Epigenetic modifiers MMSET and EZH2 physically interact and cooperate to support Multiple Myeloma pathophysiology [ChIP-seq]

Multiple myeloma (MM) is a malignant B cell dyscrasia characterized by the accumulation of clonal plasma cells (PC) within the bone marrow. Epigenetic factors are involved in MM initiation, progression, and occurrence of chemoresistance. Among them EZH2, the Polycomb Repressive Complex 2 (PRC2) catalytic subunit and NSD2 (MMSET), the target oncogene of t(4;14) primary translocation, are both associated with poor prognosis values and contribute to MM disease. In this study, we identified a physical interaction between EZH2 and MMSET in MM. We used MMSET-depleted MM cells and MAK-683, an allosteric inhibitor of EZH2, to disrupt this interaction and understand its implication in MM biology and resistance to anti-MM drugs. Through its interaction with EZH2, MMSET regulates PRC2 nuclear localization in MM cells, promotes a particularly poor prognosis in MM patients, and modulates the expression of tumor-suppressor genes involved in p53 pathway. We also demonstrated that MAK-683 can interfere with this interaction and synergizes with conventional drugs used in MM treatment: Melphalan, an alkylating agent triggering DNA Damage Response (DDR); and Panobinostat, a Histone De-Acetylase (HDAC) inhibitor directedly regulating p53 acetylation and stability. To investigate to cooperative function of EZH2-MMSET complex in the regulation of MM cells, we established two MMSET-CRISPR cell lines (MMSET-CRISPR-1 and MMSET-CRISPR-2) in which MMSET has been depleted by a CRISPR-Cas9 system. We then performed Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for EZH2 and histone modification H3K27me3 in XG7, MMSET-CRISPR-1 and MMSET-CRISPR-2 cells.