ZEB1 Is Regulated by K811 Acetylation to Promote Stability, NuRD Complex Interactions, EMT, and NSCLC Metastasis

Epithelial-to-mesenchymal transition results in loss of specialized epithelial cell contacts and acquisition of mesenchymal invasive capacity. The transcription repressor zinc finger E-box-binding homeobox 1 (ZEB1) binds to E-boxes of gene promoter regions to suppress the expression of epithelial genes. ZEB1 has inconsistent molecular weights, which have been attributed to posttranslational modifications (PTM). We performed mass spectrometry and identified K811 acetylation as a novel PTM in ZEB1. To define the role of ZEB1 acetylation in regulating function, we generated ZEB1 acetyl-mimetic (K811Q) and acetyl-deficient (K811R) mutant-expressing non-small cell lung cancer cell lines (NSCLC). We demonstrate that the K811R ZEB1 (125 kDa) has a shorter protein half-life than wild-type (WT) ZEB1 and K811Q ZEB1 (∼225 kDa), suggesting that lack of ZEB1 acetylation in the lower molecular weight form affects protein stability. Further, the acetylated form of ZEB1 recruits the nucleosome remodeling and deacetylase (NuRD) complex to bind the promoter of its target genes mir200c-141 and SEMA3F. RNA-sequencing revealed that WT ZEB1 and K811Q ZEB1 downregulate the expression of epithelial genes to promote lung adenocarcinoma invasion and metastasis, whereas the K811R ZEB1 does not. Our findings establish that the K811 acetylation promotes ZEB1 protein stability, interaction with other protein complexes, and subsequent invasion/metastasis of lung adenocarcinoma via epithelial-to-mesenchymal transition.

IMPLICATIONS

The molecular mechanisms by which ZEB1 is regulated by K811 acetylation to promote protein stability, NuRD complex and promoter interactions, and function are relevant to the development of treatment strategies to prevent and treat metastasis in patients with NSCLC.

Abstract 676: ZEB1 acetylation regulates dimerization and protein stability to promote lung adenocarcinoma progression and metastasis

Lung cancer is the leading cause of cancer-related death worldwide due to the ability of cancer cells to metastasize. Therefore, it is essential to expand our current knowledge of the biological processes that contribute to metastasis to guide the discovery of novel therapeutic modalities. The Epithelial-to-mesenchymal transition (EMT) is a mechanism for metastasis, which changes polarized epithelial cells into invasive mesenchymal cells. High expression of the Zinc finger E-box binding homeobox 1 (ZEB1) transcription factor is correlated to poor outcomes in cancer, including therapeutic resistance and EMT-mediated metastasis. ZEB1 has a predicted molecular weight of 125kDa; however, multiple groups have reported discrepancies in the observed molecular weight (approximately 190-250kDa). This has been attributed to dimerization mediated by post-translational modifications (PTMs). Therefore, we performed mass spectrometry and identified a novel PTM - K811 acetylation - that may regulate ZEB1 dimerization and function. To define the role of ZEB1 acetylation, we generated ZEB1 acetyl mimetic (K811Q) and deficient (K811R) mutants in a panel of lung adenocarcinoma cell lines. We hypothesize that ZEB1 acetylation regulates dimerization and protein stability to promote lung adenocarcinoma progression and metastasis. We determined that the acetyl-deficient mutant (125kDa) exhibits a decreased half-life compared to WT and acetylated ZEB1, suggesting that disruption of acetylation hinders dimerization and protein stability. However, the acetyl-mimetic mutant (250kDa) protects ZEB1 from proteasomal degradation brought by the action of the E3 ubiquitin ligase SIAH1. siRNA-mediated silencing of SIAH1 increased the mRNA and protein levels of ZEB1 WT and both acetylation mutants. Importantly, silencing of SIAH1 markedly increased the half-life of 250kDa ZEB1 WT from 18.0hrs to 25.4hrs and acetyl-mimetic from 12.3hrs to 24.0hrs, as well as 125kDa ZEB1 acetyl-deficient from 9.7hrs to 18.3hrs. Although we determined that 250kDa ZEB1 is significantly more stable than 125kDa ZEB1, the increase in the stability by silencing SIAH1 contributes to ZEB1 acetyl-deficient binding at the promoter of its target genes mir200c-141 and SEMA3F. 250kDa ZEB1 WT and acetyl-mimetic recruits the histone deacetylases (HDACs) containing the nucleosome remodeling and deacetylase (NuRD) complex, to promote lung adenocarcinoma invasion and metastasis compared to ZEB1 acetyl-deficient. We further established that the stability of ZEB1 is integral to promoting these mesenchymal features. Our results suggest that ZEB1_K811ac regulates its dimerization and stability to promote lung adenocarcinoma via EMT. Future studies are focused on understanding the role of ZEB1 protein stability to recruit NuRD co-repressor and subsequently mediate tumorigenesis and metastasis.

