Sequence-Based Evidence for Antigen Selection in Mantle Cell Lymphoma: Remarkable Immunoglobulin Gene Repertoire Biases, Stereotyped Antigen-Binding Sites and Recurrent Hypermutations in Certain Subsets.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1933-1933 ◽  
Author(s):  
Anastasia Hadzidimitriou ◽  
Andreas Agathagelidis ◽  
Fiona Murray ◽  
Marie-Helene Delfau-Larue ◽  
Nikos Darzentas ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Conflicts Of Interest ◽  
Cell Lymphoma ◽  
Somatic Hypermutation ◽  
Antigen Binding ◽  
Gene Repertoire ◽  
Immunoglobulin Gene ◽  
Antigen Binding Site ◽  
Ighv Gene ◽  
Mantle Cell

Abstract Abstract 1933 Poster Board I-956 According to the 2008 WHO Classification, mantle cell lymphoma (MCL) most likely derives from neoplastic transformation of a peripheral B cell of the inner mantle zone, mostly of naïve pre-germinal center type. Analysis of the immunoglobulin (IG) repertoire in MCL has revealed a bias in IG heavy variable (IGHV) gene usage and a predominance of unmutated rearrangements, with a variable minor proportion of cases carrying mutated IGHV genes (according to the 98% identity cutoff). However, limited knowledge exists regarding antigen-binding site sequence restrictions or specific somatic hypermutation (SHM) patterns in MCL. We examined the productive IGHV-D-J rearrangements of 651 MCL cases (including 398 cases from the European MCL Network), the largest series to date. We confirm and significantly extend previous observations that the IGHV gene repertoire is remarkably biased, with only three genes accounting for 40.3% of cases (IGHV3-21, 16.7%; IGHV4-34, 15.3%; IGHV1-8: 8.3%). Using bioinformatics approaches previously applied to CLL, biased associations of certain IGHV, IGHD and IGHJ genes with restricted (stereotyped) heavy complementarity-determining regions (HCDR3s) were identified in 68/651 cases (10.4%). Overall, 24 subsets of cases with stereotyped HCDR3s were recognized. Eight of 24 subsets included 3-7 cases each (“confirmed”), while the remaining 16 subsets included two cases each and were considered “provisional”. Stereotyped HCDR3s were found predominantly amongst rearrangements utilizing the IGHV3-21 and IGHV4-34 genes and the IGHJ6 gene. Notably, the MCL HCDR3 stereotypes identified here were distinct from those previously reported in CLL. Based on SHM analysis, the sequences were divided into three groups: (i) truly unmutated (100% germline identity, GI): 189/651 sequences (29.2%); (ii) minimally/borderline mutated (98-99.9% GI): 306/651 sequences (47%); and (iii) mutated (<98% GI): 155/651 sequences (23.8%), of which 93 had a GI<97%. In keeping with previous reports, the IGHV gene repertoire of the three identity groups differed considerably. For instance, the IGHV3-21 gene was used by 7% of rearrangements with <98% identity vs. 22.8% of rearrangements with 100% identity. In contrast, the IGHV3-23 gene was over-represented among mutated rearrangements (26.4%). Shared (“stereotyped”) amino acid (AA) changes across the entire IGHV gene sequence were identified for certain groups of sequences, especially those utilizing the IGHV1-8, IGHV3-21 and IGHV3-23 genes. A comparison to published series from other entities, in particular CLL, revealed that several stereotyped mutations identified in MCL were “disease-biased”. Importantly, stereotyped AA changes were also observed in the borderline or minimally mutated groups, indicating that even a low level of mutations may be functionally relevant. In conclusion, MCL is characterized by a highly distinctive IG gene repertoire with restricted HCDR3s and very precisely targeted and, probably, functionally driven SHM, strongly implying a role for antigen-driven selection of the clonogenic progenitors. Based on the evidence presented here, an antigen-driven origin of MCL could be envisaged, at least for subsets of cases. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Is there a role for antigen selection in mantle cell lymphoma? Immunogenetic support from a series of 807 cases

