Nobuyoshi Sugito

RNASEN Regulates Cell Proliferation and Affects Survival in Esophageal Cancer Patients

Purpose: MicroRNAs (miRNA) are small noncoding RNAs thought to be involved in physiologic and developmental processes by negatively regulating the expression of target genes. Little is known about the role of miRNAs in normal and cancer cells. It is possible that deregulation of miRNA may contribute to the oncogenesis of some cancers. We studied the expression level of the miRNA processing enzyme (DICER1, DGCR8, and RNASEN) in esophageal squamous cell carcinoma (ESCC). Experimental Design: The expression levels of DICER1, DGCR8, and RNASEN mRNA in 73 ESCC tissues were compared with that in corresponding normal esophageal epithelium by Taqman real-time reverse-transcription PCR. We also examined RNASEN protein expression in 27 cell lines. The role of RNASEN in cell proliferation in ESCC cells was assessed by small interfering RNA. Paraffin sections of ESCC patients were immunohistochemically investigated. Results: We found that RNASEN expression levels were enhanced in a fraction of esophageal cancers. Multivariate Cox regression analysis showed that the prognostic effect of RNASEN (P = 0.0036) seems to be independent of disease stage (P = 0.0060). Knockdown of RNASEN in esophageal cancer cell lines resulted in a 46% to 85% reduction in cell number. In an immunohistochemical study, the intensity of RNASEN expression was often increased in the tumor compared with that in normal epithelium. Conclusions: The relationship between the RNASEN expression and the prognosis of the ESCC patients warrants a further study on the role of miRNA and tumor progression.

Counterbalance between RB inactivation and miR-17-92 overexpression in reactive oxygen species and DNA damage induction in lung cancers.

Small-cell lung cancer (SCLC) is a highly aggressive disease that exhibits rapid growth and genetic instability. We found earlier frequent overexpression of the miR-17–92 microRNA cluster, and showed that SCLC cells were addicted to continued expressions of miR-17–5p and miR-20a, major components of this microRNA cluster. In this study, we identified the frequent presence of constitutively phosphorylated H2AX (γ-H2AX), which reflects continuing DNA damage, preferentially in SCLC. Knockdown of RB induced γ-H2AX foci formation in non-small cell lung cancer (NSCLC) cells with wild-type RB, in association with growth inhibition and reactive oxygen species (ROS) generation, which was canceled by overexpression of miR-17–92. Conversely, induction of γ-H2AX was observed in a miR-17–92-overexpressing SCLC cell line with miR-20a antisense oligonucleotides. These findings suggest that miR-17–92 overexpression may serve as a fine-tuning influence to counterbalance the generation of DNA damage in RB-inactivated SCLC cells, thus reducing excessive DNA damage to a tolerable level and consequently leading to genetic instability. Therefore, miR-17–92 may be an excellent therapeutic target candidate to elicit excessive DNA damage in combination with DNA-damaging chemotherapeutics.

Identification of Decatenation G2 Checkpoint Impairment Independently of DNA Damage G2 Checkpoint in Human Lung Cancer Cell Lines

It has been suggested that attenuation of the decatenation G2 checkpoint function, which ensures sufficient chromatid decatenation by topoisomerase II before entering into mitosis, may contribute to the acquisition of genetic instability in cancer cells. To date, however, very little information is available on this type of checkpoint defect in human cancers. In this study, we report for the first time that a proportion of human lung cancer cell lines did not properly arrest before entering mitosis in the presence of a catalytic, circular cramp-forming topoisomerase II inhibitor ICRF-193, whereas the decatenation G2 checkpoint impairment was present independently of the impaired DNA damage G2 checkpoint. In addition, the presence of decatenation G2 checkpoint dysfunction was found to be associated with diminished activation of ataxia-telangiectasia mutated in response to ICRF-193, suggesting the potential involvement of an upstream pathway sensing incompletely catenated chromatids. Interestingly, hypersensitivity to ICRF-193 was observed in cell lines with decatenation G2 checkpoint impairment and negligible activation of ataxia-telangiectasia mutated. These findings suggest the possible involvement of decatenation G2 checkpoint impairment in the development of human lung cancers, as well as the potential clinical implication of selective killing of lung cancer cells with such defects by this type of topoisomerase II inhibitor.

