Details of a Researcher - SASAKI Yasushi

Papers - SASAKI Yasushi

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Small interfering RNA-induced CHFR silencing sensitizes oral squamous cell cancer cells to microtubule inhibitors.

Kazuhiro Ogi, Minoru Toyota, Hiroaki Mita, Ayumi Satoh, Lisa Kashima, Yasushi Sasaki, Hiromu Suzuki, Kimishige Akino, Noriko Nishikawa, Makoto Noguchi, Yasuhisa Shinomura, Kohzoh Imai, Hiroyoshi Hiratsuka, Takashi Tokino

Cancer biology & therapy 4 ( 7 ) 773 - 80 2005.07 [Refereed] [International journal]

Alterations in the function of cell cycle checkpoints are frequently detected in oral squamous cell carcinomas (OSCCs), and are often associated with the sensitivity of the cancer cells to chemotherapeutic drugs. Recently, a mitotic checkpoint gene, Chfr, was shown to be inactivated by promoter methylation and point mutations in various human tumors. Here we show that the absence of its product, CHFR, is associated with mitotic checkpoint dysfunction, and that cancer cells lacking CHFR are sensitive to microtubule inhibitors. Checkpoint impairment appears to be caused by a prophase defect in this case, as OSCC cells lacking CHFR showed phosphorylation of histone H3 on Ser10 and translocation of cyclin B1 to the nucleus. When CHFR-deficient OSCC cells were treated with a microtubule inhibitor (docetaxel or paclitaxel), significant numbers of apoptotic cells were observed. Moreover, disruption of CHFR using small interfering RNA (siRNA) impaired the mitotic checkpoint, thereby reducing the ability of OSCC cells to arrest at G2/M phase and making them more sensitive to microtubule inhibitors. Our results suggest that CHFR could be a useful molecular target for chemotherapy.

DOI PubMed

The Ras effector RASSF2 is a novel tumor-suppressor gene in human colorectal cancer.

Kimishige Akino, Minoru Toyota, Hiromu Suzuki, Hiroaki Mita, Yasushi Sasaki, Mutsumi Ohe-Toyota, Jean-Pierre J Issa, Yuji Hinoda, Kohzoh Imai, Takashi Tokino

Gastroenterology 129 ( 1 ) 156 - 69 2005.07 [Refereed] [International journal]

BACKGROUND & AIMS:Activation of Ras signaling is a hallmark of colorectal cancer (CRC), but the roles of negative regulators of Ras are not fully understood. Our aim was to address that question by surveying genetic and epigenetic alterations of Ras-Ras effector genes in CRC cells. METHODS:The expression and methylation status of 6 RASSF family genes were examined using RT-PCR and bisulfite PCR in CRC cell lines and in primary CRCs and colorectal adenomas. Colony formation assays and flow cytometry were used to assess the tumor suppressor activities of RASSF1 and RASSF2. Immunofluorescence microscopy was used to determine the effect of altered RASSF2 expression on cell morphology. Mutations of K- ras , BRAF, and p53 were identified using single-strand conformation analysis and direct sequencing. RESULTS:Aberrant methylation and histone deacetylation of RASSF2 was associated with the gene's silencing in CRC. The activities of RASSF2, which were distinct from those of RASSF1, included induction of morphologic changes and apoptosis; moreover, its ability to prevent cell transformation suggests that RASSF2 acts as a tumor suppressor in CRC. Primary CRCs that showed K- ras /BRAF mutations also frequently showed RASSF2 methylation, and inactivation of RASSF2 enhanced K- ras -induced oncogenic transformation. RASSF2 methylation was also frequently identified in colorectal adenomas. CONCLUSIONS:RASSF2 is a novel tumor suppressor gene that regulates Ras signaling and plays a pivotal role in the early stages of colorectal tumorigenesis.

DOI PubMed

Identification of pigment epithelium-derived factor as a direct target of the p53 family member genes.

Yasushi Sasaki, Yasuyoshi Naishiro, Yuichiro Oshima, Kohzoh Imai, Yusuke Nakamura, Takashi Tokino

Oncogene 24 ( 32 ) 5131 - 6 2005.07 [Refereed] [International journal]

Authorship： Lead author

p63 and p73 show a high degree of structural homology to p53 and are members of a family of transcriptional factors that can activate transcription of p53-responsive genes. p53 is mutated in more than 50% of human cancers, whereas p63 and p73 are rarely mutated. Studies of knockout mice also revealed an unexpected functional diversity among the p53 family. To determine how p63 and p73 are involved in tumorigenesis and normal development, we used cDNA microarray to examine 9216 genes in human colorectal cancer cells. We discovered that the expression of pigment epithelium-derived factor (PEDF) was specifically induced by either p63 or p73, but not by p53. We also report here that the PEDF gene contains a response element specific for p63 and p73 in its promoter region and is a direct target of p63 and p73. Collectively, p63 and p73 may be involved in cell fate by inducing PEDF expression.

