[Variant fusion transcripts and genomic DNA breakpoint of sil-tal1 in T-ALL cells]

The aim of this study was to investigate the nucleotide sequence of one distinct fusion transcript of sil-tal1 in childhood T-ALL. The PCR product was cloned into plasmid vector and then sequenced. Genomic DNA was analyzed with PCR using the designed primer pairs representing distinct sequences. The product was sequenced and analyzed with database. The results indicated that 4 different fusion transcripts were detected at cDNA level, in which a part of exons or introns of sil are reserved respectively, and some additions and deletions existed. After analyzing genomic DNA sequence of leukemic cells, the breakpoint in gene sil of this case was proved to be different at DNA level from references. Hence, the sil-tal1 rearrangement was defined to be a new type. It is concluded tal1 rearrangement of leukemic cells in this case is a new type, which expresses classical and at least 3 variant fusion transcripts, presumably caused by extraordinary mechanisms of splicing and transcription in leukemic stem cells.

Molecular approach to human leukemia: isolation and characterization of the first human retrovirus HTLV-1 and its impact on tumorigenesis in adult T-cell leukemia

Molecular biology of mouse and chicken retroviruses had identified oncogenes and provided a revolutionary concept in understanding of cancers. A human retrovirus was established during 1980-1982 in linkage with a unique human leukemia, concurrently in Japan and USA. This review covers our efforts on the discovery of new retrovirus, Human T-cell Leukemia Virus Type 1 (HTLV-1), first introducing to a new class of retroviruses with a unique regulatory factors, Tax and Rex. Then it is followed by analyses of molecular interaction of the vial Tax with cellular machineries involved in the pathogenesis of Adult T-cell Leukemia (ATL). And then a probable mechanism of pathogenesis of ATL is proposed including recent findings on HBZ after our efforts.

Functional DNA repair system analysis in haematopoietic progenitor cells using host cell reactivation

Deficiencies in individual DNA repair systems are involved in both de novo and therapy-related acute myeloid leukaemia (t-AML), as indicated by genetic markers involving nucleotide excision repair (NER gene polymorphisms), double-strand-break (DSB) or mismatch repair (microsatellite instability (MSI)). We modified a host cell reactivation (HCR) assay for functional DNA repair system analysis of living primary haematopoietic cells; 2 x 10(5) normal peripheral blood lymphocytes (PBLs) and cord blood CD34+ progenitor cells were cryopreserved, thawed and transfected with 75-250 ng luciferase reporter plasmid (pCMVLuc) using DEAE-dextran (0.1 mg/mL) in a transfection volume of 250 microL. We obtained luciferase activities of approximately 300-fold above background in CD34+ progenitor cells and approximately 2000-fold in PBLs, thus rendering these cells applicable for DNA repair analysis. We then evaluated the NER (UV-irradiated pCMVLuc) and DSB repair capacity (linearized pCMVLuc) of normal lymphocytes and several leukaemic cell lineages. Kasumi-1 and HL-60 AML cells exhibited a reduced NER capacity compared to normal GM03715 lymphocytes, PBLs and CD34+ progenitor cells (6.2 +/- 0.9%, 6.5 +/- 0.9% vs. 12.3 +/- 1.8%, 13.5 +/- 0.7% and 13.5 +/- 2.0%, respectively). Kasumi-1 AML tells exhibited a reduced DSB repair capacity compared to AG10107 and GM03715 normal lymphocytes as well as CEM acute T-cell lymphoblastic leukaemia cells (6.4 +/- 0.8% vs. 10.8 +/- 0.7%, 27.3 +/- 1.1% and 20.5 +/- 1.6%, respectively). The modified HCR assay can be used for functional DNA repair analysis in living cells of patients with pre- and post-leukaemic conditions as well as in leukaemic blasts to elucidate the role of DNA repair in de novo and t-AML leukaemogenesis and to determine the individual susceptibility to t-AML prior to chemotherapy.

Is there a difference in childhood T-cell acute lymphoblastic leukaemia and T-cell lymphoblastic lymphoma?

