Oncogenic NSD2 drives Eph-ephrin signaling between myeloma and bone marrow stromal cells

The t(4;14) translocation occurs in 15-20% of multiple myeloma cases and upregulates the histone methyltransferase NSD2 to drive oncogenic transcriptional dysregulation. Patients with t(4;14)+ myeloma are high risk with shorter survival and higher incidence of bone lesions when compared to patients with other cytogenetic subtypes, suggesting an oncogenic role of NSD2. Counterintuitively, under standard culture conditions, NSD2 knockout in t(4;14)+ models only demonstrated a modest growth inhibition phenotype. Therefore, we hypothesized that oncogenic NSD2 epigenetically modulates signaling between myeloma cells and the bone marrow microenvironment (BMME) to drive myeloma progression. To test this, we utilized both pharmacological inhibition and CRISPR/Cas9 knockout of NSD2 in human myeloma cells lines with varying genetic backgrounds. We assessed proliferation and viability under standard conditions, in co-culture with bone marrow stromal cells (BMSCs), or in BMSC-conditioned media. BMSC co-culture or exposure to BMSC-conditioned media strikingly increased the sensitivity of myeloma lines to NSD2 inhibition, thereby supporting our hypothesis. RNA-sequencing and pathway analysis revealed that oncogenic NSD2 regulates Eph-ephrin signaling, and epigenetic profiling showed NSD2-dependent remodeling of H3K36me2 and H3K27me3 at corresponding Eph-ephrin genomic loci in myeloma cells, suggesting a direct regulation by NSD2. To assess the importance of ephrin receptor signaling between myeloma cells and the BMME, we conducted CRISPR/Cas9 knockout of Eph-ephrin genes and assessed myeloma growth and viability. CRISPR/Cas9 knockout of Eph-ephrin signaling genes caused significantly stronger growth inhibition of myeloma cells with oncogenic NSD2 status in BMSC-conditioned media, while overexpression of ephrin receptor partially rescued the growth defect of NSD2 knockout myeloma cells in BMSC-conditioned media. To assess the clinical relevance of our findings, we analyzed publicly available data from the MMRF CoMMpass patient cohort, which confirmed higher tumor expression of Eph-ephrin genes in t(4;14)+ myeloma patients, correlating with inferior overall and progression-free survival. These findings implicate Eph-ephrin signaling as a key mediator of t(4;14)+ myeloma biology and an attractive therapeutic target. In summary, oncogenic NSD2 reshapes the chromatin of myeloma cells to promote Eph-ephrin signaling, thereby conferring bone marrow microenvironment-dependent fitness in t(4;14)+ multiple myeloma. These data highlight Eph-ephrin signaling as an actionable therapeutic pathway for t(4:14)+ and NSD2 mutant myeloma.