DOI PubMed

Aberrant DNA methylation associated with silencing BNIP3 gene expression in haematopoietic tumours.

Murai M, Toyota M, Satoh A, Suzuki H, Akino K, Mita H, Sasaki Y, Ishida T, Shen L, Garcia-Manero G, Issa JP, Hinoda Y, Tokino T, Imai K

British Journal of Cancer 92 ( 6 ) 1165 - 1172 2005.03 [Refereed]

Hypoxia is a key factor contributing to the progression of human neoplasias and to the development of resistance to chemotherapy. BNIP3 is a proapoptotic member of the Bcl-2 protein family involved in hypoxia-induced cell death. We evaluated the expression and methylation status of BNIP3 gene to better understand the role of epigenetic alteration of its expression in haematopoietic tumours. Methylation of the region around the BNIP3 transcription start site was detected in four acute lymphocytic leukaemia, one multiple myeloma and one Burkitt lymphoma cell lines, and was closely associated with silencing the gene. That expression of BNIP3 was restored by treatment with 5-aza2'-deoxycytidine (5-aza-dC), a methyltransferase inhibitor, which confirmed the gene to be epigenetically inactivated by methylation. Notably, re-expression of BNIP3 using 5-aza2-dC also restored hypoxia-mediated cell death in methylated cell lines. Acetylation of histone H3 in the 5' region of the gene, which was assessed using chromatin immunoprecipitation assays, correlated directly with gene expression and inversely with DNA methylation. Among primary tumours, methylation of BNIP3 was detected in five of 34 (15%) acute lymphocytic leukaemias, six of 35 (17%) acute myelogenous leukaemias and three of 14 (21%) multiple myelomas. These results suggest that aberrant DNA methylation of the 5' CpG island and histone deacetylation play key roles in silencing BNIP3 expression in haematopoietic tumours.

DOI PubMed

Abnormal beta-catenin expression in oral cancer with no gene mutation: correlation with expression of cyclin D1 and epidermal growth factor receptor, Ki-67 labeling index, and clinicopathological features.

Tetsuyo Odajima, Yasushi Sasaki, Nobuyuki Tanaka, Yuko Kato-Mori, Hiroko Asanuma, Tatsuru Ikeda, Masaaki Satoh, Hiroyoshi Hiratsuka, Takashi Tokino, Norimasa Sawada

Human pathology 36 ( 3 ) 234 - 41 2005.03 [Refereed] [International journal]

Beta-Catenin not only acts as a regulator of E-cadherin-mediated cell-cell adhesion but also plays an important role in Wnt signaling. To assess the prevalence of Wnt signaling, we examined beta-catenin mutation and its immunohistochemical protein expression in oral cancers. The results were linked with expression of cyclin D1, one of the target genes of Wnt signaling, expression of epidermal growth factor receptor (EGFR) relevant to beta-catenin tyrosine phosphorylation, Ki-67 labeling index, clinicopathological features, and survival. In the analysis based on membranous expression of beta-catenin, 75 (68.2%) of 110 cases showed a reduced membranous pattern, and the remaining 35 (31.8%) had a preserved membranous pattern similar to that in oral epithelium. In the analysis of another category of beta-catenin expression, a cytoplasmic/nuclear pattern was observed in 21 (19.1%) of the 110 tumors. Most (19/21, 90.5%) of these tumors had a concomitant reduction of membranous expression of beta-catenin. The reduced membranous or cytoplasmic/nuclear pattern of beta-catenin was significantly associated with an invasive growth pattern, EGFR expression, an increased Ki-67 labeling index, and shorter survival but not with cyclin D1 expression. Mutational analyses of beta-catenin were performed for 39 cases, including the 21 tumors with a cytoplasmic/nuclear pattern, but no mutations in the beta-catenin gene exon 3 were detected in these samples. Our data indicate that altered expression of beta-catenin may play an important role in tumor progression through increased proliferation and invasiveness under EGFR activation. However, mutations of beta-catenin do not appear to be responsible for tumor development and abnormal expression of beta-catenin in oral cancers.

DOI PubMed

Aberrant methylation and silencing of the BNIP3 gene in colorectal and gastric cancer.

