear Proteins/physiology MafB Transcription Factor Maf Transcription Factors, Large Islets of Langerhans/*metabolism Insulin/*genetics Humans Homeodomain Proteins/physiology Hela Cells *Gene Expression Regulation *Transcription Genetic Maf Transcription Factors Large 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. P01-DK42502/DK/NIDDK NIH HHS/United StatesP60 DK20593/DK/NIDDK NIH HHS/United StatesR01-DK58096/DK/NIDDK NIH HHS/United StatesJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.United States http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15665000