Abstract 2498: Over-expression of dual-specificity phosphatase 4 (DUSP4) in multiple myeloma

Super-enhancers are unique genomic domains with dense binding of transcription factors (TFs)/cofactors that drive expression of genes defining cell identity. They also contribute to over-expression of oncogenes. The abundance of multiple TFs and coactivators at the super-enhancers favors their cooperative binding and synergistic gene activation. Thus, super-enhancers are more sensitive to perturbation of TF levels than typical enhancers, providing a therapeutic window for preferential targeting oncogenic expression in cancer cells. Recently, a list of super-enhancer associated genes (SEAG) was identified in a multiple myeloma (MM) cell line MM1S and inhibition of transcriptional coactivator BRD4 by JQ1 selectively repressed MYC oncogene expression through reduction of BRD4 binding at the associated super-enhancer. Significances of SEAG other than MYC in myeloma cells remains unclear. By unsupervised hierarchical clustering analysis of expression of 682 identified SEAG in 74 MM, 28 relapsed MM and 15 normal plasma cells (NPC) (GSE6477), distinct expression pattern of SEAG was associated with MM as compared to NPC, indicating their importance in MM. Among the upregulated genes, DUSP4 (Dual Specificity Phosphatase 4), an inducible phosphatase of MAPK (Mitogen-Activated Protein Kinases), was significantly overexpressed in MM and further upregulated in the relapsed MM. High expression was associated with inferior patient outcomes. The overexpression was confirmed in our patient cohort which includes CD138-immunosorted myeloma cells from 30 untreated and 3 relapsed MM patients, 6 smoldering MM patients and 5 MGUS patients, 5 sorted normal plasma cells (NPC) and 7 MM cell lines. Using the cutoff for over-expression as higher than the mean level of NPC plus 2X Standard Deviation, 10 out of 30 MM and all the 3 relapsed samples showed significant DUSP4 over-expression. Functional significance of DUSP4 in MM was explored by siRNA knockdown and the knockdown inhibited myeloma cell growth, implying an oncogenic role of DUSP4 in MM. To study the significances of super-enhancer in regulation of DUSP4 expression, JQ1 was used and inhibition of BRD4 by JQ1 in MM1S, L363 and OPM2 repressed both DUSP4 expression and MM cell growth. By ChIP-PCR, we demonstrated BRD4 specifically bound onto the proximal region of DUSP4 promoter and the binding was blocked by JQ1. Taken together, the oncogenic role of DUSP4 as SEAG in MM was revealed and the preferential targeting SEAG by BRD4 inhibitor could provide insights into further developments of effective therapeutic approaches for MM patients. Citation Format: Tian Xia, Kin-Mang Lau, Chi Keung Cheng, Nelson CN Chan, Margaret H. L. Ng. Over-expression of dual-specificity phosphatase 4 (DUSP4) 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 2498.