scholarly journals DYRK1A Is a Therapeutic Target in B-ALL in Children with Down Syndrome

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2721-2721
Author(s):  
Paul Lee ◽  
Rahul Bhansali ◽  
Malini Rammohan ◽  
Nobuko Hijiya ◽  
Shai Izraeli ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Down Syndrome ◽  
Cell Division ◽  
B Cells ◽  
Therapeutic Target ◽  
Genetic Alterations ◽  
Chromosome 21 ◽  
Cyclin D3 ◽  
Children With Down Syndrome ◽  
Stat Signaling

Abstract Children with Down syndrome have a spectrum of associated disorders including a 20-fold increased incidence of B-cell acute lymphoblastic leukemia (DS-ALL). Although a number of genetic alterations have been found in this ALL subtype, such as activating mutations in JAK2 and overexpression of CRLF2, the mechanisms by which trisomy 21 promotes the leukemia are largely unknown. Previous studies have implicated chromosome 21 genes HMGN1 and DYRK1A in both malignant and normal lymphopoiesis. DYRK1A is a member of the dual-specificity tyrosine phosphorylation-regulated kinase family that has been well studied in non-hematopoietic tissues. Its targets include proteins that regulate multiple pathways including cell signaling, cell cycle, and brain development. We have previously shown that DYRK1A is a megakaryoblastic leukemia-promoting gene through its negative regulation of NFAT transcription factors. Furthermore, in studies with a conditional Dyrk1a knock-out mouse, we found that the kinase is required for lymphoid, but not myeloid cell development. In developing lymphocytes, Dyrk1a regulates the cell cycle by destabilizing cyclin D3. Consequently, loss of Dyrk1a resulted in the failure of these cells to switch from a proliferative to quiescent phase for subsequent maturation (Thompson et al. J. Exp. Med. 2015 212:953-70). Despite this deficiency in exiting the cell cycle, Dyrk1a-deficient lymphocytes also exhibit impaired proliferation before undergoing apoptosis. These data reveal a critical role for DYRK1A in lymphopoiesis and suggest that it may be a target for therapeutic intervention. We assayed the activity of the highly selective and potent DYRK1 inhibitor, EHT 1610, in multiple ALL cell lines. EHT 1610 inhibited the growth of Jurkat and MHH-CALL-4 cells with EC50s of 0.83mM and 0.49mM, respectively. Next, we treated primary human ALL blasts with EHT 1610 and the less selective DYRK1A inhibitor harmine. Growth of 16 out of 30 specimens, which included DS-ALL, pre-B ALL, and T-ALL, was sensitive to DYRK1A inhibition at doses between 0.5 and 10mM. Of note, growth of 9 of the 11 of the DS-ALL samples was inhibited by EHT 1610. This result indicates that the increased dosage of DYRK1A in DS samples sensitizes the cells to DYRK1A inhibition. To further study the contributions of DYRK1A to normal and malignant lymphopoiesis, we performed phosphoproteomic analysis on primary murine pre-B cells treated with EHT 1610. After 2 hours of EHT 1610 treatment, the cells were collected and analyzed for changes in the phosphoproteome. Phosphorylation of 36 proteins was significantly altered. Bioinformatics analysis led to the identification of a number of notable pathways that appear to be regulated by DYRK1A including cell cycle, cell division and mitosis, RNA metabolism, and JAK-STAT signaling. Differentially phosphorylated proteins included geminin, which is important in cell division and whose loss enhances megakaryopoiesis, and POLR2M, which is intriguing because DYRK1A phosphorylates the CTD of RNA Pol II and binds chromatin at specific sites in glioblastoma cells. Another interesting target is STAT3, which is phosphorylated by DYRK1A on Ser727, a residue whose phosphorylation is required for maximal STAT3 activation. Treatment of murine pre-B cells with EHT 1610 significantly reduced the level of phosphorylation of Ser727 and Tyr705, suggesting that DYRK1A may provide a priming event for STAT3 activation similar to its priming effect on GSK3b phosphorylation. Consistent with a role for JAK/STAT signaling and STAT3 activity, B-ALL cells were highly sensitive to ruxolitinib therapy. Taken together, our study suggests that DYRK1A is a therapeutic target in DS-ALL and likely functions in part by enhancing JAK/STAT signaling. Disclosures No relevant conflicts of interest to declare.

