scholarly journals B cell Sirt1 deacetylates histone and non-histone proteins for epigenetic modulation of AID expression and the antibody response

2020 ◽  
Vol 6 (14) ◽  
pp. eaay2793 ◽  
Author(s):  
Huoqun Gan ◽  
Tian Shen ◽  
Daniel P. Chupp ◽  
Julia R. Taylor ◽  
Helia N. Sanchez ◽  
...  
Keyword(s):  
Antibody Response ◽  
B Cell ◽  
Histone Deacetylases ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Dna Recombination ◽  
Sirtuin 1 ◽  
B Cell Differentiation ◽  
Class Iii ◽  
Nonhistone Proteins

Activation-induced cytidine deaminase (AID) mediates immunoglobulin class switch DNA recombination (CSR) and somatic hypermutation (SHM), critical processes for maturation of the antibody response. Epigenetic factors, such as histone deacetylases (HDACs), would underpin B cell differentiation stage–specific AID expression. Here, we showed that NAD+-dependent class III HDAC sirtuin 1 (Sirt1) is highly expressed in resting B cells and down-regulated by stimuli inducing AID. B cell Sirt1 down-regulation, deprivation of NAD+ cofactor, or genetic Sirt1 deletion reduced deacetylation of Aicda promoter histones, Dnmt1, and nuclear factor–κB (NF-κB) p65 and increased AID expression. This promoted class-switched and hypermutated T-dependent and T-independent antibody responses or led to generation of autoantibodies. Genetic Sirt1 overexpression, Sirt1 boost by NAD+, or allosteric Sirt1 enhancement by SRT1720 repressed AID expression and CSR/SHM. By deacetylating histone and nonhistone proteins (Dnmt1 and NF-κB p65), Sirt1 transduces metabolic cues into epigenetic changes to play an important B cell–intrinsic role in modulating antibody and autoantibody responses.

The TNF Family Members BAFF and APRIL Play an Important Role in Hodgkin Lymphoma.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 22-22 ◽  
Author(s):  
April Chiu ◽  
Xugang Qiao ◽  
Bing He ◽  
Elizabeth Hyjjek ◽  
Joong Lee ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Hodgkin Lymphoma ◽  
Cell Lines ◽  
Plasma Cells ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Dna Recombination ◽  
Classical Pathway ◽  
Bax Protein

Abstract Introduction. B cell-activating factor of the TNF family (BAFF) and a proliferation-inducing ligand (APRIL), a BAFF-related molecule, play a key role in the survival and proliferation of mature B cells. In addition, BAFF and APRIL cooperate with IL-4 to induce class switch DNA recombination (CSR) from IgM (or IgG) to IgG, IgA or IgE. This process requires activation-induced-cytidine deaminase (AID), a DNA-editing enzyme involved also in Ig somatic hypermutation and lymphomagenesis. BAFF and APRIL are usually produced by myeloid cells, including dendritic cells, macrophages and granulocytes, and engage three receptors preferentially expressed on B cells, including transmembrane activator and calcium modulator and cyclophylin ligand interactor (TACI), B cell maturation antigen (BCMA), and BAFF receptor (BAFF-R). Our previous studies show that BAFF and APRIL are EBV-inducible molecules implicated in B cell non-Hodgkin’s lymphoma (NHL). The scope of the present studies was to elucidate the expression and function of BAFF, APRIL, TACI, BCMA and BAFF-R in Hodgkin lymphoma (HL). Methods. Tissue sections from 5 primary EBV+ HL cases and 5 primary EBV− HL cases were analyzed for BAFF, APRIL, TACI, BCMA, and BAFF-R expression through immunohistochemistry. RS cells from 6 primary cases were microdissected and analyzed for the expression of AID and CSR byproducts by RT-PCR. The expression of BAFF, APRIL, TACI, BCMA, BAFF-R, AID, and CSR byproducts was also analyzed in 5 HL cell lines cultured in the presence or absence of recombinant BAFF, APRIL and cytokines as previously described1,2,3. Results. We found that the reactive infiltrate of primary HL tumors comprises non-malignant elements, such as macrophages, granulocytes and plasma cells, expressing BAFF and APRIL. Also a variable proportion of malignant CD30+ Reed-Sternberg (RS) cells from both EBV+ and EBV− HL cases express BAFF and APRIL. Unlike NHL B cells, which usually express BAFF-R, primary RS cells and RS cell lines lack BAFF-R, but express TACI and BCMA. In the presence of BAFF or APRIL, RS cell lines are rescued from spontaneous or induced apoptosis. This effect is associated with activation of NF-κB through a classical pathway. Increased RS cell survival is also associated with up-regulation of the pro-survival BCL-2 and BCL-XL proteins, and down-regulation of the pro-apoptotic BAX protein. Finally, in the presence of BAFF or APRIL and IL-4, RS cell lines up-regulate AID expression and increase their spontaneous CSR activity. Of note, AID expression extends to primary RS cells and is associated with ongoing CSR. Conclusions. Our studies indicate that BAFF and APRIL stimulate malignant RS cells through both autocrine and paracrine pathways. Engagement of TACI and BCMA receptors by BAFF and APRIL may enhance the expansion of RS cells by attenuating apoptosis through a mechanism involving NF-κB and BCL family proteins. By up-regulating AID, signals emanating from TACI and BCMA receptors might also introduce genomic instability. Finally, considering that TACI, BCMA and AID are B cell-specific molecules and that CSR is a process confined to B cells, our findings consolidate the notion that RS cells derive from a B cell precursor.

