Inactivation of tumor suppressor genes and the progression of adult T-cell leukemia-lymphoma

Biology and Molecular Pathogenesis of Mature T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCLs) constitute a highly heterogeneous group of hematological diseases with complex clinical and molecular features consistent with the diversity of the T-cell type from which they originate. In the past several years, the systematic implementation of high-throughput genomic technologies for the analysis of T-cell malignancies has supported an exponential progress in our understanding of the genetic drivers of oncogenesis and unraveled the molecular complexity of these diseases. Recent findings have helped redefine the classification of T-cell malignancies and provided novel biomarkers to improve diagnosis accuracy and analyze the response to therapy. In addition, multiple novel targeted therapies including small-molecule inhibitors, antibody-based approaches, and immunotherapy have shown promising results in early clinical analysis and have the potential to completely change the way T-cell malignancies have been treated traditionally.

TET2 Mutation in Adult T-Cell Leukemia/Lymphoma

Loss-of-function of ten-eleven translocation-2 (TET2) is a common event in myeloid malignancies, and plays pleiotropic roles, including augmenting stem cell self-renewal and skewing hematopoietic cells to the myeloid lineage. TET2 mutation has also been reported in lymphoid malignancies; 5.7～12% of diffuse large B-cell lymphomas and 18～83% of angioimmunoblastic T-cell lymphomas had TET2 mutations. We investigated TET2 mutations in 22 adult T-cell leukemia/lymphoma (ATLL) patients and identified a missense mutation in 3 cases (14%). TET2 mutation occurred in a number of ATLL patients and was likely involved in their leukemogenesis.

Multiple Pathways Control the Reactivation of Telomerase in HTLV-I-Associated Leukemia

While telomerase (hTERT) activity is absent from normal somatic cells, reactivation of hTERT expression is a hallmark of cancer cells. Telomerase activity is required for avoiding replicative senescence and supports immortalization of cellular proliferation. Only a minority of cancer cells rely on a telomerase-independent process known as alternative lengthening of telomeres, ALT, to sustain cancer cell proliferation. Multiple genetic, epigenetic, and viral mechanisms have been found to de-regulate telomerase gene expression, thereby increasing the risk of cellular transformation. Here, we review the different strategies used by the Human T-cell leukemia virus type 1, HTLV-I, to activate hTERT expression and stimulate its enzymatic activity in virally infected CD4 T cells. The implications of hTERT reactivation in HTLV-I pathogenesis and disease treatment are discussed.

Cluster Analysis of Tumor Suppressor Genes in Canine Leukocytes Identifies Activation State

Cells of the immune system undergo activation and subsequent proliferation in the normal course of an immune response. Infrequently, the molecular and cellular events that underlie the mechanisms of proliferation are dysregulated and may lead to oncogenesis, leading to tumor formation. The most common forms of immunological cancers are lymphomas, which in dogs account for 8%–20% of all cancers, affecting up to 1.2% of the dog population. Key genes involved in negatively regulating proliferation of lymphocytes include a group classified as tumor suppressor genes (TSGs). These genes are also known to be associated with progression of lymphoma in humans, mice, and dogs and are potential candidates for pathological grading and diagnosis. The aim of the present study was to analyze TSG profiles in stimulated leukocytes from dogs to identify genes that discriminate an activated phenotype. A total of 554 TSGs and three gene set collections were analyzed from microarray data. Cluster analysis of three subsets of genes discriminated between stimulated and unstimulated cells. These included 20 most upregulated and downregulated TSGs, TSG in hallmark gene sets significantly enriched in active cells, and a selection of candidate TSGs, p15 (CDKN2B), p18 (CDKN2C), p19 (CDKN1A), p21 (CDKN2A), p27 (CDKN1B), and p53 (TP53) in the third set. Analysis of two subsets suggested that these genes or a subset of these genes may be used as a specialized PCR set for additional analysis.

TESTIN suppresses tumor growth and invasion via manipulating cell cycle progression in endometrial carcinoma

BACKGROUND

The TESTIN gene was demonstrated to be a tumor suppressor in prostate and breast cancer through inhibiting tumor growth and invasion. Herein, we aimed to investigate the detailed functions of TESTIN in the highly sexual hormone (estrogen)-dependent malignancy, endometrial carcinoma.

MATERIAL AND METHODS

TESTIN mRNA and protein expression were measured by qRT-PCR, Western blot and immunohistochemistry. Upregulation of TESTIN was achieved by transfecting the pcDNA3.1-TESTIN plasmids into AN3CA cells. Knockdown of TESTIN was achieved by transfecting the shRNA-TESTIN into Ishikawa cells. MTT assay, colony formation assay, and Transwell assay were used to investigate the effects of TESTIN on cellular proliferation and invasion. The apoptotic status and cell cycle were analyzed using flow cytometry. MMP2 secretion was determined by ELISA assay. The xenograft assay was used to investigate the functions of TESTIN in nude mice.