To distinguish the similarities or differences between T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL), we retrospectively analyzed the clinical, immunophenotypic, cytogenetic, and molecular characteristics in 37 children diagnosed between December 1990 and December 2003. Comparative Expressed Sequence Hybridisation (CESH) was used to determine gene expressing profile in both diseases. Twenty two patients suffered from T-ALL and 15 patients were diagnosed as T-LBL. Immunophenotyping demonstrated a more immature phenotype in T-ALL and a more mature phenotype in T-LBL. Cytogenetic and molecular genetic aberrations were found in 82% of T-ALL compared with 73% of T-LBL. By CESH gene expression profiling, the investigated cases were segregated into two groups that largely corresponded with T-ALL and T-LBL. The clinical presentation and cytogenetic characteristics are largely similar for T-ALL and T-LBL supporting the concept that both represent a spectrum of one single disease. The differences that were found between both neoplasms, in particular in their phenotype and in their expression profile may suggest that most T-ALL derive from a T-cell progenitor of the bone marrow, while thymocytes represent the normal counterpart of T-LBL.

Murine leukemias with retroviral insertions at Lmo2 are predictive of the leukemias induced in SCID-X1 patients following retroviral gene therapy

Five X-linked severe combined immunodeficiency patients (SCID-X1) successfully treated with autologous bone marrow stem cells infected ex vivo with an IL2RG-containing retrovirus subsequently developed T-cell leukemia and four contained insertional mutations at LMO2. Genetic evidence also suggests a role for IL2RG in tumor formation, although this remains controversial. Here, we show that the genes and signaling pathways deregulated in murine leukemias with retroviral insertions at Lmo2 are similar to those deregulated in human leukemias with high LMO2 expression and are highly predictive of the leukemias induced in SCID-X1 patients. We also provide additional evidence supporting the notion that IL2RG and LMO2 cooperate in leukemia induction but are not sufficient and require additional cooperating mutations. The highly concordant nature of the genetic events giving rise to mouse and human leukemias with mutations at Lmo2 are an encouraging sign to those wanting to use mice to model human cancer and may help in designing safer methods for retroviral gene therapy.

Twenty patients with X-linked severe combined immunodeficiency (SCID-X1) have been successfully treated by gene therapy. Unfortunately, five of these patients have developed T-cell leukemia two or more years after receiving the therapeutic gene IL2RG on a retroviral vector. The leukemias developed because the vector inserted itself near cancer-causing genes and disrupted their normal regulation. Remarkably, in four patients, the vector inserted near a known T-cell oncogene, LMO2. We have found that in mice, similar retroviruses cause T-cell leukemias by inserting near Lmo2. We have found two leukemias that have retroviral insertions near Lmo2 and Il2rg in the same cell. The probability of these insertions happening by chance is exceedingly small and these results imply that these two genes are deregulated together to induce leukemia. Our data show that Lmo2 and Il2rg cooperate but may not be sufficient for leukemia development and additional mutations contribute to leukemia development. We have also found cooperating retroviral insertions in genes that are abnormally expressed in human T-cell leukemias. The mouse models provide unique insight into the pathogenesis of T-cell leukemia, and they are highly predictive of the leukemias caused by SCID-X1 gene therapy.

RelB-dependent stromal cells promote T-cell leukemogenesis

BACKGROUND

The Rel/NF-kappaB transcription factors are often activated in solid or hematological malignancies. In most cases, NF-kappaB activation is found in malignant cells and results from activation of the canonical NF-kappaB pathway, leading to RelA and/or c-Rel activation. Recently, NF-kappaB activity in inflammatory cells infiltrating solid tumors has been shown to contribute to solid tumor initiation and progression. Noncanonical NF-kappaB activation, which leads to RelB activation, has also been reported in breast carcinoma, prostate cancer, and lymphoid leukemia.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report a novel role for RelB in stromal cells that promote T-cell leukemogenesis. RelB deficiency delayed leukemia onset in the TEL-JAK2 transgenic mouse model of human T acute lymphoblastic leukemia. Bone marrow chimeric mouse experiments showed that RelB is not required in the hematopoietic compartment. In contrast, RelB plays a role in radio-resistant stromal cells to accelerate leukemia onset and increase disease severity.