scholarly journals miR-181b negatively regulates activation-induced cytidine deaminase in B cells

2008 ◽  
Vol 205 (10) ◽  
pp. 2199-2206 ◽  
Author(s):  
Virginia G. de Yébenes ◽  
Laura Belver ◽  
David G. Pisano ◽  
Susana González ◽  
Aranzazu Villasante ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Molecular Mechanisms ◽  
Bystander Effect ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Fine Tuning ◽  
Functional Screening ◽  
Activation Induced Cytidine Deaminase ◽  
Activated B Cells

Activated B cells reshape their primary antibody repertoire after antigen encounter by two molecular mechanisms: somatic hypermutation (SHM) and class switch recombination (CSR). SHM and CSR are initiated by activation-induced cytidine deaminase (AID) through the deamination of cytosine residues on the immunoglobulin loci, which leads to the generation of DNA mutations or double-strand break intermediates. As a bystander effect, endogenous AID levels can also promote the generation of chromosome translocations, suggesting that the fine tuning of AID expression may be critical to restrict B cell lymphomagenesis. To determine whether microRNAs (miRNAs) play a role in the regulation of AID expression, we performed a functional screening of an miRNA library and identified miRNAs that regulate CSR. One such miRNA, miR-181b, impairs CSR when expressed in activated B cells, and results in the down-regulation of AID mRNA and protein levels. We found that the AID 3′ untranslated region contains multiple putative binding sequences for miR-181b and that these sequences can be directly targeted by miR-181b. Overall, our results provide evidence for a new regulatory mechanism that restricts AID activity and can therefore be relevant to prevent B cell malignant transformation.

Clonal Analysis of IgM Cells in Multiple Myeloma Patients Suggests the Co-Existence of Normal and Malignant Arms of the Myeloma Clone.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1415-1415
Author(s):  
Brian J. Taylor ◽  
Ming Ye ◽  
Erin R. Strachan ◽  
Tara M. Tiffinger ◽  
Andrew R. Belch ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
B Cell ◽  
Plasma Cells ◽  
Somatic Hypermutation ◽  
Immunomagnetic Separation ◽  
B Cell Differentiation ◽  
Reading Frame ◽  
A Minor ◽  
Pcr Targeting ◽  
Insight Into

