Adult T-cell leukemia cells are characterized by abnormalities of Helios expression that promote T cell growth

RUNX1 expression is regulated by a super-enhancer and is a therapeutic target in adult T-cell leukemia/lymphoma

Super-enhancers (SEs) play an important role in regulating tumor-specific gene expression. JQ1, a Bromodomain-containing protein 4 (BRD4) inhibitor, exerts antitumor effects by disrupting SE-mediated regulation of gene expression. We investigated the anti-adult T-cell leukemia/lymphoma (ATL) effects of JQ1. JQ1 induced apoptosis and inhibited ATL cell proliferation. JQ1 suppressed RUNX1expression through the disruption of SE-mediated gene regulation. In the previous reports, it was shown that IC50s of AI-10-104 and Ro5-3335, RUNX1 inhibitors were 1-10 µM for lymphoblastic leukemia cell lines carrying RUNX1 mutations. In the present study, we demonstrated that IC50s of AI-10-104 and Ro5-3335 were also 1-10 µM or lower for ATL cell lines. Simultaneously, AI-10-104 suppressed MYC proto-oncogene (c-MYC) expression. RUNX1 is a potential therapeutic target for ATL that promotes c-MYC expression. We showed that RUNX1 expression is regulated via SEs in ATL and that RUNX1 may be a novel therapeutic target for ATL.

Disease-associated AIOLOS variants lead to immune deficiency/dysregulation by haploinsufficiency and redefine AIOLOS functional domains

AIOLOS, also known as IKZF3, is a transcription factor that is highly expressed in the lymphoid lineage and is critical for lymphocyte differentiation and development. Here, we report on 9 individuals from 3 unrelated families carrying AIOLOS variants Q402* or E82K, which led to AIOLOS haploinsufficiency through different mechanisms of action. Nonsense mutant Q402* displayed abnormal DNA binding, pericentromeric targeting, posttranscriptional modification, and transcriptome regulation. Structurally, the mutant lacked the AIOLOS zinc finger (ZF) 5-6 dimerization domain, but was still able to homodimerize with WT AIOLOS and negatively regulate DNA binding through ZF1, a previously unrecognized function for this domain. Missense mutant E82K showed overall normal AIOLOS functions; however, by affecting a redefined AIOLOS protein stability domain, it also led to haploinsufficiency. Patients with AIOLOS haploinsufficiency showed hypogammaglobulinemia, recurrent infections, autoimmunity, and allergy, but with incomplete clinical penetrance. Altogether, these data redefine the AIOLOS structure-function relationship and expand the spectrum of AIOLOS-associated diseases.

High Expression of IKZF2 in Malignant T Cells Promotes Disease Progression in Cutaneous T Cell Lymphoma

Cutaneous T cell lymphoma is a generally indolent disease derived from skin-homing mature T cells. However, in advanced stages, cutaneous T cell lymphoma may manifest aggressive clinical behaviour and lead to a poor prognosis. The mechanism of disease progression in cutaneous T cell lymphoma remains unknown. This study, based on a large clinical cohort, found that IKZF2, an essential transcription factor during T cell development and differentiation, showed stage-dependent overexpression in the malignant T cells in mycosis fungoides lesions. IKZF2 is specifically over-expressed in advanced-stage mycosis fungoides lesions, and correlates with poor prognosis. Mechanistically, overexpression of IKZF2 promotes cutaneous T cell lymphoma progression via inhibiting malignant cell apoptosis and may contribute to tumour immune escape by downregulating major histocompatibility complex II molecules and up-regulating the production of anti-inflammatory cytokine interleukin-10 by malignant T cells. These results demonstrate the important role of IKZF2 in high-risk cutaneous T cell lymphoma and pave the way for future targeted therapy.

Loss-of-function mutation in IKZF2 leads to immunodeficiency with dysregulated germinal center reactions and reduction of MAIT cells

[Figure: see text].

