Transcription Factor BETA2 Acts Cooperatively with E2A and PDX1 to Activate the Insulin Gene Promoter

Eitan Glick, Dena Leshkowitz, Michael D. Walker
2000 Journal of Biological Chemistry  
The insulin gene is efficiently expressed only in pancreatic beta cells. Using reverse transcriptase-polymerase chain reaction analysis, we show that insulin mRNA levels are at least 10 5 -fold higher in beta cells than nonbeta cells. To examine the underlying mechanisms, we expressed beta cell transcription factors by transfection of non-beta cells. Separate expression of BETA2, E2A, or PDX1 led to modest (<10-fold) activation of the insulin promoter, whereas co-expression of the three
more » ... produced synergistic, high level activation (160-fold). This level of activity is ϳ25% that observed in transfected beta cell lines. Of the three factors studied, BE-TA2 appears to play a dominant role. Efficient transcription required a C-terminal activation domain of BETA2 and an N-terminal region, which does not function as an independent activation domain. The myogenic basic helix-loop-helix (bHLH) protein MyoD was unable to bind and activate the promoter, even when its DNA binding region was replaced with that of BETA2. Our results demonstrate the central importance of BETA2 in insulin gene transcription and the importance of sequences outside the canonical DNA binding domain in permitting efficient DNA binding and cell-specific activity of the insulin gene promoter.
doi:10.1074/jbc.275.3.2199 pmid:10636926 fatcat:jru2ht7ok5bylpiqbg7v3u5zty