Big brain, a Drosophila homologue of mammalian aquaporin, is regulated by the DRE/DREF system

Drosophila big brain (bib) encodes for a protein similar to members of the major intrinsic protein family, which includes the water- and ion-conducting aquaporin (AQP) channels. In mammals, AQP dysregulation has been implicated in a variety of diseases, including colorectal cancer and colonic injury. However, the regulatory mechanisms of AQP expression remain to be clearly elucidated. In this study, as we found a DREF binding site (DRE) in the 5′-flanking regions of both the Drosophila bib gene and the human AQP1 gene, we assessed the role of DREF in bib gene expression. DREF in Drosophila and humans has been demonstrated to function as a key transcriptional activator for cell proliferation-related genes. Herein, we demonstrate that the DRE is required for optimal promoter activity of Drosophila bib gene, particularly in the larval imaginal discs, which are actively proliferating tissues, as well as the adult hindgut. Our results may provide insight into the mechanisms inherent to the regulation of mammalian AQP genes.