Differential RNA splicing analysis with or without IL-6 in multiple myeloma cells

Multiple myeloma (MM) is a plasma cell neoplasm that depends on the bone marrow (BM) microenvironment; however, the underlying mechanisms of epigenetic contribution to the pathogenesis of MM are incompletely understood. Here, we delineate the epigenetic-driven transcriptional and splicing program crucial for MM. We recharacterized transcriptional program induced by IL-6/JAK/STAT3 pathway by ChIP-seq and RNA-seq analyses combined with CRIPSR knockout screening database, and identified B cell lineage factors, POU2AF1 and ELL2, as crucial IL-6/JAK/STAT3 targets that are essential for MM cell growth and survival. Genetic depletion of these factors suppressed MM cell growth in vitro and in the xenograft model of IL-6 humanized mice. Mechanistically, POU2AF1 and ELL2 govern MM-distinct transcriptional program representing immaturity, and IL-6/JAK/STAT3 pathway augments this program through upregulating and recruiting these factors to the MM-signature genes. Furthermore, we showed that IL-6 induces alternative splicing that is partly mediated by POU2AF1. Proteomic study identified novel POU2AF1-associated factors that converge in regulation of RNA, including RNA splicing. Indeed, POU2AF1 is adjacent to multiple splicing factors required for MM cell survival and is involved in the organization of nuclear speckles. Finally, we showed that gapmer antisense oligonucleotides (ASOs) targeting POU2AF1 inhibit its expression and MM cell growth in the presence of soluble BM stromal cell factors, including IL-6. Our data demonstrate that IL-6-driven B cell-lineage factors are the vulnerability of MM cells and may represent novel therapeutic targets for this incurable tumor.