Tasuku Honjo

Publications of Tasuku Honjo

• TRIM28 prevents autoinflammatory T cell development in vivo.

  Authors: Shunsuke Chikuma, Naomasa Suita, Il-Mi Okazaki, Shiro Shibayama, Tasuku Honjo

  Nature immunology. 04/2012;

  TRIM28 is a component of heterochromatin complexes whose function in the immune system is unknown. By studying mice with conditional T cell-specific deletion of TRIM28 (CKO mice), we found thatTRIM28 is a component of heterochromatin complexes whose function in the immune system is unknown. By studying mice with conditional T cell-specific deletion of TRIM28 (CKO mice), we found that TRIM28 was phosphorylated after stimulation via the T cell antigen receptor (TCR) and was involved in the global regulation of CD4(+) T cells. The CKO mice had a spontaneous autoimmune phenotype that was due in part to early lymphopenia associated with a defect in the production of interleukin 2 (IL-2) as well as incomplete cell-cycle progression of their T cells. In addition, CKO T cells showed derepression of the cytokine TGF-β3, which resulted in an altered cytokine balance; this caused the accumulation of autoreactive cells of the T(H)17 subset of helper T cells and of Foxp3(+) T cells. Notably, CKO Foxp3(+) T cells were unable to prevent the autoimmune phenotype in vivo. Our results show critical roles for TRIM28 in both T cell activation and T cell tolerance.

• An evolutionary view of the mechanism for immune and genome diversity.

  Authors: Lucia Kato, Andre Stanlie, Nasim A Begum, Maki Kobayashi, Masatoshi Aida, Tasuku Honjo

  Journal of immunology (Baltimore, Md. : 1950). 04/2012; 188(8):3559-66.

  An ortholog of activation-induced cytidine deaminase (AID) was, evolutionarily, the first enzyme to generate acquired immune diversity by catalyzing gene conversion and probably somatic hypermutationAn ortholog of activation-induced cytidine deaminase (AID) was, evolutionarily, the first enzyme to generate acquired immune diversity by catalyzing gene conversion and probably somatic hypermutation (SHM). AID began to mediate class switch recombination (CSR) only after the evolution of frogs. Recent studies revealed that the mechanisms for generating immune and genetic diversity share several critical features. Meiotic recombination, V(D)J recombination, CSR, and SHM all require H3K4 trimethyl histone modification to specify the target DNA. Genetic instability related to dinucleotide or triplet repeats depends on DNA cleavage by topoisomerase 1, which also initiates DNA cleavage in both SHM and CSR. These similarities suggest that AID hijacked the basic mechanism for genome instability when AID evolved in jawless fish. Thus, the risk of introducing genome instability into nonimmunoglobulin loci is unavoidable but tolerable compared with the advantage conferred on the host of being protected against pathogens by the enormous Ig diversification.

• The DSIF Subunits Spt4 and Spt5 Have Distinct Roles at Various Phases of Immunoglobulin Class Switch Recombination.

  Authors: Andre Stanlie, Nasim A Begum, Hideo Akiyama, Tasuku Honjo

  PLoS genetics. 04/2012; 8(4):e1002675.

  Class-switch recombination (CSR), induced by activation-induced cytidine deaminase (AID), can be divided into two phases: DNA cleavage of the switch (S) regions and the joining of the cleaved ends ofClass-switch recombination (CSR), induced by activation-induced cytidine deaminase (AID), can be divided into two phases: DNA cleavage of the switch (S) regions and the joining of the cleaved ends of the different S regions. Here, we show that the DSIF complex (Spt4 and Spt5), a transcription elongation factor, is required for CSR in a switch-proficient B cell line CH12F3-2A cells, and Spt4 and Spt5 carry out independent functions in CSR. While neither Spt4 nor Spt5 is required for transcription of S regions and AID, expression array analysis suggests that Spt4 and Spt5 regulate a distinct subset of transcripts in CH12F3-2A cells. Curiously, Spt4 is critically important in suppressing cryptic transcription initiating from the intronic Sμ region. Depletion of Spt5 reduced the H3K4me3 level and DNA cleavage at the Sα region, whereas Spt4 knockdown did not perturb the H3K4me3 status and S region cleavage. H3K4me3 modification level thus correlated well with the DNA breakage efficiency. Therefore we conclude that Spt5 plays a role similar to the histone chaperone FACT complex that regulates H3K4me3 modification and DNA cleavage in CSR. Since Spt4 is not involved in the DNA cleavage step, we suspected that Spt4 might be required for DNA repair in CSR. We examined whether Spt4 or Spt5 is essential in non-homologous end joining (NHEJ) and homologous recombination (HR) as CSR utilizes general repair pathways. Both Spt4 and Spt5 are required for NHEJ and HR as determined by assay systems using synthetic repair substrates that are actively transcribed even in the absence of Spt4 and Spt5. Taken together, Spt4 and Spt5 can function independently in multiple transcription-coupled steps of CSR.