scholarly journals The Chromosome 21 Kinase DYRK1A and Its Substrate FOXO1 Constitute a Novel Therapeutic Pathway in B-ALL

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 548-548
Author(s):  
Rahul S. Bhansali ◽  
Malini Rammohan ◽  
Ji Heon Paul Lee ◽  
Sebastien Malinge ◽  
Yi-Chien Tsai ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Damage ◽  
B Cells ◽  
Cell Lines ◽  
Research Funding ◽  
Negative Regulator ◽  
Chromosome 21 ◽  
Cyclin D3 ◽  
B Lymphopoiesis

Abstract Dual Specificity Tyrosine-Phosphorylation-Regulated Kinase 1A (DYRK1A) is a serine/threonine kinase that regulates diverse pathways such as splicing, cell cycle, differentiation, apoptosis, and transcription. DYRK1A is encoded within the Down syndrome (DS) critical region of chromosome 21, underlying its importance in DS-related pathologies, such as Alzheimer's disease. Children with DS have an increased risk of developing hematologic malignancies, namely acute megakaryoblastic leukemia (DS-AMKL) and B-cell acute lymphoblastic leukemia (DS-ALL). We previously reported that DYRK1A promotes DS-AMKL by regulating subcellular localization of its substrate NFAT. In a subsequent study, we examined its role in normal hematopoiesis and found that DYRK1A is necessary for B and T cell development through phosphorylation and destabilization of Cyclin D3. Dyrk1a-deficient large pre-B cells and double negative thymocytes are unable to enter quiescence for maturation. Despite elevated levels of Cyclin D3, however, these cells lose proliferative capacity due to a block at the G2-M transition. This observation suggests that DYRK1A inhibition may exhibit anti-tumor activity in lymphocytes by first stimulating exit from quiescence but then blocking repeated rounds of cell division. Notably, DYRK1A is overexpressed in acute leukemias, including both T-ALL and B-ALL, relative to normal hematopoietic counterparts. Moreover, overexpression of dominant-negative DYRK1A-K188R impairs proliferation in human B-ALL cell lines, suggesting that DYRK1A kinase activity is required for B-ALL growth. In order to assess the physiologic relevance of targeting DYRK1A in vivo, we generated a murine model of B-ALL with a floxed Dyrk1a allele and observed significant survival advantages with homozygous (p=0.0045) and heterozygous deletion (p=0.0015). Additionally, both B-ALL cell lines and patient samples were sensitive to EHT1610, a potent and selective DYRK1 inhibitor. Relevant to the localization of DYRK1A on chromosome 21, DS-ALL samples were especially sensitive to kinase inhibition. EHT1610 also conferred synergistic growth inhibition of B-ALL cells when combined with cytotoxic chemotherapy drugs used in traditional ALL treatment regimens, such as dexamethasone, methotrexate and cytarabine. We next aimed to elucidate the mechanism by which DYRK1A inhibition cause a failure of G2-M progression. Using global and directed phosphoproteomic studies, we identified several DYRK1A substrates in pre-B cells that are involved in cell cycle, splicing, transcriptional regulation, and RNA metabolism. In addition to Cyclin D3, a notable substrate is FOXO1, an indispensable transcription factor in B lymphopoiesis. We observed that inhibition of DYRK1A led to an accumulation of FOXO1 in the nucleus of large pre-B cells despite intact PI3K/Akt signaling, which is the predominant negative regulator of FOXO1. Treatment of pre-B cells with AS1842856, an inhibitor of FOXO1 nuclear translocation, rescued the G2-M blockade and proliferative impairment induced by EHT1610 treatment. Despite FOXO1 acting as a tumor suppressor in normal lymphocytes, B-ALL cell lines and patient samples were paradoxically sensitive to FOXO1 inhibition, suggesting a unique requirement in the survival of B-ALL cells. This may be due to regulation of DNA damage, as DYRK1A inhibition alone led to negligible changes in gamma-H2AX foci, whereas FOXO1 inhibition increased DNA damage. When DYRK1A and FOXO1 were inhibited in combination, we observed a synergistic accumulation of DNA damage along with cell death in B-ALL cell lines. Finally, as both EHT1610 and AS1842856 are potent inhibitors of B-ALL cell growth in vitro, we assessed their in vivo efficacy. Both EHT1610 and AS1842856 significantly increased survival in xenograft models of B-ALL (p=0.0002 and p=0.001, respectively). We therefore conclude that both DYRK1A and its substrate FOXO1 are therapeutic targets in B-ALL. Importantly, EHT1610 represents the first selective DYRK1A inhibitor with suitable in vivo activity. Ultimately, we have determined that the DYRK1A pathway is integral to the maintenance of normal and malignant B-lymphopoiesis, the latter which can be effectively targeted through 1) a primary proliferative impairment, 2) sensitization to cell cycle-dependent chemotherapy, and 3) downstream inhibition of DYRK1A substrates such as FOXO1. Disclosures Lee: AbbVie: Employment. Bourquin:Amgen: Other: Travel Support. Crispino:Scholar Rock: Research Funding; Forma Therapeutics: Research Funding.

