TCL1 Overexpression Research Articles

In Vitro and In Vivo Models of CLL-T Cell Interactions: Implications for Drug Testing.

Simple SummaryChronic lymphocytic leukemia (CLL) cells in the peripheral blood and lymphoid microenvironment display substantially different gene expression profiles and proliferative capaci-ty. It has been suggested that CLL–T-cell interactions are key pro-proliferative stimuli in immune niches. We review in vitro and in vivo model systems that mimic CLL-T-cell interactions to trigger CLL proliferation and study therapy resistance. We focus on studies describing the co-culture of leukemic cells with T cells, or supportive cell lines expressing T-cell factors, and simplified models of CLL cells’ stimulation with recombinant factors. In the second part, we summarize mouse models revealing the role of T cells in CLL biology and implications for generating patient-derived xenografts by co-transplanting leukemic cells with T cells.T cells are key components in environments that support chronic lymphocytic leukemia (CLL), activating CLL-cell proliferation and survival. Here, we review in vitro and in vivo model systems that mimic CLL–T-cell interactions, since these are critical for CLL-cell division and resistance to some types of therapy (such as DNA-damaging drugs or BH3-mimetic venetoclax). We discuss approaches for direct CLL-cell co-culture with autologous T cells, models utilizing supportive cell lines engineered to express T-cell factors (such as CD40L) or stimulating CLL cells with combinations of recombinant factors (CD40L, interleukins IL4 or IL21, INFγ) and additional B-cell receptor (BCR) activation with anti-IgM antibody. We also summarize strategies for CLL co-transplantation with autologous T cells into immunodeficient mice (NOD/SCID, NSG, NOG) to generate patient-derived xenografts (PDX) and the role of T cells in transgenic CLL mouse models based on TCL1 overexpression (Eµ-TCL1). We further discuss how these in vitro and in vivo models could be used to test drugs to uncover the effects of targeted therapies (such as inhibitors of BTK, PI3K, SYK, AKT, MEK, CDKs, BCL2, and proteasome) or chemotherapy (fludarabine and bendamustine) on CLL–T-cell interactions and CLL proliferation.

Longitudinal analyses of CLL in mice identify leukemia-related clonal changes including a Myc gain predicting poor outcome in patients

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy mainly occurring at an advanced age with no single major genetic driver. Transgenic expression of TCL1 in B cells leads after a long latency to a CLL-like disease in aged Eµ-TCL1 mice suggesting that TCL1 overexpression is not sufficient for full leukemic transformation. In search for secondary genetic events and to elucidate the clonal evolution of CLL, we performed whole exome and B-cell receptor sequencing of longitudinal leukemia samples of Eµ-TCL1 mice. We observed a B-cell receptor stereotypy, as described in patients, confirming that CLL is an antigen-driven disease. Deep sequencing showed that leukemia in Eµ-TCL1 mice is mostly monoclonal. Rare oligoclonality was associated with inability of tumors to develop disease upon adoptive transfer in mice. In addition, we identified clonal changes and a sequential acquisition of mutations with known relevance in CLL, which highlights the genetic similarities and therefore, suitability of the Eµ-TCL1 mouse model for progressive CLL. Among them, a recurrent gain of chromosome 15, where Myc is located, was identified in almost all tumors in Eµ-TCL1 mice. Interestingly, amplification of 8q24, the chromosomal region containing MYC in humans, was associated with worse outcome of patients with CLL.