Citation Format: Mabel G. Perez-Oquendo, Roxsan Manshouri, Don Gibbons. ZEB1 acetylation regulates dimerization and protein stability to promote lung adenocarcinoma progression and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 676.

Abstract LBA023: Regulation and function of ZEB1 dimerization in lung adenocarcinoma progression and metastasis

Lung cancer is the leading cause of cancer-related death worldwide due to the ability of cancer cells to metastasize. Therefore, it is essential to expand our current knowledge of the biological processes that contribute to metastasis to guide the discovery of novel therapeutic modalities. The Epithelial-to-mesenchymal transition (EMT) is a mechanism for metastasis, which changes polarized epithelial cells into invasive mesenchymal cells. High expression of the Zinc finger E-box binding homeobox 1 (ZEB1) transcription factor is correlated to poor outcomes in cancer, including therapeutic resistance and EMT-mediated metastasis. ZEB1 has a predicted molecular weight of 125kDa; however, multiple groups have reported discrepancies in the observed molecular weight (approximately 190-250kDa). This has been attributed to dimerization mediated by post-translational modifications (PTMs). Therefore, we performed mass spectrometry and identified a novel PTM - K811 acetylation - that may regulate ZEB1 dimerization and function. To define the role of ZEB1 acetylation, we generated ZEB1 acetyl mimetic (K811Q) and deficient (K811R) mutants in the 393P lung adenocarcinoma cell line. We hypothesize that ZEB1 acetylation regulates dimerization and protein stability to promote lung adenocarcinoma progression and metastasis. We determined that the acetyl-deficient mutant (125kDa) exhibits a decreased half-life compared to WT and acetylated ZEB1, suggesting that disruption of acetylation hinders dimerization and protein stability. However, the acetyl-mimetic mutant (250kDa) protects ZEB1 from proteasomal degradation brought by the action of the E3 ubiquitin ligase SIAH1. siRNA-mediated silencing of SIAH1 increased the mRNA and protein levels of ZEB1 WT and both acetylation mutants. Importantly, silencing of SIAH1 markedly increased the half-life of 250kDa ZEB1 WT from 28.03hrs to 44.37hrs and acetyl-mimetic from 19.43hrs to 41.25hrs, as well as 125kDa ZEB1 acetyl-deficient from 9.38hrs to 12.70hrs. Although, we determined that 250kDa ZEB1 is significantly more stable than 125kDa ZEB1, the increase in the stability by silencing SIAH1 contributes to ZEB1 acetyl-deficient binding at the promoter of its target genes mir200c-141 and SEMA3F by Chromatin Immunoprecipitation. 250kDa ZEB1 WT and acetyl-mimetic promotes lung adenocarcinoma invasion and metastasis compared to ZEB1 acetyl-deficient. We further established that the stability of ZEB1 is integral to promoting these mesenchymal features. Our results suggest that PTMs (acetylation and ubiquitination) regulate ZEB1 to promote its stability and progression of lung adenocarcinoma via EMT. Future studies are focused on further understanding the role of ZEB1 dimerization to recruit co-repressors and subsequently mediate tumorigenesis, invasion and metastasis

Citation Format: Mabel Perez-Oquendo, Roxsan Manshouri, Don L. Gibbons. Regulation and function of ZEB1 dimerization in lung adenocarcinoma progression and metastasis [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA023.