Abstract Analysis of immunoglobulin V genes, which undergo stepwise changes during B cell differentiation such as VDJ rearrangement, somatic hypermutation, and class switch recombination, provides insight into the point of transformation of B cell tumors. In Multiple Myeloma (MM), clonotypic VDJ sequences of malignant plasma cells are mutated, homogeneous, and associated with post-switch constant regions (either IgG or IgA, called the clinical isotype), suggesting the malignant arm of the MM clone arises from transformation events in the late stages of the germinal centre reaction. By contrast, the existence of clonotypic VDJ associated with pre-switch IgM is well established, and we have shown persistent clonotypic IgM is associated with advanced disease at diagnosis and poor survival in MM. Whether clonotypic IgM cells represent a malignant progenitor or a non-malignant population that parallels disease severity is unclear. To address these possibilities, we focused our analysis of clonotypic VDJ mutation profiles on IgM+ cells sorted by immunomagnetic separation from MM patient peripheral blood cells (PBMC). IgM clonotypic transcripts were amplified by hemi-nested RT-PCR targeting the CDR2-C mu constant region in IgM+ cells from 4/7 patients. These products were cloned, and 122, 28, 27, and 25 IgM clonotypic colonies were identified by specific CDR2/CDR3 PCR for patients 1–4 respectively. Each of these clones was sequenced, and mutations were identified by comparison with the closest germline V gene and tumor derived plasma cell VDJ sequences. An average mutation frequency of 0.005, significantly greater than the Taq error rate, was obtained for the 250–280 bp fragment downstream of CDR2, including the D-J-C mu region. Typically, MM clones were observed with 1–2 mutations in this region, many localizing to the D-J-C mu region. Small deletions that preserve reading frame were also observed in the D region of single clones of patients 1 and 4 respectively. The detection of intraclonal heterogeneity amongst clonotypic IgM cells may reflect a normal arm of the myeloma clone that co-exists with the post-switch malignant arm. In previous work examining bulk PBMC populations we had detected diversified clonotypic cells in the non-clinical isotype compartment of one patient, but, in accordance with studies performed by several other groups, were unable to detect diversified pre-switch counterparts. In this work we have focused on IgM+ MM B cells, a compartment of the MM clone that may remain driven by antigenic selection and undergo persistent clonal expansion. Our analysis gives insight into the nature of this proposed normal arm of the myeloma clone, revealing two coexisting subsets of pre-switch clonotypic IgM cells: a major set exhibiting homogeneity, identity with post-switch tumor VDJ, and questionable transformation status, and a minor clonally heterogeneous set which may represent the pre-malignant clone from which myeloma arose.

Activation Induced Cytidine Deaminase (AID) Is Required for Germinal-Center Derived Lymphomagenesis.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 223-223
Author(s):  
Laura Pasqualucci ◽  
Mara Compagno ◽  
Tongwei Mo ◽  
Paula Smith ◽  
Herbert C. Morse ◽  
...  
Keyword(s):  
Gene Expression ◽  
B Cells ◽  
B Cell ◽  
Germinal Center ◽  
Somatic Hypermutation ◽  
Profile Analysis ◽  
Cytidine Deaminase ◽  
Receptor Gene ◽  
Activation Induced Cytidine Deaminase ◽  
Hodgkin's Lymphomas