Actionable perturbations of damage responses by TCL1/ATM and epigenetic lesions form the basis of T-PLL

T-cell prolymphocytic leukemia (T-PLL) is a rare and poor-prognostic mature T-cell malignancy. Here we integrated large-scale profiling data of alterations in gene expression, allelic copy number (CN), and nucleotide sequences in 111 well-characterized patients. Besides prominent signatures of T-cell activation and prevalent clonal variants, we also identify novel hot-spots for CN variability, fusion molecules, alternative transcripts, and progression-associated dynamics. The overall lesional spectrum of T-PLL is mainly annotated to axes of DNA damage responses, T-cell receptor/cytokine signaling, and histone modulation. We formulate a multi-dimensional model of T-PLL pathogenesis centered around a unique combination of TCL1 overexpression with damaging ATM aberrations as initiating core lesions. The effects imposed by TCL1 cooperate with compromised ATM toward a leukemogenic phenotype of impaired DNA damage processing. Dysfunctional ATM appears inefficient in alleviating elevated redox burdens and telomere attrition and in evoking a p53-dependent apoptotic response to genotoxic insults. As non-genotoxic strategies, synergistic combinations of p53 reactivators and deacetylase inhibitors reinstate such cell death execution.

Comparison of karyotyping, TCL1 fluorescence in situ hybridisation and TCL1 immunohistochemistry in T cell prolymphocytic leukaemia

AimsT cell prolymphocytic leukaemia (T-PLL) is defined as an aggressive T cell leukaemia composed of small to medium-sized lymphocytes with a mature T cell immunophenotype. Most of these cases are...

Characteristics, Outcomes and Treatment of Patients with T-Cell Prolymphocytic Leukemia (T-PLL) - Single-Center Experience

Background: T-cell prolymphocytic leukemia (T-PLL) is a rare and aggressive mature T-cell lymphoid leukemia. T-PLL is diagnosed based on characteristic immunophenotype, cytogenetic, and molecular aberrations (including members of the JAK-STAT signaling pathway) which may explain its aggressive clinical course. Cytogenetic features include chromosome (chr) 14 aberrations, accompanied by gene rearrangement involving proto-oncogenes TCL1 or MTCP1. In this analysis, we report our single-institution experience with T-PLL over the last 25 years.Methods: We reviewed the clinico-pathologic records of 101 consecutive patients (pts) with T-PLL, who presented to our institution between 1990 and 2015. The survival (OS) of pts was calculated from the date of initial presentation to the date of last follow up. Kaplan-Meier product limit method was used to estimate the median OS.Results: Median age of pts was 64 years (range 35-87 years). Eighteen pts (18%) presented with a performance status of 2 or higher. Lymphadenopathy, splenomegaly, skin lesions, hepatomegaly and pleural effusion were seen in 58%, 37%, 30%, 8%, and 7% of pts, respectively. Complex karyotype and aberrations in chr 14 were seen in 54 (63%) and 42 (49%) pts, respectively. TCL1 expression by immunohistochemistry was performed in 29 pts. The overexpression of TCL1 was detected in 23/29 pts (79%). Among untreated pts, 18/47 (38%) had a chr abnormality involving TCL-1. At initial presentation to our center, 59 pts (58%) were untreated and 42 pts (42%) had relapsed/refractory disease with a median of 2 prior treatments (range 1-6). Seventy-one pts (70%) were treated at our institution. Median overall OS from diagnosis in all pts was 21.7 mos (Range 1.5-107.7 mos). Median OS was longer in untreated pts than in pts with relapsed/refractory disease (27 mos vs. 17 mos; P=0.08). In a multivariate analysis for assessing the prognostic factors for OS in 43 untreated pts in whom all variables were available, we found that the presence of a pleural effusion HR (95% CI) 5.21 (1-27; P <0.04), high absolute lymphocyte count 1.009 (1.002-1.016; P = 0.006) and complex karyotype 4.6 (1.2-16.9; P = 0.02) predicted for increased risk of death. Fifty four evaluable pts (32 untreated and 22 with relapsed disease) received treatment with alemtuzumab based regimen, 36 as monotherapy and 18 in combination with pentostatin. Seventeen evaluable pts (1 untreated and 16 with relapsed disease) were treated with nelarabine. Overall response rate (ORR), complete remission rate (CR), median OS and progression free survival (PFS) are summarized in Table-1. Among 39 previously untreated pts who received treatment at our institution, the distribution of treatment regimen was alemtuzumab-based (n=32), nelarabine (n=1), other nucleoside analogues (n=5) and combination chemotherapy (n=1). Twenty two pts (56%) achieved complete remission (CR) after frontline treatment. Ten pts underwent allogeneic stem cell transplantation (SCT) after achieving a remission after initial treatment with alemtuzumab either as a monotherapy or in combination with pentostatin. We did not observe any significant difference in OS (Figure-1A) or PFS among pts who did/did not undergo stem cell transplantation after achieving an initial remission with the frontline therapies. Furthermore, we observed that there was no significant difference in OS among pts with or without a chr abnormality involving TCL-1 after frontline therapy (Figure-1B).Conclusions: In this retrospective analysis, we have observed that outcomes in T-PLL remain poor. We have shown that alemtuzumab has some therapeutic activity in pts with T-PLL but durable remissions are uncommon. Rarity of this disease limits the conduct of large scale clinical trials; hence multicenter collaborative effort is required to conduct prospective studies. In pts who achieve a CR, consolidation treatment with SCT did not improve survival in our series. Studies to further define the genomic imbalances in pts with T-PLL and identify potential therapeutic targets and pathways providing drug resistance in T-PLL are underway. [Display omitted] [Display omitted] DisclosuresO'Brien:Pharmacyclics, LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria. Wierda:Acerta: Research Funding; Novartis: Research Funding; Gilead: Research Funding; Abbvie: Research Funding; Genentech: Research Funding. Jain:Novartis: Consultancy, Honoraria; Pharmacyclics: Consultancy, Honoraria, Research Funding; Novimmune: Consultancy, Honoraria; Abbvie: Research Funding; Servier: Consultancy, Honoraria; Seattle Genetics: Research Funding; Genentech: Research Funding; Celgene: Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; ADC Therapeutics: Consultancy, Honoraria, Research Funding; Infinity: Research Funding; Incyte: Research Funding; BMS: Research Funding. Thompson:Pharmacyclics: Consultancy, Honoraria. Kantarjian:BMS, Pfizer, Amgen, Novartis: Research Funding.