Blood ◽  
2011 ◽  
Vol 118 (11) ◽  
pp. 3088-3095 ◽  
Author(s):  
Anastasia Hadzidimitriou ◽  
Andreas Agathangelidis ◽  
Nikos Darzentas ◽  
Fiona Murray ◽  
Marie-Helene Delfau-Larue ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Germ Line ◽  
Cell Lymphoma ◽  
Somatic Hypermutation ◽  
Lymphocytic Leukemia ◽  
Gene Repertoire ◽  
Immunoglobulin Gene ◽  
Ighv Gene ◽  
Mantle Cell ◽  
Selection Of

Abstract We examined 807 productive IGHV-IGHD-IGHJ gene rearrangements from mantle cell lymphoma (MCL) cases, by far the largest series to date. The IGHV gene repertoire was remarkably biased, with IGHV3-21, IGHV4-34, IGHV1-8, and IGHV3-23 accounting for 46.3% of the cohort. Eighty-four of 807 (10.4%) cases, mainly using the IGHV3-21 and IGHV4-34 genes, were found to bear stereotyped heavy complementarity-determining region 3 (VH CDR3) sequences and were placed in 38 clusters. Notably, the MCL stereotypes were distinct from those reported for chronic lymphocytic leukemia. Based on somatic hypermutation (SHM) status, 238/807 sequences (29.5%) carried IGHV genes with 100% germ line identity; the remainder (569/807; 70.5%) exhibited different SHM impact, ranging from minimal (in most cases) to pronounced. Shared replacement mutations across the IGHV gene were identified for certain subgroups, especially those using IGHV3-21, IGHV1-8, and IGHV3-23. Comparison with other entities, in particular CLL, revealed that several of these mutations were “MCL-biased.” In conclusion, MCL is characterized by a highly restricted immunoglobulin gene repertoire with stereotyped VH CDR3s and very precise SHM targeting, strongly implying a role for antigen-driven selection of the clonogenic progenitors. Hence, an antigen-driven origin of MCL could be envisaged, at least for subsets of cases.

Mantle cell lymphoma with t(11;14) and unmutated or mutated VH genes expresses AID and undergoes isotype switch events

Blood ◽  
2004 ◽  
Vol 103 (7) ◽  
pp. 2795-2798 ◽  
Author(s):  
Gavin Babbage ◽  
Richard Garand ◽  
Nelly Robillard ◽  
Niklas Zojer ◽  
Freda K. Stevenson ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Tumor Cells ◽  
Germinal Center ◽  
Cell Lymphoma ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Activation Induced Cytidine Deaminase ◽  
Mantle Cell ◽  
Vh Genes ◽  
A Minor

Abstract Isotype switch commonly follows onset of somatic hypermutation in the germinal center (GC), with activation-induced cytidine deaminase (AID) as a prerequisite. Mantle cell lymphoma (MCL) with t(11;14) includes a subset with unmutated (UM) and a minor subset with mutated (MUT) VH genes. Here, we investigated whether switch events and AID expression occur in MCL. In 4 of 6 UM and 4 of 7 MUT MCLs, alternative tumor-derived Cγ,α,ϵ transcripts were identified. AID transcripts, including a splice variant, were common to both subsets. AID expression correlated with switch in 8 of 8 cases, but in 3 of 5 cases it occurred with switch absent. Circle transcripts (Iγ-Cμ/Iα-Cμ) were identified in 5 of 7 evaluated cases. In 1 of 12 cases, 12% of tumor cells expressed immunoglobulin L-restricted surface IgA. Ongoing switch recombination events appear to be a feature of MCL, likely restricted to a minor tumor subpopulation, with occasional variant sIg expression. UM MCLs implicate origins from pre-GC B cells and reveal switch events at ectopic sites. (Blood. 2004;103:2795-2798)

CD10-positive mantle cell lymphoma: biologically distinct entity or an aberrant immunophenotype? Insight, through gene expression profile in a unique case series

2015 ◽  
Vol 68 (10) ◽  
pp. 844-848 ◽  
Author(s):  
Ariz Akhter ◽  
Etienne Mahe ◽  
Lesley Street ◽  
Payam Pournazari ◽  
Marco Perizzolo ◽  
...  
Keyword(s):  
Gene Expression ◽  
Mantle Cell Lymphoma ◽  
Gene Expression Profile ◽  
Expression Profile ◽  
Cell Lymphoma ◽  
Somatic Hypermutation ◽  
Case Series ◽  
Convincing Evidence ◽  
Minimal Impact ◽  
Mantle Cell

