41 results found
Pfeifer M, Brem R, Lippert T, et al., 2019, SSB1/SSB2 proteins safeguard B-cell development by protecting the genomes of B-cell precursors, Journal of Immunology, Vol: 202, Pages: 3423-3433, ISSN: 1550-6606
Induction of programmed DNA damage and its recognition and repair are fundamental for B cell development. The ssDNA-binding protein SSB1 has been described in human cells as essential for the recognition and repair of DNA damage. To study its relevance for B cells, we recently developed Ssb1−/− and conditional Ssb1−/− mice. Although SSB1 loss did not affect B cell development, Ssb1−/− cells exhibited compensatory expression of its homolog SSB2. We have now generated Ssb2−/− mice and show in this study that SSB2 is also dispensable for B cell development and DNA damage response activation. In contrast to the single loss of Ssb1 or Ssb2, however, combined SSB1/2 deficiency caused a defect in early B cell development. We relate this to the sensitivity of B cell precursors as mature B cells largely tolerated their loss. Toxicity of combined genetic SSB1/2 loss can be rescued by ectopic expression of either SSB1 or SSB2, mimicked by expression of SSB1 ssDNA-binding mutants, and attenuated by BCL2-mediated suppression of apoptosis. SSB1/2 loss in B cell precursors further caused increased exposure of ssDNA associated with disruption of genome fragile sites, inefficient cell cycle progression, and increased DNA damage if apoptosis is suppressed. As such, our results establish SSB1/2 as safeguards of B cell development and unveil their differential requirement in immature and mature B lymphocytes.
Parzych K, Saavedra Garcia P, Valbuena G, et al., 2019, The coordinated action of VCP/p97 and GCN2 regulates cancer cell metabolism and proteostasis during nutrient limitation, Oncogene, Vol: 38, Pages: 3216-3231, ISSN: 0950-9232
VCP/p97 regulates numerous cellular functions by mediating protein degradation through its segregase activity. Its key role in governing protein homoeostasis has made VCP/p97 an appealing anticancer drug target. Here, we provide evidence that VCP/p97 acts as a regulator of cellular metabolism. We found that VCP/p97 was tied to multiple metabolic processes on the gene expression level in a diverse range of cancer cell lines and in patient-derived multiple myeloma cells. Cellular VCP/p97 dependency to maintain proteostasis was increased under conditions of glucose and glutamine limitation in a range of cancer cell lines from different tissues. Moreover, glutamine depletion led to increased VCP/p97 expression, whereas VCP/p97 inhibition perturbed metabolic processes and intracellular amino acid turnover. GCN2, an amino acid-sensing kinase, attenuated stress signalling and cell death triggered by VCP/p97 inhibition and nutrient shortages and modulated ERK activation, autophagy, and glycolytic metabolite turnover. Together, our data point to an interconnected role of VCP/p97 and GCN2 in maintaining cancer cell metabolic and protein homoeostasis.
Macdougall CE, Wood EG, Loschko J, et al., 2018, Visceral adipose tissue immune homeostasis Is regulated by the crosstalk between adipocytes and dendritic cell subsets, Cell Metabolism, Vol: 27, Pages: 588-+, ISSN: 1550-4131
Visceral adipose tissue (VAT) has multiple roles in orchestrating whole-body energy homeostasis. In addition, VAT is now considered an immune site harboring an array of innate and adaptive immune cells with a direct role in immune surveillance and host defense. We report that conventional dendritic cells (cDCs) in VAT acquire a tolerogenic phenotype through upregulation of pathways involved in adipocyte differentiation. While activation of the Wnt/β-catenin pathway in cDC1 DCs induces IL-10 production, upregulation of the PPARγ pathway in cDC2 DCs directly suppresses their activation. Combined, they promote an anti-inflammatory milieu in vivo delaying the onset of obesity-induced chronic inflammation and insulin resistance. Under long-term over-nutrition, changes in adipocyte biology curtail β-catenin and PPARγ activation, contributing to VAT inflammation.
