Molecular pathogenesis of mantle cell lymphoma

The tumour microenvironment in B cell lymphomas

B cell lymphomas are cancers that arise from cells that depend on numerous highly orchestrated interactions with immune and stromal cells in the course of normal development. Despite the recent focus on dissecting the genetic aberrations within cancer cells, it has been increasingly recognized that tumour cells retain a range of dependence on interactions with the non-malignant cells and stromal elements that constitute the tumour microenvironment. A fundamental understanding of these interactions gives insight into the pathogenesis of most B cell lymphomas and, moreover, identifies novel therapeutic opportunities for targeting oncogenic pathways, both now and in the future.

Requirement for CDK6 in MLL-rearranged acute myeloid leukemia

Chromosomal rearrangements involving the H3K4 methyltransferase mixed-lineage leukemia (MLL) trigger aberrant gene expression in hematopoietic progenitors and give rise to an aggressive subtype of acute myeloid leukemia (AML). Insights into MLL fusion-mediated leukemogenesis have not yet translated into better therapies because MLL is difficult to target directly, and the identity of the genes downstream of MLL whose altered transcription mediates leukemic transformation are poorly annotated. We used a functional genetic approach to uncover that AML cells driven by MLL-AF9 are exceptionally reliant on the cell-cycle regulator CDK6, but not its functional homolog CDK4, and that the preferential growth inhibition induced by CDK6 depletion is mediated through enhanced myeloid differentiation. CDK6 essentiality is also evident in AML cells harboring alternate MLL fusions and a mouse model of MLL-AF9-driven leukemia and can be ascribed to transcriptional activation of CDK6 by mutant MLL. Importantly, the context-dependent effects of lowering CDK6 expression are closely phenocopied by a small-molecule CDK6 inhibitor currently in clinical development. These data identify CDK6 as critical effector of MLL fusions in leukemogenesis that might be targeted to overcome the differentiation block associated with MLL-rearranged AML, and underscore that cell-cycle regulators may have distinct, noncanonical, and nonredundant functions in different contexts.

Current regimens and novel agents for mantle cell lymphoma

Mantle cell lymphoma is a heterogeneous subtype of non-Hodgkin lymphoma. Conventional treatment with immunochemotherapy followed by autologous stem cell transplantation or intensive immunochemotherapy alone has improved outcomes, but the disease remains incurable. Recent advances in basic and translational research have significantly enhanced our understanding of disease pathogenesis and have sparked the development of novel therapies. Novel agents include the proteasome inhibitor bortezomib, the immunomodulatory agent lenalidomide, the phosphatidylinositol-4,5-bisphosphate 3-kinase pathway inhibitor idelalisib and the Bruton tyrosine kinase inhibitor ibrutinib. Preliminary results from clinical trials, especially from studies of ibrutinib, have proven these agents to be effective. In ongoing studies, these agents are being integrated into conventional immunochemotherapy regimens to hopefully improve patient outcomes.

Downregulation of deoxycytidine kinase in cytarabine-resistant mantle cell lymphoma cells confers cross-resistance to nucleoside analogs gemcitabine, fludarabine and cladribine, but not to other classes of anti-lymphoma agents

BACKGROUND

Mantle cell lymphoma (MCL) is an aggressive type of B-cell non-Hodgkin lymphoma associated with poor prognosis. Implementation of high-dose cytarabine (araC) into induction therapy became standard-of-care for all newly diagnosed younger MCL patients. However, many patients relapse even after araC-based regimen. Molecular mechanisms responsible for araC resistance in MCL are unknown and optimal treatment strategy for relapsed/refractory MCL patients remains elusive.

METHODS

Five araC-resistant (R) clones were derived by long-term culture of five MCL cell lines (CTRL) with increasing doses of araC up to 50 microM. Illumina BeadChip and 2-DE proteomic analysis were used to identify gene and protein expression changes associated with araC resistance in MCL. In vitro cytotoxicity assays and experimental therapy of MCL xenografts in immunodeficient mice were used to analyze their relative responsiveness to a set of clinically used anti-MCL drugs. Primary MCL samples were obtained from patients at diagnosis and after failure of araC-based therapies.

