Activin A-induced expression of PAX4 in AR42J-B13 cells involves the increase in transactivation of E47/E12

Pax4 is a paired-homeodomain containing transcriptional factor that controls the differentiation of pancreatic β cells. The aim of this study was to investigate the mechanism of PAX4 expression by activin A. By reporter gene analysis using AR42J-B13 cells, in which treatment with activin A induced PAX4 mRNA expression, we identified that a short sequence located ∼1930 bp upstream of the transcriptional start site is essential for activin A induced PAX4 promoter activation. This region contains an E box and binding sites for hepatocyte nuclear factor (HNF)-1α. Mutation introduced in each binding site markedly reduced activin A responsiveness. It has been reported that HNF-1α synergizes with basic helix-loop-helix (bHLH) proteins in activating the PAX4 promoter, and we demonstrated that activin A strongly enhanced the functional activity of E47/E12 without the increase in its binding ability. In addition, suppression of E47/E12 expression in AR42J-B13 cells using siRNA oligonucleotides results in the significant decrease in the intrinsic activin A-induced PAX4 expression. Our results suggest that activin A enhances PAX4 expression by enhanced transactivation of E47/E12 proteins and might result in a cumulative transactivation of the promoter.