Akifumi Takaori-Kondo

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.

The Enzymatic Activity of CEM15/Apobec-3G Is Essential for the Regulation of the Infectivity of HIV-1 Virion but Not a Sole Determinant of Its Antiviral Activity

Human immunodeficiency virus, type 1 (HIV-1) Vif protein plays an essential role in the regulation of the infectivity of HIV-1 virion. Vif functions to counteract an anti-HIV-1 cellular factor in non-permissive cells, CEM15/Apobec-3G, which shares a cytidine deaminase motif. CEM15/Apobec-3G deaminates dC to dU in the minus strand DNA of HIV-1, resulting in G to A hypermutation in the plus strand DNA. In this study, we have done the mutagenesis analysis on two cytidine deaminase motifs in CEM15/Apobec-3G and examined their antiviral functions as well as the DNA editing activity. Point mutations in the C-terminal active site such as E259Q and C291A almost completely abrogated the antiviral function, while those in the N-terminal active site such as E67Q and C100A retained this activity to a lesser extent as compared with that of the wild type. The DNA editing activities of E67Q and E259Q mutants were both retained but impaired to the same extent. This indicates that the enzymatic activity of this protein is essential but not a sole determinant of the antiviral activity. Furthermore, all the deletion mutants tested in this study lost the antiviral activity because of the loss of the activity for dimerization, suggesting that the entire protein structure is necessary for the antiviral function.

Activation of OX40 Signal Transduction Pathways Leads to Tumor Necrosis Factor Receptor-associated Factor (TRAF) 2- and TRAF5-mediated NF-κB Activation

We investigated the intracellular signaling of OX40, a member of the tumor necrosis factor receptor family. Activation of NF-κB in OX40-transfected HSB-2 cells was detected by electrophoretic mobility shift assay within 30 min after the binding of the ligand gp34. In vitro binding experiments showed that tumor necrosis factor receptor-associated factor (TRAF) 1, TRAF2, TRAF3, and TRAF5 but not TRAF4 associated with glutathioneS-transferase-OX40 fusion protein. The cotransfection experiments using human embryo kidney cell derived HEK 293T cells showed that TRAF2, TRAF3, and TRAF5 associated with OX40 in vivo. Studies with OX40 deletion mutants demonstrated that the cytoplasmic portion consisting of amino acid sequence 256–263 (GGSFRTPI) was required for the association with TRAFs and NF-κB activation. The introduction of the dominant negative mutants of TRAF2 and TRAF5 into HSB-2-OX40 cells suppressed NF-κB activation in a dose-dependent manner. In addition, the introduction of TRAF3 together with the dominant negative mutants of TRAF2 or TRAF5 further reduced NF-κB activation. These results indicate that the NF-κB activation resulting from OX40 stimulation is mediated by both TRAF2 and TRAF5, and is likely to be negatively modulated by TRAF3.

Natural Alpha Interferon-Producing Cells Respond to Human Immunodeficiency Virus Type 1 with Alpha Interferon Production and Maturation into Dendritic Cells

ABSTRACT Natural alpha interferon (IFN-α)-producing cells (IPCs) are now recognized as identical to plasmacytoid dendritic cell (DC) precursors in human blood and are thought to play an important role in antiviral immunity. In the present study, we examined the susceptibility as well as the cellular responses of IPCs to human immunodeficiency virus type 1 (HIV-1) infection. HLA-DR+ CD11c− lineage-negative cells (IPCs) were purified from peripheral blood mononuclear cells by magnetic-bead separation and cell sorting. We substantiated that IPCs expressing the major HIV-1 coreceptors, CXCR4 and CCR5, are susceptible to infection of both T-cell-line-tropic NL4-3 and macrophage-tropic JR-CSF HIV-1 by quantification of HIV-1 p24 in the culture supernatants and by provirus integration assay using human conserved Alu-HIV-1 long terminal repeat PCR. To evaluate the cellular response of IPCs to HIV-1, we examined IFN-α production and their differentiation into DCs. After incubation with either NL4-3 or JR-CSF, IPCs produced a large amount of IFN-α and at the same time underwent morphological differentiation into DCs with upregulation of CD80 and CD86. Heat inactivation of the supernatants containing HIV-1 did not affect the IFN-α production and maturation, whereas removal of virions by ultracentrifugation completely nullified both biological effects, indicating that these cellular responses do not require actual HIV-1 infection but are elicited by interaction with HIV-1 virions or certain viral components. In conclusion, these data strongly suggest that IPC can directly recognize and respond to HIV-1 with IFN-α production, which is crucial for preventing progress of HIV-1 infection and occurrence of opportunistic infection.