CONCLUSIONS/SIGNIFICANCE

The present results are the first to uncover a role for RelB in the crosstalk between non-hematopoietic stromal cells and leukemic cells. Thus, besides its previously reported role intrinsic to specific cancer cells, the noncanonical NF-kappaB pathway may also play a pro-oncogenic role in cancer microenvironmental cells.

Notch-1 mutations are secondary events in some patients with T-cell acute lymphoblastic leukemia

PURPOSE

Activating Notch-1 mutations are frequent in T-cell acute lymphoblastic leukemia (T-ALL), occurring in >50% of patients. In murine models of T-ALL, Notch-1 activation can both directly initiate leukemia and cooperate secondarily to other primary events. Whether acquisition of Notch-1 mutations is an early initiating event or a secondary event in the pathogenesis of human T-ALL is unclear.

EXPERIMENTAL DESIGN

We used denaturing high-performance liquid chromatography, sequencing, and fragment analysis to analyze Notch-1 mutational status and mutant level in 62 patients at presentation as well as 16 matched presentation-relapse samples.

RESULTS

We detected Notch-1 mutations in 47 patients (76%). Seven of these were low-level mutations (quantified at < or =10%), despite high blast counts, suggesting that they were acquired as a secondary event in a subclone. Of 16 matched presentation-relapse samples studied, 7 were wild-type at both presentation and relapse. Five of nine mutant-positive patients at presentation relapsed with the same mutation(s) at the same high level. Four patients had evidence of a change in mutant at relapse. One lost a PEST mutation and became wild-type. Two others lost mutations at relapse but acquired different mutations, despite unchanged T-cell receptor rearrangements, suggesting that the latter event predated the acquisition of the Notch-1 mutation. One relapsed with a secondary T-cell leukemia and different Notch mutation.

CONCLUSIONS

These results suggest that Notch-1 mutations can sometimes be acquired as secondary events in leukemogenesis and must be used cautiously as solitary minimal residual disease markers.

WT1 protein expression in childhood acute leukemia

In patients with acute leukemia, Wilms' tumor gene 1 (WT1) has been used as a target for the detection of minimal residual disease (MRD) by PCR techniques. The expression of WT1 protein, however, has not been extensively studied. To determine the relation between expression of WT1 transcripts and of the encoded protein, we examined leukemic cell lines and primary childhood leukemia samples using both real-time quantitative PCR (RQ-PCR) and flow cytometry. WT1 protein was highly expressed in the leukemic cell lines K562, HL-60, PLB 985, KG-1a and CEM. By contrast, 40 primary samples of acute lymphoblastic leukemia (ALL; B-ALL, n = 15 and T-ALL, n = 10) and acute myeloid leukemia (n = 15) expressed low levels of WT1 protein. RQ-PCR detected WT1 transcript levels in the same range as reported in earlier studies in childhood acute leukemia. The results of this study indicate the following: (i) there are considerable discrepancies between WT1 transcripts and protein expression; (ii) WT1 is not a suitable marker for flow cytometric MRD detection in childhood acute leukemia.

Rearranged NF-kappa B2 gene in an adult T-cell leukemia cell line

Adult T-cell leukemia (ATL) is an aggressive type of leukemia, originating from T-cells infected with human T-cell leukemia virus type 1. Accumulating evidence suggests the aberrant activation of NF-kappaB to be a causative factor mediating the abnormal proliferation of leukemic cells, thus resulting in the development of ATL. A rearranged NF-kappa B2/p100 gene was isolated from an ATL-derived cell line, which was generated by a chromosomal translocation. The isolated NF-kappa B2 mutant is fused with the with no (lysine) deficient protein kinase 1 gene, coding for a 58 kDa protein that retains the DNA binding Rel homology domain, but it lacks the entire ankyrin repeat inhibitory domain, thus suggesting its constitutive activation. This rearranged NF-kappa B2 gene product (p58) was localized in the nucleus, and formed a complex with NF-kappaB p65 or RelB. Moreover, a T-cell line expressing p58 increased the amount of an NF-kappa B2-inducible gene, NF-kappa B2/p100 by itself. These results suggest that such NF-kappa B2 gene rearrangement may therefore be a factor in the constitutive activation of NF-kappaB in ATL, and thereby playing a role in the ATL pathogenesis.

