[show abstract][hide abstract] ABSTRACT: We have previously reported that LITAF is silenced by promoter hypermethylation in germinal centre-derived B-cell lymphomas, but beyond these data the regulation and function of lipopolysaccharide-induced tumour necrosis factor (TNF) factor (LITAF) in B cells are unknown. Gene expression and immunohistochemical studies revealed that LITAF and BCL6 show opposite expression in tonsil B-cell subpopulations and B-cell lymphomas, suggesting that BCL6 may regulate LITAF expression. Accordingly, BCL6 silencing increased LITAF expression, and chromatin immunoprecipitation and luciferase reporter assays demonstrated a direct transcriptional repression of LITAF by BCL6. Gain- and loss-of-function experiments in different B-cell lymphoma cell lines revealed that, in contrast to its function in monocytes, LITAF does not induce lipopolysaccharide-mediated TNF secretion in B cells. However, gene expression microarrays defined a LITAF-related transcriptional signature containing genes regulating autophagy, including MAP1LC3B (LC3B). In addition, immunofluorescence analysis co-localized LITAF with autophagosomes, further suggesting a possible role in autophagy modulation. Accordingly, ectopic LITAF expression in B-cell lymphoma cells enhanced autophagy responses to starvation, which were impaired upon LITAF silencing. Our results indicate that the BCL6-mediated transcriptional repression of LITAF may inhibit autophagy in B cells during the germinal centre reaction, and suggest that the constitutive repression of autophagy responses in BCL6-driven lymphomas may contribute to lymphomagenesis.
British Journal of Haematology 06/2013; · 4.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: B cell maturation and germinal center (GC) formation are dependent on the interplay between BCL6 and other key transcriptional regulators. FOXP1 is a transcription factor that regulates early B cell development, but whether it plays a role in mature B cells is unknown. Analysis of human tonsillar B cell subpopulations revealed that FOXP1 shows opposite expression pattern to BCL6, suggesting that FOXP1 regulates the transition from resting follicular B cell to activated GC B cell. ChIP-on-chip and gene expression assays on B cells indicated that FOXP1 acts as a transcriptional activator and repressor of genes typically involved in the GC reaction, half of which are also BCL6 targets. To study FOXP1 function in vivo, we developed transgenic mice expressing human FOXP1 in lymphoid cells. These mice exhibited irregular formation of GCs in the spleen, showing a modest increase in naïve and marginal-zone B cells, and a significant decrease in GC B cells. Furthermore, aberrant expression of FOXP1 impaired the transcription of non-coding γ1 germline transcripts (GLTs) and inhibited efficient class-switching to the IgG1 isotype. These studies show that FOXP1 is physiologically down-regulated in GC B cells and that aberrant expression of FOXP1 impairs mechanisms triggered by B cell activation, potentially contributing to B cell lymphomagenesis.
[show abstract][hide abstract] ABSTRACT: Earlier work demonstrated that the transcription factor C/EBPa can convert immature and mature murine B lineage cells into functional macrophages. Testing >20 human lymphoma and leukemia B cell lines, we found that most can be transdifferentiated at least partially into macrophage-like cells, provided that C/EBPa is expressed at sufficiently high levels. A tamoxifen-inducible subclone of the Seraphina Burkitt lymphoma line, expressing C/EBPaER, could be efficiently converted into phagocytic and quies-cent cells with a transcriptome resembling normal macrophages. The converted cells retained their phenotype even when C/EBPa was inactivated, a hallmark of cell reprogramming. Interestingly, C/EBPa induction also impaired the cells' tumorige-nicity. Likewise, C/EBPa efficiently converted a lymphoblastic leukemia B cell line into macro-phage-like cells, again dramatically impairing their tumorigenicity. Our experiments show that human cancer cells can be induced by C/EBPa to trans-differentiate into seemingly normal cells at high frequencies and provide a proof of principle for a potential new therapeutic strategy for treating B cell malignancies.
