Epigenetic dysregulation of eukaryotic initiation factor 3 subunit E (eIF3E) by lysine methyltransferase REIIBP confers a pro-inflammatory phenotype in t(4;14) myeloma

REIIBP is a lysine methyltransferase aberrantly expressed through alternative promoter usage of NSD2 locus in t(4;14)-translocated multiple myeloma (MM). Clinically, t(4;14) translocation is an adverse prognostic factor found in approximately 15% of MM patients. The contribution of REIIBP relative to other NSD2 isoforms as a dependency gene in t(4;14)-translocated MM remains to be evaluated. Here, we demonstrated that despite homology with NSD2, REIIBP displayed distinct substrate specificity by preferentially catalyzing H3K4me3 and H3K27me3, with little activity on H3K36me2. Furthermore, REIIBP was regulated through microRNAs by EZH2 in a Dicer-dependent manner, exemplifying a role of REIIBP in SET-mediated H3K27me3. ChIP-sequencing revealed chromatin remodeling characterized by changes in genome-wide and loci-specific occupancy of these opposing histone marks, allowing a bidirectional regulation of its target genes. Transcriptomics indicated that REIIBP induced a pro-inflammatory gene signature through upregulation of TLR7, which in turn led to B-cell receptor (BCR)-independent activation of BTK and driving NFĸB-mediated production of cytokines such as IL-6. Activation of this pathway is targetable using Ibrutinib and partially mitigated bortezomib resistance in an REIIBP xenograft model. Mechanistically, REIIBP upregulated TLR7 through eIF3E, and this relied on eIF3E RNA-binding function instead of its canonical protein synthesis activity, as demonstrated by direct binding to the 3'UTR of TLR7 mRNA. Altogether, we provided a rationale that coexistence of different NSD2 isoforms induced diversified oncogenic programs that should be considered in the strategies for t(4;14)-targeted therapy.

Determinants of response to daratumumab in Epstein-Barr virus-positive natural killer and T-cell lymphoma

Background

The potential therapeutic efficacy of daratumumab in natural killer T-cell lymphoma (NKTL) was highlighted when its off-label usage produced sustained remission in a patient with highly refractory disease. This is corroborated recently by a phase II clinical trial which established that daratumumab monotherapy is well tolerated and displayed encouraging response in relapsed/refractory NKTL patients. However, little is known regarding the molecular factors central to the induction and regulation of the daratumumab-mediated antitumor response in NKTL.

Methods

CD38 expression was studied via immunohistochemistry, multiplex immunofluorescence and correlated with clinical characteristics of the patient. The therapeutic efficacy of daratumumab was studied in vitro via CellTiter-Glo (CTG) assay, complement-dependent cytotoxicity (CDC), antibody-dependent cell cytotoxicity (ADCC), and in vivo, via a patient-derived xenograft mouse model of NKTL, both as a single agent and in combination with L-asparaginase. Signaling mechanisms were characterized via pharmacologic treatment, RNA silencing, flow cytometry and corroborated with public transcriptomic data of NKTL.

Results

Epstein-Barr virus-positive NKTL patients significantly express CD38 with half exhibiting high expression. Daratumumab effectively triggers Fc-mediated ADCC and CDC in a CD38-dependent manner. Importantly, daratumumab monotherapy and combination therapy with L-asparaginase significantly suppresses tumor progression in vivo. Ablation of complement inhibitory proteins (CIP) demonstrate that CD55 and CD59, not CD46, are critical for the induction of CDC. Notably, CD55 and CD59 expression were significantly elevated in the late stages of NKTL. Increasing the CD38:CIP ratio through sequential CIP knockdown, followed by CD38 upregulation via All-Trans Retinoic Acid treatment, potently augments complement-mediated lysis in cells previously resistant to daratumumab. The CD38:CIP ratio consistently demonstrates a statistically superior correlation to antitumor efficacy of daratumumab than CD38 or CIP expression alone.

Conclusion

This study characterizes CD38 as an effective target for a subset of NKTL patients and the utilization of the CD38:CIP ratio as a more robust identifier for patient stratification and personalisation of treatment. Furthermore, elucidation of factors which sensitize the complement-mediated response provides an alternative approach toward optimizing therapeutic efficacy of daratumumab where CDC remains a known limiting factor. Altogether, these results propose a strategic rationale for further evaluation of single or combined daratumumab treatment in the clinic for NKTL.