Oocyte Factors Suppress Mitochondrial Polynucleotide Phosphorylase to Remodel the Metabolome and Enhance Reprogramming.

Oocyte factors not only drive somatic cell nuclear transfer reprogramming but also augment the efficiency and quality of induced pluripotent stem cell (iPSC) reprogramming. Here, we show that the oocyte-enriched factors Tcl1 and Tcl1b1 significantly enhance reprogramming efficiency. Clonal analysis of pluripotency biomarkers further show that the Tcl1 oocyte factors improve the quality of reprogramming. Mechanistically, we find that the enhancement effect of Tcl1b1 depends on Akt, one of its putative targets. In contrast, Tcl1 suppresses the mitochondrial polynucleotide phosphorylase (PnPase) to promote reprogramming. Knockdown of PnPase rescues the inhibitory effect from Tcl1 knockdown during reprogramming, whereas PnPase overexpression abrogates the enhancement from Tcl1 overexpression. We further demonstrate that Tcl1 suppresses PnPase's mitochondrial localization to inhibit mitochondrial biogenesis and oxidation phosphorylation, thus remodeling the metabolome. Hence, we identified the Tcl1-PnPase pathway as a critical mitochondrial switch during reprogramming.

Novel role of B cell receptor signaling in regulation of Tcl1, an oncogene, and Par-4, a tumor suppressor gene, in B cell chronic lymphocytic leukemia (IRM10P.619)