ZEB1/NuRD complex suppresses TBC1D2b to stimulate E-cadherin internalization and promote metastasis in lung cancer

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide, due in part to the propensity of lung cancer to metastasize. Aberrant epithelial-to-mesenchymal transition (EMT) is a proposed model for the initiation of metastasis. During EMT cell-cell adhesion is reduced allowing cells to dissociate and invade. Of the EMT-associated transcription factors, ZEB1 uniquely promotes NSCLC disease progression. Here we apply two independent screens, BioID and an Epigenome shRNA dropout screen, to define ZEB1 interactors that are critical to metastatic NSCLC. We identify the NuRD complex as a ZEB1 co-repressor and the Rab22 GTPase-activating protein TBC1D2b as a ZEB1/NuRD complex target. We find that TBC1D2b suppresses E-cadherin internalization, thus hindering cancer cell invasion and metastasis.

Non-small cell lung cancer (NSCLC) is often associated with metastasis to the lungs. Here, the authors perform independent screens and identify NuRD as a co-repressor of ZEB1, and demonstrate TBC1D2b as a downstream target of ZEB1/NuRD complex regulating NSCLC metastasis.

The ALK inhibitor ASP3026 eradicates NPM-ALK⁺ T-cell anaplastic large-cell lymphoma in vitro and in a systemic xenograft lymphoma model

NPM-ALK⁺ T-cell anaplastic large-cell lymphoma (ALCL) is an aggressive type of cancer. Standard treatment of NPM-ALK⁺ ALCL is CHOP polychemotherapy. Although patients initially respond favorably to CHOP, resistance, relapse, and death frequently occur. Recently, selective targeting of ALK has emerged as an alternative therapeutic strategy. ASP3026 is a second-generation ALK inhibitor that can overcome crizotinib resistance in non-small cell lung cancer, and is currently being evaluated in clinical trials of patients with ALK⁺ solid tumors. However, NPM-ALK⁺ ALCL patients are not included in these trials. We studied the effects of ASP3026 on NPM-ALK⁺ ALCL cell lines in vitro and on systemic lymphoma growth in vivo. ASP3026 decreased the viability, proliferation, and colony formation, as well as induced apoptotic cell death of NPM-ALK⁺ ALCL cells. In addition, ASP3026 significantly reduced the proliferation of 293T cells transfected with NPM-ALK mutants that are resistant to crizotinib and downregulated tyrosine phosphorylation of these mutants. Moreover, ASP3026 abrogated systemic NPM-ALK⁺ ALCL growth in mice. Importantly, the survival of ASP3026-treated mice was superior to that of control and CHOP-treated mice. Our data suggest that ASP3026 is an effective treatment for NPM-ALK⁺ ALCL, and support the enrollment of patients with this lymphoma in the ongoing clinical trials.

Abstract A80: In vitro and in vivo antitumor activity of the selective ALK inhibitor ASP3026 against NPM-ALK+ T-cell anaplastic large-cell lymphoma