BackgroundMantle cell lymphoma (MCL) is an aggressive disease with genetic heterogeneity and discrete clinical subtypes. MCL is rarely CD10 positive. These cases raise the question whether a subset of MCL may be germinal centre (GC) derived, and have distinct clinicopathological characteristics.Aims and methodsA series of nine CD10-positive MCL cases is described herein. The clinicopathological and immunophenotypic features, immunoglobulin somatic hypermutation (SHM) status and gene expression profile (GEP) data are detailed. These features were compared with two independent sets (n=20, each) of CD10-negative MCL cases (controls), which were randomly selected from our institutional registry.ResultsGEP showed distinct expression of a GC signature in CD10-positive MCL cases with minimal impact on downstream signalling pathways. There were no significant differences in the clinicopathological features or clinical outcome between our CD10-positive and CD10-negative MCL cases. The frequency of SHM was comparable with established data.ConclusionsThis study provides convincing evidence that CD10 expression is related to a distinct GC signature in MCL cases, but without clinical or biological implications.

Bendamustine for Mantle Cell Lymphoma: Retrospective Analysis of the Spanish Experience

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 4942-4942
Author(s):  
Ana García-Noblejas ◽  
Belén Navarro Matilla ◽  
Carolina Da Silva Rodriguez ◽  
Raquel De Oña Navarrete ◽  
María José Ramirez Sánchez ◽  
...  
Keyword(s):  
Clinical Trials ◽  
Mantle Cell Lymphoma ◽  
Retrospective Analysis ◽  
Conflicts Of Interest ◽  
Cell Lymphoma ◽  
Alkylating Agents ◽  
Stage Iv ◽  
Progression Free Survival ◽  
Median Number ◽  
Mantle Cell

Abstract Abstract 4942 INTRODUCTION. Patients with Mantle cell lymphoma (MCL) have an adverse outcome after relapse due to chemorefractory disease with conventional treatments. Bendamustine, a nitrogen mustard compound chemically related to the alkylating agents, has demonstrated high efficacy with a low toxicity profile in reported clinical trials. AIM. To analyze the Spanish experience in patients with relapsed/refractory MCL treated with Bendamustine. METHODS. Retrospective analysis of spanish experience in relapsed/refractory MCL treated with Bendamustine alone or in combination. This study has been approved by local ethical committees. RESULTS. Currently, there are 36 patients registered and 28 are available for this analysis. Patients'characteristics: 69% male, median age 65 years old (range 41–81), 87% ECOG≤ 1, 83% Ann Arbor stage IV, 37% high risk MIPI and 9% blastic variant. Previous regimens were CHOP or CHOP like ± R in 42.5%, HyperCVAD/MtxAraC ± R in 42.5%, R-CVP in 9% and other regimens in 6%. Median number of previous treatments were 2.6 (range 1–6), all patients had received prior Rituximab and 73% had chemosensitive disease to the last treatment. Bendamustine regimen was R-B (R-375mg/m2 D1, B-90 mg/m2 D1-2) in 78% patients, R-B with B-70 mg/m2 in 8%, B alone in 3%, R-B-Bortezomib in 3% and R-B plus consolidation (SCT, Y90Ibritumomab-tiuxetan) in 8%. Median number of cycles was 4.61 (range 1–7). G- CSF support was administered in 43% of cycles. Response: Overall response rate was 73%, with 43% CR & uCR and 30% PR. Survival: Median overall survival from diagnosis is 8,26 years (range: 1.6–11,6 years) without plateau. Median progression free survival (PFS) after Bendamustine treatment was 16 months (95% CI: 11.7–20.4), data that compares favourably with patients' PFS to previous therapy (12 months, 95% CI: 6.5–17.5). Median PFS for patients who achieved CR/uCR is 32.6 months (95% CI: 19.9–45.4) versus 11 months in patients with PR (95% CI: 3.9–18.8). With a median follow-up for surviving patients of 12 months since Bendamustine treatment, the estimated OS at 3 years is 47% (+ SD 14%). Toxicity: No treatment related mortality has been described so far. Over 152 cycles, only 10 hospitalizations due to febrile neutropenia were reported. No one case of lysis tumoral syndrome has been reported. CONCLUSION. Bendamustine plus Rituximab is a good rescue treatment in non selected pretreated patients with mantle cell lymphoma. CR rate and duration of response seem to reproduce in current clinical practice the good data reported in previous clinical trials and compares favourably with other available treatments. Disclosures: No relevant conflicts of interest to declare.