Correlation between asparaginase sensitivity and asparagine synthetase protein content, but not mRNA, in acute lymphoblastic leukemia cell lines

BACKGROUND

Asparaginase (ASNase) is an essential component of most treatment protocols for childhood acute lymphoblastic leukemia (ALL). Although increased asparagine synthetase (ASNS) expression may contribute to ASNase resistance, there is conflicting data from patient samples with regard to correlation between ASNS mRNA content and ASNase sensitivity.

PROCEDURE

Both T-cell and B-cell derived ALL cell lines were treated with ASNase and then monitored for cell proliferation, cell death, and ASNS mRNA and protein expression.

RESULTS

Despite elevated ASNS mRNA following ASNase treatment, different ALL cell lines varied widely in translation to ASNS protein. Although ASNS mRNA levels did not consistently reflect ASNase sensitivity, there was an inverse correlation between ASNS protein and ASNase-induced cell death. Expression of ASNS in an ASNase-sensitive cell line resulted in enhanced ASNase resistance, and conversely, siRNA-mediated inhibition of ASNS expression promoted increased drug sensitivity.

CONCLUSIONS

These observations provide an explanation for the ASNase sensitivity of ALL cells and demonstrate the importance of measuring ASNS protein rather than mRNA in predicting ASNase responsiveness.

Aggressive Langerhans cell histiocytosis following T-ALL: clonally related neoplasms with persistent expression of constitutively active NOTCH1

Langerhans cell histiocytosis (LCH) and related entities are neoplasms of unknown pathogenesis. Here, we describe studies assessing the role of NOTCH1 mutations in LCH, which were based on a case of fatal Langerhans cell tumor after T-cell acute lymphoblastic leukemia (T-ALL). Although the two types of neoplasm in this patient were temporally and pathologically distinct, molecular analyses showed that they harbored the same T-cell receptor gene rearrangements and two activating NOTCH1 mutations involving exons 27 and 34. The exon 27 mutation altered a conserved cysteine residue in the N-terminal portion of the NOTCH1 heterodimerization domain, while the mutation in exon 34 introduced a premature stop codon that results in the deletion of C-terminal negative regulatory PEST domain. Analysis of cDNA prepared from the aggressive Langerhans cell tumor showed that the NOTCH1 mutations were aligned in cis, a configuration that caused synergistic increases in NOTCH1 signal strength in reporter gene assays. Immunohistochemistry confirmed that the Langerhans cell tumor also expressed NOTCH1 protein. Although these data suggested that NOTCH1 mutations might contribute to the pathogenesis of typical sporadic LCH and related neoplasms occurring in the absence of T-ALL, an analysis of 24 cases of LCH and Rosai-Dorfman Disease occurring in patients without an antecedent history of T-ALL revealed no mutations. Thus, activating NOTCH1 mutations appear to be unique to aggressive Langerhans cell tumors occurring after T-ALL. Persistent expression of NOTCH1 in such tumors suggests that Notch pathway inhibitors could have a role in the treatment of these unusual neoplasms.

CAG regimen enables relapsed or refractory T-cell acute lymphocytic leukemia patients to achieve complete remission: a report of six cases

Patients with either relapsed or refractory T-cell acute lymphocytic leukemia (T-ALL) are candidates for allogeneic hematopoietic stem cell transplantation (allo-HSCT). Achieving complete remission (CR) in these patients is difficult but crucial for the success of allo-HSCT. In this study, we examined 6 relapsed or refractory T-ALL patients. In the patient group, 4 were male and 2 were female, with ages ranging from 15 to 57 years (median=29 years). All 6 patients presented with the nonmature T-ALL phenotype. Cytogenetically, only one had an i(7q) anomaly, whereas the remaining 5 cases had normal karyotypes. One of these patients had the MLL/AF9 fusion transcript, as shown by molecular study. After initial remission-induction therapy, two patients achieved CR, one showed a partial remission, and all relapsed soon. The other 3 cases failed the therapy. The CAG regimen (cytosine arabinoside 10 mg/m(2) subcutaneously every 12 hr, day 1-14; aclarubicin 5-7 mg/m(2) intravenously daily, day 1-8; and concurrent use of G-CSF 200 microg/m(2)/day subcutaneously) was devised originally for the treatment of relapsed acute myelogenous leukemia. After CAG therapy, all the T-ALL patients in our study achieved CR, indicating that the CAG regimen is beneficial to the treatment of relapsed or refractory T-ALL. The efficacy of CR-induction in T-ALL patients and the adverse effects of the CAG regimen need to be further studied.

