IRF4 regulates the proliferative capacity of activated B cells during B cell differentiation

Abstract Cell division is essential for B cell differentiation to a plasma cell (PC). While the cell division coupled changes in the expression of transcription factors that coordinate the PC program have been described, it is unclear how these factors coordinate the proliferative program. To address this, we used an adoptive transfer system and monitored the cell division/differentiation kinetics in response to LPS, NP-ficoll, and X31 influenza. In this system, wild-type (WT) B cells undergo at least 8 cell divisions before differentiating into PC. In contrast, Interferon Regulatory Factor 4-null (IRF4−/−) B cells began dividing normally but stalled during the proliferative response. To assess the scope of IRF4-dependent reprogramming, WT and IRF4−/− B cells in divisions 0, 1, and 3–6 were sorted for ATAC- and RNA-seq. RNA-seq data revealed hundreds of differentially expressed genes (DEG) when IRF4 was deleted that encompassed a number of gene sets critical for B cell reprogramming, including glycolysis, OXPHOS, and mTORC1 signaling. Further, MYC target genes became progressively dysregulated across divisions. Indeed, IRF4−/− cells failed to fully upregulate MYC compared to WT cells and consequently, we observed aberrant cell cycle distribution, cell growth defects, and fewer actively proliferating cells. Overexpressing MYC in IRF4−/− B cells rescued cell growth and significantly improved proliferation. ATAC-seq data also exposed hundreds of differentially accessible regions, the majority of which contained a known IRF4 binding motif and mapped to a corresponding DEG. Together, these data create a road map defining the role of IRF4 throughout differentiation, revealing a critical function in coordinating the proliferative response.