An IRF4–MYC–mTORC1 Integrated Pathway Controls Cell Growth and the Proliferative Capacity of Activated B Cells during B Cell Differentiation In Vivo

Abstract

Cell division is an essential component of B cell differentiation to Ab-secreting plasma cells, with critical reprogramming occurring during the initial stages of B cell activation. However, a complete understanding of the factors that coordinate early reprogramming events in vivo remain to be determined. In this study, we examined the initial reprogramming by IRF4 in activated B cells using an adoptive transfer system and mice with a B cell–specific deletion of IRF4. IRF4-deficient B cells responding to influenza, 4-hydroxy-3-nitrophenylacetyl–Ficoll, and LPS divided but stalled during the proliferative response. Gene expression profiling of IRF4-deficient B cells at discrete divisions revealed IRF4 was critical for inducing MYC target genes, oxidative phosphorylation, and glycolysis. Moreover, IRF4-deficient B cells maintained an inflammatory gene expression signature. Complementary chromatin accessibility analyses established a hierarchy of IRF4 activity and identified networks of dysregulated transcription factor families in IRF4-deficient B cells, including E-box binding bHLH family members. Indeed, B cells lacking IRF4 failed to fully induce Myc after stimulation and displayed aberrant cell cycle distribution. Furthermore, IRF4-deficient B cells showed reduced mTORC1 activity and failed to initiate the B cell activation unfolded protein response and grow in cell size. Myc overexpression in IRF4-deficient cells was sufficient to overcome the cell growth defect. Together, these data reveal an IRF4–MYC–mTORC1 relationship critical for controlling cell growth and the proliferative response during B cell differentiation.

B cell‐intrinsic changes with age do not impact antibody‐secreting cell formation but delay B cell participation in the germinal centre reaction

“…IRF4 is a transcription factor lowly expressed in naïve cells, absent in GC B cells and upregulated in plasma cells (Willis et al, 2014 ). In particular, IRF4 has been shown to be important for regulating the proliferative capacity of B cells during activation and is required for early GC B cells formation in a B cell‐intrinsic manner (Patterson et al, 2021 ; Willis et al, 2014 ). Thus, the lower expression of IRF4 by B cells from older donors may result in early proliferative defects, as previously reported (Blaeser et al, 2008 ) and contribute to the reduced early GC response, as we observed in our mouse studies.…”

Citrulline enteral administration markedly reduces immunosuppressive extrafollicular plasma cell differentiation in a preclinical model of sepsis

“…4E). Sustained and high Irf4 expression was shown to promote PC differentiation while antagonizing the GC path [26], a mechanism that requires IRF4‐induced MYC target genes [27]. In agreement with Irf4 downregulation, Myc expression was significantly decreased in CD19 + cells (p = 0.0087), and its target genes Cdc25a and Ccnd2 were downregulated with citrulline diet (p = 0.0284 for Cdc25a and p = 0.0519 for Ccnd2 expression; Fig.…”

An arrayed CRISPR screen of primary B cells reveals the essential elements of the antibody secretion pathway

“…The CTY dilution profiles of cells transduced with sgRNAs targeting Prdm1 and Plpp5 overlapped with the untransduced controls, indicating that these genes do not influence B cell proliferation ( Figure 3B ) . It has previously been demonstrated that Irf4 -deficient B cells have a reduced proliferative capacity in response to LPS compared to WT B cells ( 27 , 36 ). This proliferative defect was confirmed by our data and was most notable at later timepoints where cells transduced with Irf4 targeting sgRNAs had stalled in their proliferation ( Figure 3B ) .…”

“…Comparison with the differentiation results demonstrated that some of these genes ( Irf4 , Hspa5 and Sec61a1 ) affected both cell number and differentiation, while the other genes identified only influenced cell number ( Supplementary Figure 2B ). Irf4 has been linked to cell division in activated B cells as it directly induces the expression of genes involved in proliferation, including Myc ( 27 , 28 ). Sumo2 has previously been implicated in proliferation and cell survival as Sumo2-deficient mouse embryonic fibroblasts have decreased cell cycling and an increased cell death compared to WT cells ( 29 ).…”