The EZH2 histone methyltransferase is required for B cells to form germinal centers (GC). Here we show that EZH2 mediates GC formation through repression of cyclin-dependent kinase inhibitor CDKN1A ...(p21
). Deletion of Cdkn1a rescues the GC reaction in Ezh2
mice. Using a 3D B cell follicular organoid system that mimics the GC reaction, we show that depletion of EZH2 suppresses G1 to S phase transition of GC B cells in a Cdkn1a-dependent manner. GC B cells of Cdkn1a
Ezh2
mice have high levels of phospho-Rb, indicating that loss of Cdkn1a enables progression of cell cycle. Moreover, the transcription factor E2F1 induces EZH2 during the GC reaction. E2f1
mice manifest impaired GC responses, which is rescued by restoring EZH2 expression, thus defining a positive feedback loop in which EZH2 controls GC B cell proliferation by suppressing CDKN1A, enabling cell cycle progression with a concomitant phosphorylation of Rb and release of E2F1.The histone methyltransferase EZH2 silences genes by generating H3K27me3 marks. Here the authors use a 3D GC organoid and show EZH2 mediates germinal centre (GC) formation through epigenetic silencing of CDKN1A and release of cell cycle checkpoints.
Follicular lymphomas (FLs) are slow-growing, indolent tumors containing extensive follicular dendritic cell (FDC) networks and recurrent EZH2 gain-of-function mutations. Paradoxically, FLs originate ...from highly proliferative germinal center (GC) B cells with proliferation strictly dependent on interactions with T follicular helper cells. Herein, we show that EZH2 mutations initiate FL by attenuating GC B cell requirement for T cell help and driving slow expansion of GC centrocytes that become enmeshed with and dependent on FDCs. By impairing T cell help, mutant EZH2 prevents induction of proliferative MYC programs. Thus, EZH2 mutation fosters malignant transformation by epigenetically reprograming B cells to form an aberrant immunological niche that reflects characteristic features of human FLs, explaining how indolent tumors arise from GC B cells.
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•EZH2 mutations initiate lymphomagenesis by reprogramming the GC microenvironment•EZH2 mutation attenuates B cell requirement for T cell help•Mutant EZH2 drives expansion of GC centrocytes that are dependent on FDCs•Mutant EZH2 establishes the characteristic follicular lymphoma immunological niche
Béguelin et al. show that mutant EZH2 epigenetically reprograms germinal center B cells to alter their interactions with T follicular helper cells and follicular dendritic cells, facilitating malignant transformation and establishing characteristic features of the follicular lymphoma immunological niche.
During the germinal center (GC) reaction, B cells undergo extensive redistribution of cohesin complex and three-dimensional reorganization of their genomes. Yet, the significance of cohesin and ...architectural programming in the humoral immune response is unknown. Herein we report that homozygous deletion of Smc3, encoding the cohesin ATPase subunit, abrogated GC formation, while, in marked contrast, Smc3 haploinsufficiency resulted in GC hyperplasia, skewing of GC polarity and impaired plasma cell (PC) differentiation. Genome-wide chromosomal conformation and transcriptional profiling revealed defects in GC B cell terminal differentiation programs controlled by the lymphoma epigenetic tumor suppressors Tet2 and Kmt2d and failure of Smc3-haploinsufficient GC B cells to switch from B cell- to PC-defining transcription factors. Smc3 haploinsufficiency preferentially impaired the connectivity of enhancer elements controlling various lymphoma tumor suppressor genes, and, accordingly, Smc3 haploinsufficiency accelerated lymphomagenesis in mice with constitutive Bcl6 expression. Collectively, our data indicate a dose-dependent function for cohesin in humoral immunity to facilitate the B cell to PC phenotypic switch while restricting malignant transformation.
During the germinal center (GC) reaction, B cells undergo profound transcriptional, epigenetic and genomic architectural changes. How such changes are established remains unknown. Mapping chromatin ...accessibility during the humoral immune response, we show that OCT2 was the dominant transcription factor linked to differential accessibility of GC regulatory elements. Silent chromatin regions destined to become GC-specific super-enhancers (SEs) contained pre-positioned OCT2-binding sites in naive B cells (NBs). These preloaded SE 'seeds' featured spatial clustering of regulatory elements enriched in OCT2 DNA-binding motifs that became heavily loaded with OCT2 and its GC-specific coactivator OCAB in GC B cells (GCBs). SEs with high abundance of pre-positioned OCT2 binding preferentially formed long-range chromatin contacts in GCs, to support expression of GC-specifying factors. Gain in accessibility and architectural interactivity of these regions were dependent on recruitment of OCAB. Pre-positioning key regulators at SEs may represent a broadly used strategy for facilitating rapid cell fate transitions.
Eribulin is a microtubule-targeting agent approved for the treatment of advanced or metastatic breast cancer (BC) previously treated with anthracycline- and taxane-based regimens. PIK3CA mutation is ...associated with worse response to chemotherapy in oestrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic BC. We aimed to evaluate the role of phosphoinositide 3-kinase (PI3K)/AKT pathway mutations in eribulin resistance.