Disruption of ETV6 in intron 2 results in upregulatory and insertional events in childhood acute lymphoblastic leukaemia

We describe four cases of childhood B-cell progenitor acute lymphoblastic leukaemia (BCP-ALL) and one of T-cell (T-ALL) with unexpected numbers of interphase signals for ETV6 with an ETV6-RUNX1 fusion probe. Three fusion negative cases each had a telomeric part of 12p terminating within intron 2 of ETV6, attached to sequences from 5q, 7p and 7q, respectively. Two fusion positive cases, with partial insertions of ETV6 into chromosome 21, also had a breakpoint in intron 2. Fluorescence in situ hybridisation (FISH), array comparative genomic hybridization (aCGH) and Molecular Copy-Number Counting (MCC) results were concordant for the T-cell case. Sequences downstream of TLX3 on chromosome 5 were deleted, leaving the intact gene closely apposed to the first two exons of ETV6 and its upstream promoter. qRT-PCR showed a significant upregulation of TLX3. In this study we provide the first incontrovertible evidence that the upstream promoter of ETV6 attached to the first two exons of the gene was responsible for the ectopic expression of a proto-oncogene that became abnormally close as the result of deletion and translocation. We have also shown breakpoints in intron 2 of ETV6 in two cases of insertion with ETV6-RUNX1 fusion.

Identification of HLA class I-restricted tumor-associated antigens in adult T cell leukemia cells by mass spectrometric analysis

OBJECTIVE

In this study, we attempted a comprehensive analysis of MHC class I-bound peptides in adult T cell leukemia (ATL) cells in order to identify as many tumor-associated antigens (TAAs) as possible that could be used for CTL-based immunotherapy.

METHODS AND RESULTS

Using mass spectrometry combined with reversed-phase liquid chromatography, we could sequence 188 HLA class I-restricted candidate peptides from three ATL-derived cell lines. In accordance with the restrained expression of HTLV-I viral RNA in these cell lines, there were no HTLV-I-encoded peptides among these candidates. Based on the differential expression between ATL cells and normal CD4+ T cells, we selected 10 novel peptides as T cell epitopes of overexpressed source proteins. RT-PCR analysis revealed that 5 source proteins including PRAME, a known tumor-testis antigen, were highly expressed in the majority of 16 ATL cases. Furthermore we could induce PRAME-specific CTLs in vitro from an HLA-B62+ healthy donor that showed specific cytotoxicity against HLA-B62+ PRAME+ ATL cells.

CONCLUSION

These results demonstrate that comprehensive analysis of HLA class I-bound peptides by mass spectrometry is useful for identification of TAA-derived peptides in ATL. Considering that expression patterns of leukemia/lymphoma-associated antigens vary from case to case, this approach appears to be suitable for the tailor-made immunotherapy of hematological malignancies.

Upregulation of CC chemokine ligand 18 and downregulation of CX3C chemokine receptor 1 expression in human T-cell leukemia virus type 1-associated lymph node lesions: Results of chemokine and chemokine receptor DNA chip analysis

Adult T-cell leukemia/lymphoma (ATLL) is a human malignancy associated with human T-cell leukemia virus type 1 (HTLV-1). The pathological features of the lymph nodes of ATLL change from those of lymphadenitis to Hodgkin's-like features and those of lymphoma. Chemokines and their receptors are closely associated with T-cell subgroups and immune responses. To clarify the relationship between chemokines and their receptor expression, as well as the development of ATLL, 17 cases with ATLL were analyzed using DNA chips of chemokines and their receptors. All cases showed a varied and mixed pattern of upregulated and downregulated gene expression of Th1, Th2, naïve, and cytotoxic cell-associated chemokine genes. As CC chemokine ligand 18 (CCL18) accounted for the most upregulated gene and CX3C chemokine receptor 1 (CX3CR1) for the most downregulated gene, they were selected for immunohistochemical analysis. Immunohistochemical staining showed expression of the two genes in immunological cells, with a positive expression for reticulum cells, but not for ATLL cells. HTLV-1-associated lymphadenitis type (n = 13) and Hodgkin's-like type (n = 12) cases showed significantly higher CCL18 expression than the non-specific lymphadenitis cases (n = 10) (P < 0.05). However, all HTLV-1-associated cases showed significantly lower CX3CR1 expression than the non-specific lymphadenitis cases (P < 0.05). These results suggest that upregulation of CCL18 expression and downregulation of CX3CR1 expression play a role in immune responses against the ATLL cells.