Abstract B cell malignancies such as non-Hodgkin’s Lymphoma have a probability of affecting 1 in 43 people in the United States, contributing to 7% of all cancer related deaths. The most aggressive forms of non-Hodgkin’s Lymphomas, which include Chronic Lymphocytic Leukemia (CLL), express elevated levels of T cell leukemia 1 (Tcl1), an oncogene that promotes cell survival. CLL is characterized by clonally expanded population of CD5+CD19+ B lymphocytes with impaired apoptotic mechanisms. The Eµ-Tcl1 mouse, serves as an excellent model for the development of CLL due to Tcl1 overexpression in B cells through the Ig VH promoter and Eµ enhancer. In these CLL cells the B-cell receptor (BCR) signaling pathway is activated as shown by constitutive tyrosine phosphorylation of the Src Family Kinases (SFK) and total expression of Lyn, compared to normal B cells. Treatment of B-CLL cells with dasatinib, an SFK inhibitor, results in decreased proliferation and cell death, a decrease in Tcl1, and surprisingly, a decrease in prostate apoptosis response-4 (Par-4), a pro-apoptotic protein. Knockdown of Lyn with shRNA in B-lymphoma cells, also reduced Par-4 suggesting a specific role of Lyn in Par-4 regulation. Par-4 was also downregulated after inhibition of other non-receptor tyrosine kinases such as Syk and Btk involved in BCR signaling. Presently, we are determining the importance of Par-4 in the growth of B-CLL and the mechanism of novel regulation of Par-4 and Tcl1 through BCR signaling.

Functional Analysis of Tcl1 Using Tcl1-Deficient Mouse Embryonic Stem Cells

Tcl1 is highly expressed in embryonic stem (ES) cells, but its expression rapidly decreases following differentiation. To assess Tcl1’s roles in ES cells, we generated Tcl1-deficient and -overexpressing mouse ES cell lines. We found that Tcl1 was neither essential nor sufficient for maintaining the undifferentiated state. Tcl1 is reported to activate Akt and to enhance cell proliferation. We found that Tcl1 expression levels correlated positively with the proliferation rate and negatively with the apoptosis of ES cells, but did not affect Akt phosphorylation. On the other hand, the phosphorylation level of β-catenin decreased in response to Tcl1 overexpression. We measured the β-catenin activity using the TOPflash reporter assay, and found that wild-type ES cells had low activity, which Tcl1 overexpression enhanced 1.8-fold. When the canonical Wnt signaling is activated by β-catenin stabilization, it reportedly helps maintain ES cells in the undifferentiated state. We then performed DNA microarray analyses between the Tcl1-deficient and -expressing ES cells. The results revealed that Tcl1 expression downregulated a distinct group of genes, including Ndp52, whose expression is very high in blastocysts but reduced in the primitive ectoderm. Based on these results, we discuss the possible roles of Tcl1 in ES cells.

Overexpression of TCL1 activates the endoplasmic reticulum stress response: a novel mechanism of leukemic progression in mice

AbstractChronic lymphocytic leukemia (CLL) represents 30% of adult leukemia. TCL1 is expressed in ∼ 90% of human CLL. Transgenic expression of TCL1 in murine B cells (Eμ-TCL1) results in mouse CLL. Here we show for the first time that the previously unexplored endoplasmic reticulum (ER) stress response is aberrantly activated in Eμ-TCL1 mouse and human CLL. This includes activation of the IRE-1/XBP-1 pathway and the transcriptionally up-regulated expression of Derlin-1, Derlin-2, BiP, GRP94, and PDI. TCL1 associates with the XBP-1 transcription factor, and causes the dysregulated expression of the transcription factors, Pax5, IRF4, and Blimp-1, and of the activation-induced cytidine deaminase. In addition, TCL1-overexpressing CLL cells manufacture a distinctly different BCR, as we detected increased expression of membrane-bound IgM and altered N-linked glycosylation of Igα and Igβ, which account for the hyperactive BCR in malignant CLL. To demonstrate that the ER stress-response pathway is a novel molecular target for the treatment of CLL, we blocked the IRE-1/XBP-1 pathway using a novel inhibitor, and observed apoptosis and significantly stalled growth of CLL cells in vitro and in mice. These studies reveal an important role of TCL1 in activating the ER stress response in support for malignant progression of CLL.