CRLF2 Overexpression Demonstrates Enhanced Leukemogenicity in Down Syndrome Hematopoietic Cells

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2708-2708
Author(s):  
Jacob J. Junco ◽  
Shan Liang ◽  
Vishal Gokani ◽  
Vincent Ulysses Gant ◽  
Jaime Munoz ◽  
...  
Keyword(s):  
Down Syndrome ◽  
B Cells ◽  
B Cell ◽  
Fold Increase ◽  
Colony Growth ◽  
Genetic Alterations ◽  
Chromosome 21 ◽  
Lower Percentage ◽  
Hematopoietic Stem ◽  
B Lymphoid

Abstract Introduction: Children with Down syndrome (DS) are 10-20 times more likely than children without DS to develop acute lymphoblastic leukemia (ALL), and they demonstrate a distinctive spectrum of genetic alterations. Approximately 50% of DS-ALL cases demonstrate CRLF2 rearrangements (CRLF2-R), an approximately 10-fold higher frequency than in non-DS ALL. We sought to identify the functional basis for the increased incidence of ALL, and specifically CRLF2-R ALL, in children with DS. Methods: We created retroviral vectors which induce overexpression of CRLF2 and green fluorescent protein (GFP) for transduction into bone marrow (BM) cells isolated from the Dp16(1)Yey (Dp16) mouse model of DS, which is trisomic for the approximately 115 human chromosome 21 gene orthologs present on mouse chromosome 16. Transduced BM cells from Dp16 and wild-type (WT) control mice were co-cultured with OP9 stromal cells for one week to promote B-lymphoid lineage development, and then characterized by flow cytometric Hardy fraction analysis, or grown in B-lymphoid-promoting methylcellulose medium for colony growth assays. Results: We achieved efficient transduction (80-95%) of Dp16 and WT BM enriched for hematopoietic stem cells (HSCs) with CRLF2-GFP+ and control GFP+ viruses. Following OP9 co-culture, transduced HSCs were characterized by Hardy fraction analysis. CRLF2-GFP+ Dp16 lymphoid cells demonstrated significantly higher percentages of immature Fraction A (pre-pro-B) cells compared with GFP+ Dp16 cells (39.9% vs 15.7%, p=0.004, Fig. 1A). This CRLF2-GFP-induced immature immunophenotype was more pronounced in Dp16 versus WT HSCs, with a significantly higher percentage of Fraction A cells (39.9% in Dp16 vs 24.0% in WT, p=0.0002) and a significantly lower percentage of more mature Fraction B (pro-B) cells (24.3% in Dp16 vs 49.1% in WT, p=0.02, Fig. 1A,B). In methylcellulose colony assays, CRLF2-GFP+ Dp16 cells yielded a 36-fold increase in B cell colonies compared to GFP+ Dp16 cells (Fig 1C). Again, the effect of CRLF2 transduction was magnified in the Dp16 versus WT background. CRLF2-GFP+ WT cells demonstrated only a 2.9-fold increase in B cell colonies (Fig 1C). Conclusions: Here we demonstrate that CRLF2 overexpression results in a more immature B-lineage immunophenotype and increased lymphoid colony growth in vitro, and that these effects are significantly greater in a murine DS versus WT genetic background. Experiments to investigate the pathways involved and to evaluate these effects in vivo are ongoing. This work provides functional evidence of the enhanced leukemogenicity of CRLF2 overexpression in DS-ALL, and creates a tractable model system for additional future genetic studies. Disclosures No relevant conflicts of interest to declare.