Boulianne B, Feldhahn N, 2017, Transcribing malignancy: transcription-associated genomic instability in cancer., Oncogene, ISSN: 0950-9232
Transcription is an essential process in all living cells. However, transcription also sensitises genomic DNA to damage from a number of endogenous sources. Although various mechanisms protect the integrity of DNA during transcription, transcription-associated genomic instability occurs in normal and malignant cells and, if unrepaired, can result in genomic alterations. Numerous studies have implicated genomic alterations found in cancer genomes to transcription. Hence, transcription-associated genomic instability can be considered as a major driver of cancer development. In this review, we summarise the body of knowledge on transcription-associated genomic instability and highlight recent discoveries in the field on both healthy and malignant cells. We also discuss how transcription-associated DNA damage might promote transforming lesions at cell type- and lineage-specific genes.Oncogene advance online publication, 6 November 2017; doi:10.1038/onc.2017.402.
Boulianne B, Robinson ME, May PC, et al., 2017, Lineage-specific genes are prominent DNA damage hotspots during leukemic transformation of B-cell precursors, Cell Reports, Vol: 18, Pages: 1687-1698, ISSN: 2211-1247
In human leukemia, lineage-specific genes represent predominant targets of deletion, with lymphoid-specific genes frequently affected in lymphoid leukemia and myeloid-specific genes in myeloid leukemia. To investigate the basis of lineage-specific alterations, we analyzed global DNA damage in primary B-cell precursors expressing leukemia-inducing oncogenes by ChIP-Seq. We identified >1000 sensitive regions, of which B-lineage-specific genes constitute the most prominent targets. Identified hotspots at B-lineage genes relate to DNA-DSBs, affect genes that harbor genomic lesions in human leukemia, and associate with ectopic deletionin successfully transformed cells. We further show that mostidentified regions overlap with gene bodies of highly expressed genes, and that induction of a myeloidlineage phenotype in transformed B-cell precursors promotes de novoDNA damage atmyeloid loci. Hence, we demonstrate thatlineage-specific transcriptionpredisposeslineage-specificgenes in transformed B-cell precursorsto DNA damage, whichis likely to promote the frequent alteration oflineage-specific genes in human leukemia.
Robbiani DF, Deroubaix S, Feldhahn N, et al., 2015, Plasmodium Infection Promotes Genomic Instability and AID-Dependent B Cell Lymphoma, CELL, Vol: 162, Pages: 727-737, ISSN: 0092-8674
Bacrot S, Doyard M, Huber C, et al., 2015, Mutations in SNRPB, Encoding Components of the Core Splicing Machinery, Cause Cerebro-Costo-Mandibular Syndrome, HUMAN MUTATION, Vol: 36, Pages: 187-190, ISSN: 1059-7794
Jankovic M, Feldhahn N, Oliveira TY, et al., 2013, 53BP1 alters the landscape of DNA rearrangements and suppresses AID-induced B cell lymphoma, Mol Cell, Vol: 49, Pages: 623-631, ISSN: 1097-4164
Deficiencies in factors that regulate the DNA damage response enhance the incidence of malignancy by destabilizing the genome. However, the precise influence of the DNA damage response on regulation of cancer-associated rearrangements is not well defined. Here we examine the genome-wide impact of tumor protein P53-binding protein 1 (53BP1) deficiency in lymphoma and translocation. While both activation-induced cytidine deaminase (AID) and 53BP1 have been associated with cancer in humans, neither AID overexpression nor loss of 53BP1 is sufficient to produce malignancy. However, the combination of 53BP1 deficiency and AID deregulation results in B cell lymphoma. Deep sequencing of the genome of 53BP1(-/-) cancer cells and translocation capture sequencing (TC-Seq) of primary 53BP1(-/-) B cells revealed that their chromosomal rearrangements differ from those found in wild-type cells in that they show increased DNA end resection. Moreover, loss of 53BP1 alters the translocatome by increasing rearrangements to intergenic regions.
Di Virgilio M, Callen E, Yamane A, et al., 2013, Rif1 prevents resection of DNA breaks and promotes immunoglobulin class switching, Science, Vol: 339, Pages: 711-715, ISSN: 0036-8075
DNA double-strand breaks (DSBs) represent a threat to the genome because they can lead to the loss of genetic information and chromosome rearrangements. The DNA repair protein p53 binding protein 1 (53BP1) protects the genome by limiting nucleolytic processing of DSBs by a mechanism that requires its phosphorylation, but whether 53BP1 does so directly is not known. Here, we identify Rap1-interacting factor 1 (Rif1) as an ATM (ataxia-telangiectasia mutated) phosphorylation-dependent interactor of 53BP1 and show that absence of Rif1 results in 5'-3' DNA-end resection in mice. Consistent with enhanced DNA resection, Rif1 deficiency impairs DNA repair in the G(1) and S phases of the cell cycle, interferes with class switch recombination in B lymphocytes, and leads to accumulation of chromosome DSBs.
