Transcription factors IRF8 and PU.1 are required for follicular B cell development and BCL6-driven germinal center responses

Abstract

The IRF and Ets families of transcription factors regulate the expression of a range of genes involved in immune cell development and function. However, the understanding of the molecular mechanisms of each family member has been limited due to their redundancy and broad effects on multiple lineages of cells. Here, we report that double deletion of floxed Irf8 and Spi1 (encoding PU.1) by Mb1-Cre (designated DKO mice) in the B cell lineage resulted in severe defects in the development of follicular and germinal center (GC) B cells. Class-switch recombination and antibody affinity maturation were also compromised in DKO mice. RNA-seq (sequencing) and ChIP-seq analyses revealed distinct IRF8 and PU.1 target genes in follicular and activated B cells. DKO B cells had diminished expression of target genes vital for maintaining follicular B cell identity and GC development. Moreover, our findings reveal that expression of B-cell lymphoma protein 6 (BCL6), which is critical for development of germinal center B cells, is dependent on IRF8 and PU.1 in vivo, providing a mechanism for the critical role for IRF8 and PU.1 in the development of GC B cells. IRF8 | PU.1 | follicular B cells | BCL6 | germinal center B cell development in the bone marrow (BM) has been wellcharacterized as involving three consecutive stages: (i) B cell lineage specification and commitment at the pre-pro-B cell stage, (ii) pre-B cell receptor (BCR) expression and selection at the pre-B cell stage, and (iii) IgM BCR expression and selection at the immature B cell stage. Several transcription factors are vital for progression through these stages. For example, EBF, E2A, and Pax5 are key regulators for B cell lineage commitment and identity maintenance (1). The IFN regulatory factor (IRF) family members IRF4 and IRF8 and Ets family members PU.1 and SpiB are essential for Ig light-chain gene expression and the generation of immature B cells (2-4). Studies of PU.

A dichotomy in association of core transcription factors and gene regulation during the activated B-cell to plasmablast transition

“…In human plasmablasts the strongest associations for BLIMP1 are with occupancy at regulatory elements linked to predominantly repressive chromatin marks, and genes expressed at the ABC stage that are repressed in plasmablasts. These include key transcriptional regulators such as SPIB and IRF8 , 55–57 which are also observed as targets in murine cells and aligns with features of human B-cell lymphomas with BLIMP1 inactivation. 58, 59…”

Serine-threonine kinase ROCK2 regulates germinal center B cell positioning and cholesterol biosynthesis

“…Other transcription factors also play important roles in the regulation of GC responses. In particular, interferon regulatory factor 8 (IRF8) and PU.1 control GC development through several mechanisms including the regulation of BCL6 expression (6)(7)(8)(9)(10) and FOXO1, a DZ-specific transcription factor that helps maintain GC architectural polarity (11)(12)(13).…”

Role of non-coding RNA networks in leukemia progression, metastasis and drug resistance

“…Furthermore, HOTAIRM1 expression is also modulated by another transcription factor, PU.1, during granulocyte differentiation [208]. PU.1 is a master regulator of myeloid differentiation, while PU.1, along with IRF8, is known to control the fates of follicular (FO) and germinal centers (GO) B cells [209]. Double knockout of IRF8 and PU.1 in B cells has been shown to impair the development of FO and GC B cells [209].…”

“…PU.1 is a master regulator of myeloid differentiation, while PU.1, along with IRF8, is known to control the fates of follicular (FO) and germinal centers (GO) B cells [209]. Double knockout of IRF8 and PU.1 in B cells has been shown to impair the development of FO and GC B cells [209]. This signifies that HOTAIRM1 can modulate tumor immunity in leukemia by interacting with other regulatory molecules.…”