CLCP1 interacts with semaphorin 4B and regulates motility of lung cancer cells

We previously established a highly metastatic subline, LNM35, from the NCI-H460 lung cancer cell line, and demonstrated upregulation of a novel gene, CLCP1 (CUB, LCCL-homology, coagulation factor V/VIII homology domains protein), in LNM35 and lung cancer specimens. In this study, we focused on the potential roles of that gene in cancer metastasis. First, we established stable LNM35 RNAi clones, in which CLCP1 expression was suppressed by RNAi, and found that their motility was significantly reduced, although growth rates were not changed. Next, in vitro selection of a phage display library demonstrated that a phage clone displaying a peptide similar to a sequence within the Sema domain of semaphorin 4B (SEMA4B) interacted with LNM35. Immunoprecipitation experiments confirmed interaction of CLCP1 with SEMA4B, regulation of CLCP1 protein by ubiquitination and proteasome degradation enhanced in the presence of SEMA4B. These results are the first to indicate that CLCP1 plays a role in cell motility, whereas they also showed that at least one of its ligands is SEMA4B and that their interaction mediates proteasome degradation by CLCP1. Although the physiological role of the interaction between CLCP1 and SEMA4B remains to be investigated, this novel gene may become a target of therapy to inhibit metastasis of lung cancers.

Histone modification in the TGFβRII gene promoter and its significance for responsiveness to HDAC inhibitor in lung cancer cell lines

We previously reported silencing of the TGF‐β type II receptor gene (TGFβRII), involving histone deacetylation, instead of DNA methylation (DNA‐Me). Because different histone modifications may play crucial roles in the epigenetic alterations, we further studied links with silencing of the TGFβRII gene promoter in six lung cancer cell lines. ChIP assays demonstrated three chromatin patterns for this gene silencing (Pattern I: histone H3 acetylation (H3‐Ac)(+/−)/histone H3 lysine 4 methylation (H3K4‐Me)(+)/DNA‐Me(−), Pattern II; H3‐Ac(−)/H3K4‐Me(+/−)/DNA‐Me(−), and Pattern III; H3‐Ac(−)/H3K4‐Me(−)/DNA‐Me(+)), indicating possible progressive alterations with H3K4‐Me alteration. With exposure to a histone deacetylase inhibitor (HDAC‐I), trichostatin A, cell lines with the pattern II demonstrated strong and persistent induction of TGFβRII expression, while those with the pattern III showed only weak or no induction. ACC‐LC‐91 cell line, one of the pattern II examples demonstrated strong and continuous induction of H3K4‐Me similar to TGFβRII expression. In contrast, ACC‐LC‐176 with the pattern III showed only weak and transient induction of H3K4‐Me, similar to TGFβRII expression. Treatment with 5‐aza‐2′‐deoxycytidine (5aza‐dC) in addition to HDAC‐I resulted in strong and continuous induction of TGFβRII expression and H3K4‐Me in ACC‐LC‐176, although 5aza‐dC alone was without such effects. In ACC‐LC‐91, both H3‐Ac and H3K4‐Me were promptly and simultaneously induced by HDAC‐I, and similarly inhibited by wortmannin, a PI3K family inhibitor, together with TGFβRII induction. These findings suggested progressive alterations of chromatin configuration including H3K4‐Me alteration in TGFβRII gene silencing. A possible involvement of a wortmannin‐sensitive kinase in histone modification was also suggested.

Novel NBS1 Heterozygous Germ Line Mutation Causing MRE11-Binding Domain Loss Predisposes to Common Types of Cancer