Abstract Most B cell non-Hodgkin’s lymphomas (B-NHL) derive from germinal center (GC) B cells and their pathogenesis is associated with the accumulation of distinct genetic lesions, including chromosomal translocations and a more recently identified mechanism of genomic instability, termed aberrant somatic hypermutation. These alterations are thought to be due to mistakes occurring during two GC-associated immunoglobulin (Ig) genes remodeling processes: class switch recombination (CSR) and somatic hypermutation (SHM). However, this model has never been formally proven. To conclusively investigate the role of CSR and SHM in the pathogenesis of B-NHL, we examined whether lymphoma development in mice requires the function of activation induced cytidine deaminase (AID), a DNA editing enzyme expressed specifically in GC and activated B cells and essential for both processes. Three transgenic mouse models were generated by crossing lymphoma-prone mice (λMYC, λMYC/IμHABCL6 and IμHABCL6) with mice (AID−/−) that are unable to undergo both SHM and CSR. The λMYC mice develop a diffusely infiltrating monoclonal proliferation of pre-GC origin, with unmutated IgV genes and lack of BCL6 expression, and therefore presumably independent from AID-associated DNA remodeling events. Conversely, lymphomas in λMYC/IμHABCL6 and IμHABCL6 mice recapitulate GC/post GC-derived malignancies, in that the former display somatically mutated IgV genes and upregulation of post-GC markers (CD138) in most of the cases, while the latter develop a splenic lymphoproliferative syndrome that culminates, past 12 months of age, in clonal B cell lymphomas with DLBCL morphology and somatically mutated IgV genes (~70% of the animals) (Cattoretti et al., Cancer Cell 7:445–455, 2005). Mice were monitored for tumor incidence and survival, and a combination of histologic, immunophenotypic and gene expression profiling analysis was used for tumor characterization. As expected, no significant differences in event-free survival and lymphoma type were observed between AID-proficient and AID-deficient λMYC mice, in agreement with their pre-GC derivation. Conversely, a phenotypic shift of the tumor was observed in λMYC/IμHABCL6 mice when bred into an AID−/− background, with >80% of the cases (N=21/26) reverting to a pre-GC phenotype (loss of GC/post GC markers) undistinguishable from that of the λMYC and λMYC/AID−/− mice. Gene expression profile analysis on representative cases (N=10 λMYC/IμHABCL6 and 5 each for λMYC, λMYC/AIDKO, λMYC/IμHABCL6/AIDKO) confirmed significant phenotypic similarities between pre-GC derived λMYC lymphomas and the λMYC/IμHABCL6/AID −/− lymphomas, which co-segregated in a separate cluster from λMYC/IμHABCL6 tumors. Analogously, a significant reduction in DLBCL frequency was observed in the IμHABCL6/AIDKO cohort as compared to IμHABCL6 mice (N= 4/19, 21% vs 8/14, 57%; p=0.03). Taken together, these results indicate that GC-derived lymphomas cannot develop in the absence of AID, thereby providing direct support to the notion that AID-mediated mistakes in antigen receptor gene modification events (CSR and SHM) represent major contributors to B-NHL pathogenesis.

Mucosal Epithelial Cells Initiate Frontline Immunoglobulin Class Switching through an SLPI-Regulated Pathway.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3898-3898
Author(s):  
Andrea Cerutti ◽  
Bing He ◽  
April Chiu ◽  
Meimei Shan ◽  
Paul Santini ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
B Cells ◽  
Epithelial Cells ◽  
B Cell ◽  
Antibody Production ◽  
Cytidine Deaminase ◽  
Dna Recombination ◽  
Class Switching ◽  
Class Switch

Abstract Introduction. Class switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods. Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in class switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results. We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing class switch DNA recombination (CSR). Epithelial cells released innate class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial class switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions. The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.

scholarly journals Neddylation Regulates Class IIa and III Histone Deacetylases to Mediate Myoblast Differentiation

2021 ◽  
Vol 22 (17) ◽  
pp. 9509
Author(s):  
Hongyi Zhou ◽  
Huabo Su ◽  
Weiqin Chen
Keyword(s):  
Transcriptional Activation ◽  
Nuclear Export ◽  
Histone Deacetylases ◽  
Molecular Mechanisms ◽  
Myogenic Differentiation ◽  
The Body ◽  
Muscle Disease ◽  
Sirtuin 1 ◽  
Myoblast Differentiation ◽  
Class Iii