RESULTS

Marked downregulation of deoxycytidine-kinase (DCK) mRNA and protein expression was identified as the single most important molecular event associated with araC-resistance in all tested MCL cell lines and in 50% primary MCL samples. All R clones were highly (20-1000x) cross-resistant to all tested nucleoside analogs including gemcitabine, fludarabine and cladribine. In vitro sensitivity of R clones to other classes of clinically used anti-MCL agents including genotoxic drugs (cisplatin, doxorubicin, bendamustine) and targeted agents (bortezomib, temsirolimus, rituximab) remained unaffected, or was even increased (ibrutinib). Experimental therapy of immunodeficient mice confirmed the anticipated loss of anti-tumor activity (as determined by overall survival) of the nucleoside analogs gemcitabine and fludarabine in mice transplanted with R clone compared to mice transplanted with CTRL cells, while the anti-tumor activity of cisplatin, temsirolimus, bortezomib, bendamustine, cyclophosphamide and rituximab remained comparable between the two cohorts.

CONCLUSIONS

Acquired resistance of MCL cells to araC is associated with downregulation of DCK, enzyme of the nucleotide salvage pathway responsible for the first phosphorylation (=activation) of most nucleoside analogs used in anti-cancer therapy. The data suggest that nucleoside analogs should not be used in the therapy of MCL patients, who relapse after failure of araC-based therapies.

Clinical, morphologic, phenotypic, and genetic evidence of cyclin D1-positive diffuse large B-cell lymphomas with CYCLIN D1 gene rearrangements

Overexpression of cyclin D1 in diffuse large B-cell lymphomas (DLBCLs) is observable in about 5% of cases and is linked to gains of additional CYCLIN D1 gene copies or deregulation at the mRNA level. All cyclin D1-positive DLBCL cases reported so far lack the canonical t(11;14)(q13;q32) translocation that is a genetic hallmark and the primary cause of cyclin D1 overexpression in mantle cell lymphoma (MCL). Using standard histologic and genetic techniques, complemented with genome-wide aberration analysis by array comparative genomic hybridization, we characterized 2 exceptional cases of blastoid B-cell lymphomas with cyclin D1 overexpression, both bearing genetic rearrangements in the CYCLIN D1 gene locus. One of them had a t(11;14)(q13;q32) translocation and featured morphology, immunophenotype, and genetic copy number aberrations typical of DLBCL. The second case had a complex t(4;11;14) translocation, but the other features were intermediate between DLBCL and MCL and did not allow unambiguous classification in any of the current diagnostic lymphoma categories. On the basis of these findings, we conclude that detection of t(11;14) should not preclude a diagnosis of cyclin D1-positive DLBCL when all other parameters are in agreement with such a diagnosis. Moreover, a yet unacknowledged diagnostic "gray zone" may exist between DLBCL and MCL.

Targeting Bruton's tyrosine kinase in B cell malignancies

Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signalling and functions as an important regulator of cell proliferation and cell survival in various B cell malignancies. Small-molecule inhibitors of BTK have shown antitumour activity in animal models and, recently, in clinical studies. High response rates were reported in patients with chronic lymphocytic leukaemia and mantle cell lymphoma. Remarkably, BTK inhibitors have molecular effects that cannot be explained by the classic role of BTK in BCR signalling. In this Review, we highlight the importance of BTK in various signalling pathways in the context of its therapeutic inhibition.

