Hiroto Ishihara

mel-18 negatively regulates cell cycle progression upon B cell antigen receptor stimulation through a cascade leading to c-myc/cdc25

mel-18 is a mammalian Polycomb group gene encoding a transcriptional repressor with tumor suppressive activity. Overexpression of mel-18 in mice results in cell cycle arrest of B cells upon B cell receptor stimulation with downregulation of c-myc. This phenotype is rescued in mel-18/c-myc double-transgenic mice, suggesting that c-myc locates downstream of mel-18. In mel-18 transgenic mice, the downregulation of cyclins D2 and E; CDK4, -6, and -7; and CDC25A causes the impairment in the activities of cyclin-dependent kinases, resulting in hypophosphorylation of the retinoblastoma protein. In contrast, the upregulation of c-Myc, CDC25, and CDC2/CDK2 kinase activities results in the augmentation of B cell proliferation in mel-18-deficient mice. We therefore propose that mel-18 negatively regulates the cell cycle through a c-myc/cdc25 cascade.

Impact of aging on the development of hepatocellular carcinoma in patients with hepatitis C virus infection in Japan

Background: It is difficult to study the long-term outcome of hepatitis C virus (HCV) infection because chronic infection is often asymptomatic and duration of the disease is prolonged. The clinical outcome of HCV infection remains unclear in patients of advanced age. Methods: Among 575 patients consecutively diagnosed with hepatocellular carcinoma (HCC) from 1988 to 1999 at Hiroshima University, we examined 430 with HCV. We studied the differences between males and females in the following characteristics: age at first diagnosis of HCC, Child grade, various tumour factors, history of blood transfusion, duration to development of HCC, and history of alcohol intake. Results: The incidence of HCC patients with HCV increased in elderly persons, including female patients. Background liver function was significantly better for female patients ( P r < r 0.001). In both genders, the duration between blood transfusion and diagnosis of HCC was significantly shorter when the patients received blood transfusion at an older age ( P r < r 0.001). In habitual drinkers, the average age at first diagnosis of HCC was significantly younger ( P r < r 0.001), and duration to development of HCC significantly shorter ( P r < r 0.05). The percentage of atomic bomb survivors among HCV-positive HCC patients was significantly higher than that among HCV-negative HCC patients ( P r < r 0.05). Conclusions: Patients with HCV might exhibit slow disease progression and develop HCC finally with aging regardless of gender. Patients of advanced age with HCV, even female patients, should therefore be closely followed.BACKGROUND It is difficult to study the long-term outcome of hepatitis C virus (HCV) infection because chronic infection is often asymptomatic and duration of the disease is prolonged. The clinical outcome of HCV infection remains unclear in patients of advanced age. METHODS Among 575 patients consecutively diagnosed with hepatocellular carcinoma (HCC) from 1988 to 1999 at Hiroshima University, we examined 430 with HCV. We studied the differences between males and females in the following characteristics: age at first diagnosis of HCC, Child grade, various tumour factors, history of blood transfusion, duration to development of HCC, and history of alcohol intake. RESULTS The incidence of HCC patients with HCV increased in elderly persons, including female patients. Background liver function was significantly better for female patients (P < 0.001). In both genders, the duration between blood transfusion and diagnosis of HCC was significantly shorter when the patients received blood transfusion at an older age (P < 0.001). In habitual drinkers, the average age at first diagnosis of HCC was significantly younger (P < 0.001), and duration to development of HCC significantly shorter (P < 0.05). The percentage of atomic bomb survivors among HCV-positive HCC patients was significantly higher than that among HCV-negative HCC patients (P < 0.05). CONCLUSIONS Patients with HCV might exhibit slow disease progression and develop HCC finally with aging regardless of gender. Patients of advanced age with HCV, even female patients, should therefore be closely followed.

Polycomb Group Gene mel-18 Regulates Early T Progenitor Expansion by Maintaining the Expression of Hes-1, a Target of the Notch Pathway

Polycomb group (PcG) proteins play a role in the maintenance of cellular identity throughout many rounds of cell division through the regulation of gene expression. In this report we demonstrate that the loss of the PcG gene mel-18 impairs the expansion of the most immature T progenitor cells at a stage before the rearrangement of the TCR β-chain gene in vivo and in vitro. This impairment of these T progenitors appears to be associated with increased susceptibility to cell death. We also show that the expression of Hes-1, one of the target genes of the Notch signaling pathway, is drastically down-regulated in early T progenitors isolated from mel-18−/− mice. In addition, mel-18−/− T precursors could not maintain the Hes-1 expression induced by Delta-like-1 in monolayer culture. Collectively, these data indicate that mel-18 contributes to the maintenance of the active state of the Hes-1 gene as a cellular memory system, thereby supporting the expansion of early T progenitors.

Dimerization of the Polycomb-group protein Mel-18 is regulated by PKC phosphorylation.