Masafumi Murai, Minoru Toyota, Hiromu Suzuki, Ayumi Satoh, Yasushi Sasaki, Kimishige Akino, Masako Ueno, Fumihiko Takahashi, Masanobu Kusano, Hiroaki Mita, Kazuyoshi Yanagihara, Takao Endo, Yuji Hinoda, Takashi Tokino, Kohzoh Imai

Clinical cancer research : an official journal of the American Association for Cancer Research 11 ( 3 ) 1021 - 7 2005.02 [Refereed] [International journal]

BNIP3 protein is a proapoptotic member of the Bcl-2 family that is expressed in hypoxic regions of tumors. To examine its role in the progression of gastrointestinal cancer, we examined the expression and DNA methylation status of BNIP3 gene in a panel of colorectal and gastric cancer cell lines. BNIP3 was not expressed in 14 of the 24 cell lines tested, and its absence was not caused by gene mutation or by altered expression of hypoxia inducible factor-1, a key transcription factor that regulates BNIP3 expression. On the other hand, methylation of the 5' CpG island of BNIP3 was closely correlated with silencing the gene. Moreover, treating methylated cells with the methyltransferase inhibitor 5-aza-2'-deoxycytidine restored hypoxia-induced expression of BNIP3 mRNA and protein, which in turn led to cell death. Aberrant methylation of BNIP3 was also detected in 66% of primary colorectal and 49% of primary gastric cancers, but not in normal tissue samples collected from areas adjacent to the tumors. Apparently, epigenetic alteration of BNIP3 is a frequent and cancer-specific event, which suggests that inactivation of BNIP3 likely plays a key role in the progression of some gastrointestinal cancers and that it may be a useful molecular target for therapy.

PubMed

Identification of a specific target sequence for p53 family in the Jagged2 gene

Yuichiro Oshima, Setsuko Ishida, Reo Maruyama, Minoru Toyota, Toshihiko Yamashita, Takashi Tokino, Yasushi Sasaki

Tumor Research 40 13 - 24 2005 [Refereed]

Inactivation of the tumour suppressor p53 is the most common defect in cancer cells. The p53 family members, p73 and p63, have remarkable structural similarities with p53 and can activate transcription of p53-responsive genes. In contrast to p53 however, p73 and p63 are rarely mutated in human cancers. Mice that lack p53 are developmentally normal, while p73 and p63 appear to play critical roles in normal development. In our earlier study, we showed that both p73 and p63 regulate the ligands for the Notch receptor, Jagged1 (JAG1) and Jagged2 (JAG2). We also identified a p63-binding site in the second intron of the human JAG1 gene. Here, we have analyzed the responsive element within the human JAG2 gene for p73/p63-dependent induction of gene expression. Using a chromatin immunoprecipitation assay, we identified a p73/p63-binding site located in the second intron of the JAG2 gene. A heterologous reporter assay revealed that this binding site is a functional response element and is relatively specific for p73 and p63 among the p53 family. This binding site consists of four copies of 10-bp consensus p53-binding motif and is highly conserved between human and rodents. Furthermore, both JAG1 and JAG2 mRNA were specifically up-regulated by either p63 or p73, but not by p53 in mouse embryo fibroblasts. Our findings demonstrate that JAG2 is indeed a direct and evolutionarily conserved transcriptional target of p73 and p63, and suggest a potential molecular mechanism for the involvement of the p53 family genes in normal development.

Epigenetic inactivation of class II transactivator (CIITA) is associated with the absence of interferon-gamma-induced HLA-DR expression in colorectal and gastric cancer cells.

Ayumi Satoh, Minoru Toyota, Hideyuki Ikeda, Yoshikazu Morimoto, Kimishige Akino, Hiroaki Mita, Hiromu Suzuki, Yasushi Sasaki, Takayuki Kanaseki, Yukio Takamura, Hidenobu Soejima, Takeshi Urano, Kazuyoshi Yanagihara, Takao Endo, Yuji Hinoda, Masahiro Fujita, Masao Hosokawa, Noriyuki Sato, Takashi Tokino, Kohzoh Imai

Oncogene 23 ( 55 ) 8876 - 86 2004.11 [Refereed] [International journal]

Tightly regulated at the level of transcription, expression of MHC class II molecules varies significantly among gastrointestinal cancers. High levels of MHC class II expression are often associated with a better prognosis, which is indicative of the involvement of CD4+ lymphocytes in tumor suppression, but the molecular mechanism by which MHC class II expression is regulated remains unclear. In the present study, we investigated the expression of one inducible MHC class II molecule, HLA-DR, and its coactivators in a panel of colorectal and gastric cancer cell lines. Interferon-gamma induced expression of HLA-DR in 14 of 20 cell lines tested; the remaining six cell lines did not express HLA-DR. Analysis of the expression of transcription factors and coactivators associated with HLA-DR revealed that the loss of CIITA expression was closely associated with the absence of HLA-DR induction. Moreover, DNA methylation of the 5' CpG island of CIITA-PIV was detected in all cancer cells that lacked CIITA. The methylation and resultant silencing of CIITA-PIV depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3B, and their genetic inactivation restored CIITA-PIV expression. It thus appears that CIITA methylation is a key mechanism that enables some gastrointestinal cancer cells to escape immune surveillance.