Perinucleolar relocalization and nucleolin as crucial events in the transcriptional activation of key genes in mantle cell lymphoma

In mantle cell lymphoma (MCL), one allele of the cyclin D1 (Ccnd1) gene is translocated from its normal localization on chromosome 11 to chromosome 14. This is considered as the crucial event in the transformation process of a normal naive B-cell; however, the actual molecular mechanism leading to Ccnd1 activation remains to be deciphered. Using a combination of three-dimensional and immuno-fluorescence in situ hybridization experiments, the radial position of the 2 Ccnd1 alleles was investigated in MCL-derived cell lines and malignant cells from affected patients. The translocated Ccnd1 allele was observed significantly more distant from the nuclear membrane than its nontranslocated counterpart, with a very high proportion of IgH-Ccnd1 chromosomal segments localized next to a nucleolus. These perinucleolar areas were found to contain active RNA polymerase II (PolII) clusters. Nucleoli are rich in nucleolin, a potent transcription factor that we found to bind sites within the Ccnd1 gene specifically in MCL cells and to activate Ccnd1 transcription. We propose that the Ccnd1 transcriptional activation in MCL cells relates to the repositioning of the rearranged IgH-Ccnd1-carrying chromosomal segment in a nuclear territory with abundant nucleolin and active PolII molecules. Similar transforming events could occur in Burkitt and other B-cell lymphomas.

Inhibition of lymphoma vascularization and dissemination by estrogen receptor β agonists

Most lymphomas show an increased incidence and poorer prognosis in males vs females, suggesting endocrine regulation. We have previously shown that tumor growth in vivo of a murine T-cell-derived lymphoma is repressed following activation of estrogen receptor β (ERβ, ESR2). By using ERβ-deficient mice, we now demonstrate that this inhibition is mediated via a direct effect on the tumor cells and not on the microenvironment. Furthermore, we show that the growth-suppressing effects of ERβ agonist are also valid for human B-cell lymphomas as demonstrated in tumors derived from Granta-519 mantle cell lymphoma (MCL) and Raji Burkitt lymphoma (BL) cells. In Granta-519 MCL tumors, activation of ERβ reduced expression of BAFF and GRB7, 2 important molecules involved in B-cell proliferation and survival. Importantly, activation of ERβ inhibited angiogenesis and lymphangiogenesis, possibly mediated by impaired vascular endothelial growth factor C expression. Furthermore, using disseminating Raji BL cells, we show that ERβ activation reduces dissemination of grafted Raji BL tumors. We also show by immunohistochemistry that ERβ is expressed in primary MCL tissue. These results suggest that targeting ERβ with agonists may be valuable in the treatment of some lymphomas, affecting several aspects of the malignant process, including proliferation, vascularization, and dissemination.

Cyclin D1 transcriptional activation in MCL

In this issue of Blood, Allinne et al propose the nucleolin-dependent activation of the translocated CCND1 allele in mantle cell lymphoma (MCL) because of its relocalization to a transcriptionally favorable area in the perinucleolar region.

Synergistic antitumor activity of lenalidomide with the BET bromodomain inhibitor CPI203 in bortezomib-resistant mantle cell lymphoma

Bortezomib therapy has shown promising clinical activity in mantle cell lymphoma (MCL), but the development of resistance to proteasome inhibition may limit its efficacy. To unravel the factors involved in the acquisition of bortezomib resistance in vivo, immunodeficient mice were engrafted with a set of MCL cell lines with different levels of sensitivity to the drug, followed by gene expression profiling of the tumors and functional validation of the identified gene signatures. We observed an increased tumorigenicity of bortezomib-resistant MCL cells in vivo, which was associated with plasmacytic differentiation features, like interferon regulatory factor 4 (IRF4) and Blimp-1 upregulation. Lenalidomide was particularly active in this subgroup of tumors, targeting IRF4 expression and plasmacytic differentiation program, thus overcoming bortezomib resistance. Moreover, repression of the IRF4 target gene MYC in bortezomib-resistant cells by gene knockdown or treatment with CPI203, a BET (bromodomain and extra terminal) bromodomain inhibitor, synergistically induced cell death when combined with lenalidomide. In mice, addition of CPI203 to lenalidomide therapy further decreased tumor burden, involving simultaneous MYC and IRF4 downregulation and apoptosis induction. Together, these results suggest that exacerbated IRF4/MYC signaling is associated to bortezomib resistance in MCL in vivo and warrant clinical evaluation of lenalidomide plus BET inhibitor combination in MCL cases refractory to proteasome inhibition.