Chronic Lymphocytic Leukemia B Cells Variably Express Functional Activation-Induced Cytosine Deaminase Protein

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 378-378
Author(s):  
Piers EM Patten ◽  
Charles C Chu ◽  
Rajendra N Damle ◽  
Steven L. Allen ◽  
Jonathan E Kolitz ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
B Cells ◽  
Disease Progression ◽  
Peripheral Blood ◽  
Lymphoid Tissues ◽  
Class Switching ◽  
Variable Nature ◽  
Leukemic Clone ◽  
Number Of Cells

Abstract Abstract 378 During the course of CLL, ongoing genetic changes occur within the leukemic clone and such changes associate with disease progression. Activation-induced cytidine deaminase (AID), the enzyme required for IGV gene somatic hypermutation and isotype class switching in B cells, is a candidate enzyme for causing such changes. Depending upon the detection method, circulating CLL cells express mRNA for AID in 40 – 100% of patients, although at any point only a very small percentage of cells within the clone express this message. Because B lymphocytes must be in the cell cycle for AID-induced DNA changes to occur, we hypothesized that AID protein would be contained within recently divided CLL cells and that these cells would exhibit new IGV mutations and/or class switching. Using appropriate markers for recently divided cells, we found that AID mRNA is enriched in/limited to this subset. Furthermore, because dividing cells in CLL are principally found within bone marrow and secondary lymphoid tissues, we analyzed such cells in lymph nodes (LNs) for AID protein expression and activity. In 50% of LNs infiltrated with CLL (n=10), AID protein was detected in large cells expressing a CLL phenotype; these cells were predominantly in the cell cycle. Nevertheless, even in those cases where CLL cells expressed AID, most cycling cells were AID protein negative. FACS analysis of dispersed LN cells confirmed the presence of AID protein-expressing cells and such cells had the phenotype of recently divided cells. To demonstrate that AID protein was functionally competent, we co-cultured peripheral blood CLL cells with anti-CD40 mAb and IL-4 in the presence of irradiated CD32-transfected fibroblasts, a model that mimics the tissue microenvironment. In 16 patients, we showed that peripheral blood leukemic cells could express AID protein, although the degree of upregulation was highly variable between cases. Using the dye CFSE to track CD5+CD19+ cell division, we found that AID protein always occurred when multiply divided cells were present. Some cases showed immediate AID production prior to division, while others exhibited no or little expression until passing through several cell cycles. AID protein causes double strand breaks (DSBs) within DNA, for example in IG switch regions during class switch recombination. We therefore used confocal microscopy to detect the presence of phospho-histone H2A.X (pH2AX), which localizes to DSBs, in CFSE-labeled cells stimulated for 14 days by the conditions mentioned above. At least 10 × 60 magnification images from 3 cultures showing cell division and AID upregulation were obtained, and the fluorescent signals for CFSE and pH2AX quantified from greater than 250 CD23+ CLL cells in each case. A mean of 20.4% of cells (range 10.4 – 38.2%) showed increased fluorescence with anti-pH2AX compared to unstimulated cells. Moreover, stimulated cultures demonstrated increased anti-pH2AX signal in a significantly greater number of cells with diminished CFSE intensity, which are the most divided cells, as compared to less/undivided cells with higher CFSE intensity (p<0.0001 in all cases analyzed, Fisher's exact test). In addition, 20 cell aliquots of unstimulated CLL cells and stimulated CFSE-labeled CLL cells were sorted after culture, yielding pure populations of either undivided cells or cells that had undergone 5 – 6 divisions. While all sorted populations yielded unswitched mu IG transcripts (≥75% wells positive in all groups), switched gamma transcripts with the same V-D-J rearrangement as the leukemic clone were only obtained from divided cells (range 4–9% wells positive), and not present in either undivided or unstimulated cells (0% wells positive). Taken together, the presence of heightened numbers of DSBs in the most divided cells compared to no/minimally divided cells and evidence of IG class switching in the former, indicate that AID protein was functional in these activated CLL peripheral blood cultures. In all, these data demonstrate that in CLL functional AID protein predominates in cells that are dividing or have a recently divided phenotype, although cases vary in the number of cells expressing AID as well as the relative amounts of enzyme expression. Differential AID activity between discrete CLL cases may relate to the development of new DNA mutations leading to clonal evolution and the variable nature of disease progression seen in this disease. Disclosures: No relevant conflicts of interest to declare.