As the largest tissue in the body, skeletal muscle has multiple functions in movement and energy metabolism. Skeletal myogenesis is controlled by a transcriptional cascade including a set of muscle regulatory factors (MRFs) that includes Myogenic Differentiation 1 (MYOD1), Myocyte Enhancer Factor 2 (MEF2), and Myogenin (MYOG), which direct the fusion of myogenic myoblasts into multinucleated myotubes. Neddylation is a posttranslational modification that covalently conjugates ubiquitin-like NEDD8 (neural precursor cell expressed, developmentally downregulated 8) to protein targets. Inhibition of neddylation impairs muscle differentiation; however, the underlying molecular mechanisms remain less explored. Here, we report that neddylation is temporally regulated during myoblast differentiation. Inhibition of neddylation through pharmacological blockade using MLN4924 (Pevonedistat) or genetic deletion of NEDD8 Activating Enzyme E1 Subunit 1 (NAE1), a subunit of the E1 neddylation-activating enzyme, blocks terminal myoblast differentiation partially through repressing MYOG expression. Mechanistically, we found that neddylation deficiency enhances the mRNA and protein expressions of class IIa histone deacetylases 4 and 5 (HDAC4 and 5) and prevents the downregulation and nuclear export of class III HDAC (NAD-Dependent Protein Deacetylase Sirtuin-1, SIRT1), all of which have been shown to repress MYOD1-mediated MYOG transcriptional activation. Together, our findings for the first time identify the crucial role of neddylation in mediating class IIa and III HDAC co-repressors to control myogenic program and provide new insights into the mechanisms of muscle disease and regeneration.

Activation-Induced Cytidine Deaminase Accelerates Clonal Evolution of BCR-ABL1-Driven B Cell Lineage Acute Lymphoblastic Leukemia.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 181-181
Author(s):  
Tanja Gruber ◽  
Mi Sook Chang ◽  
Richard Sposto ◽  
Markus Müschen
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
B Cell ◽  
Genetic Instability ◽  
Tumor Suppressor Genes ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Lymphoblastic Leukemia ◽  
Clonal Evolution ◽  
Activation Induced Cytidine Deaminase

Abstract Abstract 181 Activation-Induced Cytidine Deaminase (AID) is required for somatic hypermutation and immunoglobulin (Ig) class switch recombination in germinal center (GC) B cells. Occasionally, AID can target non-Ig genes and thereby promote GC B cell lymphomagenesis. We recently demonstrated that the oncogenic BCR-ABL1 kinase induces aberrant expression of AID in pre-B acute lymphoblastic leukemia (ALL). Compared to other ALL subtypes, BCR-ABL1 ALL is considered high risk and is characterized by a high degree of genetic instability. Because aberrant mutational activity of AID is associated with malignant transformation in B cell lymphoma, we sought to determine whether aberrant AID expression contributes to clonal evolution and genetic instability in Ph+ ALL. To investigate the function of AID expression in Ph+ ALL, we established a genetic loss-of-function model for Ph+ ALL: Bone marrow cells from AID−/− mice and AID+/+ controls were transformed by retroviral transduction with BCR-ABL1 under B lymphoid culture conditions and subsequently injected into lethally irradiated congenic recipients. Mice transplanted with AID−/−BCR-ABL1 ALL had prolonged median survival as compared to mice transplanted with leukemia cells generated from AID+/+ bone marrow (AID−/− 34 days (n=18) vs AID+/+ 13 days (n=21); p<0.0001). In secondary and tertiary transplant experiments, however, the difference between AID−/− and AID+/+BCR-ABL1 ALL narrowed as determined by a decreasing hazard ratio (from 25.5 in the primary transplant to 5.1 in the secondary and 2.9 in the tertiary transplantation). These findings suggest that aberrant AID expression accelerates clonal evolution of Ph+ ALL, but AID-independent factors exist that are sufficient for transformation. In support of enzymatic activity of AID in BCR-ABL1-transformed ALL cells, we observed that aberrant somatic hypermutation of non-immunoglobulin genes in these leukemias was largely dependent on AID: mutations in the known hypermutation target genes Pax5 and Rhoh were increased in AID+/+ but not AID−/−BCR-ABL1 ALL cells. Mutations in the first intron of Rhoh as observed here are relevant because they interfere with Rhoh transcription. Indeed, we found that Rhoh mRNA levels are significantly higher in AID−/− compared to AID+/+BCR-ABL1 ALL cells. Rhoh is a hematopoietic specific GTPase that negatively regulates Rac-mediated signaling downstream of the oncogenic BCR-ABL1 kinase. AID-dependent mutation and transcriptional inactivation of Rhoh in BCR-ABL1 ALL therefore likely augments oncogenic BCR-ABL1 signaling. Consistent with a causative role of AID in genetic instability, AID−/− leukemia had a lower frequency of amplifications (17+2 vs 45+7; p=0.002) and deletions (11+2 vs 40+7; p=0.003) as compared to AID+/+ leukemias. AID−/− and AID+/+ ALL cells showed a markedly distinct gene expression pattern with 2,365 differentially expressed genes (p=0.003; FDR 0.05). A detailed analysis of these differences in gene expression revealed that AID−/−BCR-ABL1 ALL cells failed to downregulate a number of tumor suppressor genes including p53, Rhoh, Cdkn1a (p21), and Blnk (SLP65). AID-dependent downregulation of p53 in BCR-ABL1 ALL cells is of particular importance, because previous work demonstrated that transcriptional repression of p53 in normal GC B cells is required to make these cells permissive to high levels of AID expression. AID-induced DNA damage would otherwise activate p53 and rapidly induce apoptosis. Compared to AID-deficient BCR-ABL1 ALL, AID+/+BCR-ABL1 ALL cells are more resistant to Imatinib-treatment. However, acquisition of BCR-ABL1 kinase domain mutations does not appear to be the main cause of drug-resistance in this experiment, since only one relevant mutation was amplified from AID+/+ ALL cells (no mutations in AID−/− ALL cells). We conclude that AID accelerates clonal evolution in BCR-ABL1 ALL by enhancing genetic instability, aberrant somatic hypermutation, and by negative regulation of tumor suppressor genes. Disclosures: No relevant conflicts of interest to declare.