Feldhahn N, Ferretti E, Robbiani DF, et al., 2012, The hSSB1 orthologue Obfc2b is essential for skeletogenesis but dispensable for the DNA damage response in vivo, EMBO J, Vol: 31, Pages: 4045-4056, ISSN: 1460-2075
Human single-stranded DNA-binding protein 1 (hSSB1), encoded by OBFC2B, was recently characterized as an essential factor for the initiation of DNA damage checkpoints and the maintenance of genomic stability. Here, we report that loss of Obfc2b in mice results in perinatal lethality characterized by growth delay and skeletal abnormalities. These abnormalities are associated with accumulation of gammaH2ax, apoptosis and defective pre-cartilage condensation, which is essential for normal bone formation. However, deficiency of Obfc2b does not affect the initiation of DNA damage checkpoints, Atm activation, or the maintenance of genomic stability in B lymphocytes and primary fibroblasts. Loss of Obfc2b results in increased expression of its homologue Obfc2a (hSSB2). In contrast to Obfc2b deficiency, depletion of Obfc2a in fibroblasts results in impaired proliferation, accumulation of gammaH2ax and increased genomic instability. Thus, the hSSB1 orthologue Obfc2b has a unique function during embryogenesis limited to cell types that contribute to bone formation. While being dispensable in most other cell lineages, its absence leads to a compensatory increase in Obfc2a protein, a homologue required for the maintenance of genomic integrity.
Feldhahn N, Arutyunyan A, Stoddart S, et al., 2012, Environment-mediated drug resistance in Bcr/Abl-positive acute lymphoblastic leukemia, Oncoimmunology, Vol: 1, Pages: 618-629, ISSN: 2162-402X
Although cure rates for acute lymphoblastic leukemia (ALL) have increased, development of resistance to drugs and patient relapse are common. The environment in which the leukemia cells are present during the drug treatment is known to provide significant survival benefit. Here, we have modeled this process by culturing murine Bcr/Abl-positive acute lymphoblastic leukemia cells in the presence of stroma while treating them with a moderate dose of two unrelated drugs, the farnesyltransferase inhibitor lonafarnib and the tyrosine kinase inhibitor nilotinib. This results in an initial large reduction in cell viability of the culture and inhibition of cell proliferation. However, after a number of days, cell death ceases and the culture becomes drug-tolerant, enabling cell division to resume. Using gene expression profiling, we found that the development of drug resistance was accompanied by massive transcriptional upregulation of genes that are associated with general inflammatory responses such as the metalloproteinase MMP9. MMP9 protein levels and enzymatic activity were also increased in ALL cells that had become nilotinib-tolerant. Activation of p38, Akt and Erk correlated with the development of environment-mediated drug resistance (EMDR), and inhibitors of Akt and Erk in combination with nilotinib reduced the ability of the cells to develop resistance. However, inhibition of p38 promoted increased resistance to nilotinib. We conclude that development of EMDR by ALL cells involves changes in numerous intracellular pathways. Development of tolerance to drugs such as nilotinib may therefore be circumvented by simultaneous treatment with other drugs having divergent targets.
Arutyunyan A, Stoddart S, Yi SJ, et al., 2012, Expression of cassini, a murine gamma-satellite sequence conserved in evolution, is regulated in normal and malignant hematopoietic cells, BMC Genomics, Vol: 13, ISSN: 1471-2164
ABSTRACT: BACKGROUND: Acute lymphoblastic leukemia (ALL) cells treated with drugs can become drug-tolerant if co-cultured with protective stromal mouse embryonic fibroblasts (MEFs). RESULTS: We performed transcriptional profiling on these stromal fibroblasts to investigate if they were affected by the presence of drug-treated ALL cells. These mitotically inactivated MEFs showed few changes in gene expression, but a family of sequences of which transcription is significantly increased was identified. A sequence related to this family, which we named cassini, was selected for further characterization. We found that cassini was highly upregulated in drug-treated ALL cells. Analysis of RNAs from different normal mouse tissues showed that cassini expression is highest in spleen and thymus, and can be further enhanced in these organs by exposure of mice to bacterial endotoxin. Heat shock, but not other types of stress, significantly induced the transcription of this locus in ALL cells. Transient overexpression of cassini in human 293 embryonic kidney cells did not increase the cytotoxic or cytostatic effects of chemotherapeutic drugs but provided some protection. Database searches revealed that sequences highly homologous to cassini are present in rodents, apicomplexans, flatworms and primates, indicating that they are conserved in evolution. Moreover, CASSINI RNA was induced in human ALL cells treated with vincristine. Surprisingly, cassini belongs to the previously reported murine family of gamma-satellite/major satellite DNA sequences, which were not known to be present in other species. CONCLUSIONS: Our results show that the transcription of at least one member of these sequences is regulated, suggesting that this has a function in normal and transformed immune cells. Expression of these sequences may protect cells when they are exposed to specific stress stimuli.