DNA damage response (DDR) pathways maintain genomic stability. A 657del5 mutation of NBS1, a key DDR component, causing the rare cancer-predisposing Nijmegen breakage syndrome has been reported nearly exclusively in Slavic populations. In this study, we describe the first identification in a Japanese population of an unprecedented type of heterozygous NBS1 mutant, termed IVS11+2insT, lacking the MRE11- and ATM-binding site at the COOH terminus. Profoundly defective in crucial binding to MRE11, MDC1, BRCA1, and wild-type NBS1, the mutant caused impaired ATM phosphorylation in response to low-dose irradiation in a heterozygous state. Importantly, whereas IVS11+2insT was found in only 2 (0.09%) of 2,348 control subjects, it was identified in 2% (2 of 96) of heterozygotes with gastric cancer, 0.8% (3 of 376) of those with colorectal cancer, and 0.4% (2 of 532) of those with lung cancer, which were comparable to frequencies reported for other DDR-related genes known to confer cancer susceptibility. The presence of the heterozygous IVS11+2insT mutation seemed to be associated with an increased risk for gastrointestinal cancers, with an odds ratio of 12.6 and 95% confidence interval (95% CI) of 2.05 to 132.1 (P = 0.0001). The odds ratios separately calculated for gastric and colorectal cancers were 25.0 (95% CI, 1.78-346.0) and 9.43 (95% CI, 1.08-113.1), respectively. These findings suggest that IVS11+2insT is associated with an increased risk for the development of certain types of common cancers, warranting future investigation including detailed phenotypic characterization of age of onset and penetrance in heterozygotes, as well as screening in other ethnic groups.

Relationship between expression of 5-fluorouracil metabolic enzymes and 5-fluorouracil sensitivity in esophageal carcinoma cell lines

5-Fluorouracil (5-FU) is a key drug in the treatment of esophageal squamous cell carcinoma (ESCC). Gene expression of 5-FU metabolic enzymes such as thymidylate synthase (TS), thymidine phosphorylase (TP), dihydropyrimidine dehydrogenase (DPD) and orotate phosphoribosyl transferase (OPRT), has recently been investigated in order to predict the 5-FU sensitivity of several cancers. We examined the relationship between such gene expression and 5-FU sensitivity in 25 ESCC cell lines. TS, DPD, TP and OPRT mRNA levels were assessed by real-time polymerase chain reaction. The 50% inhibitory concentrations (IC50) of 5-FU in 25 ESCC cell lines were determined by cell proliferation assay. IC50 values for 5-FU ranged from 1.00 to 39.81 micromol/L. There were significant positive correlations between IC50 and TS mRNA expression (R(2) = 0.5781, P < 0.0001) and DPD mRNA expression (R(2) = 0.3573, P = 0.0016). There were no correlations between IC50 and TP or OPRT mRNA expression. TS and DPD mRNA expression levels may be useful indicators in predicting the anti-tumor activity of 5-FU in ESCC.

NOTCH1 activates the Wnt/β-catenin signaling pathway in colon cancer

Purpose and Methods The translocation of β-catenin/CTNNB1 to the nucleus activates Wnt signaling and cell proliferation; however, the precise mechanism underlying this phenomenon remains unknown. Previous reports have provided evidence that NOTCH1 is involved in the Wnt signaling pathway. Therefore, we sought to determine the mechanism by which NOTCH1 influences the Wnt/β-catenin pathway. We constructed a vector expressing the NOTCH1 intracellular domain (NICD1) and transfected the vector into HCT116 which has low expression of NICD1. Furthermore, inhibition of NOTCH signal pathway in SW480 which has abundant NICD1 expression, was performed by transfection of siNICD1 or DAPT, gamma secretase inhibitor, treatment. In addition, we evaluated NICD1 and β-catenin localization in colon cancer cell lines and in 189 colon cancer tissue samples and analyzed the correlation between the nuclear localization of NICD1 and the clinicopathological features of colon cancer patients. Results Immunohistochemical assays demonstrated that NICD1 and β-catenin exhibited a similar localization pattern in colon cancer tissues. In addition, we found that NICD1 induced the translocation of β-catenin to the nucleus and that NICD1 and β-catenin co-localized in the nucleus. Overexpression of NICD1 increased luciferase activity of Wnt signal pathway. On the other hand, reduction of NICD1 reduced luciferase activity of Wnt signaling pathway. In the 189 analyzed colon cancer cases, multivariate COX regression analysis demonstrated the independent prognostic impact of nuclear localization of NICD1(p=0.0376). Conclusion NOTCH1 plays a key role in the Wnt pathway and activation of NOTCH1 is associated with the translocation of β-catenin to the nucleus.