The Drosophila histone methyltransferase NSD is positively regulated by the DRE/DREF system

The Drosophila nuclear receptor-binding SET domain protein (NSD) gene encodes the Drosophila ortholog of mammalian NSD family members that are important in many aspects of development and disease in humans. In this study, we observed that overexpression of Drosophila NSD in imaginal discs induces organ atrophy. Thus, to gain an understanding of the transcriptional regulation of the gene, we analyzed the NSD promoter region. First, we identified the presence of three putative DNA replication-related element (DRE) sequences in its promoter region, where DRE-binding factor (DREF) could bind for transcriptional activation. In the experiments with the fly GAL4-UAS system, we demonstrated that overexpressed DREF increased the endogenous NSD transcription. To confirm the role of DREF as a transcriptional activator on the NSD expression, we generated a series of luciferase reporter gene constructs containing deleted portions of the 5'-flanking regions as well as point mutations in the putative DRE sites. When transiently transfected into S2 cells, the deletion construct containing no DRE sites showed dramatic decrease in the NSD promoter activity, but only two sites near the transcriptional start site were important. Furthermore, we verified the direct interaction of DREF with the two positively cis-acting sequences on the NSD promoter by chromatin immunoprecipitation assay. Taken together, these results demonstrated that NSD is one of the downstream targets of the DRE/DREF pathway that is associated with various cellular processes in Drosophila, indicating that our findings may contribute to the understanding of molecular mechanisms in complex disorders associated with NSD family members in humans.