The EZH2 histone methyltransferase is highly expressed in germinal center (GC) B-cells and targeted by somatic mutations in B-cell lymphomas. Here we find that EZH2 deletion or pharmacologic inhibition suppresses GC formation and functions in mice. EZH2 represses proliferation checkpoint genes and helps establish bivalent chromatin domains at key regulatory loci to transiently suppress GC B-cell differentiation. Somatic mutations reinforce these physiological effects through enhanced silencing of EZH2 targets in B-cells, and in human B-cell lymphomas. Conditional expression of mutant EZH2 in mice induces GC hyperplasia and accelerated lymphomagenesis in cooperation with BCL2. GCB-type DLBCLs are mostly addicted to EZH2, regardless of mutation status, but not the more differentiated ABC-type DLBCLs, thus clarifying the therapeutic scope of EZH2 targeting.

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PURPOSE Effective treatment options are limited for patients with acute myeloid leukemia (AML) who cannot tolerate intensive chemotherapy. An international phase Ib/II study evaluated the safety and preliminary efficacy of venetoclax, a selective B-cell leukemia/lymphoma-2 inhibitor, together with low-dose cytarabine (LDAC) in older adults with AML. PATIENTS AND METHODS Adults 60 years or older with previously untreated AML ineligible for intensive chemotherapy were enrolled. Prior treatment of myelodysplastic syndrome, including hypomethylating agents (HMA), was permitted. Eighty-two patients were treated at the recommended phase II dose: venetoclax 600 mg per day orally in 28-day cycles, with LDAC (20 mg/m2 per day) administered subcutaneously on days 1 to 10. Key end points were tolerability, safety, response rates, duration of response (DOR), and overall survival (OS). RESULTS Median age was 74 years (range, 63 to 90 years), 49% had secondary AML, 29% had prior HMA treatment, and 32% had poor-risk cytogenetic features. Common grade 3 or greater adverse events were febrile neutropenia (42%), thrombocytopenia (38%), and WBC count decreased (34%). Early (30-day) mortality was 6%. Fifty-four percent achieved complete remission (CR)/CR with incomplete blood count recovery (median time to first response, 1.4 months). The median OS was 10.1 months (95% CI, 5.7 to 14.2), and median DOR was 8.1 months (95% CI, 5.3 to 14.9 months). Among patients without prior HMA exposure, CR/CR with incomplete blood count recovery was achieved in 62%, median DOR was 14.8 months (95% CI, 5.5 months to not reached), and median OS was 13.5 months (95% CI, 7.0 to 18.4 months). CONCLUSION Venetoclax plus LDAC has a manageable safety profile, producing rapid and durable remissions in older adults with AML ineligible for intensive chemotherapy. High remission rate and low early mortality combined with rapid and durable remission make venetoclax and LDAC an attractive and novel treatment for older adults not suitable for intensive chemotherapy.

The multiple myeloma SET domain (MMSET) protein is overexpressed in multiple myeloma (MM) patients with the translocation t(4;14). Although studies have shown the involvement of MMSET/ Wolf-Hirschhorn syndrome candidate 1 in development, its mode of action in the pathogenesis of MM is largely unknown. We found that MMSET is a major regulator of chromatin structure and transcrip- IntroductionMultiple myeloma is an incurable malignancy of mature plasma cells, associated in approximately 40% of cases with recurrent chromosomal translocations that lead to overexpression of known and putative oncogenes. 1,2 MMSET (WHSC1, NSD2) is linked to the immunoglobulin promoter/enhancer in t(4;14) translocations, found in 15%-20% of multiple myeloma. 3 Chromosomal fusion leads to overexpression of MMSET and FGFR3 genes; however, approximately 30% of the patient samples overexpress only the MMSET gene, suggesting its pivotal role in the disease. [4][5][6] The other nuclear receptor Su(var)3-9, Enhancer-of-zeste, Trithorax (SET) domain-containing (NSD) family members, NSD1 and NSD3, were both found to be rearranged as fusion proteins with NUP98 in rare cases of acute myeloid leukemia, and NSD3 is overexpressed in breast cancer, 7,8 suggesting that deregulation of these proteins plays a causative role in malignancy. The MMSET gene undergoes complex alternative splicing and differential promoter usage, giving rise to a number of different transcripts from the locus, most of which are overexpressed in t(4;14) myelomas ( Figure 1A). 2,9,10 The protein domains found in full-length MMSET include 2 conserved Pro-Trp-Trp-Pro motif (PWWP) domains, 4 plant homeo domain fingers, and 1 SET domain, all of which are commonly found in transcriptional regulators. 11,12 Our previous report suggested that MMSET may be part of a corepressor complex. 13 SET domain-containing proteins can methylate lysine residues on histone tails. 14 Methylation and other covalent modifications of histone tails, such as acetylation, phosphorylation, ubiquitination, or sumoylation, can alter gene expression depending on the residue altered, the type of the modification, and whether the modified histone residue is found in a gene promoter, enhancer, or the body of a gene. 15 Promoters of actively transcribed genes are marked by the presence of H3K4me3, whereas the transcribed body of active genes is characterized by methylation at H3K36 (H3K36me3). 16,17 By contrast, CpG islands are depleted of H3K36 methylation. 18 Inactive and silenced genes show methylation at H3K27me3 and H3K9me3, respectively. 16,17,19 Previous reports suggested promiscuous activity of the SET domains of the NSD family proteins. NSD1 was initially shown to methylate both H3 and H4 histones, and more recently its specificity has been narrowed down to lysine 36 on histone H3. 8 Likewise, MMSET was able to methylate both H3 and H4 histones in vitro. 13,20 A recent report showed that the histone methyl-transferase (HMT) activity of NSD proteins is substrate specific, helping explain these discrepa...

Overexpression of the histone methyltransferase MMSET in t(4;14)+ multiple myeloma patients is believed to be the driving factor in the pathogenesis of this subtype of myeloma. MMSET catalyzes dimethylation of lysine 36 on histone H3 (H3K36me2), and its overexpression causes a global increase in H3K36me2, redistributing this mark in a broad, elevated level across the genome. Here, we demonstrate that an increased level of MMSET also induces a global reduction of lysine 27 trimethylation on histone H3 (H3K27me3). Despite the net decrease in H3K27 methylation, specific genomic loci exhibit enhanced recruitment of the EZH2 histone methyltransferase and become hypermethylated on this residue. These effects likely contribute to the myeloma phenotype since MMSET-overexpressing cells displayed increased sensitivity to EZH2 inhibition. Furthermore, we demonstrate that such MMSET-mediated epigenetic changes require a number of functional domains within the protein, including PHD domains that mediate MMSET recruitment to chromatin. In vivo, targeting of MMSET by an inducible shRNA reversed histone methylation changes and led to regression of established tumors in athymic mice. Together, our work elucidates previously unrecognized interplay between MMSET and EZH2 in myeloma oncogenesis and identifies domains to be considered when designing inhibitors of MMSET function.