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase with structural similarities to the insulin receptor. ALK is physiologically expressed in neuronal cells at early stages of human development. Thereafter, ALK expression is largely limited to malignant neoplasms including T-cell anaplastic large-cell lymphoma (ALCL), non-small cell lung cancer (NSCLC), and neuroblastoma. It has been previously established that ALK, in the form of chimeric proteins or constitutively activated mutants, plays a central role in the survival of these tumors. Hence, targeting ALK is considered a legitimate and likely successful strategy to eradicate these tumors. Nucleophosmin-ALK-expressing (NPM-ALK+) T-cell ALCL is an aggressive type of cancer. It is one of the most common hematological neoplasms in children as it comprises 40% of the non-Hodgkin lymphomas in this age group. Recently, a selective ALK inhibitor, ASP3026, was developed utilizing an ALK kinase inhibition assay aimed at the chimeric tyrosine kinase echinoderm-microtubule-associated protein-like 4-ALK (EML4-ALK), which is expressed in a subgroup of NSCLC tumors.1 Initial studies showed that not only ASP3026 possesses remarkable inhibitory effects on EML4-ALK but also it overcomes the resistance of EML4-ALK+ NSCLC to crizotinib; a prototype ALK and c-MET inhibitor. ASP3026 is currently being tested in phase I clinical trials that include EML4-ALK+ NSCLC patients. Of important note is that the effects and therapeutic potential of ASP3026 in NPM-ALK+ T-cell ALCL are not known. We systematically analyzed the effects of ASP3026 (ChemieTek, Indianapolis, IN) in NPM-ALK+ T-cell ALCL using in vitro and in vivo experimental approaches. ASP3026 (0.1 to 3.0 µM; 24 and 72 h) induced a concentration- and time-dependent decrease in the viability and proliferation of NPM-ALK+ T-cell ALCL cell lines including Karpas 299, SU-DHL-1, SUP-M2, SR-786, and DEL. In contrast, these negative effects were not observed in normal human T lymphocytes. Furthermore, ASP3026 reduced anchorage-independent colony formation of NPM-ALK+ T-cell ALCL cells. The effects of ASP3026 could be explained, at least in part, by successful induction of apoptotic cell death in these cells. At the biochemical level, ASP3026 decreased significantly the levels of pNPM-ALK and the activated/phosphorylated form of its interacting oncogenic protein type I insulin-like growth factor receptor (pIGF-IR). We are performing additional experiments to further characterize the biochemical effects of ASP3026 in NPM-ALK+ T-cell ALCL cells. To further evaluate the therapeutic potential of ASP3026, we utilized an in vivo systemic lymphoma model developed in our laboratory. Briefly, Karpas 299 cells (1 × 106 cells per mouse), engineered to simultaneously express humanized firefly luciferase and GFP, were injected intravenously in CB-17 SCID mice (Taconic; female; 6-8 weeks old). Systemic lymphoma tumors, detected by using IVIS whole body imaging system after intraperitoneal injection of D-lucifern, were established at approximately 3 weeks after lymphoma cell injections.Thereafter, vehicle or ASP3026 (30 mg/kg/day) was administered daily to the mice (10 mice per group) through oral gavage. Also, standard CHOP combination chemotherapy was used in another group. Treatment with ASP3026 for only 2 weeks was associated with complete lymphoma eradication, which persisted with the daily administration of ASP3026 and until study termination at 6-8 weeks from treatment initiation. In contrast, cessation of ASP3026 after 2 weeks of treatment was associated with lymphoma relapse. Although CHOP initially eradicated the lymphoma, most of the CHOP-treated mice developed significant toxicity and relapsed at 4 weeks after treatment. Importantly, vehicle- and CHOP-treated mice had inferior overall survival compared with mice treated with ASP3026. Taken together, our results provide strong evidence that ASP3026 could represent a novel approach to efficiently treat NPM-ALK+ T-cell ALCL.

1Kuromitsu S, et al. Mol. Cancer Ther. 2011;10[Supp. 1]: A227

DV and SKG equally contributed to this work

Citation Format: Deeksha Vishwamitra, Suraj Konnath George, Roxsan Manshouri, Ping Shi, Hesham M. Amin. In vitro and in vivo antitumor activity of the selective ALK inhibitor ASP3026 against NPM-ALK+ T-cell anaplastic large-cell lymphoma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A80.

Abstract 960: Targeting Egr-1 is an effective strategy for overcoming kinase inhibitor resistance in CML