• Nonimmunoglobulin target loci of activation-induced cytidine deaminase (AID) share unique features with immunoglobulin genes.

  Authors: Lucia Kato, Nasim A Begum, A Maxwell Burroughs, Tomomitsu Doi, Jun Kawai, Carsten O Daub, Takahisa Kawaguchi, Fumihiko Matsuda, Yoshihide Hayashizaki, Tasuku Honjo

  Proceedings of the National Academy of Sciences of the United States of America. 02/2012; 109(7):2479-84.

  Activation-induced cytidine deaminase (AID) is required for both somatic hypermutation and class-switch recombination in activated B cells. AID is also known to target nonimmunoglobulin genes andActivation-induced cytidine deaminase (AID) is required for both somatic hypermutation and class-switch recombination in activated B cells. AID is also known to target nonimmunoglobulin genes and introduce mutations or chromosomal translocations, eventually causing tumors. To identify as-yet-unknown AID targets, we screened early AID-induced DNA breaks by using two independent genome-wide approaches. Along with known AID targets, this screen identified a set of unique genes (SNHG3, MALAT1, BCL7A, and CUX1) and confirmed that these loci accumulated mutations as frequently as Ig locus after AID activation. Moreover, these genes share three important characteristics with the Ig gene: translocations in tumors, repetitive sequences, and the epigenetic modification of chromatin by H3K4 trimethylation in the vicinity of cleavage sites.

• The AID Dilemma: Infection, or Cancer?

  Authors: Tasuku Honjo, Maki Kobayashi, Nasim Begum, Ai Kotani, Somayeh Sabouri, Hitoshi Nagaoka

  Advances in cancer research. 01/2012; 113:1-44.

  Activation-induced cytidine deaminase (AID), which is both essential and sufficient for forming antibody memory, is also linked to tumorigenesis. AID is found in many B lymphomas, in myeloidActivation-induced cytidine deaminase (AID), which is both essential and sufficient for forming antibody memory, is also linked to tumorigenesis. AID is found in many B lymphomas, in myeloid leukemia, and in pathogen-induced tumors such as adult T cell leukemia. Although there is no solid evidence that AID causes human tumors, AID-transgenic and AID-deficient mouse models indicate that AID is both sufficient and required for tumorigenesis. Recently, AID's ability to cleave DNA has been shown to depend on topoisomerase 1 (Top1) and a histone H3K4 epigenetic mark. When the level of Top1 protein is decreased by AID activation, it induces irreversible cleavage in highly transcribed targets. This finding and others led to the idea that there is an evolutionary link between meiotic recombination and class switch recombination, which share H3K4 trimethyl, topoisomerase, the MRN complex, mismatch repair family proteins, and exonuclease 3. As Top1 has recently been shown to be involved in many transcription-associated genome instabilities, it is likely that AID took advantage of basic genome instability or diversification to evolve its mechanism for immune diversity. AID targets are therefore not highly specific to immunoglobulin genes and are relatively abundant, although they have strict requirements for transcription-induced H3K4 trimethyl modification and repetitive sequences prone to forming non-B structures. Inevitably, AID-dependent cleavage takes place in nonimmunoglobulin targets and eventually causes tumors. However, battles against infection are waged in the context of acute emergencies, while tumorigenesis is rather a chronic, long-term process. In the interest of survival, vertebrates must have evolved AID to prevent infection despite its long-term risk of causing tumorigenesis.

