Overexpression of histone methyltransferase NSD in Drosophila induces apoptotic cell death via the Jun-N-terminal kinase pathway.

The nuclear receptor-binding SET domain protein gene (NSD) family encodes a group of highly conserved SET domain-containing histone lysine methyltransferases that are important in multiple aspects of development in various organisms. The association of NSD1 duplications has been reported with growth retardation diseases in humans. In this study, to gain insight into the molecular mechanisms by which the overexpression of NSD1 influences the disease progression, we analyzed the gain-of-function mutant phenotypes of the Drosophila NSD using the GAL4/UAS system. Ubiquitous overexpression of NSD in the fly caused developmental delay and reduced body size at the larval stage, resulting in pupal lethality. Moreover, targeted overexpression in various developing tissues led to significant phenotype alterations, and the gain-of-function phenotypes were rescued by NSD RNAi knockdown. We also demonstrated that NSD overexpression not only enhanced the transcription of pro-apoptotic genes but also activated caspase. The atrophied phenotype of NSD-overexpressing wing was strongly suppressed by a loss-of-function mutation in hemipterous, which encodes a Drosophila Jun N-terminal kinase. Taken together, our findings suggest that NSD induces apoptosis via the activation of JNK, and thus contributes to the understanding of the molecular mechanisms involved in NSD1-related diseases in humans.