DOI PubMed

Identification of SCN3B as a novel p53-inducible proapoptotic gene.

Katsuya Adachi, Minoru Toyota, Yasushi Sasaki, Toshiharu Yamashita, Setsuko Ishida, Mutsumi Ohe-Toyota, Reo Maruyama, Yuji Hinoda, Tsuyoshi Saito, Kohzoh Imai, Ryuichi Kudo, Takashi Tokino

Oncogene 23 ( 47 ) 7791 - 8 2004.10 [Refereed] [International journal]

Authorship： Lead author

Tumor suppressor p53 is a transcription factor that induces growth arrest and/or apoptosis in response to cellular stress. To identify novel p53-inducible genes, we compared the expression of genes in normal mouse embryo fibroblasts (MEFs) to p53-null cells by cDNA representational difference analysis. We report here that expression of endogenous sodium channel subunit beta 3 (SCN3B) is upregulated in mouse embryonic fibroblasts by DNA damage in a p53-dependent manner. In addition, we found that SCN3B levels are upregulated in human cancer cell lines by DNA damaging agents, as well as by overexpression of p53, but not significantly by p63 or p73. Furthermore, we identified two putative p53-binding sites upstream of the first exon (RE1) and in the third intron (RE2). The p53 protein can directly interact with the putative p53-binding sites in vivo, as assessed by chromatin immunoprecipitation. A reporter gene assay revealed that these two p53-binding sites are functional response elements. The SCN3B protein appears to be localized to the endoplasmic reticulum (ER). Introduction of the SCN3B gene into T98G and Saos2 cells potently suppressed colony formation. Furthermore, we found that adenovirus-mediated transfer of SCN3B induced apoptosis when combined with anticancer agents. The results presented here suggest that SCN3B mediates a p53-dependent apoptotic pathway and may be a candidate for gene therapy combined with anticancer drugs.

DOI PubMed

Aberrant methylation and histone deacetylation associated with silencing of SLC5A8 in gastric cancer

M Ueno, M Toyota, K Akino, H Suzuki, M Kusano, A Satoh, H Mita, Y Sasaki, M Nojima, K Yanagihara, Y Hinoda, T Tokino, K Imai

TUMOR BIOLOGY ( KARGER ) 25 ( 3 ) 134 - 140 2004 [Refereed]

Aberrant methylation of a sodium co-transporter, solute carrier family 5 member 8 gene (SLC5A8), has been detected in a subset of colorectal cancers, suggesting SLC5A8 may also serve as a tumor suppressor. To further investigate the role of epigenetic inactivation of SLC5A8 expression in gastric cancer, we determined the methylation status of the SLC5A8 5' CpG island (CGI) in a panel of gastric cancer cell lines and primary gastric cancers. We detected methylation of the 5' CGI in ten of twelve gastric cancer cell lines, and five of those showed dense methylation, which correlated with the absence of SLC5A8 transcription. Aberrant methylation of SLC5A8 was also detected in 23 of 71 (30%) primary gastric cancers, indicating that epigenetic inactivation of SLC5A8 is not a cell-line-specific phenomenon. SLC5A8 expression was restored in methylated cell lines by treatment with 5-aza-2'-deoxycytidine, a methyltransferase inhibitor. In addition, chromatin immunoprecipitation assays showed that acetylation of histone H3 in the 5' region of the gene correlated directly with SLC5A8 expression and inversely with DNA methylation. It thus appears that aberrant methylation of its 5' CGI and histone deacetylation play key roles in silencing SLC5A8 expression in gastric cancers. Copyright (C) 2004 S. Karger AG, Basel.

DOI PubMed

Epigenetic inactivation of CHFR and sensitivity to microtubule inhibitors in gastric cancer.

Ayumi Satoh, Minoru Toyota, Fumio Itoh, Yasushi Sasaki, Hiromu Suzuki, Kazuhiro Ogi, Takefumi Kikuchi, Hiroaki Mita, Toshiharu Yamashita, Takashi Kojima, Masanobu Kusano, Masahiro Fujita, Masao Hosokawa, Takao Endo, Takashi Tokino, Kohzoh Imai

Cancer research 63 ( 24 ) 8606 - 13 2003.12 [Refereed] [International journal]