The HTLV-1 viral oncoproteins Tax and HBZ reprogram the cellular mRNA splicing landscape

Viral infections are known to hijack the transcription and translation of the host cell. However, the extent to which viral proteins coordinate these perturbations remains unclear. Here we used a model system, the human T-cell leukemia virus type 1 (HTLV-1), and systematically analyzed the transcriptome and interactome of key effectors oncoviral proteins Tax and HBZ. We showed that Tax and HBZ target distinct but also common transcription factors. Unexpectedly, we also uncovered a large set of interactions with RNA-binding proteins, including the U2 auxiliary factor large subunit (U2AF2), a key cellular regulator of pre-mRNA splicing. We discovered that Tax and HBZ perturb the splicing landscape by altering cassette exons in opposing manners, with Tax inducing exon inclusion while HBZ induces exon exclusion. Among Tax- and HBZ-dependent splicing changes, we identify events that are also altered in Adult T cell leukemia/lymphoma (ATLL) samples from two independent patient cohorts, and in well-known cancer census genes. Our interactome mapping approach, applicable to other viral oncogenes, has identified spliceosome perturbation as a novel mechanism coordinated by Tax and HBZ to reprogram the transcriptome.

Tax and HBZ are two viral regulatory proteins encoded by the human T-cell leukemia virus type 1 (HTLV-1) via sense and antisense transcripts, respectively. Both proteins are known to drive oncogenic processes that culminate in a T-cell neoplasm, known as Adult T cell leukemia/lymphoma (ATLL). We measured the effects of Tax and HBZ on host gene expression pathway by analyzing the interactome with cellular transcriptional and post-transcriptional regulators, and the transcriptome and mRNA splicing of cell lines expressing either Tax or HBZ. We compared our results with data obtained from independent cohorts of Japanese and Afro-Caribbean patients, and identified common splicing changes that might represent clinically useful biomarkers for ATLL. Finally, we provide evidence that the viral protein Tax can reprogram initial steps of the T-cell transcriptome diversification by hijacking the U2AF complex, a key cellular regulator of pre-mRNA splicing.

Clinical application of genomic aberrations in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATL) is an aggressive peripheral T-cell malignancy with a markedly poor prognosis. The low prevalence of ATL among human T-cell leukemia virus type-1 (HTLV-1) carriers and the long latency period before ATL onset suggest that additional genetic lesions are required for ATL leukemogenesis. Recently, a large-scale genetic analysis clarified the entire picture of genetic alterations, identified a number of novel driver genes, and delineated their characteristics. Frequent alterations are observed in the molecules belonging to T-cell receptor/NF-κB signaling and other T-cell-related pathways. A notable feature of the ATL genome is the predominance of gain-of-function alterations, including activating mutations in PLCG1, PRKCB, and CARD11. As many as one-fourth of all ATL cases harbor structural variations disrupting the 3'-untranslated region of the PD-L1 gene, leading to immune evasion of tumor cells. The frequency and pattern of these somatic alterations differ among clinical subtypes. Aggressive subtypes are associated with an increased burden of genetic alterations, and higher frequencies of TP53 and IRF4 mutations, PD-L1 amplifications, and CDKN2A deletions than indolent subtypes. In contrast, STAT3 mutations are more characteristic of indolent ATL. Furthermore, these subtypes are further classified into molecularly distinct subsets with a different prognosis by genetic alterations. We present an overview of the current understanding of somatic alterations in ATL, with specific focus on their utility in clinical settings. Furthermore, we highlight their genetic features by exploring their similarities and differences among peripheral T-cell lymphomas.

Coexpression of FOXP3 and a Helios isoform enhances the effectiveness of human engineered regulatory T cells

Regulatory T cells (Tregs) are a subset of immune cells that suppress the immune response. Treg therapy for inflammatory diseases is being tested in the clinic, with moderate success. However, it is difficult to isolate and expand Tregs to sufficient numbers. Engineered Tregs (eTregs) can be generated in larger quantities by genetically manipulating conventional T cells to express FOXP3. These eTregs can suppress in vitro and in vivo but not as effectively as endogenous Tregs. We hypothesized that ectopic expression of the transcription factor Helios along with FOXP3 is required for optimal eTreg immunosuppression. To test this theory, we generated eTregs by retrovirally transducing total human T cells (CD4+ and CD8+) with FOXP3 alone or with each of the 2 predominant isoforms of Helios. Expression of both FOXP3 and the full-length isoform of Helios was required for eTreg-mediated disease delay in a xenogeneic graft-versus-host disease model. In vitro, this corresponded with superior suppressive function of FOXP3 and full-length Helios-expressing CD4+ and CD8+ eTregs. RNA sequencing showed that the addition of full-length Helios changed gene expression in cellular pathways and the Treg signature compared with FOXP3 alone or the other major Helios isoform. Together, these results show that functional human CD4+ and CD8+ eTregs can be generated from total human T cells by coexpressing FOXP3 and full-length Helios.