Resistance to eribulin was evaluated in HER2- BC cell lines and patient-derived tumour xenografts, and correlated with a mutation in the PI3K/AKT pathway.
Eleven out of 23 HER2- BC xenografts treated with eribulin exhibited disease progression. No correlation with ER status was detected. Among the resistant models, 64% carried mutations in PIK3CA, PIK3R1 or AKT1, but only 17% among the sensitive xenografts (P = 0.036). We observed that eribulin treatment induced AKT phosphorylation in vitro and in patient tumours. In agreement, the addition of PI3K inhibitors reversed primary and acquired resistance to eribulin in xenograft models, regardless of the genetic alterations in PI3K/AKT pathway or ER status. Mechanistically, PI3K blockade reduced p21 levels likely enabling apoptosis, thus sensitising to eribulin treatment.
PI3K pathway activation induces primary resistance or early adaptation to eribulin, supporting the combination of PI3K inhibitors and eribulin for the treatment of HER2- BC patients.
Experimental and clinical evidence points to a critical role of progesterone and the nuclear progesterone receptor (PR) in controlling mammary gland tumorigenesis. However, the molecular mechanisms ...of progesterone action in breast cancer still remain elusive. On the other hand, micro RNAs (miRNAs) are short ribonucleic acids which have also been found to play a pivotal role in cancer pathogenesis. The role of miRNA in progestin-induced breast cancer is poorly explored. In this study we explored progestin modulation of miRNA expression in mammary tumorigenesis.
We performed a genome-wide study to explore progestin-mediated regulation of miRNA expression in breast cancer. miR-16 expression was studied by RT-qPCR in cancer cell lines with silenced PR, signal transducer and activator of transcription 3 (Stat3) or c-Myc, treated or not with progestins. Breast cancer cells were transfected with the precursor of miR-16 and proliferation assays, Western blots or in vivo experiments were performed. Target genes of miR-16 were searched through a bioinformatical approach, and the study was focused on cyclin E. Reporter gene assays were performed to confirm that cyclin E 3'UTR is a direct target of miR-16.
We found that nine miRNAs were upregulated and seven were downregulated by progestin in mammary tumor cells. miR-16, whose function as a tumor suppressor in leukemia has already been shown, was identified as one of the downregulated miRNAs in murine and human breast cancer cells. Progestin induced a decrease in miR-16 levels via the classical PR and through a hierarchical interplay between Stat3 and the oncogenic transcription factor c-Myc. A search for miR-16 targets showed that the CCNE1 gene, encoding the cell cycle regulator cyclin E, contains conserved putative miR-16 target sites in its mRNA 3' UTR region. We found that, similar to the molecular mechanism underlying progestin-modulated miR-16 expression, Stat3 and c-Myc participated in the induction of cyclin E expression by progestin. Moreover, overexpression of miR-16 abrogated the ability of progestin to induce cyclin E upregulation, revealing that cyclin E is a novel target of miR-16 in breast cancer. Overexpression of miR-16 also inhibited progestin-induced breast tumor growth in vitro and in vivo, demonstrating for the first time, a role for miR-16 as a tumor suppressor in mammary tumorigenesis. We also found that the ErbB ligand heregulin (HRG) downregulated the expression of miR-16, which then participates in the proliferative activity of HRG in breast tumor cells.
In this study, we reveal the first progestin-regulated miRNA expression profile and identify a novel role for miR-16 as a tumor suppressor in progestin- and growth factor-induced growth in breast cancer.
Metastasis is the leading cause of cancer mortality. Chromatin remodeling provides the foundation for the cellular reprogramming necessary to drive metastasis. However, little is known about the ...nature of this remodeling and its regulation. Here, we show that metastasis-inducing pathways regulate histone chaperones to reduce canonical histone incorporation into chromatin, triggering deposition of H3.3 variant at the promoters of poor-prognosis genes and metastasis-inducing transcription factors. This specific incorporation of H3.3 into chromatin is both necessary and sufficient for the induction of aggressive traits that allow for metastasis formation. Together, our data clearly show incorporation of histone variant H3.3 into chromatin as a major regulator of cell fate during tumorigenesis, and histone chaperones as valuable therapeutic targets for invasive carcinomas.
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•Metastasis inducers lead to a decline in CAF-1 suppressing canonical H3 incorporation•EMT and metastatic colonization occur as a function of CAF-1 levels•Histone H3.3 variant is essential for tumor progression and aggressive phenotypes•HIRA-mediated H3.3 gap filling induces a pro-metastatic transcriptional reprogramming
Gomes et al. reveal metastatic stimuli reduce histone H3.1/H3.2 deposition on chromatin by suppressing the CAF-1 complex in breast and NSCLC cancer cells, leading to increased incorporation of non-canonical histone H3.3, which in turn induces chromatin remodeling and expression of metastatic genes.
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