High Expression of Activation-Induced Cytidine Deaminase and in Vivo Class Switch Recombination in Mantle Cell Lymphoma: Further Support for Antigen Involvement in Lymphomagenesis

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1538-1538
Author(s):  
Aliki Xochelli ◽  
Fotini Marantidou ◽  
Evangelia Stalika ◽  
Lesley-Ann Sutton ◽  
Alba Navarro ◽  
...  
Keyword(s):  
Somatic Hypermutation ◽  
Splice Variants ◽  
Cytidine Deaminase ◽  
Gene Repertoire ◽  
Transcript Levels ◽  
Class Switch ◽  
Ighv Gene ◽  
Activation Induced Cytidine Deaminase ◽  
Mantle Cell

Abstract Abstract 1538 According to the WHO 2008 Classification, the cellular origin of mantle cell lymphoma (MCL) is traced to a peripheral B cell of the inner mantle zone, mostly of naïve pre-germinal center type. This notion, however, is seriously challenged by both the remarkable restrictions of the immunoglobulin gene repertoire in MCL and, furthermore, by the fact that the great majority of cases exhibit imprints of somatic hypermutation (SHM) in rearranged IGHV genes, ranging from (mostly) minimal to pronounced. These findings support an antigen-driven origin for MCL, at least for a substantial fraction of the entire cohort. Activation-induced cytidine deaminase (AID) is induced in B cells following contact with antigen and is critically implicated in both somatic hypermutation (SHM) and class switch recombination (CSR). Although the available information about AID expression and in vivo CSR in MCL is limited and contradictory, at least some MCL cases have been reported to express AID and undergo ongoing CSR. With this in mind, here we investigated AID-mRNA isoform expression and isotype switch events in a large series of MCL cases and explored possible associations with IGHV gene repertoire and SHM status. Overall, 107 cases were included in the study and tumor-involved diagnostic tissue samples of different types were evaluated, including: fresh-frozen lymph nodes (LN, n=53), peripheral blood (PB, n=42), spleen (n=5), bone marrow biopsies (n=3) and other (n=4). The neoplastic lymphocytic infiltration ranged from 52–98% (median 80%). Thirty-five of 107 cases (32.7%) carried IGHV genes with 100% identity to the germline (GI) whereas the remaining 72 cases bore some imprint of SHM: in particular, 48/107 cases (44.9%) carried IGHV genes with 97–99.9% GI and, finally, 24/107 cases (22.4%) carried IGHV genes with <97% GI. In keeping with the literature, the IGHV gene repertoire of the present cohort was remarkably biased, with the IGHV3–21, IGHV4–34, IGHV3–23 and IGHV1–8 genes accounting for 55.1% of cases. Profiling of AID mRNA expression was performed by RQ-PCR for the full-length AID (AID-FL) as well as the most frequent splice variants, namely AID-ΔE4a (lacking the first 30 nucleotides from exon 4), and AID-ΔE4 (loss of the entire exon 4). AID transcript levels were calculated as the percentage of AID copy number divided by the copy number of the reference transcript (c-ABL). AID-FL transcripts were detected in 104/107 (97%) cases whereas the AID-ΔE4a and AID-ΔE4 splice variants were detected in 72/107 (67.3%) and 107/107 cases (100%), respectively. The median values for AID-FL, AID-ΔE4a and AID-ΔE4 transcripts were 4.45%, 0.133% and 0.918%, respectively. AID transcript levels varied between different cases by up to 5-log for AID-FL transcripts and 4-log for splice variants. Not unexpectedly, the median transcript levels in LN samples were higher (up to 1-log) compared to PB samples. A highly significant (p<0.001) association was noted between medium-to-high AID-FL transcript levels (AID-FL/ABL○1%) and IGHV GI 100%. Given the difference in tissue origin of our samples, we also performed a separate analysis for LN samples only and found that cases with 100% IGHV GI expressed high AID-FL transcript levels (AID-FL/ABL○10%) significantly (p=0.04) more frequently than cases carrying mutated IGHV genes. Isotype switch events were investigated in 41 cases: overall, 4 cases (9.7%), all with GI<100%, carried alternative tumor-derived Cγ (n=1) or Cα (n=3) transcripts. In conclusion, the present analysis documents AID expression in the vast majority of MCL, thus corroborating our previous hypothesis for antigen involvement in MCL ontogeny. Ongoing CSR events appear to be a feature of MCL, further supporting an activated status, at least for subset of cases. Disclosures: No relevant conflicts of interest to declare.