APOBEC3G Targets Specific Virus Species

ABSTRACT Human APOBEC3G (huAPOBEC3G), also known as CEM15, is a broad antiretroviral host factor that deaminates dC to dU in the minus strand DNA of human immunodeficiency virus type 1 (HIV-1), other lentiviruses, and murine leukemia virus (MLV), thereby creating G-to-A hypermutation in the plus strand DNA to inhibit the infectivity of these viruses. In this study, we examined the antiretroviral function of a murine homologue of APOBEC3G (muAPOBEC3G) on several retrovirus systems with different producer cells. MuAPOBEC3G did not suppress the infectivity of murine retroviral vectors produced from human or murine cells, whereas it showed antiviral activity on both wild-type and Δvif virions of HIV-1 in human cells. In contrast, huAPOBEC3G showed broad antiviral activity on HIV-1 and murine retroviral vectors produced from human cells as well as murine cells. These data suggested that muAPOBEC3G does not possess antiretroviral activity on murine retroviruses and has a different target specificity from that of huAPOBEC3G and that huAPOBEC3G works as a broad antiviral factor not only in human cells but also in murine cells. A functional interaction study between human and murine APOBEC3G supported the former hypothesis. Furthermore, studies on the expression of APOBEC3G in producer cells and its incorporation into virions revealed that muAPOBEC3G is incorporated into HIV-1 virions but not into MLV virions. Thus, muAPOBEC3G cannot suppress the infectivity of murine retrovirus because it is not incorporated into virions. We suggest that murine retroviruses can replicate in murine target cells expressing muAPOBEC3G because they are not targets for this enzyme.

APOBEC3G targets human T-cell leukemia virus type 1

BackgroundApolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G) is a host cellular protein with a broad antiviral activity. It inhibits infectivitiy of a wide variety of retroviruses by deaminating deoxycytidine (dC) into deoxyuridine (dU) in newly synthesized minus strand DNA, resulting in G-to-A hypermutation of the viral plus strand DNA. To clarify the mechanism of its function, we have examined the antiviral activity of APOBEC3G on human T-cell leukemia virus type 1 (HTLV-1), the first identified human retrovirus.ResultsIn this study, we have demonstrated that overexpressed as well as endogenous APOBEC3G were incorporated into HTLV-1 virions and that APOBEC3G inhibited the infection of HTLV-1. Interestingly, several inactive mutants of APOBEC3G also inhibited HTLV-1 and no G-to-A hypermutation was induced by APOBEC3G in HTLV-1 genome. Furthermore, we introduced the human immunodeficiency virus type 1 (HIV-1) vif gene into HTLV-1 producing cell line, MT-2, to antagonize APOBEC3G by reducing its intracellular expression and virion incorporation, which resulted in upregulation of the infectivity of produced viruses.ConclusionAPOBEC3G is incorporated into HTLV-1 virions and inhibits the infection of HTLV-1 without exerting its cytidine deaminase activity. These results suggest that APOBEC3G might act on HTLV-1 through different mechanisms from that on HIV-1 and contribute to the unique features of HTLV-1 infection and transmission.

B7‐H1 expression is regulated by MEK/ERK signaling pathway in anaplastic large cell lymphoma and Hodgkin lymphoma

B7‐H1 is a member of the B7 family that inhibits the function of T‐cells through its receptor programmed death‐1 (PD‐1). We examined B7‐H1 expression in anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) and found that it was constitutively expressed in both clinical samples and cell lines. In anaplastic lymphoma kinase–positive (ALK+) ALCL cells, B7‐H1 expression was suppressed by the blocking of extracellular signal‐regulated kinase (ERK) signaling and upregulated by the augmentation of ERK activity by phorbol 13‐myristate 12‐acetate stimulation, suggesting that B7‐H1 expression is regulated by ERK signaling pathway in ALCL. ERK is one of the downstream mediators of nucleophosmin (NPM)/ALK signaling in ALK+ALCL, and pharmacological inhibition of ALK was shown to dephosphorylate ERK and down‐regulate B7‐H1. The involvement of NPM/ALK in B7‐H1 expression was also demonstrated by introducing the construct into human non‐ALCL lymphoid cell lines, which resulted in B7‐H1 expression. In the case of HL, B7‐H1 expression was shown to be dependent on the ERK and p38 mitogen‐activated protein kinase (MAPK) signaling pathways. These results suggest that B7‐H1 expression is controlled by common ERK signaling pathways in ALCL and HL cells. Our findings provide a potentially effective immunotherapeutic strategy for these B7‐H1‐expressing tumors. (Cancer Sci 2009)

Singlet oxygen is essential for neutrophil extracellular trap formation.