The primary oncogene associated with CML is BCR/ABL which controls proliferative and survival signaling and is a potent inducer of reactive oxygen species (ROS). ROS play both positive and negative roles in proliferation and survival; this dual nature has been exploited by leukemia cells to promote growth, genomic instability, and drug resistance. However, the distinct molecular alterations that occur as a result of BCR/ABL-induced ROS are not well described. BCR/ABL-targeted therapeutics have improved clinical response rates, therefore the number of CML patients living with detectable disease burden is rising. Complete hematologic responses to tyrosine kinase inhibitor (TKI) therapy are seen in ∼10-30% of CML patients, so acquired drug resistance and relapse remain major issues. Thus, novel targets for combined therapeutics are needed. We have shown that early growth response 1 (Egr-1) is a BCR/ABL-dependent, redox-responsive transcription factor that modulates expression of the non-receptor tyrosine kinase Fyn in CML leading to proliferation and survival. Tissue microarray analysis of 26 CML patients (10 chronic phase, 6 accelerated phase, and 10 blast crisis), corroborated by western blotting on independent patient samples, showed that Egr-1 protein expression increased as CML progresses from chronic phase to the more treatment resistant accelerated phase and blast crisis. Egr-1 protein expression was also elevated 2.5 fold in a model of acquired pan-TKI resistance (K562-STI) when compared with parental K562 cells. When Egr-1 was genetically inhibited, proliferation of K562-STI cells decreased by 56%. Egr-1 knockdown was also sufficient to sensitize K562-STI cells to growth inhibition caused by first and second generation BCR/ABL-directed TKI, further implicating Egr-1 in acquired TKI resistance. Egr-1 is well known as a redox-responsive transcription factor, and we found that ROS were elevated in K562-STI vs. K562 cells. While analysis of mitochondrial respiration using a Seahorse Bioanalyzer showed no increase in mitochondrial respiration, spare respiratory capacity, nor proton leak in K562-STI vs. K562, there remained a basal level of oxygen consumption from non-mitochondrial sources in both cell lines. Interestingly, fluorigenic and western blotting assays showed increases in NADPH oxidase (NOX) activity (1.35 fold) and p47phox (2 fold), an essential component of the NOX complex, respectively in K562-STI cells, suggesting NOX as a source of ROS in these cells. To this end, inhibition of the NOX complex with diphenyleneiodonium decreased ROS levels and Egr-1 expression by 50% in K562-STI but not K562 cells. These data suggest that K562-STI have altered regulation of Egr-1 controlled, in part, by NOX. Together, our findings suggest that targeting the transcription factor Egr-1 directly, or through the NOX complex, may be beneficial for improving outcomes for CML patients.

Citation Format: Mary E. Irwin, Roxsan Manshouri, Blake Johnson, Hesham M. Amin, Joya Chandra. Targeting Egr-1 is an effective strategy for overcoming kinase inhibitor resistance in CML. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 960. doi:10.1158/1538-7445.AM2014-960

NPM-ALK up-regulates iNOS expression through a STAT3/microRNA-26a-dependent mechanism

NPM-ALK chimeric oncogene is aberrantly expressed in an aggressive subset of T-cell lymphomas that frequently occurs in children and young adults. The mechanisms underlying the oncogenic effects of NPM-ALK are not completely elucidated. Inducible nitric oxide synthase (iNOS) promotes the survival and maintains the malignant phenotype of cancer cells by generating NO, a highly active free radical. We tested the hypothesis that iNOS is deregulated in NPM-ALK(+) T-cell lymphoma and promotes the survival of this lymphoma. In line with this possibility, an iNOS inhibitor and NO scavenger decreased the viability, adhesion, and migration of NPM-ALK(+) T-cell lymphoma cells, and an NO donor reversed these effects. Moreover, the NO donor salvaged the viability of lymphoma cells treated with ALK inhibitors. In further support of an important role of iNOS, we found iNOS protein to be highly expressed in NPM-ALK(+) T-cell lymphoma cell lines and in 79% of primary tumours but not in human T lymphocytes. Although expression of iNOS mRNA was identified in NPM-ALK(+) T-cell lymphoma cell lines and tumours, iNOS mRNA was remarkably elevated in T lymphocytes, suggesting post-transcriptional regulation. Consistently, we found that miR-26a contains potential binding sites and interacts with the 3'-UTR of iNOS. In addition, miR-26a was significantly decreased in NPM-ALK(+) T-cell lymphoma cell lines and tumours compared with T lymphocytes and reactive lymph nodes. Restoration of miR-26a in lymphoma cells abrogated iNOS protein expression and decreased NO production and cell viability, adhesion, and migration. Importantly, the effects of miR-26a were substantially attenuated when the NO donor was simultaneously used to treat lymphoma cells. Our investigation of the mechanisms underlying the decrease in miR-26a in this lymphoma revealed novel evidence that STAT3, a major downstream substrate of NPM-ALK tyrosine kinase activity, suppresses MIR26A1 gene expression.