Rictor Overexpression and mTORC2 Signaling in Chronic Lymphocytic Leukemia

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3884-3884 ◽  
Author(s):  
Gwen Jordaan ◽  
Wei Liao ◽  
Joe Gera ◽  
Sanjai Sharma
Keyword(s):  
Western Blot ◽  
Mantle Cell Lymphoma ◽  
Blot Analysis ◽  
Western Blot Analysis ◽  
Conflicts Of Interest ◽  
Cell Lymphoma ◽  
Parp Cleavage ◽  
Mantle Cell ◽  
Bcr Signaling ◽  
Mtorc2 Complex

Abstract Abstract 3884 Signaling via the B-cell receptor (BCR) stimulates growth and survival of CLL leukemic cells and inhibits apoptosis by phosphorylating immunoreceptor tyrosine based activation motifs. This signaling subsequently activates PI3 Kinase/AKT, mTOR, ERK and other pathways. Activation of Akt in turn requires phosphorylation by mTOR kinase, which assembles in two complexes mTORC1 and mTORC2 and it is the mTORC2 complex that phosphorylates and activates Akt. This phosphorylation of Akt in CLL specimen's upregulates anti-apoptotic proteins such as Mcl-1, Bcl-xl and XIAP. We have identified that Rictor, a component of mTORC2 complex is over-expressed in CLL specimens as compared to normal peripheral mononuclear B cells. This over-expression was noted by real time PCR that showed 1.5 to 4 fold upregulation (n=12). Western blot analysis also showed Rictor overexpression in all the twelve CLL specimens tested. Rictor overexpression was also seen in Mantle cell lymphoma cell lines and to study its role in BCR signaling, stable Mantle cell lymphoma lines with SiRNA mediated Rictor knockdown were established. Rictor knockdown resulted in a significant decrease in Akt activation as phosphorylation (phospho S473) of Akt both in unstimulated cells and when the cells were stimulated with BCR crosslinking was decreased. To determine the effect of Rictor and mTORC2 inhibition on CLL specimens, we tested the activity of three compounds isolated via yeast two hybrid drug screen designed to identify molecules that inhibit Rictor/mTOR interaction. When tested on CLL specimens in the presence of BCR crosslinking, these mTORC2 inhibitor compounds inhibited the downstream phosphorylation of Akt S473. Functionally the inhibitors also induced apoptosis in CLL cells with 40–60% of CLL cells undergoing apoptosis (1.0mM, cells treated for 48 hours). In comparison, rapamycin (mTORC1 inhibitor) and ppp242 (mTORC1, 2 inhibitor) were comparatively less active in CLL specimens as they were less effective in the induction of apoptosis. Western blot analysis of mTORC2 inhibitor treated cells also showed PARP cleavage and an increase in the pro-apoptotic protein BAD. Our data indicates that Rictor overexpression in CLL specimens is required for Akt phosphorylation activation and downstream BCR signaling. Inhibition of this pathway by mTORC2 inhibitors in CLL will be an effective therapeutic strategy. Disclosures: No relevant conflicts of interest to declare.

Human Mesenchymal Stem Cells Promote Resistance to Death Signals By Potentiating FGF Signaling in Mantle Cell Lymphoma

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 5119-5119
Author(s):  
Lalit Sehgal ◽  
Rohit Mathur ◽  
Frank K Braun ◽  
Zuzana Berkova ◽  
Sattva Neelapu ◽  
...  
Keyword(s):  
Mantle Cell Lymphoma ◽  
Conflicts Of Interest ◽  
Cell Lymphoma ◽  
Death Receptor ◽  
Treatment Strategies ◽  
Human Mesenchymal Stem Cells ◽  
Pcr Analysis ◽  
Tumor Initiating Cells ◽  
Autocrine Loop ◽  
Mantle Cell

