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Depletion of H3K36me2 recapitulates epigenomic and phenotypic changes induced by the H3.3K36M oncohistone mutation

Significance Recurrent histone H3K36M mutations are found in multiple cancer types yet their oncogenic mechanisms remain incompletely understood. Biochemically, H3K36M oncohistone dominantly inhibits several H3K36-specific methyltransferases such as NSD1/2 and SETD2, resulting in decreases in all methylation states of H3K36. We report here that genetic ablation of NSD1 and NSD2, methyltransferases specific for H3K36 dimethylation (H3K36me2), is sufficient to recapitulate H3K36M’s effects on enhancer activation, gene expression, differentiation blockade, and drug sensitivity. Our results suggest that depletion of H3K36me2 represents a key event downstream of the H3K36M mutation and also exposes potential therapeutic vulnerability of H3K36M-mutant tumor cells. Hotspot histone H3 mutations have emerged as drivers of oncogenesis in cancers of multiple lineages. Specifically, H3 lysine 36 to methionine (H3K36M) mutations are recurrently identified in chondroblastomas, undifferentiated sarcomas, and head and neck cancers. While the mutation reduces global levels of both H3K36 dimethylation (H3K36me2) and trimethylation (H3K36me3) by dominantly inhibiting their respective specific methyltransferases, the relative contribution of these methylation states to the chromatin and phenotypic changes associated with H3K36M remains unclear. Here, we specifically deplete H3K36me2 or H3K36me3 in mesenchymal cells, using CRISPR-Cas9 to separately knock out the corresponding methyltransferases NSD1/2 or SETD2. By profiling and comparing the epigenomic and transcriptomic landscapes of these cells with cells expressing the H3.3K36M oncohistone, we find that the loss of H3K36me2 could largely recapitulate H3.3K36M’s effect on redistribution of H3K27 trimethylation (H3K27me3) and gene expression. Consistently, knockout of Nsd1/2, but not Setd2, phenocopies the differentiation blockade and hypersensitivity to the DNA-hypomethylating agent induced by H3K36M. Together, our results support a functional divergence between H3K36me2 and H3K36me3 and their nonredundant roles in H3K36M-driven oncogenesis.