Therapy-related B lymphoblastic leukemia with t(4;11)(q21;q23)/AF4-MLL in a patient with mantle cell lymphoma after recent aggressive chemotherapy: a unique case report

Mantle cell lymphoma (MCL) is a mature B-cell lymphoma associated with the hallmark translocation t(11;14)(q13;32), which involves the cyclin D1 (CCND1) and immunoglobin heavy chain (IgH) genes. It may transform to a more aggressive blastoid or pleomorphic variant, with or without acquisition of chromosomal abnormalities. MCL could also present with a leukemic phase with marked lymphocytosis. A literature search did not reveal any prior reports of MCL transforming to or followed by a B-cell lymphoblastic leukemia (B-ALL).

Common consensus LNA probe for quantitative PCR assays in cancer: vehicles for minimal residual disease detection in t(11;14) and t(14;18) positive malignant lymphomas

The use of locked nucleic acid (LNA) probes and primers potentially improves sensitivity and specificity of quantitative PCR (qPCR) assays. One area of application is that of minimal residual cancer where PCR techniques have proved to be highly relevant tools in patient follow-up. We present here sensitive and specific consensus qPCR assays for quantification of the malignant lymphoma translocations, t(11;14) and t(14;18), by taking advantage of the thermodynamic properties of LNA. The assays were applied to genomic DNA from patients diagnosed with mantle cell lymphoma (MCL) and follicular lymphoma (FL), respectively. Two consensus forward primers targeting the BCL1 and BCL2 genes were designed together with a common consensus reverse primer and hydrolysis probe, the latter consisting exclusively of LNA, both targeting the J segments of the immunoglobulin heavy chain (IgH) gene. The quantitative range of both assays was 1×10(0) to 5×10(-5), and the sensitivity was 10(-5), without the need for patient-specific primers. Peripheral blood (PB) and bone marrow (BM) samples from 36 patients diagnosed with MCL and nine patients diagnosed with FL were analysed using this novel qPCR approach. The level of minimal residual disease (MRD) using t(11;14) and t(14;18) as genetic targets reflected the clinical status of the patients: low levels of MRD at clinical remission, and increasing levels at disease progression. The present assays could prove as useful tools in lymphoma therapy.

Clonal B-cell lymphocytosis exhibiting immunophenotypic features consistent with a marginal-zone origin: is this a distinct entity?

Clonal B-cell lymphocytosis of potential marginal-zone origin (CBL-MZ) rarely progresses to a well-recognized lymphoma. CBL-MZ does not require treatment in the absence of progressive disease.

A microenvironment-mediated c-Myc/miR-548m/HDAC6 amplification loop in non-Hodgkin B cell lymphomas

A dynamic interaction occurs between the lymphoma cell and its microenvironment, with each profoundly influencing the behavior of the other. Here, using a clonogenic coculture growth system and a xenograft mouse model, we demonstrated that adhesion of mantle cell lymphoma (MCL) and other non-Hodgkin lymphoma cells to lymphoma stromal cells confers drug resistance, clonogenicity, and induction of histone deacetylase 6 (HDAC6). Furthermore, stroma triggered a c-Myc/miR-548m feed-forward loop, linking sustained c-Myc activation, miR-548m downregulation, and subsequent HDAC6 upregulation and stroma-mediated cell survival and lymphoma progression in lymphoma cell lines, primary MCL and other B cell lymphoma cell lines. Treatment with an HDAC6-selective inhibitor alone or in synergy with a c-Myc inhibitor enhanced cell death, abolished cell adhesion–mediated drug resistance, and suppressed clonogenicity and lymphoma growth ex vivo and in vivo. Together, these data suggest that the lymphoma-stroma interaction in the lymphoma microenvironment directly impacts the biology of lymphoma through genetic and epigenetic regulation, with HDAC6 and c-Myc as potential therapeutic targets.