Molecular heterogeneity in peripheral T-cell lymphoma, not otherwise specified revealed by comprehensive genetic profiling

Peripheral T-cell lymphoma, not otherwise specified (PTCL, NOS) is a diagnosis of exclusion, being the most common entity in mature T-cell neoplasms, and its molecular pathogenesis remains significantly understudied. Here, combining whole-exome and targeted-capture sequencing, gene-expression profiling, and immunohistochemical analysis of tumor samples from 133 cases, we have delineated the entire landscape of somatic alterations, and discovered frequently affected driver pathways in PTCL, NOS, with and without a T-follicular helper (TFH) cell phenotype. In addition to previously reported mutational targets, we identified a number of novel recurrently altered genes, such as KMT2C, SETD1B, YTHDF2, and PDCD1. We integrated these genetic drivers using hierarchical clustering and identified a previously undescribed molecular subtype characterized by TP53 and/or CDKN2A mutations and deletions in non-TFH PTCL, NOS. This subtype exhibited different prognosis and unique genetic features associated with extensive chromosomal instability, which preferentially affected molecules involved in immune escape and transcriptional regulation, such as HLA-A/B and IKZF2. Taken together, our findings provide novel insights into the molecular pathogenesis of PTCL, NOS by highlighting their genetic heterogeneity. These results should help to devise a novel molecular classification of PTCLs and to exploit a new therapeutic strategy for this group of aggressive malignancies.

IKZF2 Drives Leukemia Stem Cell Self-Renewal and Inhibits Myeloid Differentiation

Leukemias exhibit a dysregulated developmental program mediated through both genetic and epigenetic mechanisms. Although IKZF2 is expressed in hematopoietic stem cells (HSCs), we found that it is dispensable for mouse and human HSC function. In contrast to its role as a tumor suppressor in hypodiploid B-acute lymphoblastic leukemia, we found that IKZF2 is required for myeloid leukemia. IKZF2 is highly expressed in leukemic stem cells (LSCs), and its deficiency results in defective LSC function. IKZF2 depletion in acute myeloid leukemia (AML) cells reduced colony formation, increased differentiation and apoptosis, and delayed leukemogenesis. Gene expression, chromatin accessibility, and direct IKZF2 binding in MLL-AF9 LSCs demonstrate that IKZF2 regulates a HOXA9 self-renewal gene expression program and inhibits a C/EBP-driven differentiation program. Ectopic HOXA9 expression and CEBPE depletion rescued the effects of IKZF2 depletion. Thus, our study shows that IKZF2 regulates the AML LSC program and provides a rationale to therapeutically target IKZF2 in myeloid leukemia.

A comprehensive manually-curated compendium of bovine transcription factors

Transcription factors (TFs) are pivotal regulatory proteins that control gene expression in a context-dependent and tissue-specific manner. In contrast to human, where comprehensive curated TF collections exist, bovine TFs are only rudimentary recorded and characterized. In this article, we present a manually-curated compendium of 865 sequence-specific DNA-binding bovines TFs, which we analyzed for domain family distribution, evolutionary conservation, and tissue-specific expression. In addition, we provide a list of putative transcription cofactors derived from known interactions with the identified TFs. Since there is a general lack of knowledge concerning the regulation of gene expression in cattle, the curated list of TF should provide a basis for an improved comprehension of regulatory mechanisms that are specific to the species.

