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Spatiotemporal dynamics of Bach2 orchestrates B cell responses and fate decision II

ABSTRACT: The molecular circuits that direct early T-dependent B cell responses and alternative cell-fate decisions remain poorly understood. Here, we show that either B cell receptor (BCR) or CD40 signals promoted mTORC1-dependent translation of the transcription factor Bach2. Transient up-regulation of Bach2 protein restrained activated B cell expansion and differentiation into plasma cell while promoting the germinal center (GC) and memory B cell fates at the pre-GC stage. However, enforced Bach2 expression facilitated memory B cell generation versus other cell fates. Mechanistically, Bach2 limited access of AP-1 factors and formed a reciprocal repression loop with IRF4. BCR and CD40 signals also down-regulated Bach2 transcript in antigen-activated B cells, and diversified its abundance in various effector populations, predisposing Bach2 protein expression and subsequent cell-fate choices during memory recall and GC reaction. Thus signaling-induced differential dynamics of Bach2 protein and mRNA in activated B cell control their cell-fate outcomes and imprint the fate of their descendant effector cells.

ORGANISM(S): Mus musculus

PROVIDER: GSE180460 | GEO | 2022/06/08

REPOSITORIES: GEO

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Spatiotemporal dynamics of Bach2 orchestrates B cell responses and fate decision

Project description:The molecular circuits that direct early T-dependent B cell responses and alternative cell-fate decisions remain poorly understood. Here, we show that either B cell receptor (BCR) or CD40 signals promoted mTORC1-dependent translation of the transcription factor Bach2. Transient up-regulation of Bach2 protein restrained activated B cell expansion and differentiation into plasma cell while promoting the germinal center (GC) and memory B cell fates at the pre-GC stage. However, enforced Bach2 expression facilitated memory B cell generation versus other cell fates. Mechanistically, Bach2 limited access of AP-1 factors and formed a reciprocal repression loop with IRF4. BCR and CD40 signals also down-regulated Bach2 transcript in antigen-activated B cells, and diversified its abundance in various effector populations, predisposing Bach2 protein expression and subsequent cell-fate choices during memory recall and GC reaction. Thus signaling-induced differential dynamics of Bach2 protein and mRNA in activated B cell control their cell-fate outcomes and imprint the fate of their descendant effector cells.

2021-07-18 | GSE180277 | GEO

Comparison of NP specific high and low affinity IgG1 Light zone GC B cells

Project description:Despite the importance of memory B cells for protection from recurrent infection, how these cells are selected during germinal center (GC) reactions remains unclear. We show here that light zone (LZ) GC B cells with lower affinity BCRs express a less CD40 signature and relatively high levels of Bach2, being prone to enter the memory B cell pool. We also find that Bach2 contributes to memory B cell generation in a Blimp-1 independent manner and that its higher expression confers on LZ GC cells a more advantage for entering the memory B cell compartment. Thus, our data support an instructive model in which weak T cell help keeps Bach2 expression relatively high, thereby being predisposed to enter the memory pool.

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Comparison of Bach2-tdRFP high expression and low expression NP-specific IgG1 light zone GC B cells

Project description:Despite the importance of memory B cells for protection from recurrent infection, how these cells are selected during germinal center (GC) reactions remains unclear. We show here that light zone (LZ) GC B cells with lower affinity BCRs express a less CD40 signature and relatively high levels of Bach2, being prone to enter the memory B cell pool. We also find that Bach2 contributes to memory B cell generation in a Blimp-1-independent manner and that its higher expression confers on LZ GC cells a more advantage for entering the memory B cell compartment. Thus, our data support an instructive model in which weak T cell help keep Bach2 expression relatively high, thereby being predisposed to enter the memory pool.

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Transcription factor EB sets the stage for fate decisions of antigen-primed B cells in the absence and presence of co-stimulation

Project description:Ligation of the B cell antigen receptor (BCR) initiates humoral immunity. However, mere BCR signaling without appropriate co-stimulation commits B cells to death rather than to differentiation into immune effector cells. How BCR activation depletes potentially autoreactive B cells while simultaneously primes for receiving rescue and differentiation signals from cognate T lymphocytes remains unknown. Here, using a mass spectrometry-based proteomic approach to identify cytosolic/nuclear shuttling elements, we uncover transcription factor EB (TFEB) as a central BCR-controlled rheostat that drives activation-induced apoptosis, and concurrently, promotes the reception of co-stimulatory rescue signals by supporting B cell migration and antigen presentation. CD40 co-stimulation prevents TFEB-driven cell death, while enhancing and prolonging TFEB’s nuclear residency, which hallmarks antigenic experience also of memory B cells. In mice, TFEB shapes the transcriptional landscape of germinal center B cells. Within the germinal center, TFEB facilitates the dark zone entry of light-zone-residing centrocytes through regulation of chemokine receptors and, by balancing the expression of Bcl-2/BH3-only family members, integrates antigen-induced apoptosis with T cell-provided CD40 survival signals. Thus, TFEB reprograms antigen-primed germinal center B cells for cell fate decisions.

