Interferon regulatory factor 4 mediates non-enzymatic IRE1 dependency in multiple myeloma cells [RNA-Seq]

Multiple Myeloma (MM) arises through oncogenic transformation of immunoglobulin-secreting plasma cells. MM often co-opts the central endoplasmic-reticulum (ER)-stress mitigator, inositol-requiring enzyme 1 (IRE1), to sustain malignant growth. While certain MMs require enzymatic IRE1-dependent activation of the transcription factor XBP1s, others display a nonenzymatic IRE1 dependency that is not yet mechanistically understood. Here we identify interferon regulatory factor 4 (IRF4), which stimulates genes that promote immune-cell proliferation, as a key conduit for IRE1’s nonenzymatic control of cell-cycle progression in MM. IRE1 silencing increased inhibitory S114/S270 phosphorylation on IRF4, disrupting IRF4’s chromatin-binding and transcriptional activity. IRF4 knockdown recapitulated, whereas IRF4 repletion reversed the anti-proliferative phenotype of IRE1 silencing. Furthermore, phospho-deficient, but not phospho-mimetic, IRF4 mutants rescued proliferation under IRE1 silencing. Functional studies revealed that IRF4 engages the E2F1 and CDC25A genes and promotes CDK2 activation to drive cell-cycle progression. Our results advance mechanistic understanding of IRE1 and IRF4 in MM. To follow the consequences of IRF4 silencing, we performed an RNA sequencing transcriptomic analysis of AMO1 and KMS27 human multiple myeloma cells subjected to IRF4 vs. NTC (non-targeting control) knockdown. AMO1 shIRF4 cl.1, cl. 4-3 or shNTC cells were harvested in biologic triplicates at 0 (Mock), 8, 16 and 24 h after treatment with Doxycycline (Dox, 0.2 μg/ml). KMS27 shIRF4 Cl. 20 or shNTC cells were harvested in biologic triplicates at 0 (Mock), 20 and 30 h after treatment with Doxycycline (Dox, 0.2 μg/ml).