• Decrease in topoisomerase I is responsible for activation-induced cytidine deaminase (AID)-dependent somatic hypermutation.

  Authors: Maki Kobayashi, Zahra Sabouri, Somayeh Sabouri, Yoko Kitawaki, Yves Pommier, Takaya Abe, Hiroshi Kiyonari, Tasuku Honjo

  Proceedings of the National Academy of Sciences of the United States of America. 11/2011; 108(48):19305-10.

  Somatic hypermutation (SHM) and class-switch recombination (CSR) of the Ig gene require both the transcription of the locus and the expression of activation-induced cytidine deaminase (AID). DuringSomatic hypermutation (SHM) and class-switch recombination (CSR) of the Ig gene require both the transcription of the locus and the expression of activation-induced cytidine deaminase (AID). During CSR, AID decreases the amount of topoisomerase I (Top1); this decrease alters the DNA structure and induces cleavage in the S region. Similarly, Top1 is involved in transcription-associated mutation at dinucleotide repeats in yeast and in triplet-repeat contraction in mammals. Here, we report that the AID-induced decrease in Top1 is critical for SHM. Top1 knockdown or haploinsufficiency enhanced SHM, whereas Top1 overexpression down-regulated it. A specific Top1 inhibitor, camptothecin, suppressed SHM, indicating that Top1's activity is required for DNA cleavage. Nonetheless, suppression of transcription abolished SHM, even in cells with Top1 knockdown, suggesting that transcription is critical. These results are consistent with a model proposed for CSR and triplet instability, in which transcription-induced non-B structure formation is enhanced by Top1 reduction and provides the target for irreversible cleavage by Top1. We speculate that the mechanism for transcription-coupled genome instability was adopted to generate immune diversity when AID evolved.

• Histone chaperone Spt6 is required for class switch recombination but not somatic hypermutation.

  Authors: Il-mi Okazaki, Katsuya Okawa, Maki Kobayashi, Kiyotsugu Yoshikawa, Shimpei Kawamoto, Hitoshi Nagaoka, Reiko Shinkura, Yoko Kitawaki, Hisaaki Taniguchi, Tohru Natsume, Shun-Ichiro Iemura, Tasuku Honjo

  Proceedings of the National Academy of Sciences of the United States of America. 05/2011; 108(19):7920-5.

  Activation-induced cytidine deaminase (AID) is shown to be essential and sufficient to induce two genetic alterations in the Ig loci: class switch recombination (CSR) and somatic hypermutation (SHM).Activation-induced cytidine deaminase (AID) is shown to be essential and sufficient to induce two genetic alterations in the Ig loci: class switch recombination (CSR) and somatic hypermutation (SHM). However, it is still unknown how a single-molecule AID differentially regulates CSR and SHM. Here we identified Spt6 as an AID-interacting protein by yeast two-hybrid screening and immunoprecipitation followed by mass spectrometry. Knockdown of Spt6 resulted in severe reduction of CSR in both the endogenous Ig locus in B cells and an artificial substrate in fibroblast cells. Conversely, knockdown of Spt6 did not reduce but slightly enhanced SHM in an artificial substrate in B cells, indicating that Spt6 is required for AID to induce CSR but not SHM. These results suggest that Spt6 is involved in differential regulation of CSR and SHM by AID.

• Mice carrying a knock-in mutation of Aicda resulting in a defect in somatic hypermutation have impaired gut homeostasis and compromised mucosal defense.

  Authors: Min Wei, Reiko Shinkura, Yasuko Doi, Mikako Maruya, Sidonia Fagarasan, Tasuku Honjo

  Nature immunology. 03/2011; 12(3):264-70.