Successful treatment of adult T-cell leukemia with unrelated cord blood transplantation

This study reports the first well-documented case of adult T-cell leukemia (ATL) successfully treated with unrelated cord blood transplantation (UCBT). A 49-year-old woman was diagnosed with acute-type of ATL. Chemotherapy induced complete remission, but the human T-cell leukemia virus type 1 (HTLV-1) proviral load was detected in mononuclear cells of her peripheral blood. The patient received UCBT with a conditioning regimen consisting of total body irradiation, cytarabine, and cyclophosphamide. She remains in remission 30 months after UCBT and the HTLV-1 proviral load has fallen to undetectable levels. This result suggests that UCBT should be a therapeutic option for ATL patients who do not have suitable donors and those who urgently require treatment.

Inhibitory effects and target genes of bone morphogenetic protein 6 in Jurkat TAg cells

Bone morphogenetic proteins (BMP) are multifunctional cytokines that belong to the TGF-beta superfamily. BMP have been shown to regulate haematopoietic stem cells, B lymphopoiesis and early thymocyte differentiation. In the present study we explored the role of BMP-6 in Jurkat TAg cells. BMP-6 rapidly induced phosphorylation of Smad1/5/8, p38 and ERK1/2, followed by a potent up-regulation of ID1, ID2 and ID3. ID1 and ID3 were also induced at the protein level. Genome-wide expression profiling of cells treated with BMP-6 compared to medium confirmed that ID1-ID3 were target genes of BMP-6 together with Noggin and Smad6. Furthermore, several genes involved in transcriptional regulation were also identified, including NFKBIA, HEY1, DLX2, KLF10 and early growth response 1. Stimulation with BMP-6 exerted an antiproliferative effect that was counteracted by inhibitor of DNA binding (Id)1 siRNA, indicating that Id1 is an important downstream mediator in Jurkat TAg cells. A subset of CD4(+) T cells were found to express the BMP receptors Alk-2 and Alk-3 (type I), in addition to BMPRII (type II). BMP-6 also induced phosphorylation of Smad1/5/8, followed by transcriptional increase in ID1-ID3 mRNA expression. However, we did not observe significant changes in Id protein expression in CD4(+) T cells. Altogether, the data indicate a role for BMP-6 in human T lineage cells.

Genetic alterations determine chemotherapy resistance in childhood T-ALL: modelling in stage-specific cell lines and correlation with diagnostic patient samples

Acquired drug resistance eventually leads to treatment failure in T-cell acute lymphoblastic leukaemia (T-ALL). Immunophenotypic and cytogenetic heterogeneities within T-ALL influence susceptibility to cytotoxic therapy, and little is known about the mechanisms of drug resistance at specific stages of T-cell ontogeny. We developed tolerance to therapeutic concentrations of daunorubicin (DNR) and L-asparaginase (L-asp) in Jurkat (CD1a(-), sCD3(+)) and Sup T1 (CD1a(+), sCD3(-)) cell lines, having respective 'mature' and 'cortical' stages of developmental arrest. DNR resistant cells acquired multidrug resistance: 310-fold increased resistance to vincristine (VCR) and a 120-fold increased resistance to prednisolone (PRED). Microarray analysis identified upregulation of asparagine synthetase (ASNS) and argininosuccinate synthase 1 (ASS1) to cell lines with acquired resistance to L-asp, and in the case of DNR, upregulation of ATP-binding cassette B1 (ABCB1). Suppression of ABCB1, ASNS and ASS1 by RNA interference revealed their functional relevance to acquired drug resistance. Expression profiling of these genes in 80 T-ALL patients showed correlation with treatment response. This study expands the pool of available drug resistant cell lines having cortical and mature stages of developmental arrest, introduces three new drug resistant T-ALL cell lines, and identifies gene interactions leading to L-asp and DNR resistance.