[show abstract][hide abstract] ABSTRACT: Earlier work demonstrated that the transcription factor C/EBPα can convert immature and mature murine B lineage cells into functional macrophages. Testing >20 human lymphoma and leukemia B cell lines, we found that most can be transdifferentiated at least partially into macrophage-like cells, provided that C/EBPα is expressed at sufficiently high levels. A tamoxifen-inducible subclone of the Seraphina Burkitt lymphoma line, expressing C/EBPαER, could be efficiently converted into phagocytic and quiescent cells with a transcriptome resembling normal macrophages. The converted cells retained their phenotype even when C/EBPα was inactivated, a hallmark of cell reprogramming. Interestingly, C/EBPα induction also impaired the cells' tumorigenicity. Likewise, C/EBPα efficiently converted a lymphoblastic leukemia B cell line into macrophage-like cells, again dramatically impairing their tumorigenicity. Our experiments show that human cancer cells can be induced by C/EBPα to transdifferentiate into seemingly normal cells at high frequencies and provide a proof of principle for a potential new therapeutic strategy for treating B cell malignancies.
[show abstract][hide abstract] ABSTRACT: Glioblastoma (GBM) is associated with infiltration of peritumoral parenchyma by isolated tumor cells that leads to tumor regrowth. Recently, GBM stem-like or initiating cells (GICs) have been identified in the peritumoral (PT) area, but whether these GICs have enhanced migratory and invasive capabilities compared with GICs from the tumor mass (TM) is presently unknown. We isolated GICs from the infiltrated PT tissue and the TM of three patients and found that PT cells have an advantage over TM cells in 2D and 3D migration and invasion assays. Interestingly, PT cells display a high plasticity in protrusion formation and cell shape and their migration is insensitive to substrate stiffness, which represent advantages to infiltrate microenvironments of different rigidity. Furthermore, mouse and chicken embryo xenografts revealed that only PT cells showed a dispersed distribution pattern, closely associated to blood vessels. Consistent with cellular plasticity, simultaneous Rac and RhoA activation is required for the enhanced invasive capacity of PT cells. Moreover, Rho GTPase signaling modulators αVβ3 and p27 play key roles in GIC invasiveness. Of note, p27 is upregulated in TM cells and inhibits RhoA activity. Gene silencing of p27 increased the invasive capacity of TM GICs. Additionally, β3 integrin is upregulated in PT cells. Blockade of dimeric integrin αVβ3, a Rac activator, reduced the invasive capacity of PT GICs in vitro and abrogated the spreading of PT cells into chicken embryos. Thus, our results describe the invasive features acquired by a unique subpopulation of GICs that infiltrate neighbouring tissue.
[show abstract][hide abstract] ABSTRACT: The human germinal centre-associated lymphoma gene is specifically expressed in germinal centre B-lymphocytes and germinal centre-derived B-cell lymphomas, but its function is largely unknown. Here we demonstrate that human germinal centre-associated lymphoma directly binds to Syk in B cells, increases its kinase activity on B-cell receptor stimulation and leads to enhanced activation of Syk downstream effectors. To further investigate these findings in vivo, human germinal centre-associated lymphoma transgenic mice were generated. Starting from 12 months of age these mice developed polyclonal B-cell lymphoid hyperplasia, hypergammaglobulinemia and systemic reactive amyloid A (AA) amyloidosis, leading to shortened survival. The lymphoid hyperplasia in the human germinal centre-associated lymphoma transgenic mice are likely attributable to enhanced B-cell receptor signalling as shown by increased Syk phosphorylation, ex vivo B-cell proliferation and increased RhoA activation. Overall, our study shows for the first time that the germinal centre protein human germinal centre-associated lymphoma regulates B-cell receptor signalling in B-lymphocytes which, without appropriate control, may lead to B-cell lymphoproliferation.
