Nuclear receptor-binding SET domain 2 (NSD2) is the primary oncogenic driver and represent a good druggable target due to its universal overexpression in t(4;14) MM. However, given the challenges in the development of small molecule inhibitors against NSD2, we took on a discovery approach to characterize NSD2 interactome as an alternative strategy to target NSD2. We employed SILAC-based mass-spectrometry coupled with gene ontology analysis to uncover the spectrum of NSD2-interacting proteins which are relevant in t(4;14) MM. Validation using in silico protein-protein interaction analysis and immunoprecipitation confirmed that SMARCA2, a bromodomain-containing chromatin remodeler, interacts with NSD2 independent of the SWI/SNF complex. SMARCA2 is primarily expressed in t(4;14) cell lines, and functional assays indicated that dual inhibition of SMARCA2 and NSD2 impairs growth of t(4;14)+ cells. Next, we performed RNA sequencing which led to the identification of PTP4A3 as a downstream target of NSD2 that is co-regulated by SMARCA2. Mechanistically, SMARCA2 is required for the recruitment of NSD2 to PTP4A3 promoter, leading to a transcriptionally permissive state for expression. Importantly, upregulation of PTP4A3 is sufficient for the activation of MYC, which is crucial for t(4;14) myelomagenesis. PFI-3, which belongs to the class of bromodomain and extra-terminal motif protein inhibitors (BETi), displaced SMARCA2 and NSD2 occupancy from PTP4A3 promoter, and selectively inhibited t(4;14) myeloma cell viability. Interestingly, PFI-3 treatment did not perturb the levels of NSD2 nor SMARCA2, rather, the targeting effect is achieved through their occupancy on oncogenes. Finally, high expression of NSD2 and SMARCA2 were predictive of poor survival outcome in a large cohort of myeloma patients. Collectively, we demonstrated a proof-of-concept of how histone modifying enzyme and chromatin remodeling complex cooperatively caused an altered epigenetic state in myelomagenesis through the regulation of an important myeloma gene. Our study proposed that the pharmacological inhibition of SMARCA2 may represent a novel strategy to target t(4;14) myeloma cells using BETi and also explore as combinational therapy with anti-myeloma agents that are currently in the clinics.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.