Neutrophil extracellular traps (NETs) that bind invading microbes are pivotal for innate host defense. There is a growing body of evidence for the significance of NETs in the pathogenesis of infectious and inflammatory diseases, but the mechanism of NET formation remains unclear. Previous observation in neutrophils of chronic granulomatous disease (CGD) patients, which defect NADPH oxidase (Nox) and fail to produce reactive oxygen species (ROS), revealed that ROS contributed to the formation of NETs. However, the active species were not identified. In this study, we discovered that singlet oxygen, one of the ROS, mediated Nox-dependent NET formation upon stimulation with phorbol myristate acetate. We also revealed that singlet oxygen itself could induce NET formation by a distinct system generating singlet oxygen with porfimer sodium (Photofrin) in CGD neutrophils, as well as healthy neutrophils. This was independent of Nox activation. These results show that singlet oxygen is essential for NET formation, and provide novel insights into the pathogenesis of infectious and inflammatory diseases.

APOBEC3B can impair genomic stability by inducing base substitutions in genomic DNA in human cells

Human APOBEC3 proteins play pivotal roles in intracellular defense against viral infection by catalyzing deamination of cytidine residues, leading to base substitutions in viral DNA. Activation-induced cytidine deaminase (AID), another member of the APOBEC family, is capable of editing immunoglobulin (Ig) and non-Ig genes, and aberrant expression of AID leads to tumorigenesis. However, it remains unclear whether APOBEC3 (A3) proteins affect stability of human genome. Here we demonstrate that both A3A and A3B can induce base substitutions into human genome as AID can. A3B is highly expressed in several lymphoma cells and somatic mutations occur in some oncogenes of the cells highly expressing A3B. Furthermore, transfection of A3B gene into lymphoma cells induces base substitutions in cMYC gene. These data suggest that aberrant expression of A3B can evoke genomic instability by inducing base substitutions into human genome, which might lead to tumorigenesis in human cells.

Remarkable Lethal G-to-A Mutations in vif-Proficient HIV-1 Provirus by Individual APOBEC3 Proteins in Humanized Mice

ABSTRACT Genomic hypermutation of RNA viruses, including human immunodeficiency virus type 1 (HIV-1), can be provoked by intrinsic and extrinsic pressures, which lead to the inhibition of viral replication and/or the progression of viral diversity. Human APOBEC3G was identified as an HIV-1 restriction factor, which edits nascent HIV-1 DNA by inducing G-to-A hypermutations and debilitates the infectivity of vif-deficient HIV-1. On the other hand, HIV-1 Vif protein has the robust potential to degrade APOBEC3G protein. Although subsequent investigations have revealed that lines of APOBEC3 family proteins have the capacity to mutate HIV-1 DNA, it remains unclear whether these endogenous APOBEC3s, including APOBEC3G, contribute to mutations of vif-proficient HIV-1 provirus in vivo and, if so, what is the significance of these mutations. In this study, we use a human hematopoietic stem cell-transplanted humanized mouse (NOG-hCD34 mouse) model and demonstrate the predominant accumulation of G-to-A mutations in vif-proficient HIV-1 provirus displaying characteristics of APOBEC3-mediated mutagenesis. Notably, the APOBEC3-associated G-to-A mutation of HIV-1 DNA that leads to the termination of translation was significantly observed. We further provide a novel insight suggesting that HIV-1 G-to-A hypermutation is independently induced by individual APOBEC3 proteins. In contrast to the prominent mutation in intracellular proviral DNA, viral RNA in plasma possessed fewer G-to-A mutations. Taken together, these results provide the evidence indicating that endogenous APOBEC3s are associated with G-to-A mutation of HIV-1 provirus in vivo, which can result in the abrogation of HIV-1 infection.