  To elucidate the specific role of somatic hypermutation (SHM) in mucosal immunity, we generated mice carrying a knock-in point mutation in Aicda, which encodes activation-induced cytidine deaminaseTo elucidate the specific role of somatic hypermutation (SHM) in mucosal immunity, we generated mice carrying a knock-in point mutation in Aicda, which encodes activation-induced cytidine deaminase (AID), an enzyme essential to SHM and class-switch recombination (CSR). These mutant AID(G23S) mice had much less SHM but had normal amounts of immunoglobulin in both serum and intestinal secretions. AID(G23S) mice developed hyperplasia of germinal center B cells in gut-associated lymphoid tissues, accompanied by expansion of microflora in the small intestine. Moreover, AID(G23S) mice had more translocation of Yersinia enterocolitica into mesenteric lymph nodes and were more susceptible than wild-type mice to oral challenge with cholera toxin. Together our results indicate that SHM is critical in maintaining intestinal homeostasis and efficient mucosal defense.

• IFN-α directly promotes programmed cell death-1 transcription and limits the duration of T cell-mediated immunity.

  Authors: Seigo Terawaki, Shunsuke Chikuma, Shiro Shibayama, Tamon Hayashi, Takao Yoshida, Taku Okazaki, Tasuku Honjo

  Journal of immunology (Baltimore, Md. : 1950). 03/2011; 186(5):2772-9.

  Programmed cell death-1 (PD-1) is an inhibitory coreceptor for T lymphocytes that provides feedback inhibition of T cell activation. Although PD-1's expression on T cells is known to be activationProgrammed cell death-1 (PD-1) is an inhibitory coreceptor for T lymphocytes that provides feedback inhibition of T cell activation. Although PD-1's expression on T cells is known to be activation dependent, the factors that determine the timing, intensity, and duration of PD-1 expression in immune reactions are not fully understood. To address this question, we performed a fine mapping analysis of a conserved 5'-flanking region of the PD-1 gene and identified a putative IFN stimulation response element, which was responsible for PD-1 transcription in the 2B4.11 T cell line. Consistent with this finding, activation by IFN-α enhanced both the induction and maintenance of PD-1 expression on TCR-engaged primary mouse T cells through an association IFN-responsive factor 9 (IRF9) to the IFN stimulation response element. Furthermore, PD-1 expression on Ag-specific CD8(+) T cells was augmented by IFN-α in vivo. We propose that strong innate inflammatory responses promote primary T cell activation and their differentiation into effector cells, but also cause an attenuated T cell response in sustained immune reactions, at least partially through type I IFN-mediated PD-1 transcription. Based on this idea, we demonstrate that IFN-α administration in combination with PD-1 blockade in tumor-bearing mice effectively augments the antitumor immunity, and we propose this as a novel and rational approach for cancer immunotherapy.

• PD-1 and LAG-3 inhibitory co-receptors act synergistically to prevent autoimmunity in mice.

  Authors: Taku Okazaki, Il-mi Okazaki, Jian Wang, Daisuke Sugiura, Fumio Nakaki, Taku Yoshida, Yu Kato, Sidonia Fagarasan, Masamichi Muramatsu, Tomoo Eto, Kyoji Hioki, Tasuku Honjo

  The Journal of experimental medicine. 02/2011; 208(2):395-407.

  Stimulatory and inhibitory co-receptors play fundamental roles in the regulation of the immune system. We describe a new mouse model of spontaneous autoimmune disease. Activation-induced cytidineStimulatory and inhibitory co-receptors play fundamental roles in the regulation of the immune system. We describe a new mouse model of spontaneous autoimmune disease. Activation-induced cytidine deaminase-linked autoimmunity (aida) mice harbor a loss-of-function mutation in the gene encoding lymphocyte activation gene 3 (LAG-3), an inhibitory co-receptor. Although LAG-3 deficiency alone did not induce autoimmunity in nonautoimmune-prone mouse strains, it induced lethal myocarditis in BALB/c mice deficient for the gene encoding the inhibitory co-receptor programmed cell death 1 (PD-1). In addition, LAG-3 deficiency alone accelerated type 1 diabetes mellitus in nonobese diabetic mice. These results demonstrate that LAG-3 acts synergistically with PD-1 and/or other immunoregulatory genes to prevent autoimmunity in mice.