Genomewide Detection of Genes Targeted by Aberrant Somatic Hypermutation in Lymphoma,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3474-3474
Author(s):  
Yanwen Jiang ◽  
David Soong ◽  
Chuanxin Huang ◽  
Stefano Monni ◽  
Ari Melnick ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Activation ◽  
Gene Expression Regulation ◽  
Conflicts Of Interest ◽  
Somatic Hypermutation ◽  
Clonal Selection ◽  
Reporter Assay ◽  
B Cell Differentiation ◽  
Single Nucleotide Variants

Abstract Abstract 3474 The processes of somatic hypermutation (SHM) and class switch recombination introduced by activation-induced deaminase (AID) are key steps for creating a pool of diversified antibodies in activated germinal center (GC) B cells (centroblasts; CBs) upon antigen dependent stimulation of resting naïve B cells (NBs) by T cells. Periodically, centroblasts enter the light zone of the GC where they interact with dendritic cells and T helper cells to undergo clonal selection for cells expressing high affinity antibodies. Unfortunately, AID can also accidentally introduce mutations at bystander loci, particularly within the promoter regions of a number of proto-oncogenes (BCL6, MYC, PAX5, PIM1, RhoH, S1PR2, and SOCS1) in diffuse large B cell lymphomas (DLBCL), an aggressive non-Hodgkins lymphomas. Since current methods, such as Exon Capture and RNAseq, only target mutations in coding regions, to date aberrant promoter SHMs have been studied only in a handful of genes. Given the complexity of lymphomagenesis, there may be additional genes that are targeted aberrantly by SHM at their promoters in DLBCLs. To identify genes that are targeted by SHM genomewide, we designed a novel approach to search for SHM hotspots in the genome by integrating bioinformatics tools with next generation sequencing technology. We developed a comprehensive software framework (called SHMseeqer) for discovery of single nucleotide variants (SNV) that have SHM features from ChIP-seq reads. We ran SHMseeqer on several histone H3 lysine 4 trimethylation (H3K4me3, preferentially enriched at promoters) ChIP-seq datasets obtained from two DLBCL cell lines and from normal primary NBs and CBs. We observed increased numbers of genes that harbor SHM at their promoters in DLBCL cells as compared to primary normal B cells. Moreover, in DLBCL cells, we observed promoter SHM hotspots in genes that have not been reported before, including BACH2, BTG2, EBF1, and TCL1A, etc., all of which have potential roles in B cell survival, differentiation, and malignant transformation. In addition, using BCL6 and BACH2 promoters as examples, we demonstrated that SHMs identified in these promoters greatly altered the promoter activities in a reporter assay. BACH2 is a B-cell specific transcription factor that plays an important role in gene expression regulation during B-cell activation and terminal differentiation. We observed that the SHM containing BACH2 promoter had increased transcription activity in the reporter assay as compared to widetype BACH2 promoter. We further showed that there was an elevated BACH2 level in DLBCL cells, and together with BCL6, BACH2 can block mature B-cell differentiation by repressing the expression of PRDM1. Our approach provides the first cost-efficient, genome-wide method to screen promoter mutations and SHM hotspots; an area that has not been fully explored thus far. Furthermore, by using this approach we showed that there were increased aberrant SHMs in DLBCL cells, suggesting that the process of AID-induced SHM is impaired in DLBCL cells. Moreover, the AID-induced promoter SHMs may deregulate the expression of key B-cell genes that leads to DLBCL transformation ultimately. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Sirtuins: Molecular Traffic Lights in the Crossroad of Oxidative Stress, Chromatin Remodeling, and Transcription