Abstract 4178: Tcl1 enhances keratinocytes’ survival/proliferation by promoting erk and jnk/sap phosphorylation at the expense of p38 and by controlling c-fos expression through miR-29b and miR-181a-1

Abstract The Tcl1 oncogene has been initially isolated for its involvement in chromosomal translocations of T-prolymphocytic leukemias and overexpression in B chronic lymphocytic leukemia by enhancing AKT nuclear translocation and allowing the Ser-473 transphosphorylation. Tcl1, also, acts as AP-1 transcriptional inhibitor, by interacting with c-fos and c-jun. More recent works have associated Tcl1 to proliferation and self-renewal ability of ES cells under the direct activation of OCT3/4, Zfx, KLF5 transcription factors, being Tcl1 expressed in preimplantation embryos where it allows the progression beyond the 4-cells stage. We have recently shown that the Tcl1 oncogene is expressed in epidermis and defines secondary hair germ (transient-amplifying, TA) cells differentiation at catagen-telogen (the degenerative-resting phase of the hair follicle (HF)) transition, allowing the proliferation of TA cells in anagen (regenerative phase of the HF), giving the slow-cycling stem cells, the ability to incorporate BrdU. In fact, Tcl1 mutant (Tcl1-/-) affects stem-cell marker CD34 expression and BrdU incorporation in the bulge and TA cells, resulting in skin defects in adults with the onset of alopecia followed by skin wounding. Phenomena that are almost completely rescued by K14-TCL1 transgenic expression, in vivo. Since Tcl1 has a role in maintenance of a normal skin homeostasis in mice, involving both hair growth and epidermis, we used the approach of the expression chip analysis to unravel the pathways that are affected by loss of function and overexpression of Tcl1 in epidermal keratinocytes, by using Tcl1-/- and K14-TCL1;Tcl1-/- mice models. Our findings show that Tcl1 function involves the MAPK pathway, since Tcl1-/- shows increasing in p38MAPK phosphorylation linked to terminal differentiation/senescence/apoptosis of keratinocytes, while K14-driven overexpression shows increasing of p-Erk and p-Sapk/p-Jnk phosphorylations, linked to proliferation/commitment of keratinocytes. These signals flow through the MAPK cascade lead to altered AP1 factor function. In particular, the phosphorylation of AP-1 subunit c-Jun and c-fos transcriptional regulation and cellular localization result also affected. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4178. doi:1538-7445.AM2012-4178

Tcl1 protein functions as an inhibitor of de novo DNA methylation in B-cell chronic lymphocytic leukemia (CLL).

B-cell chronic lymphocytic leukemia (CLL) is the most common human leukemia. Deregulation of the T-cell leukemia/lymphoma 1 oncogene (TCL1) in mouse B cells causes a CD5(+) leukemia similar to aggressive human CLL. To examine the mechanisms by which Tcl1 protein exerts its oncogenic activity in B cells, we performed proteomics experiments to identify its interacting partners. We found that Tcl1 physically interacts with de novo DNA methylthansferases Dnmt3A and Dnmt3B. We further investigated the effects of Tcl1 up-regulation on the enzymatic activity of Dnmt3A and found that Tcl1 overexpression drastically inhibits Dnmt3A function. In addition, B cells from TCL1 transgenic mice showed a significant decrease in DNA methylation compared with WT controls. Similarly, CLL samples with high Tcl1 expression showed a decrease in DNA methylation compared with CLL samples with low Tcl1 expression. Given the previous reports of inactivating mutations of DNMT3A in acute myelogenous leukemia and myelodysplastic syndrome, our results suggest that inhibition of de novo DNA methylation may be a common oncogenic mechanism in leukemogenesis.