scholarly journals The mTOR-Bach2 Cascade Controls Cell Cycle and Class Switch Recombination during B Cell Differentiation

2017 ◽  
Vol 37 (24) ◽  
Author(s):  
Toru Tamahara ◽  
Kyoko Ochiai ◽  
Akihiko Muto ◽  
Yukinari Kato ◽  
Nicolas Sax ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Differentiation ◽  
B Cells ◽  
B Cell ◽  
Molecular Mechanisms ◽  
Class Switch Recombination ◽  
Cyclin D3 ◽  
Immunoglobulin Gene ◽  
B Cell Differentiation ◽  
Class Switch

ABSTRACT The transcription factor Bach2 regulates both acquired and innate immunity at multiple steps, including antibody class switching and regulatory T cell development in activated B and T cells, respectively. However, little is known about the molecular mechanisms of Bach2 regulation in response to signaling of cytokines and antigen. We show here that mammalian target of rapamycin (mTOR) controls Bach2 along B cell differentiation with two distinct mechanisms in pre-B cells. First, mTOR complex 1 (mTORC1) inhibited accumulation of Bach2 protein in nuclei and reduced its stability. Second, mTOR complex 2 (mTORC2) inhibited FoxO1 to reduce Bach2 mRNA expression. Using expression profiling and chromatin immunoprecipitation assay, the Ccnd3 gene, encoding cyclin D3, was identified as a new direct target of Bach2. A proper cell cycle was lost at pre-B and mature B cell stages in Bach2-deficient mice. Furthermore, AZD8055, an mTOR inhibitor, increased class switch recombination in wild-type mature B cells but not in Bach2-deficient cells. These results suggest that the mTOR-Bach2 cascade regulates proper cell cycle arrest in B cells as well as immunoglobulin gene rearrangement.

scholarly journals Potential Role of JAK-STAT Signaling Pathway in the Neurogenic-to-Gliogenic Shift in Down Syndrome Brain

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Han-Chung Lee ◽  
Kai-Leng Tan ◽  
Pike-See Cheah ◽  
King-Hwa Ling
Keyword(s):  
Down Syndrome ◽  
Brain Development ◽  
Cell Fate ◽  
Mouse Models ◽  
Neuronal Cell ◽  
Janus Kinase ◽  
Chromosome 21 ◽  
Severe Intellectual Disability ◽  
Stat Signaling

Trisomy of human chromosome 21 in Down syndrome (DS) leads to several phenotypes, such as mild-to-severe intellectual disability, hypotonia, and craniofacial dysmorphisms. These are fundamental hallmarks of the disorder that affect the quality of life of most individuals with DS. Proper brain development involves meticulous regulation of various signaling pathways, and dysregulation may result in abnormal neurodevelopment. DS brain is characterized by an increased number of astrocytes with reduced number of neurons. In mouse models for DS, the pool of neural progenitor cells commits to glia rather than neuronal cell fate in the DS brain. However, the mechanism(s) and consequences of this slight neurogenic-to-gliogenic shift in DS brain are still poorly understood. To date, Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling has been proposed to be crucial in various developmental pathways, especially in promoting astrogliogenesis. Since both human and mouse models of DS brain exhibit less neurons and a higher percentage of cells with astrocytic phenotypes, understanding the role of JAK-STAT signaling in DS brain development will provide novel insight into its role in the pathogenesis of DS brain and may serve as a potential target for the development of effective therapy to improve DS cognition.

scholarly journals Disfagia fase oral dan faring pada anak sindrom Down

2018 ◽  
Vol 48 (1) ◽  
pp. 102
Author(s):  
Susyana Tamin ◽  
Elvie Zulka ◽  
Iman Pradana Maryadi ◽  
Rahmanofa Yunizaf
Keyword(s):  
Down Syndrome ◽  
Pediatric Patients ◽  
Partial Trisomy ◽  
Neck Surgery ◽  
Chromosome 21 ◽  
Google Scholar ◽  
Endoscopic Evaluation ◽  
Children With Down Syndrome ◽  
Feeding Difficulty ◽  
Surgery Department