Management perspective for mantle cell lymphoma

SUMMARY Mantle cell lymphoma (MCL) is genetically characterized by the t(11;14) (q13;q32) translocation resulting in the overexpression of cyclin D1. It generally has an aggressive clinical course with a poor prognosis. However, there is now a recognized subgroup with clinically indolent MCL. Management of MCL can be challenging. Early recognition of young and fit patients for potential intensive therapy and autologous stem cell transplant is important. Combination of rituximab with high-dose cytarabine should be used in upfront therapy for appropriate patients. In elderly and/or less fit patients, chemoimmunotherapy may be considered. Novel agents offer promising potential in the management of MCL and are likely to change the way it is treated.

Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm with transient response to conventional chemotherapy. We here investigated the role of the Bcl-2 homology domain 3-only protein NOXA for life–death decision in MCL. Surprisingly, NOXA (PMAIP1) mRNA and NOXA protein levels were extremely discrepant in MCL cells: NOXA mRNA was found to be highly expressed whereas NOXA protein levels were low. Chronic active B-cell receptor signaling and to a minor degree cyclin D1 overexpression contributed to high NOXA mRNA expression levels in MCL cells. The phoshatidyl-inositol-3 kinase/AKT/mammalian target of rapamycin pathway was identified as the major downstream signaling pathway involved in the maintenance of NOXA gene expression. Interestingly, MCL cells adapt to this constitutive pro-apoptotic signal by extensive ubiquitination and rapid proteasomal degradation of NOXA protein (T_½∼15–30 min). In addition to the proteasome inhibitor Bortezomib, we identified the neddylation inhibitor MLN4924 and the fatty acid synthase inhibitor Orlistat as potent inducers of NOXA protein expression leading to apoptosis in MCL. All inhibitors targeted NOXA protein turnover. In contrast to Bortezomib, MLN4924 and Orlistat interfered with the ubiquitination process of NOXA protein thereby offering new strategies to kill Bortezomib-resistant MCL cells. Our data, therefore, highlight a critical role of NOXA in the balance between life and death in MCL. The discrepancy between NOXA transcript and protein levels is essential for sensitivity of MCL to ubiquitin-proteasome system inhibitors and could therefore provide a druggable Achilles' heel of MCL cells.

Unlocking new therapeutic targets and resistance mechanisms in mantle cell lymphoma

Mantle cell lymphoma is an aggressive tumor for which new drugs targeting underlying molecular mechanisms are opening promising avenues. A recent study has elucidated the basis for targeting B cell receptor signaling in these lymphomas and identified somatic mutations in NF-κB regulatory genes that confer resistance to this therapy.

Anti-CCR7 therapy exerts a potent anti-tumor activity in a xenograft model of human mantle cell lymphoma

Background

The chemokine receptor CCR7 mediates lymphoid dissemination of many cancers, including lymphomas and epithelial carcinomas, thus representing an attractive therapeutic target. Previous results have highlighted the potential of the anti-CCR7 monoclonal antibodies to inhibit migration in transwell assays. The present study aimed to evaluate the in vivo therapeutic efficacy of an anti-CCR7 antibody in a xenografted human mantle cell lymphoma model.

Methods

NOD/SCID mice were either subcutaneously or intravenously inoculated with Granta-519 cells, a human cell line derived from a leukemic mantle cell lymphoma. The anti-CCR7 mAb treatment (3 × 200 μg) was started on day 2 or 7 to target lymphoma cells in either a peri-implantation or a post-implantation stage, respectively.

Results

The anti-CCR7 therapy significantly delayed the tumor appearance and also reduced the volumes of tumors in the subcutaneous model. Moreover, an increased number of apoptotic tumor cells was detected in mice treated with the anti-CCR7 mAb compared to the untreated animals. In addition, significantly reduced number of Granta-519 cells migrated from subcutaneous tumors to distant lymphoid organs, such as bone marrow and spleen in the anti-CCR7 treated mice. In the intravenous models, the anti-CCR7 mAb drastically increased survival of the mice. Accordingly, dissemination and infiltration of tumor cells in lymphoid and non-lymphoid organs, including lungs and central nervous system, was almost abrogated.