• Activation-induced cytidine deaminase expression in CD4+ T cells is associated with a unique IL-10-producing subset that increases with age.

  Authors: Hongyan Qin, Keiichiro Suzuki, Mikiyo Nakata, Shunsuke Chikuma, Nakako Izumi, Le Thi Huong, Mikako Maruya, Sidonia Fagarasan, Meinrad Busslinger, Tasuku Honjo, Hitoshi Nagaoka

  PloS one. 01/2011; 6(12):e29141.

  Activation-induced cytidine deaminase (AID), produced by the Aicda gene, is essential for the immunoglobulin gene (Ig) alterations that form immune memory. Using a Cre-mediated genetic system, weActivation-induced cytidine deaminase (AID), produced by the Aicda gene, is essential for the immunoglobulin gene (Ig) alterations that form immune memory. Using a Cre-mediated genetic system, we unexpectedly found CD4(+) T cells that had expressed Aicda (exAID cells) as well as B cells. ExAID cells increased with age, reaching up to 25% of the CD4(+) and B220(+) cell populations. ExAID B cells remained IgM(+), suggesting that class-switched memory B cells do not accumulate in the spleen. In T cells, AID was expressed in a subset that produced IFN-γ and IL-10 but little IL-4 or IL-17, and showed no evidence of genetic mutation. Interestingly, the endogenous Aicda expression in T cells was enhanced in the absence of B cells, indicating that the process is independent from the germinal center reaction. These results suggest that in addition to its roles in B cells, AID may have previously unappreciated roles in T-cell function or tumorigenesis.

• Histone3 lysine4 trimethylation regulated by the facilitates chromatin transcription complex is critical for DNA cleavage in class switch recombination.

  Authors: Andre Stanlie, Masatoshi Aida, Masamichi Muramatsu, Tasuku Honjo, Nasim A Begum

  Proceedings of the National Academy of Sciences of the United States of America. 12/2010; 107(51):22190-5.

  Ig class switch recombination (CSR) requires expression of activation-induced cytidine deaminase (AID) and transcription through target switch (S) regions. Here we show that knockdown of the histoneIg class switch recombination (CSR) requires expression of activation-induced cytidine deaminase (AID) and transcription through target switch (S) regions. Here we show that knockdown of the histone chaperone facilitates chromatin transcription (FACT) completely inhibited S region cleavage and CSR in IgA-switch-inducible CH12F3-2A B cells. FACT knockdown did not reduce AID or S region transcripts but did decrease histone3 lysine4 trimethylation (H3K4me3) at both the Sμ and Sα regions. Because knockdown of FACT or H3K4 methyltransferase cofactors inhibited DNA cleavage in H3K4me3-depleted S regions, H3K4me3 may serve as a mark for recruiting CSR recombinase. These findings revealed an unexpected evolutionary conservation between CSR and meiotic recombination.

• PD-1 deficiency results in the development of fatal myocarditis in MRL mice.

  Authors: Jian Wang, Il-Mi Okazaki, Taku Yoshida, Shunsuke Chikuma, Yu Kato, Fumio Nakaki, Hiroshi Hiai, Tasuku Honjo, Taku Okazaki

  International immunology. 06/2010; 22(6):443-52.

  The deficiency of programmed cell death 1 (PD-1, Pdcd1), a negative immuno-receptor belonging to the CD28/cytotoxic T lymphocyte antigen 4 (CTLA-4) family, can support various tissue-specificThe deficiency of programmed cell death 1 (PD-1, Pdcd1), a negative immuno-receptor belonging to the CD28/cytotoxic T lymphocyte antigen 4 (CTLA-4) family, can support various tissue-specific autoimmune conditions. Here, we analyzed the effect of PD-1 deficiency in MRL mice that is genetically predisposed to systemic autoimmunity. MRL-Pdcd1(-)(/-) mice developed a fatal myocarditis, which is reminiscent of CTLA-4-deficient (Ctla4(-)(/-)) mice. Massive infiltration of CD4(+) and CD8(+) T cells and myeloid cells was found in hearts of MRL-Pdcd1(-)(/-) mice concomitant with the production of high-titer auto-antibodies against cardiac myosin. In contrast to Ctla4(-)(/-) mice in which most of the CD4(+) T cells are non-specifically activated and invade various organs, T cells in the heart but not in the spleen and lymph nodes are activated in MRL-Pdcd1(-)(/-) mice, suggesting that myocarditis is mediated by antigen-specific autoimmune response. Heart infiltrating myeloid cells strongly suppressed the allogenic response of T cells in vitro, suggesting that these Mac1(+)Gr1(+) myeloid cells are phenotypically similar to myeloid suppressor cells, which can be found in tumor-bearing hosts. These findings unravel the hidden heart-specific autoimmune predisposition of MRL mice and provide MRL-Pdcd1(-)(/-) mice as a useful animal model of lymphocytic myocarditis.