Mitotic checkpoints prevent errors in chromosome segregation that can lead to neoplasia. Therefore, it is notable that gastric cancers often show impaired checkpoint function. In the present study, we examined the functional consequences of epigenetic inactivation of the mitotic checkpoint gene CHFR in gastric cancers. CHFR expression was silenced by DNA methylation of the 5' region of the gene in 20% of the gastric cancer cell lines tested and in 39% of primary gastric cancers; expression could be restored by treatment with 5-aza-2'-deoxycytidine, a methyltransferase inhibitor. In addition, histones H3 and H4 were found to be deacetylated in cell lines showing aberrant methylation, indicating a role for histone deacetylation in the methylation-dependent gene silencing. Cells not expressing CHFR showed impaired checkpoint function, which led to nuclear localization of cyclin B1 after treatment with docetaxel or paclitaxel, two microtubule inhibitors. Apparently, the absence of CHFR is associated with sensitivity of cells to mitotic stress caused by microtubule inhibition, and restoration of CHFR expression by 5-aza-2'-deoxycytidine or adenoviral gene transfer restored the checkpoint. By affecting mitotic checkpoint function, CHFR inactivation likely plays a key role in tumorigenesis in gastric cancer. Moreover, the aberrant methylation of CHFR appears to be a good molecular marker with which to predict the sensitivity of gastric cancers to microtubule inhibitors.

PubMed

Identification of HRK as a target of epigenetic inactivation in colorectal and gastric cancer.

Toshiro Obata, Minoru Toyota, Ayumi Satoh, Yasushi Sasaki, Kazuhiro Ogi, Kimishige Akino, Hiromu Suzuki, Masafumi Murai, Takefumi Kikuchi, Hiroaki Mita, Fumio Itoh, Jean-Pierre J Issa, Takashi Tokino, Kohzoh Imai

Clinical cancer research : an official journal of the American Association for Cancer Research 9 ( 17 ) 6410 - 8 2003.12 [Refereed] [International journal]

PURPOSE: Aberrant methylation of CpG islands can be a good molecular marker for identifying genes inactivated in cancer. We found the proapoptotic gene HRK to be a target for hypermethylation in human cancers and examined the role of such methylation in silencing the gene's expression. EXPERIMENTAL DESIGN: Methylation of HRK was evaluated by bisulfite-PCR and bisulfite sequencing in a group of colorectal and gastric cancer cell lines and primary cancers. Gene expression and histone acetylation were examined by reverse transcription-PCR and chromatin immunoprecipitation analyses, respectively. Apoptosis of cancer cells after treatment with a DNA methyltransferase inhibitor and/or histone deacetylase inhibitor was examined with fluorescence-activated cell-sorting analysis. RESULTS: The region around the HRK transcription start site was methylated in 36% of colorectal and 32% of gastric cancer cell lines and was closely associated with loss of expression in those cell types. HRK expression was restored by treatment with a methyltransferase inhibitor, 5-aza-deoxycytidine, and enhanced further by addition of histone deacetylase inhibitor trichostatin A or depsipeptide. Such restoration of HRK expression was well correlated with induction of apoptosis and enhancement of Adriamycin-induced apoptosis. Expression of other proapoptotic genes, including BAX, BAD, BID, and PUMA, was unaffected by treatment with 5-aza-deoxycytidine. Aberrant methylation of HRK was also frequently detected in primary colorectal cancers that showed methylation of multiple genes, including p16INK4A and hMLH1, and was associated with wild-type p53. CONCLUSION: HRK methylation can be a useful molecular target for cancer therapy in a subset of colorectal and gastric cancers.

PubMed

Identification of the interleukin 4 receptor alpha gene as a direct target for p73.

Yasushi Sasaki, Hiroaki Mita, Minoru Toyota, Setsuko Ishida, Ichiro Morimoto, Toshiharu Yamashita, Toshihiro Tanaka, Kohzoh Imai, Yusuke Nakamura, Takashi Tokino

Cancer research 63 ( 23 ) 8145 - 52 2003.12 [Refereed] [International journal]

Authorship： Lead author

p73 has a high degree of structural homology to p53 and can activate transcription of p53-responsive genes. However, analysis of p73-deficient mice revealed a marked divergence in the physiological activities of p53 family genes and distinguishes p73 from p53. Mice deficient for p73 exhibit profound defects, including hippocampal dysgenesis, chronic infection, and inflammation, as well as abnormalities in pheromone sensory pathways. p73 plays important roles in neurogenesis, sensory pathways, and homeostatic regulation. Here, we found that the interleukin 4 receptor alpha (IL-4Ralpha) gene is up-regulated by p73 but not significantly by p53 in several human cancer cell lines. IL-4Ralphatranscription is also activated in response to cisplatin, a DNA-damaging agent known to induce p73. By using small interference RNA designed to target p73, we demonstrated that silencing endogenous p73 abrogates the induction of the IL-4Ralpha gene after cisplatin treatment. Furthermore, we identified a p73-binding site in the first intron of the IL-4Ralpha gene that can directly interact with the p73 protein in vivo. This p73-binding site consists of eight copies of a 10-bp consensus p53-binding motif and is a functional response element that is relatively specific for p73 among the p53 family. p73beta promoted localized nucleosomal acetylation through recruitment of coactivator p300, indicating that p73 regulates transcription of IL-4Ralpha through the unique p73-binding site. We also found that p73beta-transfected tumor cells are sensitive to IL-4-mediated apoptosis. Our data suggest that IL-4Ralpha could mediate, in part, certain immune responses and p73-dependent cell death.