2011 ◽  
Vol 2011 ◽  
pp. 1-17 ◽  
Author(s):  
Ramkumar Rajendran ◽  
Richa Garva ◽  
Marija Krstic-Demonacos ◽  
Constantinos Demonacos
Keyword(s):  
Oxidative Stress ◽  
Dna Damage ◽  
Transcriptional Regulation ◽  
Histone Deacetylases ◽  
Molecular Mechanisms ◽  
Biological Activities ◽  
Class Iii ◽  
Nonhistone Proteins ◽  
Traffic Lights ◽  
Major Mechanism

Transcription is regulated by acetylation/deacetylation reactions of histone and nonhistone proteins mediated by enzymes called KATs and HDACs, respectively. As a major mechanism of transcriptional regulation, protein acetylation is a key controller of physiological processes such as cell cycle, DNA damage response, metabolism, apoptosis, and autophagy. The deacetylase activity of class III histone deacetylases or sirtuins depends on the presence of NAD+(nicotinamide adenine dinucleotide), and therefore, their function is closely linked to cellular energy consumption. This activity of sirtuins connects the modulation of chromatin dynamics and transcriptional regulation under oxidative stress to cellular lifespan, glucose homeostasis, inflammation, and multiple aging-related diseases including cancer. Here we provide an overview of the recent developments in relation to the diverse biological activities associated with sirtuin enzymes and stress responsive transcription factors, DNA damage, and oxidative stress and relate the involvement of sirtuins in the regulation of these processes to oncogenesis. Since the majority of the molecular mechanisms implicated in these pathways have been described for Sirt1, this sirtuin family member is more extensively presented in this paper.

scholarly journals SIRT1 and Kidney Function

2015 ◽  
Vol 1 (4) ◽  
pp. 258-265 ◽  
Author(s):  
Yi Guan ◽  
Chuan-Ming Hao
Keyword(s):  
Histone Deacetylases ◽  
Acute Stress ◽  
Kidney Diseases ◽  
Kidney Injury ◽  
Renal Medulla ◽  
Cyst Formation ◽  
Renal Physiology ◽  
Dna Integrity ◽  
Class Iii ◽  
Nonhistone Proteins

Background: SIRT1 is a nicotinamide adenine dinucleotide-dependent deacetylase belonging to the class III histone deacetylases. Abundantly expressed in the kidney, especially in the renal medulla, SIRT1 is closely involved in renal physiology and pathology. Summary: SIRT1 targets both histone and nonhistone proteins, participates in many important signaling pathways and mediates the regulation of longevity, metabolic homeostasis, acute stress response and DNA integrity. With regard to the kidney, SIRT1 attenuates diabetic albuminuria, reduces blood pressure and related cardiovascular diseases, resists acute kidney injury, delays kidney fibrogenesis, promotes cyst formation and benefits renal ageing. Key Messages: This review summarizes the biology of SIRT1 and focuses on the latest studies concerning SIRT1 as a potential therapeutic target for kidney diseases.

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