Role of a non-canonical splice variant of the Helios gene in the differentiation of acute lymphoblastic leukemic T cells

T-cell acute lymphoblastic leukemia is a hematopoietic malignant disease, which arises from a genetic defect in the T-cell maturation signaling pathway. As a result, it is necessary to identify the molecules that impact T-cell development and control lymphoid-lineage malignancy. The present study utilized Jurkat T lymphoblastic cells as a well-established approach for the investigation into the function of the non-canonical alternative splice variant of Helios for the in vitro study of T-cell differentiation and leukemogenesis. In the present study, the Jurkat T-cell lines with stable overexpression of the wild-type (Helios-1) or the non-canonical short isoform (Helios-Δ326-1431), were established. RNA microarray, reverse transcription-quantitative polymerase chain reaction and flow cytometry were used to assess changes in the gene expression profiles and to monitor the cell surface markers during T-cell differentiation. Multiple genes associated with T-cell differentiation and leukemogenesis were identified as being either activated or suppressed. In addition, the results indicated that the stable overexpression of the Helios isoforms stimulated the differentiation pathway of the T-lineage lymphoblastic cells. Therefore, these results suggest that full-length Helios-1 has a tumor suppressor-like and immunomodulatory role, in contrast to the oncogenic function of the non-canonical short isoform Helios-Δ326-1431.

An activating mutation of interferon regulatory factor 4 (IRF4) in adult T-cell leukemia

The human T-cell leukemia virus-1 (HTLV-1) oncoprotein Tax drives cell proliferation and resistance to apoptosis early in the pathogenesis of adult T-cell leukemia (ATL). Subsequently, probably as a result of specific immunoediting, Tax expression is down-regulated and functionally replaced by somatic driver mutations of the host genome. Both amplification and point mutations of interferon regulatory factor 4 (IRF4) have been previously detected in ATL., K59R is the most common single-nucleotide variation of IRF4 and is found exclusively in ATL. High-throughput whole-exome sequencing revealed recurrent activating genetic alterations in the T-cell receptor, CD28, and NF-κB pathways. We found that IRF4, which is transcriptionally activated downstream of these pathways, is frequently mutated in ATL. IRF4 RNA, protein, and IRF4 transcriptional targets are uniformly elevated in HTLV-1-transformed cells and ATL cell lines, and IRF4 was bound to genomic regulatory DNA of many of these transcriptional targets in HTLV-1-transformed cell lines. We further noted that the K59R IRF4 mutant is expressed at higher levels in the nucleus than WT IRF4 and is transcriptionally more active. Expression of both WT and the K59R mutant of IRF4 from a constitutive promoter in retrovirally transduced murine bone marrow cells increased the abundance of T lymphocytes but not myeloid cells or B lymphocytes in mice. IRF4 may represent a therapeutic target in ATL because ATL cells select for a mutant of IRF4 with higher nuclear expression and transcriptional activity, and overexpression of IRF4 induces the expansion of T lymphocytes in vivo.

Genetic alterations in adult T-cell leukemia/lymphoma

Adult T‐cell leukemia/lymphoma (ATL) is a peripheral T‐cell neoplasm with a dismal prognosis. It is caused by human T‐cell leukemia virus type‐1 (HTLV‐1) retrovirus. A long latency period from HTLV‐1 infection to ATL onset suggests that not only HTLV‐1 proteins, such as Tax and HBZ, but also additional genetic and/or epigenetic events are required for ATL development. Although many studies have demonstrated the biological functions of viral genes, alterations of cellular genes associated with ATL have not been fully investigated. Recently, a large‐scale integrated genetic analysis revealed the entire landscape of somatic aberrations in ATL. This neoplasm is characterized by frequent gain‐of‐function alterations in components of the T‐cell receptor/NF‐κB signaling pathway, including activating mutations in the PLCG1,PRKCB,CARD11 and VAV1 genes, and CTLA4‐CD28 and ICOS‐CD28 fusions. Importantly, molecules associated with immune surveillance, such as HLA‐A/B,CD58 and FAS, are affected recurrently. Among them, one notable lesion occurs as frequent structural variations that truncate the PD‐L1 3′‐untranslated region, leading to its overexpression. Other genetic targets include transcription factors (IRF4,IKZF2, and GATA3) and chemokine receptors (CCR4,CCR7 and GPR183), which are functionally relevant in normal T cells. A substantial proportion of ATL cases show widespread accumulation of repressive epigenetic changes, such as trimethylation of histone H3 lysine 27 and DNA hypermethylation of CpG islands, which coordinately modulate multiple pathways, including Cys2‐His2 zinc finger genes involved in silencing retroelements. Here we review the current understanding of the genetic/epigenetic aberrations in ATL, focusing on their relevance in its molecular pathogenesis.

