Therapeutics , Targets , and Chemical Biology NSD 2 Is Recruited through Its PHD Domain to Oncogenic Gene Loci to Drive Multiple Myeloma

Histone lysine methyltransferase NSD2 (WHSC1/MMSET) is overexpressed frequently in multiple myeloma due to the t(4;14) translocation associated with 15% to 20% of cases of this disease. NSD2 has been found to be involved in myelomagenesis, suggesting it may offer a novel therapeutic target. Here we show that NSD2 methyltransferase activity is crucial for clonogenicity, adherence, and proliferation of multiple myeloma cells on bone marrow stroma in vitro and that NSD2 is required for tumorigenesis of t(4;14)þ but not t(4;14) multiple myeloma cells in vivo. The PHD domains in NSD2 were important for its cellular activity and biological function through recruiting NSD2 to its oncogenic target genes and driving their transcriptional activation. By strengthening its disease linkage and deepening insights into its mechanism of action, this study provides a strategy to therapeutically target NSD2 in multiple myeloma patients with a t(4;14) translocation. Cancer Res; 73(20); 6277–88. 2013 AACR. Introduction Compelling data has emerged that epigenetic mechanisms are linked with various pathologies such as cancer, infectious diseases, inflammation, degenerative diseases, and neurological disorders (1–4). Many epigenetic players possess genetic alterations in human diseases (5–8), suggesting important roles in driving deregulated signaling pathways. The nuclear SET domain (NSD) containing protein family of histone methyltransferases includes NSD1, NSD2 (also named as WHSC1, Wolf–Hirschhorn syndrome candidate 1; or MMSET, multiple myeloma SET domain containing protein), and NSD3 (also known as WHSC1L1, WHSC1 like 1). Each family member has been linked to multiple diseases. NSD2 is involved in the t(4;14) translocation in 15% to 20% of multiple myeloma (9), which is the second most common translocation and associated with unfavorable prognosis (10–12). When the translocation occurs, the Em and 30 enhancer of IgH locus are fused with NSD2 and FGFR3, respectively, resulting in overexpression of both genes (13). About 5% to 10% of t(4;14)þ myeloma further develop activating mutations in FGFR3 (14–16), indicating its important role in tumor progression. However, 30% of t(4;14)þ cases lack FGFR3 expression due to loss of der(14), whereas all overexpress NSD2 (17). Furthermore, poor prognosis of t (4;14)þ myeloma is independent of FGFR3 expression (18), suggesting that NSD2 dysregulation is the crucial oncogenic event. NSD2 is a multidomain protein containing a catalytic SET (suppressor of variegation, enhancer of zeste and trithorax) domain, 2 PWWP (proline-tryptophan-tryptophan-prolin motif) domains, an HMG (high mobility group) box, 5 PHD (plant-homeodomain) zinc finger motifs, and a Cys-His rich C5HCH domain. The PWWP, HMG, and PHD domains have been shown to mediate chromatin interaction and recognition of histone marks (19–23). How different domains cross talk and contribute to the biological functions of NSD2 is not understood yet. In addition, at least 3 splicing isoforms of NSD2 have been reported: MMSET II (1-1365aa), MMSET I (1-647aa), and REIIBP (782-1365aa). Depending on the breakpoints in different t(4;14)þ myeloma cells, there can be N-terminal truncations up to the PWWP1 domain in MMSET I and MMSET II (24, 25). All variants of NSD2 are overexpressed under t(4;14) translocation whereas the outcome of t(4;14)þ myeloma is independent of the breakpoint types (26). Whether different NSD2 isoforms play differential roles remains to be determined. In t(4;14)þ myeloma, NSD2 has been linked to cell-cycle progression, DNA damage response, cell adhesion, clonogenicity, and tumorigenesis (25, 27–31), presumably by reprogramming global histone methylation and gene expression. Two Authors' Affiliations: Novartis Institutes forBioMedicalResearch (China), Shanghai, P.R. China; Genomics Institute of the Novartis Research Foundation, San Diego, California; and Novartis Institutes for BioMedical Research, Cambridge, Massachusetts Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Current address for X. Wu: Massachusetts General Hospital, Charlestown, MA 02129. Corresponding Authors: Min Hu, Novartis Institutes for BioMedical Research (China), Building 8, Lane 898 Halei Road, Zhangjiang Hi-Tech Park, Pudong New Area, Shanghai 201203, P.R. China. Phone: 86-216160-6519; Fax: 86-21-6160-6905; E-mail: min.hu@novartis.com; andYan Wang, ywang2@gnf.org doi: 10.1158/0008-5472.CAN-13-100