Study of NSD2 using a dTAG system reveals its molecular mechanism and oncogenic implications in t(4;14) multiple myeloma.

The histone H3 lysine 36 dimethylation (H3K36me2) methyltransferase NSD2 is deleted in Wolf-Hirschhorn syndrome and is aberrantly expressed in 10% to 15% of patients with multiple myeloma (MM) because of a t(4;14) translocation. Although NSD2 is thought to be a primary driver in MM, the exact molecular mechanisms by which it regulates transcription remain unclear. We applied the degradation tag (dTAG) system to acutely degrade NSD2 and used this, in combination with time-resolved thiol-linked alkylation for the metabolic sequencing of RNA (SLAM-seq), to identify 307 transcriptional targets of NSD2. Reconstitution with either wild-type NSD2 or a catalytically inactive mutant (NSD2Y1179A) showed that NSD2's transcriptional effects are almost exclusively dependent on its SET domain activity. Mechanistically, H3K36me2 deposition by NSD2 antagonizes H3K27me3 levels, and treatment with 2 distinct Polycomb repressive complex 2 inhibitors demonstrated that approximately half of the NSD2 target genes are regulated in an H3K27me3-dependent manner. Cleavage under targets and tagmentation (CUT&Tag) analysis showed that upon NSD2 depletion, there was an increase in H3K27me3 that occurred at genome-wide intergenic regions rather than at the promoters or gene bodies of NSD2 target genes. These data suggest that NSD2, via H3K36me2, antagonizes H3K27me3 deposition likely at distal regulatory elements, including enhancers, creating a chromatin landscape favorable for target gene transcription. Importantly, NSD2 target genes were enriched for key oncogenic pathways, and 24 transcription factors (TFs) implicated in neurodevelopment and acute leukemia, consistent with its role in Wolf-Hirschhorn syndrome and MM. Eight of these TFs are known oncogenic drivers in acute leukemia or MM, highlighting a novel molecular mechanism for NSD2's role in t(4;14) MM.