RESULTS

Compared to the non-malignant adjacent endometrium, 54% of tumor samples presented downregulation of TESTIN (P<0.001). Loss of TESTIN protein was correlated with advanced tumor stage (P=0.047), high grade (P=0.034), and lymphatic vascular space invasion (P=0.036). In vitro, overexpression of TESTIN suppressed cell proliferation, induced dramatic G1 arrest, and inhibited tumor invasion through blocking the secretion of MMP2. Loss of TESTIN accelerated cellular proliferation, promoted cell cycle progression, and enhanced tumor invasion by increasing the secretion of MMP2. Consistently, TESTIN could significantly delay the growth of xenografts in nude mice.

CONCLUSIONS

TESTIN was commonly downregulated in human endometrial carcinoma and was associated with poor prognostic markers. Moreover, TESTIN significantly inhibited tumor growth and invasion via arresting cell cycle in in vitro and in vivo experiments. Therefore, we propose that TESTIN might be a prognostic marker and therapeutic target for endometrial carcinoma.

Use of single nucleotide polymorphism array technology to improve the identification of chromosomal lesions in leukemia

Acute leukemias are characterized by recurring chromosomal and genetic abnormalities that disrupt normal development and drive aberrant cell proliferation and survival. Identification of these abnormalities plays important role in diagnosis, risk assessment and patient classification. Until the last decade methods to detect these aberrations have included genome wide approaches, such as conventional cytogenetics, but with a low sensitivity (5-10%), or gene candidate approaches, such as fluorescent in situ hybridization, having a greater sensitivity but being limited to only known regions of the genome. Single nucleotide polymorphism (SNP) technology is a screening method that has revolutionized our way to find genetic alterations, enabling linkage and association studies between SNP genotype and disease as well as the identification of alterations in DNA content on a whole genome scale. The adoption of this approach for the study of lymphoid and myeloid leukemias contributed to the identification of novel genetic alterations, such as losses/gains/uniparental disomy not visible by cytogenetics and implicated in pathogenesis, improving risk assessment and patient classification and in some cases working as targets for tailored therapies. In this review, we reported recent advances obtained in the knowledge of the genomic complexity of chronic myeloid leukemia and acute leukemias thanks to the use of high-throughput technologies, such as SNP array.

The microRNA regulatory network in normal- and HTLV-1-transformed T cells

Recent efforts to understand the molecular networks governing normal T cell development and driving the neoplastic transformation of T cells have brought to light the involvement of microRNAs (miRNAs), a class of noncoding RNAs of approximately 22 nucleotides that regulate gene expression at the posttranscriptional level. In the present review, we compare the expression profiles of miRNAs in normal T cell development to that of transformed T cells using as a model adult T cell leukemia/lymphoma, an aggressive malignancy of mature CD4+ T cells that is caused by infection with human T cell leukemia virus type 1.

Autocrine/paracrine cytokine stimulation of leukemic cell proliferation in smoldering and chronic adult T-cell leukemia

Adult T-cell leukemia (ATL), a heterogeneous disease, can be divided into smoldering, chronic, lymphoma, and acute types clinically. In addition to different clinical manifestations, different stages of ATL have different molecular signatures. Here, we demonstrated that smoldering/chronic ATL peripheral blood mononuclear cells spontaneously proliferated ex vivo in a cytokine (interleukin-12 [IL-12]/IL-9/IL-15)-dependent manner, while acute-type ATL peripheral blood mononuclear cells did not proliferate or proliferated independent of cytokines. Smoldering/chronic ATL cells produced IL-2 and IL-9 in 6-day ex vivo cultures. Interestingly, the addition of an anti-IL-2R-α monoclonal antibody profoundly inhibited IL-9 expression, suggesting optimal expression of IL-9 was dependent on IL-2 signaling in these patients. To determine whether there would be autonomous proliferation of ATL leukemic cells, we purified leukemic cells from patients with smoldering/chronic ATL. Purified leukemic cells cultured alone produced IL-2/IL-9, and the downstream Janus kinase/signal transducer and activator of transcription pathway was activated. However, the leukemic cells did not proliferate independently, but required coculture with autologous monocytes to induce proliferation. Moreover, interaction between leukemic cells and monocytes was contact dependent, and major histocompatibility complex class II expression may have contributed to this interaction. In conclusion, our data provide evidence that there is autocrine/paracrine cytokine stimulation of leukemic cell proliferation in patients with smoldering/chronic ATL that could be targeted for treatment.