[show abstract][hide abstract] ABSTRACT: Genomic profiling of mantle cell lymphoma (MCL) cells has enabled a better understanding of the complex mechanisms underlying the pathogenesis of disease. Besides the t(11;14)(q13;q32) leading to cyclin D1 overexpression, MCL exhibits a characteristic pattern of DNA copy number aberrations that differs from those detected in other B-cell lymphomas. These genomic changes disrupt selected oncogenes and suppressor genes that are required for lymphoma development and progression, many of which are components of cell cycle, DNA damage response and repair, apoptosis, and cell-signaling pathways. Additionally, some of them may represent effective therapeutic targets. A number of genomic and molecular abnormalities have been correlated with the clinical outcome of patients with MCL and are considered prognostic factors. However, only a few genomic markers have been shown to predict the response to current or novel targeted therapies. One representative example is the high-level amplification of the BCL2 gene, which predicts a good response to pro-apoptotic BH3 mimetic drugs. In summary, genomic analyses have contributed to the substantial advances made in the comprehension of the pathogenesis of MCL, providing a solid basis for the identification of optimal therapeutic targets and for the design of new molecular therapies aiming to cure this fatal disease.
Methods in molecular biology (Clifton, N.J.) 01/2013; 973:147-63.
[show abstract][hide abstract] ABSTRACT: MALT1 cleavage activity is linked to the pathogenesis of activated B cell-like diffuse large B cell lymphoma (ABC-DLBCL), a chemoresistant form of DLBCL. We developed a MALT1 activity assay and identified chemically diverse MALT1 inhibitors. A selected lead compound, MI-2, featured direct binding to MALT1 and suppression of its protease function. MI-2 concentrated within human ABC-DLBCL cells and irreversibly inhibited cleavage of MALT1 substrates. This was accompanied by NF-κB reporter activity suppression, c-REL nuclear localization inhibition, and NF-κB target gene downregulation. Most notably, MI-2 was nontoxic to mice, and displayed selective activity against ABC-DLBCL cell lines in vitro and xenotransplanted ABC-DLBCL tumors in vivo. The compound was also effective against primary human non-germinal center B cell-like DLBCLs ex vivo.
Cancer cell 12/2012; 22(6):812-24. · 25.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: Using high-resolution genomic microarray analysis, a distinct genomic profile was defined in 114 samples from patients with splenic marginal zone lymphoma (SMZL). Deletion or uniparental disomy of chromosome 7q were detected in 42 of 114 (37%) SMZLs but in only nine of 170 (5%) mature B-cell lymphomas (P < 0·00001). The presence of unmutated IGHV, genomic complexity, 17p13-TP53 deletion and 8q-MYC gain, but not 7q deletion, correlated with shorter overall survival of SMZL patients. Mapping studies narrowed down a commonly deleted region of 2·7 Mb in 7q32.1-q32.2 spanning a region between the SND1 and COPG2 genes. High-throughput sequencing analysis of the 7q32-deleted segment did not identify biallelic deletions/insertions or clear pathogenic gene mutations, but detected six nucleotide changes in IRF5 (n = 2), TMEM209 (n = 2), CALU (n = 1) and ZC3HC1 (n = 1) not found in healthy individuals. Comparative expression analysis found a fourfold down-regulation of IRF5 gene in lymphomas with 7q32 deletion versus non-deleted tumours (P = 0·032). Ectopic expression of IRF5 in marginal-zone lymphoma cells decreased proliferation and increased apoptosis in vitro, and impaired lymphoma development in vivo. These results show that cryptic deletions, insertions and/or point mutations inactivating genes within 7q32 are not common in SMZL, and suggest that IRF5 may be a haploinsufficient tumour suppressor in this lymphoma entity.
British Journal of Haematology 07/2012; 158(6):712-26. · 4.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: Chromosomal translocations involving the MALT1 gene are hallmarks of mucosa-associated lymphoid tissue (MALT) lymphoma. To date, targeting these translocations to mouse B cells has failed to reproduce human disease. Here, we induced MALT1 expression in mouse Sca1(+)Lin(-) hematopoietic stem/progenitor cells, which showed NF-κB activation and early lymphoid priming, being selectively skewed toward B-cell differentiation. These cells accumulated in extranodal tissues and gave rise to clonal tumors recapitulating the principal clinical, biological, and molecular genetic features of MALT lymphoma. Deletion of p53 gene accelerated tumor onset and induced transformation of MALT lymphoma to activated B-cell diffuse large-cell lymphoma (ABC-DLBCL). Treatment of MALT1-induced lymphomas with a specific inhibitor of MALT1 proteolytic activity decreased cell viability, indicating that endogenous Malt1 signaling was required for tumor cell survival. Our study shows that human-like lymphomas can be modeled in mice by targeting MALT1 expression to hematopoietic stem/progenitor cells, demonstrating the oncogenic role of MALT1 in lymphomagenesis. Furthermore, this work establishes a molecular link between MALT lymphoma and ABC-DLBCL, and provides mouse models to test MALT1 inhibitors. Finally, our results suggest that hematopoietic stem/progenitor cells may be involved in the pathogenesis of human mature B-cell lymphomas.
