Abstract IA27: Deregulation and oncogenic functions of the NSD2/MMSET histone methyl transferase in hematologic malignancies

Abstract

Abstract Epigenetic regulators of gene expression are among the commonest class of proteins mutated in human cancer. Most of these mutations lead to compete or total loss of function of the proteins leading to deregulated gene expression. Gain-of-function mutations in regulators are rare. The NSD2/MMSET histone methyltranferase is overexpressed in multiple myeloma associated with t(4;14) and leads to a global increase in histone 3 lysine 36 dimethylation, a chromatin mark associated with gene activation and a decrease of the inhibitory H3K27 methyl mark. As a result, gene expression is reprogrammed and many genes are aberrantly activated. Furthermore, the chromatin structure of cells with NSD2 overexpression is more “open.” In MM cells NSD2 overexpression increases MM cell growth and strikingly increases DNA repair processes making cells relatively resistant to chemotherapy, potentially explaining the poor prognosis of such patients. Proteomic studies show that NSD2 is associated with a variety of proteins involved in RNA metabolism, suggesting roles in both transcriptional and post-transcriptional processes. NSD2 is recurrently mutated in up to 15% of cases of relapsed childhood acute lymphocytic leukemia, in mantle cell lymphoma, and rarely in multiple myeloma and other tumors. This mutation increases the turnover rate of the enzyme in vitro and in vivo accelerates the conversion of unmodified histone to H3K36me1.The result is a global increase of H3K36me2 levels in cells with a concomitant decrease in H3k27me3 levels. Using CRISPR-mediated gene editing we eliminated this mutant allele, yielding reversal of histone methylation patterns, deceased growth, altered cellular adhesion, and increased susceptibility to chemotherapy. RNA-seq analysis showed that NSD2 mutation activated an aberrant program of cell adhesion resembling the epithelial-mesenchymal transition, increased motility, and augmented signaling and glucocorticoid and chemotherapy resistance likely associated with tumor progression. Mice harboring ALL cells with the E1099K mutation succumbed to disseminated leukemia faster than mice injected with cells in which the mutation was corrected. Furthermore, there was enhanced accumulation of cells with E1099K mutation in the brain, a common site of relapse in childhood ALL. Animal experiments suggest that knockdown of NSD2 could augment chemotherapy sensitivity motivating the search for NSD2 inhibitors. While modestly effective inhibitors have been identified to work in vitro, there are no inhibitors that are active in cells. A recently published crystal structure of an NSD2 structure is motivating our new in silico searches for candidate inhibitors. Citation Format: Jonathan D. Licht. Deregulation and oncogenic functions of the NSD2/MMSET histone methyl transferase in hematologic malignancies [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr IA27.