PubMed

Epigenetic inactivation of CHFR in human tumors.

Minoru Toyota, Yasushi Sasaki, Ayumi Satoh, Kazuhiro Ogi, Takefumi Kikuchi, Hiromu Suzuki, Hiroaki Mita, Nobuyuki Tanaka, Fumio Itoh, Jean-Pierre J Issa, Kam-Wing Jair, Kornel E Schuebel, Kohzoh Imai, Takashi Tokino

Proceedings of the National Academy of Sciences of the United States of America 100 ( 13 ) 7818 - 23 2003.06 [Refereed] [International journal]

Cell-cycle checkpoints controlling the orderly progression through mitosis are frequently disrupted in human cancers. One such checkpoint, entry into metaphase, is regulated by the CHFR gene encoding a protein possessing forkhead-associated and RING finger domains as well as ubiquitin-ligase activity. Although defects in this checkpoint have been described, the molecular basis and prevalence of CHFR inactivation in human tumors are still not fully understood. To address this question, we analyzed the pattern of CHFR expression in a number of human cancer cell lines and primary tumors. We found CpG methylation-dependent silencing of CHFR expression in 45% of cancer cell lines, 40% of primary colorectal cancers, 53% of colorectal adenomas, and 30% of primary head and neck cancers. Expression of CHFR was precisely correlated with both CpG methylation and deacetylation of histones H3 and H4 in the CpG-rich regulatory region. Moreover, CpG methylation and thus silencing of CHFR depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3b, as their genetic inactivation restored CHFR expression. Finally, cells with CHFR methylation had an intrinsically high mitotic index when treated with microtubule inhibitor. This means that cells in which CHFR was epigenetically inactivated constitute loss-of-function alleles for mitotic checkpoint control. Taken together, these findings shed light on a pathway by which mitotic checkpoint is bypassed in cancer cells and suggest that inactivation of checkpoint genes is much more widespread than previously suspected.

DOI PubMed

Analysis of lung tumorigenesis in chimeric mice indicates the Pulmonary adenoma resistance 2 (Par2) locus to operate in the tumor-initiation stage in a cell-autonomous manner: detection of polymorphisms in the Poli gene as a candidate for Par2.

Gang-Hong Lee, Hiroyuki Nishimori, Yasushi Sasaki, Hiroshi Matsushita, Tomoyuki Kitagawa, Takashi Tokino

Oncogene 22 ( 15 ) 2374 - 82 2003.04 [Refereed] [International journal]

The Pulmonary adenoma resistance 2 (Par2) locus of the BALB/cByJ mouse, located within 0.5 cM of chromosome 18, is responsible for reducing the mean multiplicity of urethane-induced lung tumors relative to those in C57BL/6J, A/J and C3H/HeJ mice. Thus, BALB/B6-Par2 congenic strain genetically identical to BALB/cByJ except carrying C57BL/6J Par2 alleles develops seven times more tumors than BALB/cByJ. To gain clues for identification of Par2 candidate genes, we analysed lung tumorigenesis in BALB/cByJ<-->BALB.B6-Par2 chimeric animals. Of 100 tumors induced by urethane in 16 chimeras, 82 originated from BALB.B6-Par2 cells, indicating the Par2 phenotype to be cell-autonomous. In addition, the BALB.B6-Par2- and BALB/cByJ-derived tumors were similar in mean size, implying that the phenotype is primarily expressed during initiation rather than in the promotion stage of carcinogenesis. Given these results, we surveyed a comprehensive mouse genome database and physically mapped Par2 within a 2.3 Mbp segment containing three known genes, Poli, Mbd2 and Dcc. Among those, the Poli seemed to be the most reasonable Par2 candidate, since it encodes an extremely error-prone DNA polymerase preferentially incorporating G or T opposite template T in vitro, reminiscent of the Kras2 activation because of an A to G or T point mutation within codon 61 with which most urethane-induced lung tumors are initiated. Indeed, our sequencing of Poli cDNAs from BALB/cByJ, C57BL/6J, A/J and C3H/HeJ lungs revealed 21 BALB/cByJ-specific single-nucleotide polymorphisms in the coding region accompanied by seven amino-acid substitutions and an elevated frequency of alternative splicing, while no polymorphisms associated with tumor susceptibility were found for either Mbd2 or Dcc. Notably, we obtained evidence that BALB/cByJ Par2 alleles may selectively decrease the frequency of Kras2-mutated tumors compared with C57BL/6J alleles. Consequently, the Poli is an intriguing Par2 candidate clearly deserving further evaluation.