Bothmer A, Robbiani DF, Di Virgilio M, et al., 2011, Regulation of DNA end joining, resection, and immunoglobulin class switch recombination by 53BP1, Mol Cell, Vol: 42, Pages: 319-329, ISSN: 1097-4164
53BP1 is a DNA damage protein that forms phosphorylated H2AX (gamma-H2AX) dependent foci in a 1 Mb region surrounding DNA double-strand breaks (DSBs). In addition, 53BP1 promotes genomic stability by regulating the metabolism of DNA ends. We have compared the joining rates of paired DSBs separated by 1.2 kb to 27 Mb on chromosome 12 in the presence or absence of 53BP1. 53BP1 facilitates joining of intrachromosomal DSBs but only at distances corresponding to gamma-H2AX spreading. In contrast, DNA end protection by 53BP1 is distance independent. Furthermore, analysis of 53BP1 mutants shows that chromatin association, oligomerization, and N-terminal ATM phosphorylation are all required for DNA end protection and joining as measured by immunoglobulin class switch recombination. These data elucidate the molecular events that are required for 53BP1 to maintain genomic stability and point to a model wherein 53BP1 and H2AX cooperate to repress resection of DSBs.
Bothmer A, Robbiani DF, Feldhahn N, et al., 2010, 53BP1 regulates DNA resection and the choice between classical and alternative end joining during class switch recombination, J Exp Med, Vol: 207, Pages: 855-865, ISSN: 1540-9538
Class switch recombination (CSR) diversifies antibodies by joining highly repetitive DNA elements, which are separated by 60-200 kbp. CSR is initiated by activation-induced cytidine deaminase, an enzyme that produces multiple DNA double-strand breaks (DSBs) in switch regions. Switch regions are joined by a mechanism that requires an intact DNA damage response and classical or alternative nonhomologous end joining (A-NHEJ). Among the DNA damage response factors, 53BP1 has the most profound effect on CSR. We explore the role of 53BP1 in intrachromosomal DNA repair using I-SceI to introduce paired DSBs in the IgH locus. We find that the absence of 53BP1 results in an ataxia telangiectasia mutated-dependent increase in DNA end resection and that resected DNA is preferentially repaired by microhomology-mediated A-NHEJ. We propose that 53BP1 favors long-range CSR in part by protecting DNA ends against resection, which prevents A-NHEJ-dependent short-range rejoining of intra-switch region DSBs.
Bunting SF, Callen E, Wong N, et al., 2010, 53BP1 inhibits homologous recombination in Brca1-deficient cells by blocking resection of DNA breaks, Cell, Vol: 141, Pages: 243-254, ISSN: 1097-4172
Defective DNA repair by homologous recombination (HR) is thought to be a major contributor to tumorigenesis in individuals carrying Brca1 mutations. Here, we show that DNA breaks in Brca1-deficient cells are aberrantly joined into complex chromosome rearrangements by a process dependent on the nonhomologous end-joining (NHEJ) factors 53BP1 and DNA ligase 4. Loss of 53BP1 alleviates hypersensitivity of Brca1 mutant cells to PARP inhibition and restores error-free repair by HR. Mechanistically, 53BP1 deletion promotes ATM-dependent processing of broken DNA ends to produce recombinogenic single-stranded DNA competent for HR. In contrast, Lig4 deficiency does not rescue the HR defect in Brca1 mutant cells but prevents the joining of chromatid breaks into chromosome rearrangements. Our results illustrate that HR and NHEJ compete to process DNA breaks that arise during DNA replication and that shifting the balance between these pathways can be exploited to selectively protect or kill cells harboring Brca1 mutations.