SMARCA2 Is a Novel Interactor of NSD2 and Regulates Prometastatic PTP4A3 through Chromatin Remodeling in t(4;14) Multiple Myeloma

NSD2 is the primary oncogenic driver in t(4;14) multiple myeloma. Using SILAC-based mass spectrometry, we demonstrate a novel role of NSD2 in chromatin remodeling through its interaction with the SWI/SNF ATPase subunit SMARCA2. SMARCA2 was primarily expressed in t(4;14) myeloma cells, and its interaction with NSD2 was noncanonical and independent of the SWI/SNF complex. RNA sequencing identified PTP4A3 as a downstream target of NSD2 and mapped NSD2-SMARCA2 complex on PTP4A3 promoter. This led to a focal increase in the permissive H3K36me2 mark and transcriptional activation of PTP4A3. High levels of PTP4A3 maintained MYC expression and correlated with a 54-gene MYC signature in t(4;14) multiple myeloma. Importantly, this mechanism was druggable by targeting the bromodomain of SMARCA2 using the specific BET inhibitor PFI-3, leading to the displacement of NSD2 from PTP4A3 promoter and inhibiting t(4;14) myeloma cell viability. In vivo, treatment with PFI-3 reduced the growth of t(4;14) xenograft tumors. Together, our study reveals an interplay between histone-modifying enzymes and chromatin remodelers in the regulation of myeloma-specific genes that can be clinically intervened. SIGNIFICANCE: This study uncovers a novel, SWI/SNF-independent interaction between SMARCA2 and NSD2 that facilitates chromatin remodeling and transcriptional regulation of oncogenes in t(4;14) multiple myeloma, revealing a therapeutic vulnerability targetable by BET inhibition.

MMSET I acts as an oncoprotein and regulates GLO1 expression in t(4;14) multiple myeloma cells

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. T(4;14) MM overexpresses multiple myeloma SET domain-containing protein (MMSET). MMSET has three major isoforms: the full-length form MMSET II and the short isoforms REIIBP and MMSET I. Here we show that the short isoform MMSET I is an oncoprotein that promoted cell survival and tumorigenesis in vitro and in vivo. Gene expression array analysis indicated that MMSET I increased glyoxalase I (GLO1) expression. Chromatin immunoprecipitation (ChIP) coupled with qPCR indicated that MMSET I bound upstream of the GLO1 transcription start site. Ectopic overexpression of MMSET I or its mutants showed MMSET I depended on its C terminus to regulate GLO1 expression. GLO1 knockdown (KD) induced apoptosis and reduced colony formation. MMSET I or GLO1 KD reduced the levels of anti-apoptosis factors such as MCL1 and BCL2. Ectopic overexpression of GLO1 resulted in the significant rescue of KMS11 cells from MMSET I KD-induced apoptosis and glycolysis inhibition. This suggested that GLO1 may be of functional importance target downstream of MMSET I. Cumulatively, our study suggests that MMSET I is an oncoprotein and potential therapeutic target for t(4;14) MM.

Abstract 4374: Non-canonical activation of β-catenin by PRL-3 phosphatase in acute myeloid leukemia

Aberrant activation of Wnt/β-catenin signaling pathway is essential for the development of AML; however, the mechanistic basis for the dysregulation is unclear. PRL-3 is an oncogenic phosphatase implicated in the development of LSCs. Here, we identified Leo1 as a direct and specific substrate of PRL-3. Serine-dephosphorylated form of Leo1 binds directly to β-catenin, promoting the nuclear accumulation of β-catenin and transactivation of TCF/LEF downstream target genes such as cyclin D1 and c-myc. Importantly, overexpression of PRL-3 in AML cells displayed enhanced sensitivity towards β-catenin inhibition in vitro and in vivo, suggesting that these cells are addicted to β-catenin signaling. Altogether, our study revealed a novel regulatory role of PRL-3 in the sustenance of aberrant β-catenin signaling in AML. PRL-3 may serve as a biomarker to select for the subset of AML patients subset who are likely to benefit from treatment with β-catenin inhibitors. Our study presents a new avenue of cancer inhibition driven by PRL-3 overexpression or β-catenin hyperactivation.