Identification of Human T Cell Leukemia Virus Type 1 Tax Amino Acid Signals and Cellular Factors Involved in Secretion of the Viral Oncoprotein

Human T cell leukemia virus type 1 (HTLV-1) is the etiologic agent of a number of pathologic abnormalities, including adult T cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The viral oncoprotein Tax has been implicated in the pathogenesis of these diseases. Recently, cell-free Tax was detected in the cerebrospinal fluid of HAM/TSP patients, implying that extracellular Tax may be relevant to neurologic disease. Additionally, the presence of a nuclear export signal within Tax and its active secretion has been demonstrated in vitro. However, the mechanism of Tax secretion remains to be established. Studies reported herein elucidate the process of Tax secretion and identify domains of Tax critical to its subcellular localization and secretion. Tax was shown to interact with a number of cellular secretory pathway proteins in both the model cell line BHK (baby hamster kidney)-21 and an HTLV-1-infected T cell line, C8166, physiologically relevant to HTLV-1-induced disease. Silencing of selected components of the secretory pathway affected Tax secretion, further confirming regulated secretion of Tax. Additionally, mutations in two putative secretory signals within Tax DHE and YTNI resulted in aberrant subcellular localization of Tax and significantly altered protein secretion. Together, these studies demonstrate that Tax secretion is a regulated event facilitated by its interactions with proteins of the cellular secretory pathway and the presence of secretory signals within the carboxyl-terminal domain of the protein.

In vivo reinsertion of excised episomes by the V(D)J recombinase: a potential threat to genomic stability

It has long been thought that signal joints, the byproducts of V(D)J recombination, are not involved in the dynamics of the rearrangement process. Evidence has now started to accumulate that this is not the case, and that signal joints play unsuspected roles in events that might compromise genomic integrity. Here we show both ex vivo and in vivo that the episomal circles excised during the normal process of receptor gene rearrangement may be reintegrated into the genome through trans-V(D)J recombination occurring between the episomal signal joint and an immunoglobulin/T-cell receptor target. We further demonstrate that cryptic recombination sites involved in T-cell acute lymphoblastic leukemia–associated chromosomal translocations constitute hotspots of insertion. Eventually, the identification of two in vivo cases associating episomal reintegration and chromosomal translocation suggests that reintegration events are linked to genomic instability. Altogether, our data suggest that V(D)J-mediated reintegration of episomal circles, an event likely eluding classical cytogenetic screenings, might represent an additional potent source of genomic instability and lymphoid cancer.

Lymphoid cells recognize billions of pathogens as a result of gene rearrangements that generate pathogen-specific B- and T-cell receptors. This genetic reshuffling, called V(D)J recombination, occasionally misfires and damages genomic integrity. When such aberrations dysregulate proto-oncogenes, cancer ensues. It has become increasingly clear that multiple oncogenes acting in different cellular pathways can cooperate to cause cancer. Nevertheless, in the case of T-cell acute lymphoblastic leukemia, about a third of cases display oncogene activation in the absence of identified aberration, suggesting the presence of additional mechanisms of chromosomal alteration. In the hunt for such mechanisms, episomal circles (DNA segments that are excised during V(D)J recombination) have recently drawn attention. Moreover, signal joints, short sequences formed after gene rearrangements, once considered harmless, now appear to take part in events that might compromise genomic integrity. Using ex vivo recombination assays and genetically modified mice, we demonstrate that episomal circles may be reintegrated into the genome through recombination occurring between the episomal signal joints and a T-cell receptor target. Furthermore, we show that cryptic recombination sites located in the vicinity of oncogenes constitute hotspots of episomal insertion. Altogether, our results suggest that reintegration of excised episomal circles constitute a potential source of genomic instability and cancer in leukemia and lymphoma.