Proceedings of the National Academy of Sciences 06/2012; 109(26):10534-9. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: LMO2 regulates gene expression by facilitating the formation of multipartite DNA-binding complexes. In B cells, LMO2 is specifically up-regulated in the germinal center (GC) and is expressed in GC-derived non-Hodgkin lymphomas. LMO2 is one of the most powerful prognostic indicators in diffuse large B-cell (DLBCL) patients. However, its function in GC B cells and DLBCL is currently unknown. In this study, we characterized the LMO2 transcriptome and transcriptional complex in DLBCL cells. LMO2 regulates genes implicated in kinetochore function, chromosome assembly, and mitosis. Overexpression of LMO2 in DLBCL cell lines results in centrosome amplification. In DLBCL, the LMO2 complex contains some of the traditional partners, such as LDB1, E2A, HEB, Lyl1, ETO2, and SP1, but not TAL1 or GATA proteins. Furthermore, we identified novel LMO2 interacting partners: ELK1, nuclear factor of activated T-cells (NFATc1), and lymphoid enhancer-binding factor1 (LEF1) proteins. Reporter assays revealed that LMO2 increases transcriptional activity of NFATc1 and decreases transcriptional activity of LEF1 proteins. Overall, our studies identified a novel LMO2 transcriptome and interactome in DLBCL and provides a platform for future elucidation of LMO2 function in GC B cells and DLBCL pathogenesis.
[show abstract][hide abstract] ABSTRACT: Histone deacetylases (HDACs) have been identified as therapeutic targets due to their regulatory function in chromatin structure and organization. Here, we analyzed the therapeutic effect of LBH589, a class I-II HDAC inhibitor, in acute lymphoblastic leukemia (ALL). In vitro, LBH589 induced dose-dependent antiproliferative and apoptotic effects, which were associated with increased H3 and H4 histone acetylation. Intravenous administration of LBH589 in immunodeficient BALB/c-RAG2(-/-)γc(-/-) mice in which human-derived T and B-ALL cell lines were injected induced a significant reduction in tumor growth. Using primary ALL cells, a xenograft model of human leukemia in BALB/c-RAG2(-/-)γc(-/-) mice was established, allowing continuous passages of transplanted cells to several mouse generations. Treatment of mice engrafted with T or B-ALL cells with LBH589 induced an in vivo increase in the acetylation of H3 and H4, which was accompanied with prolonged survival of LBH589-treated mice in comparison with those receiving vincristine and dexamethasone. Notably, the therapeutic efficacy of LBH589 was significantly enhanced in combination with vincristine and dexamethasone. Our results show the therapeutic activity of LBH589 in combination with standard chemotherapy in pre-clinical models of ALL and suggest that this combination may be of clinical value in the treatment of patients with ALL.
Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 02/2012; 26(7):1517-26. · 8.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: MicroRNAs (miRNAs) are small non-coding RNA molecules that can negatively regulate gene expression at the post-transcriptional level. miRNA expression patterns are regulated during development and differentiation of the hematopoietic system and have an important role in cell processes such as proliferation, apoptosis, differentiation or even in tumorigenesis of human tumors and in particular of hematological malignancies such as acute leukemias. Various miRNAs and their functions have been intensively studied in acute leukemias but the mechanisms that control their expression are largely unknown for the majority of aberrantly expressed miRNAs. miRNA expression can be regulated by the same genetic mechanism that modulate protein coding genes such as mutation, deletion, amplification, loss of heterozygosity and translocations. In this review we focus on the regulation of miRNAs in acute leukemias mediated by alterations in epigenetic mechanisms such as DNA methylation and histone code, describing the role of these alterations in the pathogenesis, diagnosis and prognosis of acute leukemias and their possible use as new therapeutic targets and biomarkers.
Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 12/2011; 26(3):395-403. · 8.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: PIM serine/threonine kinases are overexpressed, translocated, or amplified in multiple B-cell lymphoma types. We have explored the frequency and relevance of PIM expression in different B-cell lymphoma types and investigated whether PIM inhibition could be a rational therapeutic approach. Increased expression of PIM2 was detected in subsets of mantle cell lymphoma, diffuse large B-cell lymphoma (DLBLC), follicular lymphoma, marginal zone lymphoma-mucosa-associated lymphoid tissue type, chronic lymphocytic leukemia, and nodal marginal zone lymphoma cases. Increased PIM2 protein expression was associated with an aggressive clinical course in activated B-like-DLBCL patients. Pharmacologic and genetic inhibition of PIM2 revealed p4E-BP1(Thr37/46) and p4E-BP1(Ser65) as molecular biomarkers characteristic of PIM2 activity and indicated the involvement of PIM2 kinase in regulating mammalian target of rapamycin complex 1. The simultaneous genetic inhibition of all 3 PIM kinases induced changes in apoptosis and cell cycle. In conclusion, we show that PIM2 kinase inhibition is a rational approach in DLBCL treatment, identify appropriate biomarkers for pharmacodynamic studies, and provide a new marker for patient stratification.
[show abstract][hide abstract] ABSTRACT: The chromosomal translocation t(11;14)(q13;q32) leading to cyclin-D1 overexpression plays an essential role in the development of mantle cell lymphoma (MCL), an aggressive tumor that remains incurable with current treatment strategies. Cyclin-D1 has been postulated as an effective therapeutic target, but the evaluation of this target has been hampered by our incomplete understanding of its oncogenic functions and by the lack of valid MCL murine models. To address these issues, we generated a cyclin-D1-driven mouse model in which cyclin-D1 expression can be regulated externally. These mice developed cyclin-D1-expressing lymphomas capable of recapitulating features of human MCL. We found that cyclin-D1 inactivation was not sufficient to induce lymphoma regression in vivo; however, using a combination of in vitro and in vivo assays, we identified a novel prosurvival cyclin-D1 function in MCL cells. Specifically, we found that cyclin-D1, besides increasing cell proliferation through deregulation of the cell cycle at the G(1)-S transition, sequestrates the proapoptotic protein BAX in the cytoplasm, thereby favoring BCL2's antiapoptotic function. Accordingly, cyclin-D1 inhibition sensitized the lymphoma cells to apoptosis through BAX release. Thus, genetic or pharmacologic targeting of cyclin-D1 combined with a proapoptotic BH3 mimetic synergistically killed the cyclin-D1-expressing murine lymphomas, human MCL cell lines, and primary lymphoma cells. Our study identifies a role of cyclin-D1 in deregulating apoptosis in MCL cells, and highlights the potential benefit of simultaneously targeting cyclin-D1 and survival pathways in patients with MCL. This effective combination therapy also might be exploited in other cyclin-D1-expressing tumors.