Abstract Introduction Mantle cell lymphoma (MCL) represents an aggressive, incurable form of non-Hodgkin’s lymphoma (NHL). The health complications associated with advanced age of MCL patients further restrict treatment with intense chemotherapy. Translocation t(11;14), responsible for overexpression of cyclin-D1 is the hallmark of MCL. An intense analysis of primary MCL had been delayed until development of a tissue culture system, using human mesenchymal stromal cells (hMSC), suitable for propagation of primary MCL cells. We hypothesized that tumor-initiating cells are responsible for MCL relapse and chemoresistance and thus, identification of survival signals responsible for survival and maintenance of MCL-initiating cells (MCL-ICs) is essential for design of successful treatment strategies. Methods Isolates of primary MCL cells (n=24) were co-cultured with hMSC and content of MCL-ICs was analyzed by flow-cytometry based on marker expression profile; CD34-CD3-CD45+CD19-. Cytokine array was used to identify the soluble factors enriched in the cocultures and the expression of these factors was confirmed by RT-PCR analysis. The signaling pathways employed by the newly-identified factors were blocked in 3 MCL cell lines (JVM2, Mino, Z138) and cell survival was monitored. Results Co-cultures of primary MCL isolates with hMSCs supported the growth of MCL cells for over 4 weeks with continued presence of MCL-ICs (CD34-CD3-CD45+CD19-) representing about 1% of MCL cells. We found IL-6 triggered a FGF/FGFR autocrine loop in primary MCL in cocultures. Patients with MCL showing high FGFR levels in MCL tissues compared to lymphocytes, and the highest FGFR expressing cohort of patients showed a lower overall survival rated compared to those with low FGFR levels. Blockage of FGF/FGFR rendered MCL cells dead and also sensitized the cells to the killing effects of death receptor ligands. Conclusion We establish that primary MCL use an FGFR autocrine loop for propagation in cocultures with hMSCs. We defined the factors supporting MCL and MCL-ICs survival; such knowledge is essential for targeting MCL and MCL-ICs. Disclosures No relevant conflicts of interest to declare.

Myc Represses miR15a/Mir-16-1 Expression through Recruitment of HDAC3 In Mantle Cell Lymphoma

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3121-3121
Author(s):  
Xinwei Zhang ◽  
Xia Chen ◽  
Jianhong Lin ◽  
Tint Lwin ◽  
Scott A Ely ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Mantle Cell Lymphoma ◽  
Transcriptional Repression ◽  
Conflicts Of Interest ◽  
Cell Lymphoma ◽  
Luciferase Reporter ◽  
Over Expression ◽  
Mantle Cell ◽  
Mutagenesis Study ◽  
Cluster Gene

Abstract Abstract 3121 MicroRNAs (miR)-15a and miR-16-1 are known to act as tumor suppressors. Expression of these miRNAs inhibits cell proliferation, promotes apoptosis of cancer cells, and suppresses tumorigenicity by targeting multiple oncogenes. Loss or down-regulation of these miRNAs has been reported in a variety of hematopoietic and solid tumors. Our recent study demonstrated that miR-15a/16-1 are down-regulated in the majority of patients with mantle cell lymphoma (MCL, Zhao et al., Blood. 2010 1;115(13):2630-9). However, the mechanism responsible for miR-15a/16 suppression was unknown. Here, we have investigated mechanism of miR-15a/16-1 repression and its transcriptional and epigenetic regulation by Myc and histone deacetylase (HDAC) in MCL. Over-expression of Myc protein was detected in all MCL cell lines, and miR-15a/16 and DLEU-2 mRNA were significantly up-regulated in Mino and Jeko-1 cells when Myc was depleted by c-Myc siRNA. Treatment with pan HDAC inhibitor, SAHA and specific HDAC-3 shRNA resulted in increase of miR15a/16 expression. Co-immunoprecipitation study showed that c-Myc interacted with HDAC3. Moreover, chromatin immunoprecipitation (ChIP)demonstrated that both Myc and HDAC3 co-localized to the two promoters of miR-15a/16 cluster gene, DLEU-2. Luciferase reporter assay confirmed that both c-Myc and HDAC3 inhibited transcriptional activity of two E-box (Myc-binding)-specific DLEU-2 promoters. Computational analysis and mutagenesis study further supported direct association of Myc with miR-15a/16 promoter resulting in HDAC3-mediated transcriptional repression. These findings highlight an important role for HDAC-3 in Myc-driven lymphoma cell proliferation and reveal novel transcriptional and posttranscriptional mechanisms in Myc-mediated malignant transformation in MCL. Disclosures: No relevant conflicts of interest to declare.

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