DOI PubMed

Induction of tenascin-C by tumor-specific EWS-ETS fusion genes.

Goichi Watanabe, Hiroyuki Nishimori, Hideto Irifune, Yasushi Sasaki, Setsuko Ishida, Hitoshi Zembutsu, Toshihiro Tanaka, Satoshi Kawaguchi, Takuro Wada, Jun-ichi Hata, Moriaki Kusakabe, Koichi Yoshida, Yusuke Nakamura, Takashi Tokino

Genes, chromosomes & cancer 36 ( 3 ) 224 - 32 2003.03 [Refereed] [International journal]

Ewing sarcoma (ES) and peripheral primitive neuroectodermal tumors (PNETs) are associated with a chromosomal translocation resulting in a fusion of the amino-terminus of EWS with the DNA-binding domain of an ETS transcription factor (most commonly FLI1 or ERG). Although previous reports suggested that these chimera proteins would act as aberrant transcription factors, their downstream targets have not been fully elucidated. To identify downstream targets of these EWS-ETS fusion proteins, we introduced EWS-ETS fusion constructs into a human fibrosarcoma cell line, HT-1080, by retroviral transduction. Here we report that Tenascin-C (TNC) is induced to a significantly higher level in cells expressing EWS-ETSs than in cells expressing normal ETSs. Furthermore, through use of an antisense cDNA expression vector we show that expression of endogenous TNC mRNA and protein were reduced coordinately with attenuation of EWS-FLI1 fusion protein expression. A chromatin immunoprecipitation assay showed direct interaction between the TNC promoter and the EWS-FLI1 fusion protein in vivo. In addition, a luciferase reporter assay revealed that EWS-ETSs upregulated the TNC gene through four ETS binding sites in the TNC promoter. High levels of TNC expression were observed in a subset of ES cell lines (3 of 6) and primary tumors (4 of 6). Together with previous studies showing that TNC expression is involved in the invasive and malignant phenotype of several tumor types, our data suggest that the oncogenic effect of EWS-ETS may be mediated in part by upregulating of TNC expression.

DOI PubMed

The Id2 gene is a novel target of transcriptional activation by EWS-ETS fusion proteins in Ewing family tumors.

Hiroyuki Nishimori, Yasushi Sasaki, Koichi Yoshida, Hideto Irifune, Hitoshi Zembutsu, Toshihiro Tanaka, Tomoki Aoyama, Taisuke Hosaka, Satoshi Kawaguchi, Takuro Wada, Jun-Ichi Hata, Junya Toguchida, Yusuke Nakamura, Takashi Tokino

Oncogene 21 ( 54 ) 8302 - 9 2002.11 [Refereed] [International journal]

We report here that the Id2 (inhibitor of DNA binding 2) gene is a novel target of transcriptional activation by EWS-FLI1 and EWS-ERG, two fusion proteins that characterize Ewing family tumors (EFTs). To identify downstream targets of these EWS-ETS fusion proteins, we introduced EWS-ETS fusion constructs into a human fibrosarcoma cell line by retroviral transduction. cDNA microarray analysis revealed that Id2 expression was up-regulated by introducing the EWS-ETS fusion gene but not by the normal full-length ETS gene. An Id2 promoter-luciferase reporter assay showed that transactivation by EWS-ETS involves the minimal Id2 promoter and may function in cooperation with c-Myc within the full-length regulatory region. A chromatin immunoprecipitation assay revealed direct interaction between the Id2 promoter and EWS-FLI1 fusion protein in vivo. Significantly higher expression of Id2 and c-Myc was observed in all of the six EFT cell lines examined compared to six other sarcoma cell lines. Moreover, high levels of Id2 expression were also observed in five of the six primary tumors examined. Id2 is generally thought to affect the balance between cell differentiation and proliferation in development and is highly expressed in several cancer types. Considering these previous studies, our data suggest that the oncogenic effect of EWS-ETS may be mediated in part by up-regulating Id2 expression. doi:10.1038/sj.onc.1206025

DOI PubMed

DNA methylation and histone deacetylation associated with silencing DAP kinase gene expression in colorectal and gastric cancers.