MicroRNA 96 is a post-transcriptional suppressor of anaplastic lymphoma kinase expression

Anaplastic lymphoma kinase (ALK) constitutes a part of the oncogenic fusion proteins nucleophosmin-ALK and echinoderm microtubule-associated protein like 4-ALK, which are aberrantly expressed in a subset of T-cell anaplastic large-cell lymphoma and non-small-cell lung cancer, respectively. The expression of mutated, constitutively active ALK also occurs in a subset of neuroblastoma tumors. ALK is believed to play an important role in promoting tumor survival. Nevertheless, the mechanisms underlying the expression of ALK in cancer cells are not completely known. MicroRNA (miR) has been implicated in the regulation of the expression of both oncogenes and tumor suppressor genes. We tested the hypothesis that the expression of ALK could be regulated by miR. Three Internet-based algorithms identified miR-96 to potentially bind with the ALK 3'-untranslated region. Notably, miR-96 levels were markedly decreased in ALK-expressing cancer cell lines and primary human tumors compared with their normal cellular and tissue counterparts. Transfection of the cell lines with miR-96 decreased levels of the different forms of ALK protein, without significant effects on ALK mRNA. Furthermore, miR-96 decreased the phosphorylation of ALK target proteins, including Akt, STAT3, JNK, and type I insulin-like growth factor receptor, and it down-regulated JunB. These effects were associated with reduced proliferation, colony formation, and migration of ALK-expressing cancer cells. These data provide novel evidence that decreases in miR-96 could represent a mechanism underlying the aberrant expression of ALK in cancer cells.

Expression and effects of inhibition of type I insulin-like growth factor receptor tyrosine kinase in mantle cell lymphoma

BACKGROUND

Type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase induces significant oncogenic effects. Strategies to block IGF-IR signaling are being tested in clinical trials that include patients with aggressive solid malignancies. Mantle cell lymphoma is a B-cell neoplasm with poor prognosis and a tendency to develop resistance. The expression and potential significance of IGF-IR in mantle cell lymphoma are not known.

DESIGN AND METHODS

We used reverse transcriptase polymerase chain reaction, quantitative real-time polymerase chain reaction, immunoprecipitation, western blotting, flow cytometry, and immunohistochemistry to analyze the expression of IGF-IR mRNA, and IGF-IR and pIGF-IR proteins in mantle cell lymphoma cell lines and patients' specimens. Selective and specific blockade of IGF-IR was achieved using picropodophyllin and short-interfering RNA, respectively. Cell viability, apoptosis, cell cycle, cellular morphology, cell proliferation, and target proteins were then analyzed.

RESULTS

We detected the expression of IGF-IR and pIGF-IR in mantle cell lymphoma cell lines. Notably, IGF-IR molecules/cell were markedly increased in mantle cell lymphoma cell lines compared with human B-lymphocytes. IGF-IR and pIGF-IR were also detected in 78% and 74%, respectively, of 23 primary mantle cell lymphoma specimens. Treatment of serum-deprived mantle cell lymphoma cell lines with IGF-I salvaged these cells from apoptosis. Selective inhibition of IGF-IR by picropodophyllin decreased the viability and proliferation of mantle cell lymphoma cell lines, and induced apoptosis and cell cycle arrest. Selective inhibition of IGF-IR was associated with caspase-3, caspase-8, caspase-9, and PARP cleavage, cytochrome c release, up-regulation of cyclin B1, and down-regulation of cyclin D1, pCdc2, pIRS-1, pAkt, and pJnk. Similar results were obtained by using IGF-IR short-interfering RNA. In addition, picropodophyllin decreased the viability and proliferation of primary mantle cell lymphoma cells that expressed IGF-IR.

CONCLUSIONS

IGF-IR is up-regulated and frequently activated in mantle cell lymphoma. Our data suggest that IGF-IR could be a molecular target for the treatment of mantle cell lymphoma.