Citation Format: Phyllis SY Chong, Jianbiao Zhou, Jing Yuan Chooi, Wee Joo Chng, Jayantha Gunaratne, Qi Zeng. Non-canonical activation of β-catenin by PRL-3 phosphatase in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4374.

Abstract 2499: Identification of functional proteins interacting with NSD2 in multiple myeloma

Multiple myeloma (MM), characterized by the uncontrolled proliferation of malignant plasma cells, occurs mainly in the elderly population. Recurrent chromosomal translocations are central to the pathogenesis of MM, with t(4;14) being the second most common and associated with poor prognosis. The histone methyltransferase (HMTase) NSD2 is overexpressed in MM due to the t(4;14) translocation and has been suggested to play an important tumorigenic role in t(4;14) MM. However, the detailed molecular mechanism or signaling pathways describing how deregulation of NDS2 contributes to MM cell growth and survival are still uncertain. In this study, stable isotope labeling of amino acid in cell culture (SILAC)-based mass spectrometry analysis was used to determine NSD2-interacting proteins. Mass spectrometry analysis indicated that there were 75 proteins identified in the immunoprecipitation of NSD2 protein complexes. Gene ontology (GO) enrichment analysis showed that these proteins were enriched in processes related to chromatin organization, RNA processing and translation. Five high potential MMSET-interacting proteins from the most enriched functions were selected and verified by Immunoprecipitation and Western blot assays. The results indicated that there were interactions between NSD2 and SMARCA2, topoisomerase IIa, ADAR1, DDX5 and RPS6. In silico analysis with STRING database showed that SMARCA2 interacts with NSD2. SMARCA2 is the ATPase subunit of the SWI/SNF chromatin remodeling complex, which harnesses the energy from ATP to remodel the position of nucleosomes, making the DNA accessible during transcription, replication and DNA repair. Double immunofluorescence showed NSD2 and SMARCA2 co-localized in the cell nucleus. SMARCA2 was knocked down (KD) by shRNAs in t(4;14) MM cells. CellTiter-Glo Luminescent Cell Viability Assay (CTG assay) indicated that SMARCA2 KD by shRNA reduced t(4;14) MM cell growth. SMARCA2 KD also significantly inhibited the capacity to form colonies in t(4;14) MM cells on methylcellulose colony formation assay. Inhibiting SMARCA2 with active DNA-dependent ATPase A domain inhibitor (ADAADi) also reduced t(4;14) MM cell growth. In addition, SMARCA2 KD reduced cell cycle S phase. Western blot analysis showed downregulation of PRL3 and CCND1 protein level upon NSD2 or SMARCA2 KD. This study reveals a protein-protein interaction between NSD2 and SMARCA2. SMARCA2 KD showed SMARCA2 might be a novel therapeutic target for t(4;14) MM.

Citation Format: Jing Yuan Chooi, Zhigang Xie, Hannah Lee-Foon Swa, Jayantha Gunaratne, Dennis Kappei, Wee Joo Chng. Identification of functional proteins interacting with NSD2 in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2499.

Disruption of Runx1 and Runx3 leads to bone marrow failure and leukemia predisposition due to transcriptional and DNA repair defects

The RUNX genes encode transcription factors involved in development and human disease. RUNX1 and RUNX3 are frequently associated with leukemias, yet the basis for their involvement in leukemogenesis is not fully understood. Here, we show that Runx1;Runx3 double-knockout (DKO) mice exhibited lethal phenotypes due to bone marrow failure and myeloproliferative disorder. These contradictory clinical manifestations are reminiscent of human inherited bone marrow failure syndromes such as Fanconi anemia (FA), caused by defective DNA repair. Indeed, Runx1;Runx3 DKO cells showed mitomycin C hypersensitivity, due to impairment of monoubiquitinated-FANCD2 recruitment to DNA damage foci, although FANCD2 monoubiquitination in the FA pathway was unaffected. RUNX1 and RUNX3 interact with FANCD2 independently of CBFβ, suggesting a nontranscriptional role for RUNX in DNA repair. These findings suggest that RUNX dysfunction causes DNA repair defect, besides transcriptional misregulation, and promotes the development of leukemias and other cancers.