Adult T-cell leukemia/lymphoma and HTLV-1

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) was the first oncogenic human retrovirus to be discovered, more than 25 years ago. HTLV-1 infects 15 to 20 million individuals worldwide. This oncoretrovirus can be transmitted in three ways: horizontally (sexually), vertically (mother to child), and via blood transfusion. HTLV-1 causes two major diseases: adult T-cell leukemia/lymphoma (ATLL) and tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM). ATLL can be classified into four major subtypes: a smoldering type, a chronic type, a lymphoma type, and a leukemic type. Because of intrinsic chemoresistance and severe immunosuppression, the survival rate of ATLL patients, especially those who develop the acute leukemic or lymphoma forms, is very poor, and such clonal malignant CD4 expansion remains one of the most severe lymphoproliferations. This article discusses a number of recent treatments including antiretroviral therapy, aggressive chemotherapy, and allogeneic bone-marrow transplantation, as well as new drugs.

Role of microRNAs in HTLV-1 infection and transformation

Human T-cell leukemia virus type 1 (HTLV-1), a retrovirus that infects more than 20 million people worldwide, is the etiological agent of ATLL (adult T-cell leukemia/lymphoma), an aggressive leukemia of CD4+ T lymphocytes which arises in a small percentage of infected individuals after a long clinical latency. Tumor emergence is attributed primarily to the oncogenic activity of the viral protein Tax, which drives the expression of viral transcripts and controls the expression and function of a broad variety of host-cell genes involved in proliferation, genetic stability and apoptosis. Nevertheless, many aspects of HTLV-1 replication, persistence and pathogenesis remain to be understood. The emerging role of microRNAs in tumor development and viral infection has prompted investigations on the interactions between HTLV-1 and the microRNA regulatory network. In the present review we discuss recent data demonstrating changes in cellular microRNA expression in HTLV-1-infected cell lines and ATLL cells, and the functional impact of a subset microRNAs deregulated by HTLV-1 on cellular gene expression and signal transduction pathways. Mechanisms through which the viral proteins may influence microRNA expression are discussed. Results of searches for potential cellular microRNAs that target viral transcripts and for microRNAs produced by HTLV-1 are described. Observations along with regarding the expression of tRNA-derived small regulatory RNAs in HTLV-1-infected cells are presented.

Human T cell leukemia virus reactivation with progression of adult T-cell leukemia-lymphoma

BACKGROUND

Human T-cell leukemia virus-associated adult T-cell leukemia-lymphoma (ATLL) has a very poor prognosis, despite trials of a variety of different treatment regimens. Virus expression has been reported to be limited or absent when ATLL is diagnosed, and this has suggested that secondary genetic or epigenetic changes are important in disease pathogenesis.

METHODS AND FINDINGS

We prospectively investigated combination chemotherapy followed by antiretroviral therapy for this disorder. Nineteen patients were prospectively enrolled between 2002 and 2006 at five medical centers in a phase II clinical trial of infusional chemotherapy with etoposide, doxorubicin, and vincristine, daily prednisone, and bolus cyclophosphamide (EPOCH) given for two to six cycles until maximal clinical response, and followed by antiviral therapy with daily zidovudine, lamivudine, and alpha interferon-2a for up to one year. Seven patients were on study for less than one month due to progressive disease or chemotherapy toxicity. Eleven patients achieved an objective response with median duration of response of thirteen months, and two complete remissions. During chemotherapy induction, viral RNA expression increased (median 190-fold), and virus replication occurred, coincident with development of disease progression.

CONCLUSIONS

EPOCH chemotherapy followed by antiretroviral therapy is an active therapeutic regimen for adult T-cell leukemia-lymphoma, but viral reactivation during induction chemotherapy may contribute to treatment failure. Alternative therapies are sorely needed in this disease that simultaneously prevent virus expression, and are cytocidal for malignant cells.

Implication of the HTLV-I bZIP factor gene in the leukemogenesis of adult T-cell leukemia

Adult T-cell leukemia (ATL) is a leukemia derived from CD4+ mature T-cells and induced by human T-cell leukemia virus type I (HTLV-I) infection. Although previous studies have revealed many aspects of its leukemogenesis, enigmas remain about how HTLV-I transforms mature T-cells in infected individuals. Furthermore, an effective therapy for ATL has not yet been established. The critical role of a nonstructural regulatory viral protein, Tax, in transformation has been established through many molecular studies, in vitro cell culture experiments, and transgenic mouse model systems. In addition, other accessory viral proteins have been implicated in ATL pathogenesis. Recent studies of a minus strand viral gene, HTLV-I bZIP factor (HBZ), suggest it plays a role in ATL leukemogenesis. In addition to viral components, genetic and epigenetic events of the host cellular genome must be considered in developing a complete picture of the transformation process. In this review, we summarize the molecular and cellular mechanisms involved in the leukemogenesis induced by HTLV-I; we consider both viral and host cellular factors and focus particularly on the viral gene HBZ.