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B cell intrinsic TBK1 is essential for germinal center formation during infection and vaccination

Project description:Germinal center (GC) is a site where somatic hypermutation and clonal selection are coupled for antibody affinity maturation against infections. However, how GCs are formed and regulated is incompletely understood. Here, we identified an unexpected role of Tank-binding kinase-1 (TBK1) as a crucial B-cell-intrinsic factor for GC formation. Using immunization and malaria infection models, we show that TBK1-deficient B cells failed to form GC despite normal Tfh differentiation, although some malaria-infected B-cell-specific TBK1-deficient mice could survive by GC-independent mechanisms. Mechanistically, TBK1 phosphorylation elevates in B cells during GC differentiation and regulates the balance of IRF4/BCL6 expression by limiting CD40 and BCR activation through non-canonical NF-κB and AKTT308 signaling. In the absence of TBK1, CD40 and BCR signaling synergistically enhanced IRF4 expression in Pre-GC leading to BCL6 suppression, therefore failed to form GC. As a result, memory B cells generated from TBK1-deficient B cells fail to confer sterile immunity upon re-infection, suggesting that TBK1 determines B cell fate to promote long-lasting humoral immunity.

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Bach2 promotes B cell receptor-induced proliferation of B lymphocytes and represses cyclin-dependent kinase inhibitors

Project description:Bach2 (BTB and CNC homology-2) is a transcriptional repressor which is required for the formation of the germinal center (GC) and reactions including class switch recombination (CSR) and somatic hypermutation (SHM) of immunoglobulin genes in B cells within the GC. While BCR-induced proliferation is essential for GC reactions, the function of Bach2 in regulating B cell proliferation has not been elucidated. In this study, we demonstrate that Bach2 is required to sustain high levels of B cell proliferation in response to BCR signaling. Following BCR engagement in vitro, B cells from Bach2-deficient (Bach2-/-) mice showed lower incorporation of 5-bromo-2'-deoxyuridine (BrdU) and reduced cell cycle progression compared with wild-type (WT) cells. Bach2-/- B cells also underwent increased apoptosis as evidenced by an elevated frequency of sub-G1 cells and early apoptotic cells. Transcriptome analysis of BCR-engaged B cells from Bach2-/- mice revealed reduced expression of the anti-apoptotic gene Bcl2l1 encoding Bcl-XL, and an elevated expression of cyclin-dependent kinase inhibitor (CKI) family genes including Cdkn1a, Cdkn2a and Cdkn2b. Reconstitution of Bcl-XL expression partially rescued the proliferation defect of Bach2-/- B cells. Chromatin imunoprecipitation (ChIP) experiments showed that Bach2 bound to the CKI family genes, indicating that these genes are direct repression targets of Bach2. These findings identify Bach2 as a requisite factor for sustaining high levels of BCR-induced proliferation, survival and cell cycle progression, and promotes expression of Bcl-XL and repression of CKI genes, respectively. BCR-induced proliferation defects may contribute to impaired GC formation observed in Bach2-/- mice.

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Bach2 regulates B cell survival to maintain germinal centers and promote B cell memory

Project description:The transcription factor Bach2 serves as a crucial regulator of the germinal center (GC) reaction, which is required for production of high-affinity antibodies and establishment of long-lived B cell memory. However, the stage at which Bach2 controls the GC programs and the precise mechanism underlying these processes remain poorly understood. In this study, we show that genetic ablation of Bach2 in GC B cells of mice impairs their survival and maintenance, and memory B cell formation. These defects can be rescued by enforced expression of anti-apoptotic gene Bcl2. As expected, Bach2-deficient GC B cells are defective in antibody affinity maturation, but have normal somatic hyper mutation and class switch recombination of immunoglobulin genes. Mechanistically, Bach2 controls the GC programs by directly repressing pro-apoptotic gene Bim and a set of genes involved in cell stress response and metabolic processes. Thus, our work reveals the precise roles of Bach2 in the GC biology, and demonstrates that Bach2 acts as a crucial survival regulator of GC B cells, providing a key mechanism underlying GC B maintenance and B cell memory formation.

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Super-killer CTLs are generated by single gene deletion of Bach2

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2022-09-02 | PXD036457 | Pride

mTORC1 and B cell survival signal regulate formation of memory precursors in the germinal center [2]

Project description:A still unanswered question is what drives the small fraction of activated germinal center (GC) B cells that survive to become long-lived quiescent memory B cells. We found here that a small population of light zone GC cells (CD38intBcl6hi/intEfnb1+) with lower mTORC1 activity favored the memory B cell fate. Constitutively high mTORC1 activity led to defects in formation of the CD38intBcl6hi/intEfnb1+ cells; conversely, decreasing mTORC1 activity resulted in relative enrichment of this memory-prone GC population over the recycling-prone one. Furthermore, the CD38intBcl6hi/intEfnb1+ cells had higher levels of Bcl2 and surface BCR, which in turn, contributed to their survival. Given the positive correlation between the strength of T cell help and mTORC1 activity, our data suggest a model in which weak help from T cells together with provision of an increased survival signal are key for GC B cells to assume a memory B cell fate.

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