Episomal DNA circles are the by-products of immunoreceptor gene rearrangements in lymphoid cells. Episomal circles can be reintegrated into the genome by trans-V(D)J recombination and cause oncogene deregulation.

The tumor suppressor gene hCDC4 is frequently mutated in human T-cell acute lymphoblastic leukemia with functional consequences for Notch signaling

Notch signaling is of crucial importance in normal T-cell development and Notch 1 is frequently mutated in T-cell acute lymphoblastic leukemias (T-ALL), leading to aberrantly high Notch signaling. In this report, we determine whether T-ALL mutations occur not only in Notch1 but also in the F-box protein hCdc4 (Sel-10, Ago, or Fbxw7), a negative regulator of Notch1. We show that the hCDC4 gene is mutated in leukemic cells from more than 30% of patients with pediatric T-ALL and derived cell lines. Most hCDC4 mutations found were missense substitutions at critical arginine residues (Arg(465), Arg(479), and Arg(505)) localized in the substrate-binding region of hCdc4. Cells inactivated for hCdc4 and T-ALL cells containing hCDC4 mutations exhibited an increased Notch1 protein half-life, consistent with the proposed role of hCdc4 in ubiquitin-dependent proteolysis of Notch1. Furthermore, restoration of wild-type but not mutant hCdc4 in HCT 116 hCDC4-negative cells led to an increased Notch1 ubiquitylation and decreased Notch1 signaling. These results show that hCdc4 mutations interfere with normal Notch1 regulation in vivo. Finally, we found that mutations in hCDC4 and NOTCH1 can occur in the same cancers and that patients carrying hCDC4 and/or NOTCH1 mutations have a favorable overall survival. Collectively, these data show that mutation of hCDC4 is a frequent event in T-ALL and suggest that hCDC4 mutations and gain-of-function mutations in NOTCH1 might synergize in contributing to the development of pediatric T-ALL leukemogenesis.

Heat-shock induction of T-cell lymphoma/leukaemia in conditional Cre/lox-regulated transgenic zebrafish

The zebrafish is an ideal vertebrate model system to investigate the complex genetic basis of cancer because it has the capacity for in vivo tumour-cell imaging and forward genetic screens, and the molecular mechanisms regulating malignancy are remarkably conserved when compared with human. Our laboratory has previously generated transgenic zebrafish models that overexpress the mouse c-Myc gene fused to enhanced green fluorescent protein (EGFP) and develop T-cell acute lymphoblastic leukaemia (T-ALL) that recapitulates the human disease both molecularly and pathologically. Our previous models have been limited by disease onset prior to sexual maturity and by the low disease penetrance when conditional transgenic embryos are injected with Cre RNA. Here, we report a novel system in which compound transgenic fish expressed both Cre controlled by the heat-shock promoter and a rag2-promoter-regulated lox-dsRED2-lox-EGFP-mMyc cassette rag2-LDL-EMyc in developing T cells. After heat-shock treatment at 3 d postfertilisation (dpf) for 45 min at 37 degrees C, 81% of compound transgenic fish developed T-lymphoblastic lymphoma (T-LBL, mean latency 120 +/- 43 (standard deviation) days of life), which rapidly progressed to T-ALL. Heat-shock-regulated transgenic technology in zebrafish provides the missing link necessary to exploit the powerful genetic capacity of this organism to probe the multi-step molecular pathogenesis of leukaemia.

Telomere attrition induces a DNA double-strand break damage signal that reactivates p53 transcription in HTLV-I leukemic cells

Persistent inhibition of telomerase induces a severe telomere shortening in human T-cell leukemia virus type-1-infected cells which signals a DNA double-strand break damage response, formation of telomere dysfunction-induced foci and activates the ATM pathway. In turn, activation of ATM and its downstream effectors led to an increased phosphorylation and acetylation on specific residues of p53 known to be involved in transcriptional activation. Disruption of Mdm2-p53 complexes coupled with increased proteasomal degradation of MDMX further enhanced reactivation of p53 transcription, ultimately leading to senescence of tumor cells. Induction of senescence in these T-cells was associated with an increased expression of p21, p16 and activation of GSK3beta. Our results support the cancer-aging model and demonstrate that the halt of aging in cancer cells can be reversed through reactivation of p53.