Nutlin-3 Downregulates the Expression of the Oncogene TCL1 in Primary B Chronic Lymphocytic Leukemic Cells

The oncogene TCL1 plays a key role in the development of B chronic lymphocytic leukemia (B-CLL), but it is not known whether TCL1 could be modulated by therapeutic approaches. B-CLL patient samples (n = 35) and B leukemic cell lines (EHEB, JVM2, JVM3, MEC1, MEC2, and BJAB) with different p53 status were exposed to Nutlin-3, a small-molecule inhibitor of the p53-MDM2 interaction. Modulations of the steady-state mRNA levels of TCL1 were analyzed by quantitative real-time PCR and Western blotting in both primary B-CLL samples and leukemic cell lines. In addition, transfection experiments with either p53 siRNA or with a TCL1 expression plasmid were carried out in the EHEB B-CLL cell line. Upon ex vivo treatment with Nutlin-3, TCL1 was significantly (P < 0.05) decreased in 23 of 28 B-CLL p53(wild-type). The functionality of the p53 pathway in the same leukemic cell samples was underscored by the concomitant ability of Nutlin-3 to significantly (P < 0.05) upregulate the p53 target gene MDM2 in the p53(wild-type) leukemic cells. The dependence of TCL1 downregulation by a functional p53 pathway was confirmed in a panel of B lymphoblastoid cell lines and by p53 knockdown experiments with p53 siRNA. The importance of TCL1 in promoting leukemic cell survival was underscored in transfection experiments, in which TCL1 overexpression significantly counteracted the Nutlin-3-mediated induction of apoptosis in EHEB. Our data indicate that the Nutlin-3 downregulates TCL1 mRNA and protein, which likely represents an important molecular determinant in the proapoptotic activity of Nutlin-3.

Highlights of This Issue

Adoptive T-cell therapy generally fails to trigger clinically relevant anticancer immunity in patients with solid tumors. In this issue de Bruyn and colleagues developed a novel strategy to augment antitumor T-cell activity by selectively delivering TRAIL to the cell surface of T cells. T cells armed with TRAIL in this manner were up to 500-fold more effective against cancer cell lines, primary patient-derived cancer cells, and in a xenograft model of advanced colon carcinoma. The reported approach may easily be integrated into current adoptive T-cell strategies and thus may be useful for optimizing adoptive T cell therapy in patients suffering from solid cancers.The oncogene TCL1 plays a key role in promoting leukemic transformation in B chronic lymphocytic leukemia (B-CLL).Voltan and colleagues show, with primary cells from patients with B-CLL and in B leukemic cell lines with different p53 status, that activation of p53represses the transcription of TCL1. They obtained these results through ex vivo analysisof the effect of Nutlin-3, a nongenotoxic activator of the p53 pathway, on TCL1 regulation, and the results were confirmed by p53 knockdown and TCL1 overexpression experiments. The data suggest that TCL1 downregulation is an important mediator of Nutlin-3 cytotoxicity and that therapeutic strategies should be further explored to improve its antileukemic activity.The antitumor and antiangiogenic activity of oral low-dose metronomic topotecan in combination with oral pazopanib has been established in pediatric neuroblastoma, rhabdomyosarcoma, and osteosarcoma mouse models. The activity of this regimen across multiple pediatric tumor types, including metastatic models, creates an opening for development of pediatric clinical trials that incorporate this oral maintenance regimen. The hope is that this strategy will lead to control of minimal residual disease and increase survival in children with these aggressive tumors.Clusterin (CLU) is a stress-activated cytoprotective chaperone upregulated by a variety of anticancer therapies that confers treatment resistance when it is overexpressed. Preclinical studies have shown that CLU suppression resensitizes docetaxelrefractory cancer cells to docetaxel.This clinical trial provides evidence that a combination of the CLU inhibitor custirsen with chemotherapy is feasible in patients with progressive metastatic castrateresistant prostate cancer (CRPC) after first-line docetaxel therapy. In addition, because anticancer activity and pain responses were higher than expected, the results show some evidence of enhanced docetaxel activity as well. Moreover, these results reaffirm that custirsen decreases levels of serum CLU, and for the first time identify correlations between serum CLU and survival.