Proceedings of the National Academy of Sciences 07/2011; 108(30):12461-6. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Glioblastoma multiforme is one of the most devastating cancers and presents unique challenges to therapy because of its aggressive behavior. Cancer-initiating or progenitor cells have been described to be the only cell population with tumorigenic capacity in glioblastoma. Therefore, effective therapeutic strategies targeting these cells or the early precursors may be beneficial. We have established different cultures of glioblastoma-initiating cells (GICs) derived from surgical specimens and found that, after induction of differentiation, the NFκB transcriptional pathway was activated, as determined by analyzing key proteins such as p65 and IκB and the upregulation of a number of target genes. We also showed that blockade of nuclear factor (NF)κB signaling in differentiating GICs by different genetic strategies or treatment with small-molecule inhibitors, promoted replication arrest and senescence. This effect was partly mediated by reduced levels of the NFκB target gene cyclin D1, because its downregulation by RNA interference reproduced a similar phenotype. Furthermore, these results were confirmed in a xenograft model. Intravenous treatment of immunodeficient mice bearing human GIC-derived tumors with a novel small-molecule inhibitor of the NFκB pathway induced senescence of tumor cells but no ultrastructural alterations of the brain parenchyma were detected. These findings reveal that activation of NFκB may keep differentiating GICs from acquiring a mature postmitotic phenotype, thus allowing cell proliferation, and support the rationale for therapeutic strategies aimed to promote premature senescence of differentiating GICs by blocking key factors within the NFκB pathway.
[show abstract][hide abstract] ABSTRACT: Splenic marginal zone lymphomas (SMZL) are an uncommon type of B-cell non-Hodgkin's lymphoma (NHL-B) in which no specific chromosomal translocations have been described. In contrast, the most frequent cytogenetic abnormality is the loss of the long arm of chromosome 7 (7q). Previous reports have located this loss in the 7q32 region. In order to better characterize the genomic imbalances in SMZL, molecular studies were carried out in 73 patients with SMZL. To gain insight into the mapping at 7q a tiling array was also used. The results confirmed the loss of 7q as the most frequent change. In addition, several abnormalities, including 4q22.1, 1q21.3-q22, 6q25.3, 20q13.33, 3q28, 2q23.3-q24.1 and 17p13, were also present. A loss of 7q22.1 at 99925039-101348479 bp was observed in half of the cases. The region of 7q22.1 has not previously been characterised in SMZL. Our results confirmed the presence of a new region of loss on chromosome 7 in these NHL.
PLoS ONE 01/2011; 6(9):e24939. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: In Burkitt lymphoma/leukemia (BL), achievement of complete remission with first-line chemotherapy remains a challenging issue, as most patients who respond remain disease-free, whereas those refractory have few options of being rescued with salvage therapies. The mechanisms underlying BL chemoresistance and how it can be circumvented remain undetermined. We previously reported the frequent inactivation of the proapoptotic BIM gene in B-cell lymphomas. Here we show that BIM epigenetic silencing by concurrent promoter hypermethylation and deacetylation occurs frequently in primary BL samples and BL-derived cell lines. Remarkably, patients with BL with hypermethylated BIM presented lower complete remission rate (24% vs 79%; P = .002) and shorter overall survival (P = .007) than those with BIM-expressing lymphomas, indicating that BIM transcriptional repression may mediate tumor chemoresistance. Accordingly, by combining in vitro and in vivo studies of human BL-xenografts grown in immunodeficient RAG2(-/-)γc(-/-) mice and of murine B220(+)IgM(+) B-cell lymphomas generated in Eμ-MYC and Eμ-MYC-BIM(+/-) transgenes, we demonstrate that lymphoma chemoresistance is dictated by BIM gene dosage and is reversible on BIM reactivation by genetic manipulation or after treatment with histone-deacetylase inhibitors. We suggest that the combination of histone-deacetylase inhibitors and high-dose chemotherapy may overcome chemoresistance, achieve durable remission, and improve survival of patients with BL.
[show abstract][hide abstract] ABSTRACT: Sequence variants at the TERT-CLPTM1L locus in chromosome 5p have been recently associated with disposition for various cancers. Here we show that this locus including the gene encoding the telomerase reverse-transcriptase TERT at 5p13.33 is rarely but recurrently targeted by somatic chromosomal translocations to IGH and non-IG loci in B-cell neoplasms, including acute lymphoblastic leukemia, chronic lymphocytic leukemia, mantle cell lymphoma and splenic marginal zone lymphoma. In addition, cases with genomic amplification of TERT locus were identified. Tumors bearing chromosomal aberrations involving TERT showed higher TERT transcriptional expression and increased telomerase activity. These data suggest that deregulation of TERT gene by chromosomal abnormalities leading to increased telomerase activity might contribute to B-cell lymphomagenesis.