• Author's reply: Apex2 is required for efficient somatic hypermutation but not for class switch recombination of immunoglobulin genes.

  Authors: Zahra Sabouri, Il-Mi Okazaki, Reiko Shinkura, Nasim Begum, Hitoshi Nagaoka, Tasuku Honjo

  International immunology. 03/2010; 22(3):213-4.

• Preventing AID, a physiological mutator, from deleterious activation: regulation of the genomic instability that is associated with antibody diversity.

  Authors: Hitoshi Nagaoka, Thinh Huy Tran, Maki Kobayashi, Masatoshi Aida, Tasuku Honjo

  International immunology. 03/2010; 22(4):227-35.

  Activation-induced cytidine deaminase (AID) is essential and sufficient to accomplish class-switch recombination and somatic hypermutation, which are two genetic events required for the generation ofActivation-induced cytidine deaminase (AID) is essential and sufficient to accomplish class-switch recombination and somatic hypermutation, which are two genetic events required for the generation of antibody-mediated memory responses. However, AID can also introduce genomic instability, giving rise to chromosomal translocation and/or mutations in proto-oncogenes. It is therefore important for cells to suppress AID expression unless B lymphocytes are stimulated by pathogens. The mechanisms for avoiding the accidental activation of AID and thereby avoiding genomic instability can be classified into three types: (i) transcriptional regulation, (ii) post-transcriptional regulation and (iii) target specificity. This review summarizes the recently elucidated comprehensive transcriptional regulation mechanisms of the AID gene and the post-transcriptional regulation that may be critical for preventing excess AID activity. Finally, we discuss why AID targets not only Igs but also other proto-oncogenes. AID targets many genes but it is not totally promiscuous and the criteria that specify its targets are unclear. A recent finding that a non-B DNA structure forms upon a decrease in topoisomerase 1 expression may explain this paradoxical target specificity determination. Evolution has chosen AID as a mutator of Ig genes because of its efficient DNA cleavage activity, even though its presence increases the risk of genomic instability. This is probably because immediate protection against pathogens is more critical for species survival than complete protection from the slower acting consequences of genomic instability, such as tumor formation.

• Anti-programmed cell death 1 antibody reduces CD4+PD-1+ T cells and relieves the lupus-like nephritis of NZB/W F1 mice.

  Authors: Shimpei Kasagi, Seiji Kawano, Taku Okazaki, Tasuku Honjo, Akio Morinobu, Saori Hatachi, Kenichiro Shimatani, Yoshimasa Tanaka, Nagahiro Minato, Shunichi Kumagai

  Journal of immunology (Baltimore, Md. : 1950). 02/2010; 184(5):2337-47.