Expression and splicing of Ikaros family members in murine and human thymocytes

The Ikaros family of transcription factors includes five highly homologous members that can homodimerize or heterodimerize in any combination. Dimerization is essential for their ability to bind DNA and function as transcription factors. Previous studies showed that eliminating the function of the entire family blocks lymphocyte development while deletion of individual family members has relatively minor defects. These data indicate that multiple family members function during T cell development, so we examined the changes in expression of each family member as thymocytes progressed from the CD4^-CD8^- double negative (DN) to the CD4⁺CD8⁺ double positive (DP) developmental stage. Further, we compared the expression of each family member in murine and human thymocytes. In both species, Ikaros and Aiolos mRNA levels increased as thymocytes progressed through the DN to DP transition, but the corresponding increases in protein levels were only observed in mice. Further, Ikaros and Aiolos underwent extensive alternative splicing in mice, whereas only Ikaros was extensively spliced in humans. Helios mRNA and protein levels decreased during murine T cell development, but increased during human T cell development. These differences in the expression and splicing of Ikaros family members between human and murine thymocytes strongly suggest that the Ikaros family of transcription factors regulates murine and human T cell development differently, although the similarities across Ikaros family members may allow different proteins to fulfill similar functions.

Alternative Splice Variants Modulates Dominant-Negative Function of Helios in T-Cell Leukemia

The molecular defects which lead to multistep incidences of human T-cell leukemia have yet to be identified. The DNA-binding protein Helios (known as IKZF2), a member of the Ikaros family of Krüppel-like zinc-finger proteins, functions pivotally in T-cell differentiation and activation. In this study, we identify three novel short Helios splice variants which are T-cell leukemic specific, and demonstrate their dominant-negative function. We then test the cellular localization of distinct Helios isoforms, as well as their capability to form heterodimer with Ikaros, and the association with complexes comprising histone deacetylase (HDAC). In addition, the ectopic expression of T-cell leukemic Helios isoforms interferes with T-cell proliferation and apoptosis. The gene expression profiling and pathway analysis indicated the enrichment of signaling pathways essential for gene expression, translation, cell cycle checkpoint, and response to DNA damage stimulus. These data indicate the molecular function of Helios to be involved in the leukemogenesis and phenotype of T-cell leukemia, and also reveal Helios deregulation as a novel marker for T-cell leukemia.

Expression of Helios in gastric tumor cells predicts better survival in gastric cancer patients

PURPOSE

Helios belongs to Ikaros family, which plays an important role in the cell-fate decision and control cell proliferation; abnormal expressions in leukemia are associated with poor prognosis. In this study, we investigated the Helios expression between Helicobacter pylori infection and prognosis in gastric cancer patients.

METHODS

A total of 67 gastric cancer patients who received partial or full gastrectomies were enrolled. Helios expression by immunohistochemistry and mRNA was investigated with the clinical stage, Helicobacter pylori infection, CD4 expression, FoxP3 expression and prognosis.

RESULTS

From the immunohistochemistry stain, we found that the Helios was expressed in both cancer cell and tumor-infiltrated lymphocytes. The high expression of Helios in gastric tumor cells had a better median overall survival rate in gastric cancer patients (50.7 ± 3.2 vs. 34.1 ± 4.9 months; P = 0.015), Helicobacter pylori-infected patients (51.1 ± 3.5 vs. 30.4 ± 5.1 months; P = 0.007) and advanced gastric cancer patients (42.1 ± 5.5 vs. 23.2 ± 4.8 months; P = 0.043). From multivariate analysis, the Helios expression in gastric tumor cells was an independent factor to predict better survival in all gastric cancers (HR = 2.78; 95 % confidence interval [CI], 1.09-7.09; P = 0.032) and advanced gastric cancer patients (HR = 2.85; 95 % confidence interval [CI], 1.00-8.13; P = 0.03).

CONCLUSIONS

Higher expression of Helios in gastric tumor cells predicts better survival in gastric cancer patients, especially for Helicobacter pylori-infected and advanced-stage gastric cancer patients.