Latar Belakang: Sindrom Down merupakan kelainan kromosom autosomal yang terjadi akibat trisomi seluruh atau sebagian dari kromosom 21, yang terjadi kurang lebih 1 dari 700 kelahiran hidup. Berbagai studi mendapatkan bahwa gangguan makan (feeding difficulty) dan disfagia merupakan masalah yang umum terjadi dan terkadang persisten pada anak sindrom Down. Tujuan: Memaparkan karakteristik kelainan disfagia fase oral dan fase faring yang dapat timbul pada anak dengan sindrom Down menggunakan instrument pemeriksaan Fiberoptic Endoscopic Evaluation of Swallowing (FEES). Laporan kasus: Dilaporkan 8 pasien anak dengan sindrom Down yang didapatkan dari rekam medis pasien sejak Oktober 2016 hingga September 2017, yang dilakukan pemeriksaan FEES di Poli Endoskopi Bronkoesofagologi Departemen Telinga Hidung Tenggorok-Bedah Kepala Leher (THT-KL) Rumah Sakit Dr. Cipto Mangunkusumo. Metode: Pencarian literatur secara terstruktur dilakukan dengan menggunakan Pubmed, ClinicalKey, Cochrane, dan Google scholar, sesuai dengan pertanyaan klinis berupa bagaimana karakteristik disfagia pada pasien anak dengan sindrom Down melalui pemeriksaan FEES. Pemilihan artikel dilakukan berdasarkan kriteria inklusi dan eksklusi. Hasil didapatkan 1 artikel yang relevan. Hasil: Artikel yang didapat merupakan suatu studi retrospektif yang melaporkan gambaran deskriptif karakteristik disfagia pada anak dengan sindrom Down. Kesimpulan: Kelainan anatomis pada sindrom Down berperan pada terjadinya gangguan makan dan disfagia. ABSTRACTBackground: Down syndrome is an autosomal chromosomal disorder caused by entire or partial trisomy of chromosome 21, which occurs in approximately 1 out of 700 live births. Several studies had found that feeding difficulty and swallowing disorder (dysphagia) are common and persistent problems in children with Down syndrome. Purpose: to describe characteristics of abnormalities that can occur in children with Down syndrome using the Fiberoptic Endoscopic Evaluation of Swallowing (FEES) examination. Case report: 8 Pediatric patients with Down syndrome, obtained from medical record of FEES examination in Endoscopic Bronchoesophagology Clinic of Otorhinolaryngology-Head and Neck Surgery Department (ENT-HNS) Cipto Mangunkusumo Hospital, from October 2016 up to September 2017. Method: A structured literature search was performed using Pubmed, ClinicalKey, Cochrane, and Google scholar, according to clinical question of how the characteristics of dysphagia in pediatric patients with Down syndrome through FEES examination? The selection of articles is based on inclusion and exclusion criteria which resulted in 1 relevant paper. Results: The article obtained was a retrospective study reporting descriptive characteristics of dysphagia in children with Down syndrome. Conclusion: Anatomical abnormalities in children with Down syndrome play a role in eating disorders and dysphagia. Keywords:

scholarly journals Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

2020 ◽  
Author(s):  
Juhee Pae ◽  
Jonatan Ersching ◽  
Tiago B. R. Castro ◽  
Marta Schips ◽  
Luka Mesin ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Germinal Center ◽  
Clonal Expansion ◽  
Affinity Maturation ◽  
Cyclin D3 ◽  
Dark Zone ◽  
Follicular Helper ◽  
Cell Cycle Regulator Cyclin

AbstractDuring affinity maturation, germinal center (GC) B cells alternate between proliferation and so-matic hypermutation in the dark zone (DZ) and affinity-dependent selection in the light zone (LZ). This anatomical segregation imposes that the vigorous proliferation that allows clonal expansion of positively-selected GC B cells takes place ostensibly in the absence of the signals that triggered selection in the LZ, as if by “inertia.” We find that such inertial cycles specifically require the cell cycle regulator cyclin D3. Cyclin D3 dose-dependently controls the extent to which B cells proliferate in the DZ and is essential for effective clonal expansion of GC B cells in response to strong T follicular helper (Tfh) cell help. Introduction into the Ccnd3 gene of a Burkitt lymphoma-associated gain-of-function mutation (T283A) leads to larger GCs with increased DZ proliferation and, in older mice, to clonal B cell lymphoproliferation, suggesting that the DZ inertial cell cycle program can be coopted by B cells undergoing malignant transformation.