Conclusions

The anti-CCR7 mAb exerts a potent anti-tumor activity and might represent an interesting therapeutic alternative to conventional therapies.

Antitumoral activity of lenalidomide in in vitro and in vivo models of mantle cell lymphoma involves the destabilization of cyclin D1/p27KIP1 complexes

PURPOSE

Clinical responses to the immmunomodulatory drug lenalidomide have been observed in patients with relapsed/refractory mantle cell lymphoma (MCL), although its mechanism of action remains partially unknown. We investigated whether the expression and subcellular localization of cyclin D1, a major cell-cycle regulator overexpressed in MCL, and the cyclin-dependent kinase inhibitor p27(KIP1), could identify MCL cases sensitive to lenalidomide, and whether the compound could modulate cyclin D1/p27(KIP1) complexes in MCL cells.

EXPERIMENTAL DESIGN

MCL primary samples and cell lines were analyzed for subcellular levels of cyclin D1/p27(KIP1) complexes by Western blot, immunohistochemistry, immunoprecipitation, and flow cytometry. Activity of lenalidomide in vitro and its effect on cyclin D1/p27(KIP1) complexes were evaluated by real-time PCR, immunoprecipitation, immunofluorescence, and Western blot. In vivo validation was carried out in a mouse xenograft model of human MCL.

RESULTS

We found cyclin D1 and p27(KIP1) to be coordinately expressed in all the MCL samples tested. Immunoprecipitation analyses and siRNA assays suggested a direct role of cyclin D1 in the regulation of p27(KIP1) levels. The nuclear accumulation of both proteins correlated with MCL cell tumorigenicity in vivo, and sensitivity to lenalidomide activity in vitro and in vivo. Lenalidomide mechanism of action relied on cyclin D1 downregulation and disruption of cyclin D1/p27(KIP1) complexes, followed by cytosolic accumulation of p27(KIP1), cell proliferation arrest, apoptosis, and angiogenesis inhibition.

CONCLUSIONS

These results highlight a mechanism of action of lenalidomide in MCL cases with increased tumorigenicity in vivo, which is mediated by the dissociation of cyclin D1/p27(KIP1) complexes, and subsequent proliferation blockade and apoptosis induction.

Landscape of somatic mutations and clonal evolution in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive tumor, but a subset of patients may follow an indolent clinical course. To understand the mechanisms underlying this biological heterogeneity, we performed whole-genome and/or whole-exome sequencing on 29 MCL cases and their respective matched normal DNA, as well as 6 MCL cell lines. Recurrently mutated genes were investigated by targeted sequencing in an independent cohort of 172 MCL patients. We identified 25 significantly mutated genes, including known drivers such as ataxia-telangectasia mutated (ATM), cyclin D1 (CCND1), and the tumor suppressor TP53; mutated genes encoding the anti-apoptotic protein BIRC3 and Toll-like receptor 2 (TLR2); and the chromatin modifiers WHSC1, MLL2, and MEF2B. We also found NOTCH2 mutations as an alternative phenomenon to NOTCH1 mutations in aggressive tumors with a dismal prognosis. Analysis of two simultaneous or subsequent MCL samples by whole-genome/whole-exome (n = 8) or targeted (n = 19) sequencing revealed subclonal heterogeneity at diagnosis in samples from different topographic sites and modulation of the initial mutational profile at the progression of the disease. Some mutations were predominantly clonal or subclonal, indicating an early or late event in tumor evolution, respectively. Our study identifies molecular mechanisms contributing to MCL pathogenesis and offers potential targets for therapeutic intervention.