PKCβ is essential for the development of chronic lymphocytic leukemia in the TCL1 transgenic mouse model: validation of PKCβ as a therapeutic target in chronic lymphocytic leukemia

AbstractThe development and the propagation of chronic lymphocytic leukemia (CLL) has been linked to signaling via the B-cell receptor (BCR). Protein kinase C β (PKCβ) is an essential signaling element of the BCR and was recently shown to be overexpressed in human CLL. We used the TCL1 transgenic mouse model to directly target PKCβ in the development of murine CLL. TCL1 overexpression did restore the CD5+ B-cell population that is absent in PKCβ-deficient mice. However, PKCβ-deleted TCL1 transgenic mice did not develop a CLL disease, suggesting a role of PKCβ in the establishment of the malignant clone. Moreover, targeting of PKCβ with the specific inhibitor enzastaurin led to killing of human CLL samples in vitro. We thus propose that PKCβ may be a relevant target for the treatment of CLL.

Tcl1 functions as a transcriptional regulator and is directly involved in the pathogenesis of CLL

B cell chronic lymphocytic leukemia (B-CLL) is the most common human leukemia. Deregulation of the T cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. To examine the mechanisms by which Tcl1 protein exerts oncogenic activity in B cells, we investigated the effect of Tcl1 expression on NF-kappaB and activator protein 1 (AP-1) activity. We found that Tcl1 physically interacts with c-Jun, JunB, and c-Fos and inhibits AP-1 transcriptional activity. Additionally, Tcl1 activates NF-kappaB by physically interacting with p300/CREB binding protein. We then sequenced the TCL1 gene in 600 B-CLL samples and found 2 heterozygous mutations: T38I and R52H. Importantly, both mutants showed gain of function as AP-1 inhibitors. The results indicate that Tcl1 overexpression causes B-CLL by directly enhancing NF-kappaB activity and inhibiting AP-1.

Expression of Tcl-1 as a Potential Prognostic Factor for Treatment Outcome in B-Cell Chronic Lymphocytic Leukemia.

Chronic Lymphocytic Leukemia (CLL) is primarily characterized by the presence of leukemic B lymphocytes resistant to the process of apoptosis. Causes for this resistance include aberrant expression of multiple anti-apoptotic proteins, perhaps including Tcl-1 (1). Tcl-1 is expressed during normal development of both B and T cells and activates Akt to provide a survival signal through phosphorylation and inactivation of apoptotic pathway components. Overexpression of Tcl-1 in the B cells of transgenic mice results in a B-cell leukemia phenotype typical of human CLL, suggesting a primary role for Tcl-1 in CLL tumorigenesis. A recent report showed that Tcl-1 protein expression in CLL cells correlated with other biological parameters, but no data were available as to its clinical relevance (2). We therefore examined Tcl-1 expression in relation to clinical outcome using 51 peripheral blood mononuclear cell samples from a Phase II clinical trial testing the combination of pentostatin, cyclophosphamide, and rituximab in previously untreated CLL patients (Kay et al., ASH 2006). Tcl-1 protein expression was measured by immunoblot using GAPDH as a normalization control across lanes and lysate from a single Tcl-1 transgenic mouse spleen as a normalization control across immunoblots. All samples were run at least in duplicate and digital quantitation was performed using a ChemiDoc instrument (BioRad). Tcl-1 expression in patient cells was calculated in comparison to Tcl-1 expression in the mouse lysate, arbitrarily set to 1.0. Data were analyzed as a continuous measure as well as by specific cutoffs. Higher Tcl-1 expression was associated with failure to achieve a minimal residual disease-negative state after treatment. Specifically, Tcl-1 expression (measured as a continuous variable) was associated with residual disease measured by post-treatment CD5+/CD19+ cell percentages (continuous variable as well as dichotomized by cutpoint of 1.0% for CD5+/CD19+; p=0.03 for both comparisons). For the dichotomized Tcl-1 expression with the cutpoint of 0.275 (second tertile), this variable was marginally significantly associated with whether or not post-treatment CD5+/CD19+ was less than 1.0%. Using this same cutoff, there was also a suggestion that patients with reduced Tcl-1 were more likely to achieve a complete response. Finally, progression-free survival was shorter in patients with increased Tcl-1 expression, although these data did not reach statistical significance in this sample set.Tcl-1 < 0.275Tcl-1≥ 0.275p valueCD5/CD19≥ 1%15100.046CD5/CD19 < 1%162CR1730.064No CR1813Median PFS (mos.)36.517.10.137Statistically significant associations with other parameters including Rai stage, IgVH mutation status, ZAP-70 expression, CD38 expression, and interphase cytogenetics categories were not detected in this sample set. These data further support the clinical relevance of the Tcl-1 mouse model to human CLL, and provide preliminary evidence that Tcl-1 protein expression correlates with clinical outcome of CLL patients treated with chemoimmunotherapy. If validated in larger studies, Tcl-1 expression may serve as a novel prognostic factor.