Klemm L, Duy C, Iacobucci I, et al., 2009, The B Cell Mutator AID Promotes B Lymphoid Blast Crisis and Drug-Resistance in Chronic Myeloid Leukemia, 51st Annual Meeting and Exposition of the American-Society-of-Hematology, Publisher: AMER SOC HEMATOLOGY, Pages: 1267-1268, ISSN: 0006-4971
Klemm L, Duy C, Iacobucci I, et al., 2009, The B cell mutator AID promotes B lymphoid blast crisis and drug resistance in chronic myeloid leukemia, Cancer Cell, Vol: 16, Pages: 232-245, ISSN: 1878-3686
Chronic myeloid leukemia (CML) is induced by BCR-ABL1 and can be effectively treated for many years with Imatinib until leukemia cells acquire drug resistance through BCR-ABL1 mutations and progress into fatal B lymphoid blast crisis (LBC). Despite its clinical significance, the mechanism of progression into LBC is unknown. Here, we show that LBC but not CML cells express the B cell-specific mutator enzyme AID. We demonstrate that AID expression in CML cells promotes overall genetic instability by hypermutation of tumor suppressor and DNA repair genes. Importantly, our data uncover a causative role of AID activity in the acquisition of BCR-ABL1 mutations leading to Imatinib resistance, thus providing a rationale for the rapid development of drug resistance and blast crisis progression.
Scheid JF, Mouquet H, Feldhahn N, et al., 2009, A method for identification of HIV gp140 binding memory B cells in human blood, J Immunol Methods, Vol: 343, Pages: 65-67, ISSN: 1872-7905
Antibodies to HIV are potentially important reagents for basic and clinical studies. Historically, these reagents have been produced by random cloning of heavy and light chains in phage display libraries [Burton, D.R., Barbas, C.F. III, Persson, M.A.A., Koenig, S., Chanock, R.M., and Lerner, R.A., (1991), A large array of human monoclonal antibodies to type 1 immunodeficiency virus from combinatorial libraries of asymptomatic seropositive individuals. Proc. Natl. Acad. Sci. U. S. A. 88, 10134-10137.] and electrofusion techniques [Buchacher, A., Predl, R., Tauer, C., Purtscher, M., Gruber, G., Heider, R., Steindl, F., Trkola, A., Jungbauer, A., and Katinger, H., (1992), Human monoclonal antibodies against gp41 and gp120 as potential agent for passive immunization. Vaccines 92, 191-195]. Here we describe a method to identify and potentially enrich human memory B cells from HIV infected patients that show serum titers of neutralizing antibodies. When biotinylated gp140 is used to stain peripheral blood mononuclear cells it identifies a distinct population of gp140 binding B cells by flow cytometry.
Scheid JF, Mouquet H, Feldhahn N, et al., 2009, Broad diversity of neutralizing antibodies isolated from memory B cells in HIV-infected individuals, Nature, Vol: 458, Pages: 636-640, ISSN: 1476-4687
Antibodies to conserved epitopes on the human immunodeficiency virus (HIV) surface protein gp140 can protect against infection in non-human primates, and some infected individuals show high titres of broadly neutralizing immunoglobulin (Ig)G antibodies in their serum. However, little is known about the specificity and activity of these antibodies. To characterize the memory antibody responses to HIV, we cloned 502 antibodies from HIV envelope-binding memory B cells from six HIV-infected patients with broadly neutralizing antibodies and low to intermediate viral loads. We show that in these patients, the B-cell memory response to gp140 is composed of up to 50 independent clones expressing high affinity neutralizing antibodies to the gp120 variable loops, the CD4-binding site, the co-receptor-binding site, and to a new neutralizing epitope that is in the same region of gp120 as the CD4-binding site. Thus, the IgG memory B-cell compartment in the selected group of patients with broad serum neutralizing activity to HIV is comprised of multiple clonal responses with neutralizing activity directed against several epitopes on gp120.