scholarly journals Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

2020 ◽  
Vol 218 (4) ◽  
Author(s):  
Juhee Pae ◽  
Jonatan Ersching ◽  
Tiago B.R. Castro ◽  
Marta Schips ◽  
Luka Mesin ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
Germinal Center ◽  
Somatic Hypermutation ◽  
Clonal Expansion ◽  
Affinity Maturation ◽  
Cyclin D3 ◽  
Dark Zone ◽  
Follicular Helper ◽  
Cell Cycle Regulator Cyclin

During affinity maturation, germinal center (GC) B cells alternate between proliferation and somatic hypermutation in the dark zone (DZ) and affinity-dependent selection in the light zone (LZ). This anatomical segregation imposes that the vigorous proliferation that allows clonal expansion of positively selected GC B cells takes place ostensibly in the absence of the signals that triggered selection in the LZ, as if by “inertia.” We find that such inertial cycles specifically require the cell cycle regulator cyclin D3. Cyclin D3 dose-dependently controls the extent to which B cells proliferate in the DZ and is essential for effective clonal expansion of GC B cells in response to strong T follicular helper (Tfh) cell help. Introduction into the Ccnd3 gene of a Burkitt lymphoma–associated gain-of-function mutation (T283A) leads to larger GCs with increased DZ proliferation and, in older mice, clonal B cell lymphoproliferation, suggesting that the DZ inertial cell cycle program can be coopted by B cells undergoing malignant transformation.

Cyclin D3 Is Required for the Germinal Center Reaction

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2580-2580
Author(s):  
Jonathan U. Peled ◽  
J. Jessica Yu ◽  
Beibei Belinda Ding ◽  
Rita Shaknovich ◽  
Piotr Sicinski ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
B Cell Lymphoma ◽  
Affinity Maturation ◽  
Cyclin D3 ◽  
G1 Phase ◽  
Lymphoid Tissues ◽  
Cyclin D2

Abstract Germinal Centers (GC) of secondary lymphoid tissues are critical to mounting a high-affinity humoral immune response. B cells within the GC undergo rapid clonal expansion and selection while diversifying their antibody genes through class switch recombination and somatic hypermutation. Although it is generally believed that GC B cells employ a unique proliferative program to accommodate these processes, very little is known about how the GC-associated cell cycle is orchestrated. The D-type cyclins are important regulators of the G1 phase of the cell cycle and are the ultimate targets of many mitogenic and oncogenic stimuli. The Cyclin D3 gene is rearranged and over-expressed in certain mature B cell malignancies, and its overexpression has been reported to predict poor clinical outcome in patients with diffuse large B cell lymphoma. It has been observed that during their development, B cells switch from expressing cyclin D2 to cyclin D3 when they are recruited into the GC response. It is unclear, however, whether this switch simply reflects a change in the transcription factors that govern cyclin expression or serves a biological mandate. Here we report that mice deficient in cyclin D3 are profoundly impaired in their ability to form GCs as measured by immunohistochemistry and flow cytometry. Production of antigen-specific antibodies and affinity maturation, as ascertained by ELISA, are concomitantly reduced in these animals. These phenotypes can be at least partially explained by a significant block in the G1-phase of the cell cycle of GC B cells in vivo. Interestingly, this block in the G1-S transition is observed despite an apparent compensatory increase in cyclin D2 expression. In addition, naive B cells activated in vitro by either LPS or LPS and IL-4 display only minor changes in cell-cycle profile, suggesting that a specific requirement for cyclin D3 is unique to GC B cells. We also find moderately reduced Bcl6 mRNA expression in both naïve and GC B cells from the cyclin D3 knockout mice. Since Bcl6 is a master regulator of the GC response, decreased activity of this transcriptional repressor may further contribute to the severity of the GC phenotype. This is the first demonstration that cyclin D3 plays a unique role during the GC response in that it is required for its optimal structure and function. In addition to expanding appreciation for the cell type- and tissue-specific functions of the three D-type cyclin molecules, our findings have implications for understanding the role of Cyclin D3 in human B cell lymphomas.

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