  Programmed cell death 1 (PD-1) is an immunosuppressive receptor that transduces an inhibitory signal into activated T cells. Although a single nucleotide polymorphism in the gene for PD-1 isProgrammed cell death 1 (PD-1) is an immunosuppressive receptor that transduces an inhibitory signal into activated T cells. Although a single nucleotide polymorphism in the gene for PD-1 is associated with susceptibility to systemic lupus erythematosus, the role of PD-1 in systemic lupus erythematosus is still not well understood. In this study, we used NZB/W F1 mice, a model of lupus-like nephritis, to examine the function of PD-1 and its ligands. PD-1 was predominantly expressed on CD4(+) T cells that infiltrated the kidney, and CD4(+)PD-1(high) T cells produced higher levels of IFN-gamma than CD4(+)PD-1(low) or CD4(+)PD-1(-) T cells. Stimulation with PMA/ionomycin caused splenic CD4(+)PD-1(+) T cells to secrete high levels of IFN-gamma, IL-10, low levels of TNF-alpha, faint levels of IL-2, IL-21, and no IL-4, IL-17. In vivo anti-PD-1 mAb treatment reduced the number of CD4(+)PD-1(+) T cells in the kidney of NZB/W F1 mice and significantly reduced their mortality rate (p = 0.03). Conversely, blocking PD-L1 using an anti-PD-L1 mAb increased the number of CD4(+)PD-1(+) T cells in the kidney, enhanced serum IFN-gamma, IL-10, and IgG2a ds-DNA-Ab levels, accelerated the nephritis, and increased the mortality rate. We conclude that CD4(+)PD-1(high) T cells are dysregulated IFN-gamma-producing, proinflammatory cells in NZB/W F1 mice.

• Tumor cell expression of programmed cell death-1 ligand 1 is a prognostic factor for malignant melanoma.

  Authors: Ryosuke Hino, Kenji Kabashima, Yu Kato, Hiroaki Yagi, Motonobu Nakamura, Tasuku Honjo, Taku Okazaki, Yoshiki Tokura

  Cancer. 02/2010; 116(7):1757-66.

  : Melanoma tends to be refractory to various immunotherapies because of tumor-induced immunosuppression. To investigate the mechanism underlining the immunosuppression of melanoma patients, the: Melanoma tends to be refractory to various immunotherapies because of tumor-induced immunosuppression. To investigate the mechanism underlining the immunosuppression of melanoma patients, the authors focused on programmed cell death-1 (PD-1)/PD-1 ligand 1 (PD-L1) interaction between tumor cells and T cells. : Melanoma specimens were collected from 59 primary tumors, 16 lymph nodes, and 4 lesions of in-transit metastasis. Specimens stained with anti-PD-L1 monoclonal antibodies were digitalized to jpg files. To evaluate the intensity of PD-L1 expression, histograms were used, and the red density (RD) was measured. PD-1 expression on T cells was analyzed in blood samples from 10 patients who had stage IV melanoma and in 4 samples of in-transit metastases. : Twenty-five patients comprised the "low" PD-L1 expression group (RD value, <90), and 34 patients comprised the "high" group (RD value, > or =90). Breslow tumor thickness in the high-expression group was significantly higher than in the low-expression group. Univariate and multivariate analyses revealed that the overall survival rate of the high-expression group was significantly lower than that of the low-expression group. In all patients with stage IV disease who were examined, both CD8-positive and CD4-positive T cells had significantly higher PD-1 expression levels in the peripheral blood. Tumor-infiltrating T cells expressed high levels of PD-1, and its expression was elevated further during the clinical course. : The current results indicated that there is a correlation between the degree of PD-L1 expression and the vertical growth of primary tumors in melanoma. Multivariate analysis demonstrated that PD-L1 expression is an independent prognostic factor for melanoma. Cancer 2010. (c) 2010 American Cancer Society.

• Two opposing roles of RBP-J in Notch signaling.

  Authors: Kenji Tanigaki, Tasuku Honjo

  Current topics in developmental biology. 01/2010; 92:231-52.