Robbiani DF, Bunting S, Feldhahn N, et al., 2009, AID produces DNA double-strand breaks in non-Ig genes and mature B cell lymphomas with reciprocal chromosome translocations, Mol Cell, Vol: 36, Pages: 631-641, ISSN: 1097-4164
Cancer-initiating translocations such as those associated with lymphomas require the formation of paired DNA double-strand breaks (DSBs). Activation-induced cytidine deaminase (AID) produces widespread somatic mutation in mature B cells; however, the extent of "off-target" DSB formation and its role in translocation-associated malignancy is unknown. Here, we show that deregulated expression of AID causes widespread genome instability, which alone is insufficient to induce B cell lymphoma; transformation requires concomitant loss of the tumor suppressor p53. Mature B cell lymphomas arising as a result of deregulated AID expression are phenotypically diverse and harbor clonal reciprocal translocations involving a group of Immunoglobulin (Ig) and non-Ig genes that are direct targets of AID. This group includes miR-142, a previously unknown micro-RNA target that is translocated in human B cell malignancy. We conclude that AID produces DSBs throughout the genome, which can lead to lymphoma-associated chromosome translocations in mature B cells.
Klemm L, Duy C, Feldhahn N, et al., 2008, Lymphoid Blast Crisis Transformation and Development of Drug-Resistance in Chronic Myeloid Leukemia Are Driven by Aberrant Somatic Hypermutation, 50th Annual Meeting of the American-Society-of-Hematology, Publisher: AMER SOC HEMATOLOGY, Pages: 214-214, ISSN: 0006-4971
Klemm L, Feldhahn N, Hoffmann TK, et al., 2007, PAX5-mediated lineage conversion and expression of AID accelerates clonal evolution and initiates Darwinian selection of BCR-ABL1-mutants in chronic myeloid leukemia, 49th Annual Meeting of the American-Society-of-Hematology, Publisher: AMER SOC HEMATOLOGY, Pages: 305A-305A, ISSN: 0006-4971
Kaur P, Feldhahn N, Zhang B, et al., 2007, Nilotinib treatment in mouse models of P190 Bcr/Abl lymphoblastic leukemia, Mol Cancer, Vol: 6, ISSN: 1476-4598
BACKGROUND: Ph-positive leukemias are caused by the aberrant fusion of the BCR and ABL genes. Nilotinib is a selective Bcr/Abl tyrosine kinase inhibitor related to imatinib, which is widely used to treat chronic myelogenous leukemia. Because Ph-positive acute lymphoblastic leukemia only responds transiently to imatinib therapy, we have used mouse models to test the efficacy of nilotinib against lymphoblastic leukemia caused by the P190 form of Bcr/Abl. RESULTS: After transplant of 10,000 highly malignant leukemic cells into compatible recipients, untreated mice succumbed to leukemia within 21 days, whereas mice treated with 75 mg/kg nilotinib survived significantly longer. We examined cells from mice that developed leukemia while under treatment for Bcr/Abl kinase domain point mutations but these were not detected. In addition, culture of such cells ex vivo showed that they were as sensitive as the parental cell line to nilotinib but that the presence of stromal support allowed resistant cells to grow out. Nilotinib also exhibited impressive anti-leukemia activity in P190 Bcr/Abl transgenic mice that had developed overt leukemia/lymphoma masses and that otherwise would have been expected to die within 7 days. Visible lymphoma masses disappeared within six days of treatment and leukemic cell numbers in peripheral blood were significantly reduced. Treated mice survived more than 30 days. CONCLUSION: These results show that nilotinib has very impressive anti-leukemia activity but that lymphoblastic leukemia cells can become unresponsive to it both in vitro and in vivo through mechanisms that appear to be Bcr/Abl independent.