Satoh A, Toyota M, Itoh F, Kikuchi T, Obata T, Sasaki Y, Suzuki H, Yawata A, Kusano M, Fujita M, Hosokawa M, Yanagihara K, Tokino T, Imai K

British Journal of Cancer 86 ( 11 ) 1817 - 1823 2002.06 [Refereed]

Death-associated protein kinase is a positive regulator of programmed cell death induced by interferon gamma. To investigate the role of epigenetic inactivation of death-associated protein kinase in gastrointestinal cancer, we examined the methylation status of the 5' CpG island of the death-associated protein kinase gene. Methylation of the 5' CpG island was detected in 3 of 9 colorectal and 3 of 17 gastric cancer cell lines, while among primary tumours, it was detected in 4 of 28 (14%) colorectal and 4 of 27 (15%) gastric cancers. By contrast, methylation of the edge of the CpG island was detected in virtually every sample examined. Death-associated protein kinase expression was diminished in four cell lines that showed dense methylation of the 5' CpG island, and treatment with 5-aza-2'-deoxycitidine, a methyltransferase inhibitor, restored gene expression. Acetylation of histones H3 and H4 in the 5' region of the gene was assessed by chromatin immunoprecipitation and was found to correlate directly with gene expression and inversely with DNA methylation. Thus, aberrant DNA methylation and histone deacetylation of the 5' CpG island, but not the edge of the CpG island, appears to play a key role in silencing death-associated protein kinase expression in gastrointestinal malignancies.

DOI PubMed

p53ファミリー遺伝子の機能解析遺伝子治療をめざして

佐々木泰史, 時野隆至

札幌医学雑誌 ( 札幌医科大学 ) 71 ( 1〜2 ) 1 - 6 2002.04 [Refereed]

Authorship： Lead author

p53 gene therapy is being tested clinically for the treatment of human cancer, however some cancer models (in vivo and in vitro) are resistant to p53. To explore the potential use of two p53 homologues, p73 and p51/p63, in cancer gene therapy, we introduced p53, p73 and p51/p63 into colorectal cancer cell lines via adenoviral vectors, and compared their effects on cell growth. Among ten cell lines tested, six cell lines displayed a similar response following transduction of p53, p73 beta or p51A/p63 gamma, two lines underwent cell-cycle arrest, three lines exhibited apoptosis and one line showed no-effect following transduction. The effect on cell-cycle progression was variable in the other four cell lines. Interestingly, three cell lines were resistant to p53-mediated apoptosis, including two lines having endogenous wildtype p53 alleles, but underwent apoptosis after transduction of p73 beta or p51A/p63 gamma. Similar to p53, transduction of p51A/p63 gamma induced extensive apoptosis when combined with adriamycin or X-radiation in SW480 cells, which are normally resistant to apoptosis. Transduction of p73 beta and p51A/p63 gamma also reduced the tumorigenicity of two colorectal cancer cells in vivo. These results suggest that adenovirus-mediated p73 beta and p51A/p63 gamma transfer are potential novel approaches for the treatment of human cancers, particularly for tumors that are resistant to p53 gene therapy.

DOI CiNii

Identification of the osteopontin gene as a direct target of TP53.

Ichiro Morimoto, Yasushi Sasaki, Setsuko Ishida, Kohzoh Imai, Takashi Tokino

Genes, chromosomes & cancer 33 ( 3 ) 270 - 8 2002.03 [Refereed] [International journal]

The TP53 tumor suppressor gene regulates a number of genes that are involved in cell-cycle inhibition, apoptosis, and maintaining genetic stability. Recently, two genes that have a role in immunosurveillance were identified as downstream targets of TP53. These genes, TAP1 and fractalkine, may contribute to suppress tumor growth through host immunosurveillance. It has been reported that the mouse secreted phosphoprotein osteopontin (Opn) is one of the key cytokines for type 1 immune responses mediated by macrophages. It also was reported that Opn may play a role in suppressing tumor growth in vivo. Here we identified Opn as a Tp53-target gene using mRNA differential display analysis of embryonic fibroblasts from Tp53-deficient mice. Furthermore, we found that Opn expression was upregulated by DNA damage-induced Tp53 activity and by adenovirus-mediated transfer of the human TP53 gene. In addition, a luciferase assay showed that the Opn gene has a functional Tp53-responsive element in its promoter region, and a chromatin immunoprecipitation assay confirmed interaction between the Opn promoter and Tp53 protein in vivo. These results suggest that OPN is a direct transcriptional target of TP53. The TP53-directed regulation of OPN expression suggests a novel model of TP53 participation in immunosurveillance, involving interaction with the host immune system to prevent damaged cells from undergoing malignant transformation.

DOI PubMed

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<SASAKI Yasushi>

Papers - SASAKI Yasushi