The Polycomb-group (Pc-G) gene products form complexes via protein-protein interactions and maintain the transcriptional repression of genes involved in embryogenesis, cell cycle, and tumorigenesis. Previously, we have shown that mouse Mel-18, a Pc-G protein, has tumor suppressor gene-like activity and negatively regulates transcription. Here, we show in vitro by pull-down assays and in vivo in transiently transfected COS-7 cells that Mel-18 forms homodimers. Deletion analysis revealed that the N-terminal RING-finger and alpha-helix domains are required for homodimer formation. In addition, we demonstrated that Mel-18 homo-dimerization is regulated by protein kinase C (PKC) and protein phosphatases, such that dephosphorylated Mel-18 is able to homo-dimerize. These results suggest that the stoichiometry and/or equilibrium of subunits of the class II Polycomb complex containing Mel-18 might be regulated by changes in phosphorylation status via the PKC signaling pathway.

Short Communication Mammalian Polycomb group genes are categorized as a new type of early response gene induced by B-cell receptor cross-linking

Polycomb group (PcG) genes were initially described in Drosophila melanogaster as regulators of the homeobox gene. Four mammalian homologues, mel-18, bmi-1, M33 and rae-28, are analyzed in this study. They not only regulate mammalian homeotic genes by analogy with their Drosophila counterparts, but also have some influence on the growth and differentiation of B lymphocytes. Here we report that these four mammalian PcG genes are rapidly induced after antigen-receptor cross-linking in B cells. Thus we would like to propose that mammalian PcG genes can be categorized as a new type of immediate early gene.

Eicosapentaenoic Acid Could Permit Maintenance of the Original Ribavirin Dose in Chronic Hepatitis C Virus Patients during the First 12 Weeks of Combination Therapy with Pegylated Interferon-α and Ribavirin

Objective: To evaluate the efficacy of eicosapentaenoic acid (EPA) against ribavirin (RBV)-associated hemolytic anemia during the first 12 weeks in chronic hepatitis C virus (HCV) combination therapy. Methods: This study was a prospective open-label, randomized controlled trial. 100 HCV patients were randomized to either the EPA group (n = 49) or non-EPA group (n = 51) who received combination therapy with or without EPA. We compared the changes in hemoglobin level and RBV plasma concentrations at week 12 in each group with RBV dose reduction rate and performed multivariate analysis to identify independent variables associated with RBV dose reduction. Results: 8 patients (17%) in the EPA group and 20 patients (29%) in the non-EPA group required RBV dose reduction, respectively. The cumulative RBV reduction rate was significantly lower in the EPA group than in the non-EPA group (p = 0.017), while the decrease of hemoglobin and RBV plasma concentrations from baseline was not significantly different. However, in the multivariate analysis, treatment with EPA showed significant variables for the reduction of RBV dose (odds ratio 3.235, p = 0.023). Conclusion: EPA could prevent the RBV dose reduction during the first 12 weeks in combination therapy, although further large-scale double-blind randomized controlled trials are required.

Prospective study of short‐term peginterferon‐α‐2a monotherapy in patients who had a virological response at 2 weeks after initiation of interferon therapy

Background and Aims:  Long‐term interferon (IFN) therapy is effective in eliminating hepatitis C virus (HCV). However, it carries the risk of adverse effects and reduced quality of life. To assess whether short‐term IFN therapy effectively eliminates HCV, we performed a prospective pilot study of pegylated (peg)IFN‐α‐2a therapy for 8 or 24 weeks.

Chemokine-mediated thymopoiesis is regulated by a mammalian Polycomb group gene, mel-18.

Multiple chemokines are made in the thymus, and they are likely to function in the fine control of cellular migration and regulation of thymic T cell development. Mice lacking the gene mel-18, a member of the mammalian Polycomb group genes, displayed impaired thymic T cell development. Here we report that expression of chemokine receptors CXCR4 and CCR9 are regulated by mel-18 and that CXCL12/SDF-1- and CCL25/TECK-mediated chemotactic activities are also affected by the loss of mel-18. In mel-18-/- mice, high expression of CXCR4 on CD4-CD8- cells might lead to trapping in the SDF-1 rich subcapsular region, while low expression of CCR9 on CD4+CD8+ cells might reduce cell migration to the medulla. Therefore, this member of the Polycomb group genes plays a role in thymic T cell migration and differentiation via the chemokine system.

Clinical evaluation of serum PIVKA-II in small hepatocellular carcinomas using a sensitive PIVKA-II assay.

腫瘍径3cm以下の小肝細胞癌82症例 (針生検例44例, 外科的切除例38例) に対し高感度PIVKA-II測定の意義について検討した. PIVKA-II陽性率は腫瘍径3.0cm以下で34%, 2.0cm以下で21%であった. 組織型別にみると中・低分化型がそれぞれ52%, 56%と比較的高率であったが, 高分化型では3%と極めて低かった (P<0.05). また切除例における検討で, 組織学的血管侵襲を有する頻度は, PIVKA-II陽性群で56%, 陰性群で18%とPIVKA-II陽性群で有意に高かった (P<0.05). また無再発生存率はPIVKA-II陽性群は陰性群に比して有意に低率であった (P<0.05). 以上のように小肝細胞癌におけるPIVKA-IIの検出率には限界があるものの, 悪性度や予後予測に有用性が認められた.