  RBP-J/Su(H)/Lag1, the main transcriptional mediator of Notch signaling, binds DNA with the consensus sequence YRTGDGAD. Notch target genes can be controlled by two opposing activities of RBP-J. TheRBP-J/Su(H)/Lag1, the main transcriptional mediator of Notch signaling, binds DNA with the consensus sequence YRTGDGAD. Notch target genes can be controlled by two opposing activities of RBP-J. The interaction of the Notch intracellular domain with RBP-J induces a weak transcriptional activation and requires an additional tissue-specific transcriptional activator such as bHLH proteins or GATA to mediate strong target gene expression. For example, during Drosophila sensory organ precursor (SOP) cell development, proneural bHLH interacts with Da, a Drosophila orthologue of E2A, to form a tissue-specific activator of Su(H), the Drosophila orthologue of RBP-J. This complex and Su(H) act synergistically to promote the epidermal cell fate. In contrast, a complex of Su(H) with Hairless, a Drosophila functional homologue of MINT, has transcriptional repression activity that promotes SOP differentiation to neurons. Recent conditional loss-of-function studies demonstrated that transcriptional networks involving RBP-J, MINT, and E2A are conserved in mammalian cell differentiation, including multiple steps of lymphocyte development, and probably also in neuronal maturation in adult neurogenesis. During neurogenesis, Notch-RBP-J signaling was thought historically to be involved mainly in the maintenance of undifferentiated neural progenitors. However, the identification of a tissue-specific transcriptional activator of RBP-J-Notch has revealed new roles of RBP-J in the promotion of neuronal maturation. Finally, the Notch-independent function of RBP-J was recently discovered and will be reviewed here.

• B cell-specific and stimulation-responsive enhancers derepress Aicda by overcoming the effects of silencers.

  Authors: Thinh Huy Tran, Mikiyo Nakata, Keiichiro Suzuki, Nasim A Begum, Reiko Shinkura, Sidonia Fagarasan, Tasuku Honjo, Hitoshi Nagaoka

  Nature immunology. 12/2009;

  Activation-induced cytidine deaminase (AID) is essential for the generation of antibody memory but also targets oncogenes, among other genes. We investigated the transcriptional regulation of AicdaActivation-induced cytidine deaminase (AID) is essential for the generation of antibody memory but also targets oncogenes, among other genes. We investigated the transcriptional regulation of Aicda (which encodes AID) in class switch-inducible CH12F3-2 cells and found that Aicda regulation involved derepression by several layers of positive regulatory elements in addition to the 5' promoter region. The 5' upstream region contained functional motifs for the response to signaling by cytokines, the ligand for the costimulatory molecule CD40 or stimuli that activated the transcription factor NF-kappaB. The first intron contained functional binding elements for the ubiquitous silencers c-Myb and E2f and for the B cell-specific activator Pax5 and E-box-binding proteins. Our results show that Aicda is regulated by the balance between B cell-specific and stimulation-responsive elements and ubiquitous silencers.

• AID-induced decrease in topoisomerase 1 induces DNA structural alteration and DNA cleavage for class switch recombination.

  Authors: Maki Kobayashi, Masatoshi Aida, Hitoshi Nagaoka, Nasim A Begum, Yoko Kitawaki, Mikiyo Nakata, Andre Stanlie, Tomomitsu Doi, Lucia Kato, Il-Mi Okazaki, Reiko Shinkura, Masamichi Muramatsu, Kazuo Kinoshita, Tasuku Honjo

  Proceedings of the National Academy of Sciences of the United States of America. 12/2009;

  To initiate class switch recombination (CSR) activation-induced cytidine deaminase (AID) induces staggered nick cleavage in the S region, which lies 5' to each Ig constant region gene and is rich inTo initiate class switch recombination (CSR) activation-induced cytidine deaminase (AID) induces staggered nick cleavage in the S region, which lies 5' to each Ig constant region gene and is rich in palindromic sequences. Topoisomerase 1 (Top1) controls the supercoiling of DNA by nicking, rotating, and religating one strand of DNA. Curiously, Top1 reduction or AID overexpression causes the genomic instability. Here, we report that the inactivation of Top1 by its specific inhibitor camptothecin drastically blocked both the S region cleavage and CSR, indicating that Top1 is responsible for the S region cleavage in CSR. Surprisingly, AID expression suppressed Top1 mRNA translation and reduced its protein level. In addition, the decrease in the Top1 protein by RNA-mediated knockdown augmented the AID-dependent S region cleavage, as well as CSR. Furthermore, Top1 reduction altered DNA structure of the Smu region. Taken together, AID-induced Top1 reduction alters S region DNA structure probably to non-B form, on which Top1 can introduce nicks but cannot religate, resulting in S region cleavage.