The use of salivary protein secretions as an in vivo model to study Mantel cell lymphoma progression and treatment

PURPOSE

The objective of this study was to compare the salivary protein profiles from an individual diagnosed with MCL before, during, and after chemotherapy.

METHODS

Saliva specimens acquire prior, during, and after chemotherapy. Specimens were analyzed using a LC-MS/MS mass spectrometer.

RESULTS

The results of the study suggest salivary protein alterations secondary to MCL and that a number of the proteins were changed as a result of chemotherapeutic intervention suggesting that the treatment, from a proteomic perspective, was efficacious. The study suggests that salivary secretions may be used as in vivo model for studying MCL progression and treatment efficacy.

Indolent mantle cell lymphoma

Over the past decade, it has become increasingly clear that mantle cell lymphoma (MCL) is a more heterogeneous disease than originally recognized. Several groups have reported on a subgroup of patients with a less aggressive course than expected resulting in the term "indolent MCL". Unlike the recognized histologic variants, the definition of indolent mantle cell lymphoma is unclear, and patients with indolent MCL are often identified only after having undergone prolonged periods of observation. In this review, we will discuss clinical and biologic features and provide a framework for the approach in identifying patients with indolent MCL.

The EMT activator ZEB1 promotes tumor growth and determines differential response to chemotherapy in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a B-cell malignancy characterized by a poor response to treatment and prognosis. Constitutive activation of different signaling pathways in subsets of MCLs, through genetic and/or nongenetic alterations, endows tumor cells with enhanced proliferation and reduced apoptosis. The canonical Wnt pathway (β-catenin/TCF-LEF), implicated in the pathogenesis of numerous cancers, is constitutively active in half of MCLs. Here, we show that ZEB1, a transcription factor better known for promoting metastasis in carcinomas, is expressed in primary MCLs with active Wnt signaling. ZEB1 expression in MCL cells depends on Wnt, being downregulated by β-catenin knockdown or blocking of Wnt signaling by salinomycin. Knockdown of ZEB1 reduces in vitro cell viability and proliferation in MCL cells, and, importantly, tumor growth in mouse xenograft models. ZEB1 activates proliferation-associated (HMGB2, UHRF1, CENPF, MYC, MKI67, and CCND1) and anti-apoptotic (MCL1, BCL2, and BIRC5) genes and inhibits pro-apoptotic ones (TP53, BBC3, PMAIP1, and BAX). We show that ZEB1 expression in MCL cells determines differential resistance to chemotherapy drugs and regulates transporters involved in drug influx/efflux. Downregulation of ZEB1 by salinomycin increases the sensitivity of MCL cells to the cytotoxic effect of doxorubicin, cytarabine and gemcitabine. Lastly, salinomycin and doxorubicin display a synergistic effect in established and primary MCL cells. These results identify ZEB1 in MCL where it promotes cell proliferation, enhanced tumor growth and a differential response to chemotherapy drugs. ZEB1 could thus potentially become a predictive biomarker and therapeutic target in this lymphoma.

Characterization of IGH locus breakpoints in multiple myeloma indicates a subset of translocations appear to occur in pregerminal center B cells

IGH translocations in myeloma can occur through at least 5 mechanisms. t(11;14) and t(14;20) DH-JH rearrangement-mediated translocations occur indicating these appear to occur in a pregerminal center cell.

Lymphoid malignancies: many tumor types, many altered genes, many therapeutic challenges

The lymphoid tissues, including both the B and T cell lineages, are characterized by a unique level of biological complexity due to the anatomical organization of functionally distinct cell subpopulations and complex processes of genetic alteration required to generate immune responses. Not surprisingly, this physiological diversity and complexity is mirrored by the broad spectrum of malignancies derived from lymphocytes. The articles in this Review Series highlight recent progress in selected common lymphoid malignancies, with a focus on the genetic alterations that drive malignant transformation, including those identified by genome-wide analyses. These genetic alterations represent the basis from which cellular pathways of therapeutic relevance can be identified, studied, and eventually targeted.