Tcl-1 Inhibits Nuclear Export of TR3 and Is Highly Expressed in ZAP70-Positive CLL B-Cells.

Chronic Lymphocytic Leukemia (CLL) is the most frequent leukemia afflicting the Western world. Unlike other more aggressive leukemias and lymphomas, CLL B-cells do not divide at a high rate and expansion of the malignant clone appears to be due to underlying defect in apoptosis.Elevated levels of anti-apoptotic Bcl-2 are thought to be involved in the pathogenesis of CLL. The activity of Bcl-2 can be modulated my interactions with other cellular proteins. Recently, orphan nuclear receptor TR3 (nur77) was shown to exit the nucleus, bind Bcl-2, and convert Bcl-2 into a killer protein (Lin, et al., CELL , 116:527, 2004). We evaluated the expression of TR3 by immunoblotting in CLL B-cells specimens. High levels of TR3 protein were present in 8 of 8 CLL patient specimens. Subcellular fractionation studies showed predominately nuclear localization of TR3 in 2 of 2 CLL specimens examined. Because Akt is known to regulate TR3 activity in the nucleus (Pekarsky, et al., Proc. Natl. Acad. Sci. 98:3690, 2001), we also examined the expression of the Akt regulator, Tcl-1. The Tcl-1 protein was expressed in the majority of CLL samples and at high levels in 8 of 16 CLL specimens, correlating with ZAP70-positivity. In gene transfection experiments using tumor cell lines, over-expression of Tcl-1 inhibited nuclear export of TR3, as determined by immunofluorescence confocal microscopy. We propose a model in which expression of the oncogene Tcl-1 in CLL B-cells (perhaps related to ZAP70 expression) modulates nuclear Akt activity, in turn suppressing TR3 function, and thus reducing activity of the TR3-mediated pathway for conversion of Bcl-2 from protector to killer. This hypothesis requires further experimental testing.

TCL1 participates in early embryonic development and is overexpressed in human seminomas.

Overexpression of the TCL1 oncogene has been shown to play a causative role in T cell leukemias of humans and mice. The characterization of Tcl1-deficient mice in these studies indicates an important developmental role for Tcl1 in early embryogenesis. In wild-type embryos, Tcl1 is abundant in the first three mitotic cycles, during which it shuttles between nuclei and the embryo cortical regions in a cell-cycle-dependent fashion. The absence of this protein in early embryogenesis results in reduced fertility of female mice. The present studies elucidate the mechanism responsible for the reduced female fertility through analysis of the oogenesis stages and early embryo development in Tcl1-deficient mice. Even though Tcl1(-/-) females display normal oogenesis and rates of oocyte maturation/ovulation and fertilization, the lack of maternally derived Tcl1 impairs the embryo's ability to undergo normal cleavage and develop to the morula stage, especially under in vitro culture conditions. Beyond this crisis point, differentiative traits of zygotic genome activation and embryo compaction can take place normally. In contrast with this unanticipated role in early embryogenesis, we observed an overexpression of TCL1 in human seminomas. This finding suggests that TCL1 dysregulation could contribute to the development of this germinal cell cancer as well as lymphoid malignancies.