Dysregulation of c-Myb Pathway by Aberrant Expression of Proto-oncogene MYB Provides the Basis for Malignancy in Adult T-cell Leukemia/lymphoma Cells

PURPOSE

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive human T-cell malignancy induced by human T-lymphotrophic virus-1 (HTLV-1) infection. The genetic alterations in infected cells that lead to transformation have not been completely elucidated, thus hindering the identification of effective therapeutic targets for ATL. Here, we present the first assessment of MYB proto-oncogene dysregulation in ATL and an exploration of its role in the onset of ATL.

EXPERIMENTAL DESIGN

We investigated the expression patterns of MYB splicing variants in ATL. The molecular characteristics of the c-Myb-9A isoform, which was overexpressed in ATL cells, were examined using chromatin immunoprecipitation and promoter assays. We further examined the biologic impacts of abnormal c-Myb overexpression in ATL using overall c-Myb knockdown with shRNA or c-Myb-9A knockdown with morpholino oligomers.

RESULTS

Both total c-Myb and c-Myb-9A, which exhibited strong transforming activity, were overexpressed in ATL cells in a leukemogenesis- and progression-dependent manner. Knockdown of either total c-Myb or c-Myb-9A induced ATL cell death. c-Myb transactivates nine genes that encode essential regulators of cell proliferation and NF-κB signaling. c-Myb-9A induced significantly stronger transactivation of all tested genes and stronger NF-κB activation compared with wild-type c-Myb.

CONCLUSIONS

Our data demonstrate that c-Myb pathway overactivation caused by unbalanced c-Myb-9A overexpression is associated with disorders in cellular homeostasis and consequently, accelerated transformation, cell proliferation, and malignancy in ATL cells. These data support the notion of the c-Myb pathway as a promising new therapeutic target for ATL. Clin Cancer Res; 22(23); 5915-28. ©2016 AACR.

Integrated molecular analysis of adult T cell leukemia/lymphoma

Adult T cell leukemia/lymphoma (ATL) is a peripheral T cell neoplasm of largely unknown genetic basis, associated with human T cell leukemia virus type-1 (HTLV-1) infection. Here we describe an integrated molecular study in which we performed whole-genome, exome, transcriptome and targeted resequencing, as well as array-based copy number and methylation analyses, in a total of 426 ATL cases. The identified alterations overlap significantly with the HTLV-1 Tax interactome and are highly enriched for T cell receptor-NF-κB signaling, T cell trafficking and other T cell-related pathways as well as immunosurveillance. Other notable features include a predominance of activating mutations (in PLCG1, PRKCB, CARD11, VAV1, IRF4, FYN, CCR4 and CCR7) and gene fusions (CTLA4-CD28 and ICOS-CD28). We also discovered frequent intragenic deletions involving IKZF2, CARD11 and TP73 and mutations in GATA3, HNRNPA2B1, GPR183, CSNK2A1, CSNK2B and CSNK1A1. Our findings not only provide unique insights into key molecules in T cell signaling but will also guide the development of new diagnostics and therapeutics in this intractable tumor.

Interferon-γ Promotes Inflammation and Development of T-Cell Lymphoma in HTLV-1 bZIP Factor Transgenic Mice

Human T-cell leukemia virus type 1 (HTLV-1) is an etiological agent of several inflammatory diseases and a T-cell malignancy, adult T-cell leukemia (ATL). HTLV-1 bZIP factor (HBZ) is the only viral gene that is constitutively expressed in HTLV-1-infected cells, and it has multiple functions on T-cell signaling pathways. HBZ has important roles in HTLV-1-mediated pathogenesis, since HBZ transgenic (HBZ-Tg) mice develop systemic inflammation and T-cell lymphomas, which are similar phenotypes to HTLV-1-associated diseases. We showed previously that in HBZ-Tg mice, HBZ causes unstable Foxp3 expression, leading to an increase in regulatory T cells (Tregs) and the consequent induction of IFN-γ-producing cells, which in turn leads to the development of inflammation in the mice. In this study, we show that the severity of inflammation is correlated with the development of lymphomas in HBZ-Tg mice, suggesting that HBZ-mediated inflammation is closely linked to oncogenesis in CD4+ T cells. In addition, we found that IFN-γ-producing cells enhance HBZ-mediated inflammation, since knocking out IFN-γ significantly reduced the incidence of dermatitis as well as lymphoma. Recent studies show the critical roles of the intestinal microbiota in the development of Tregs in vivo. We found that even germ-free HBZ-Tg mice still had an increased number of Tregs and IFN-γ-producing cells, and developed dermatitis, indicating that an intrinsic activity of HBZ evokes aberrant T-cell differentiation and consequently causes inflammation. These results show that immunomodulation by HBZ is implicated in both inflammation and oncogenesis, and suggest a causal connection between HTLV-1-associated inflammation and ATL.