Feldhahn N, Henke N, Melchior K, et al., 2007, Activation-induced cytidine deaminase acts as a mutator in BCR-ABL1-transformed acute lymphoblastic leukemia cells, J Exp Med, Vol: 204, Pages: 1157-1166, ISSN: 0022-1007
The Philadelphia chromosome (Ph) encoding the oncogenic BCR-ABL1 kinase defines a subset of acute lymphoblastic leukemia (ALL) with a particularly unfavorable prognosis. ALL cells are derived from B cell precursors in most cases and typically carry rearranged immunoglobulin heavy chain (IGH) variable (V) region genes devoid of somatic mutations. Somatic hypermutation is restricted to mature germinal center B cells and depends on activation-induced cytidine deaminase (AID). Studying AID expression in 108 cases of ALL, we detected AID mRNA in 24 of 28 Ph(+) ALLs as compared with 6 of 80 Ph(-) ALLs. Forced expression of BCR-ABL1 in Ph(-) ALL cells and inhibition of the BCR-ABL1 kinase showed that aberrant expression of AID depends on BCR-ABL1 kinase activity. Consistent with aberrant AID expression in Ph(+) ALL, IGH V region genes and BCL6 were mutated in many Ph(+) but unmutated in most Ph(-) cases. In addition, AID introduced DNA single-strand breaks within the tumor suppressor gene CDKN2B in Ph(+) ALL cells, which was sensitive to BCR-ABL1 kinase inhibition and silencing of AID expression by RNA interference. These findings identify AID as a BCR-ABL1-induced mutator in Ph(+) ALL cells, which may be relevant with respect to the particularly unfavorable prognosis of this leukemia subset.
Feldhahn N, Klein F, Hofmann W-K, et al., 2006, Activation-induced cytidine deaminase acts as a mutator in BCR-ABL1 Transformed acute lymphoblastic leukemia cells., 48th Annual Meeting of the American-Society-of-Hematology, Publisher: AMER SOC HEMATOLOGY, Pages: 193A-193A, ISSN: 0006-4971
Feldhahn N, Henke N, Ndikung B, et al., 2006, Activation-induced cytidine deaminase acts as a BCR-ABL1-induced mutator in PH plus acute lymphoblastic leukemia cells, Publisher: SPRINGER, Pages: 21-21, ISSN: 0939-5555
Sprangers M, Feldhahn N, Liedtke S, et al., 2006, SLP65 deficiency results in perpetual V(D)J recombinase activity in pre-B-lymphoblastic leukemia and B-cell lymphoma cells, Oncogene, Vol: 25, Pages: 5180-5186, ISSN: 0950-9232
Perpetual V(D)J recombinase activity involving multiple DNA double-strand break events in B-cell lineage leukemia and lymphoma cells may introduce secondary genetic aberrations leading towards malignant progression. Here, we investigated defective negative feedback signaling through the (pre-) B-cell receptor as a possible reason for deregulated V(D)J recombinase activity in B-cell malignancy. On studying 28 cases of pre-B-lymphoblastic leukemia and 27 B-cell lymphomas, expression of the (pre-) B-cell receptor-related linker molecule SLP65 (SH2 domain-containing lymphocyte protein of 65 kDa) was found to be defective in seven and five cases, respectively. SLP65 deficiency correlates with RAG1/2 expression and unremitting V(H) gene rearrangement activity. Reconstitution of SLP65 expression in SLP65-deficient leukemia and lymphoma cells results in downregulation of RAG1/2 expression and prevents both de novo V(H)-DJ(H) rearrangements and secondary V(H) replacement. We conclude that iterative V(H) gene rearrangement represents a frequent feature in B-lymphoid malignancy, which can be attributed to SLP65 deficiency in many cases.
Sprangers M, Feldhahn N, Herzog S, et al., 2006, The SRC family kinase LYN redirects B cell receptor signaling in human SLP65-deficient B cell lymphoma cells, Oncogene, Vol: 25, Pages: 5056-5062, ISSN: 0950-9232
SLP65 represents a critical component in (pre-) B cell receptor signal transduction but is compromised in a subset of pre-B cell-derived acute lymphoblastic leukemia. Based on these findings, we investigated (i.) whether SLP65-deficiency also occurs in mature B cell-derived lymphoma and (ii.) whether SLP65-deficient B cell lymphoma cells use an alternative B cell receptor signaling pathway in the absence of SLP65. Indeed, expression of SLP65 protein was also missing in a fraction of B cell lymphoma cases. While SLP65 is essential for B cell receptor-induced Ca2+ mobilization in normal B cells, B cell receptor engagement in SLP65-deficient as compared to SLP65-reconstituted B cell lymphoma cells resulted in an accelerated yet shortlived Ca2+-signal. B cell receptor engagement of SLP65-deficient lymphoma cells involves SRC kinase activation, which is critical for B cell receptor-dependent Ca2+-mobilisation in the absence but not in the presence of SLP65. As shown by RNA interference, the SRC kinase LYN is required for B cell receptor-induced Ca2+ release in SLP65-deficient B cell lymphoma cells but dispensable after SLP65-reconstitution. B cell receptor engagement in SLP65-deficient B cell lymphoma cells also resulted in tyrosine-phosphorylation of the proliferation- and survival-related MAPK1 and STAT5 molecules, which was sensitive to silencing of the SRC kinase LYN. Inhibition of SRC kinase activity resulted in growth arrest and cell death specifically in SLP65-deficient lymphoma cells. These findings indicate that LYN can short-circuit conventional B cell receptor signaling in SLP65-deficient B cell lymphoma cells and thereby promote activation of survival and proliferation-related molecules.
Klein F, Feldhahn N, Herzog S, et al., 2006, BCR-ABL1 induces aberrant splicing of IKAROS and lineage infidelity in pre-B lymphoblastic leukemia cells, Oncogene, Vol: 25, Pages: 1118-1124, ISSN: 0950-9232
Pre-B lymphoblastic leukemia cells carrying a BCR-ABL1 gene rearrangement exhibit an undifferentiated phenotype. Comparing the genome-wide gene expression profiles of normal B-cell subsets and BCR-ABL1+ pre-B lymphoblastic leukemia cells by SAGE, the leukemia cells show loss of B lymphoid identity and aberrant expression of myeloid lineage-specific molecules. Consistent with this, BCR-ABL1+ pre-B lymphoblastic leukemia cells exhibit defective expression of IKAROS, a transcription factor needed for early lymphoid lineage commitment. As shown by inducible expression of BCR-ABL1 in human and murine B-cell precursor cell lines, BCR-ABL1 induces the expression of a dominant-negative IKAROS splice variant, termed IK6. Comparing matched leukemia sample pairs from patients before and during therapy with the BCR-ABL1 kinase inhibitor STI571 (Imatinib), inhibition of BCR-ABL1 partially corrected aberrant expression of IK6 and lineage infidelity of the leukemia cells. To elucidate the contribution of IK6 to lineage infidelity in BCR-ABL1+ cell lines, IK6 expression was silenced by RNA interference. Upon inhibition of IK6, BCR-ABL1+ leukemia cells partially restored B lymphoid lineage commitment. Therefore, we propose that BCR-ABL1 induces aberrant splicing of IKAROS, which interferes with lineage identity and differentiation of pre-B lymphoblastic leukemia cells.
Klein F, Feldhahn N, Mooster JL, et al., 2005, Tracing the pre-B to immature B cell transition in human leukemia cells reveals a coordinated sequence of primary and secondary IGK gene rearrangement, IGK deletion, and IGL gene rearrangement, J Immunol, Vol: 174, Pages: 367-375, ISSN: 0022-1767
The BCR-ABL1 kinase expressed in acute lymphoblastic leukemia (ALL) drives malignant transformation of pre-B cells and prevents further development. We studied whether inhibition of BCR-ABL1 kinase activity using STI571 can relieve this differentiation block. STI571 treatment of leukemia patients induced expression of the Ig L chain-associated transcription factors IRF4 and SPIB, up-regulation of RAG1 and RAG2, Ckappa and Clambda germline transcription, and rearrangement of Ig kappa L chain (IGK) and Ig lambda L chain (IGL) genes. However, STI571-treated pre-B ALL cells expressed lambda L, but almost no kappa L chains. This could be explained by STI571-induced rearrangement of the kappa-deleting element (KDE), which can delete productively rearranged Vkappa-Jkappa joints. Amplifying double-strand breaks at recombination signal sequences within the IGK, KDE, and IGL loci revealed a coordinated sequence of rearrangement events induced by STI571: recombination of IGK gene segments was already initiated within 1 h after STI571 treatment, followed by KDE-mediated deletion of Vkappa-Jkappa joints 6 h later and, ultimately, IGL gene rearrangement after 12 h. Consistently, up-regulation of Ckappa and Clambda germline transcripts, indicating opening of IGK and IGL loci, was detected after 1 and 6 h for IGK and IGL, respectively. Continued activity of the recombination machinery induced secondary IGK gene rearrangements, which shifted preferential usage of upstream located Jkappa- to downstream Jkappa-gene segments. Thus, inhibition of BCR-ABL1 in pre-B ALL cells 1) recapitulates early B cell development, 2) directly shows that IGK, KDE, and IGL genes are rearranged in sequential order, and 3) provides a model for Ig L chain gene regulation in the human.
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