Alternative splicing of DNA damage response genes and gastrointestinal cancers

Alternative splicing, which is a common phenomenon in mammalian genomes, is a fundamental process of gene regulation and contributes to great protein diversity. Alternative splicing events not only occur in the normal gene regulation process but are also closely related to certain diseases including cancer. In this review, we briefly demonstrate the concept of alternative splicing and DNA damage and describe the association of alternative splicing and cancer pathogenesis, focusing on the potential relationship of alternative splicing, DNA damage, and gastrointestinal cancers. We will also discuss whether alternative splicing leads to genetic instability, which is considered to be a driving force for tumorigenesis. Better understanding of the role and mechanism of alternative splicing in tumorigenesis may provide new directions for future cancer studies.

CADM1 expression and stepwise downregulation of CD7 are closely associated with clonal expansion of HTLV-I-infected cells in adult T-cell leukemia/lymphoma

PURPOSE

Cell adhesion molecule 1 (CADM1), initially identified as a tumor suppressor gene, has recently been reported to be ectopically expressed in primary adult T-cell leukemia-lymphoma (ATL) cells. We incorporated CADM1 into flow-cytometric analysis to reveal oncogenic mechanisms in human T-cell lymphotrophic virus type I (HTLV-I) infection by purifying cells from the intermediate stages of ATL development.

EXPERIMENTAL DESIGN

We isolated CADM1- and CD7-expressing peripheral blood mononuclear cells of asymptomatic carriers and ATLs using multicolor flow cytometry. Fluorescence-activated cell sorted (FACS) subpopulations were subjected to clonal expansion and gene expression analysis.

RESULTS

HTLV-I-infected cells were efficiently enriched in CADM1(+) subpopulations (D, CADM1(pos)CD7(dim) and N, CADM1(pos)CD7(neg)). Clonally expanding cells were detected exclusively in these subpopulations in asymptomatic carriers with high proviral load, suggesting that the appearance of D and N could be a surrogate marker of progression from asymptomatic carrier to early ATL. Further disease progression was accompanied by an increase in N with a reciprocal decrease in D, indicating clonal evolution from D to N. The gene expression profiles of D and N in asymptomatic carriers showed similarities to those of indolent ATLs, suggesting that these subpopulations represent premalignant cells. This is further supported by the molecular hallmarks of ATL, that is, drastic downregulation of miR-31 and upregulation of abnormal Helios transcripts.

CONCLUSION

The CADM1 versus CD7 plot accurately reflects disease progression in HTLV-I infection, and CADM1(+) cells with downregulated CD7 in asymptomatic carriers have common properties with those in indolent ATLs.

Adult T-cell leukemia cells are characterized by abnormalities of Helios expression that promote T cell growth

Molecular abnormalities involved in the multistep leukemogenesis of adult T-cell leukemia (ATL) remain to be clarified. Based on our integrated database, we focused on the expression patterns and levels of Ikaros family genes, Ikaros, Helios, and Aiolos, in ATL patients and HTLV-1 carriers. The results revealed profound deregulation of Helios expression, a pivotal regulator in the control of T-cell differentiation and activation. The majority of ATL samples (32/37 cases) showed abnormal splicing of Helios expression, and four cases did not express Helios. In addition, novel genomic loss in Helios locus was observed in 17/168 cases. We identified four ATL-specific short Helios isoforms and revealed their dominant-negative function. Ectopic expression of ATL-type Helios isoform as well as knockdown of normal Helios or Ikaros promoted T-cell growth. Global mRNA profiling and pathway analysis showed activation of several signaling pathways important for lymphocyte proliferation and survival. These data provide new insights into the molecular involvement of Helios function in the leukemogenesis and phenotype of ATL cells, indicating that Helios deregulation is one of the novel molecular hallmarks of ATL.