Yae Kanai

Cell adhesion system and human cancer morphogenesis

Cell‐cell adhesion determines the polarity of cells and participates in the maintenance of the cell societies called tissues. Cell‐cell adhesiveness is generally reduced in human cancers. Reduced intercellular adhesiveness allows cancer cells to disobey the social order, resulting in destruction of histological structure, which is the morphological hallmark of malignant tumors. Reduced intercellular adhesiveness is also indispensable for cancer invasion and metastasis. A tumor‐suppressor gene product, E‐cadherin, and its undercoat proteins, catenins, which connect cadherins to actin filaments, are located at lateral borders, concentrating on adherens junctions, of epithelial cells and establish firm cell‐cell adhesion. The E‐cadherin cell adhesion system in cancer cells is inactivated by various mechanisms that reflect the morphological and biological characteristics of the tumor. Silencing of the E‐cadherin gene by DNA hypermethylation around the promoter region occurs frequently, even in precancerous conditions. In diffuse infiltrating cancers, mutations are found in the genes for E‐cadherin and α‐and β‐catenins. At the invading front of cancers, the E‐cadherin cell adhesion system is inactivated by tyrosine phosphorylation of β‐catenin; an oncogene product, c‐erb B‐2 protein, is found to associate directly with β‐catenin. The E‐cadherin cell adhesion system cross‐talks with the Wingless/Wnt signaling pathway through β‐catenin, and expression of genes, which participate in cancer morphogenesis, may be regulated in conjunction with the Wingless/Wnt signaling pathway. Dysadherin, a newly identified cancer‐associated cell membrane glycoprotein, down‐regulates E‐cadherin and promotes cancer metastasis. In conclusion, inactivation of the E‐cadherin cell adhesion system by both genetic and epigenetic mechanisms plays a significant role during multistage human carcinogenesis.

FOXP3+ regulatory T cells affect the development and progression of hepatocarcinogenesis

Purpose: Tumor-infiltrating lymphocytes represent the host immune response to cancer. CD4+CD25+FOXP3+ regulatory T cells (Tregs) suppress the immune reaction. The aim of the present study was to investigate the clinicopathologic significance and roles of Tregs and CD8+ T cells during hepatocarcinogenesis. Experimental Design: We examined the infiltration of FOXP3+ Tregs and CD8+ T cells in the tumor stroma and nontumorous liver parenchyma using 323 hepatic nodules including precursor lesions, early hepatocellular carcinoma (HCC), and advanced HCC, along with 39 intrahepatic cholangiocarcinomas and 59 metastatic liver adenocarcinomas. We did immunohistochemical comparative studies. Results: The prevalence of Tregs was significantly higher in HCC than in the nontumorous liver (P < 0.001). The patient group with a high prevalence of Tregs infiltrating HCC showed a significantly lower survival rate (P = 0.007). Multivariate analysis revealed that the prevalence of Tregs infiltrating HCC was an independent prognostic factor. The prevalence of Tregs increased in a stepwise manner (P < 0.001) and that of CD8+ T cells decreased during the progression of hepatocarcinogenesis (P < 0.001). Regardless of the presence of hepatitis virus infection or histopathologic evidence of hepatitis, the prevalence of Tregs was significantly increased in nontumorous liver bearing primary hepatic tumors. Conclusions: Tregs play a role in controlling the immune response to HCC during the progression of hepatocarcinogenesis. It has been suggested that primary hepatic cancers develop in liver that is immunosuppressed by a marked infiltration of Tregs. A high prevalence of Tregs infiltrating HCC is thought to be an unfavorable prognostic indicator.

The E-cadherin gene is silenced by CpG methylation in human hepatocellular carcinomas

Our study was designed to clarify the significance of silencing the E‐cadherin gene, which is located on 16q22.1, due to CpG methylation during hepatocarcinogenesis. The CpG methylation status of primary hepatocellular carcinomas (HCCs) and corresponding liver tissues showing chronic hepatitis or cirrhosis, which are widely considered to be precancerous conditions, were assessed by digesting DNA with methylation‐sensitive and non‐sensitive restriction enzymes. CpG methylation around the promoter region of the E‐cadherin gene was detected in 46% of liver tissues showing chronic hepatitis or cirrhosis and 67% of HCCs examined. Immunohistochemical examination revealed reduced E‐cadherin expression in 59% of HCCs examined. CpG methylation around the promoter region correlated significantly with reduced E‐cadherin expression in HCCs (p < 0.05). CpG methylation around the promoter region, which increases during the progression from a precancerous condition to HCC, may participate in hepatocarcinogenesis through reduction of E‐cadherin expression, resulting in loss of intercellular adhesiveness and destruction of tissue morphology. Int. J. Cancer 71:355‐359, 1997.

Increased DNA Methyltransferase 1 (DNMT1) Protein Expression Correlates Significantly with Poorer Tumor Differentiation and Frequent DNA Hypermethylation of Multiple CpG Islands in Gastric Cancers

We evaluated the significance of aberrant DNA methyltransferase 1 (DNMT1) protein expression during gastric carcinogenesis. The protein expression of DNMT1, Muc2, human gastric mucin, E-cadherin, and proliferating cell nuclear antigen was examined immunohistochemically in gastric cancers and corresponding noncancerous mucosae from 134 patients. The DNA methylation status of the CpG islands of the p16, human MutL homologue 1 (hMLH1), E-cadherin, and thrombospondin-1 (THBS-1) genes and the methylated in tumor (MINT)-1, -2, -12, and -31 clones was examined by methylation-specific polymerase chain reaction and combined bisulfite restriction enzyme analysis. Epstein-Barr virus (EBV) infection was detected by in situ hybridization. Nuclear immunoreactivity for DNMT1 was not detected in any of the noncancerous epithelia, except in proliferative zones (positive internal control), but was found in 97 (72%) of the gastric cancers. DNMT1 overexpression correlated significantly with poorer tumor differentiation (P < 0.001), but not with the phenotype (gastric type versus intestinal type) of the cancer cells. It also correlated significantly with DNA hypermethylation of the CpG islands of the hMLH1 (P = 0.024) and THBS-1 genes (P = 0.043), and with the CpG island methylator phenotype in the gastric cancers (P = 0.007). Reduced E-cadherin expression correlated significantly with poorer tumor differentiation (P = 0.002), DNA hypermethylation of the E-cadherin gene (P < 0.001) and DNMT1 overexpression (P = 0.014). DNMT1 overexpression was also associated with EBV infection (a potential etiological factor in gastric carcinogenesis) but not with the proliferative activity of the cancer cells as indicated by the proliferating cell nuclear antigen-labeling index. These results suggest that DNMT1 overexpression may not be just a secondary effect of increased cancer cell proliferative activity, but may be associated with EBV infection and other etiological factors during gastric carcinogenesis. Furthermore, DNMT1 may play a significant role in the development of poorly differentiated gastric cancers by inducing frequent DNA hypermethylation of multiple CpG islands.

Immune cell infiltration as an indicator of the immune microenvironment of pancreatic cancer

Background:The host immune reaction is represented by immune/inflammatory cell infiltrates. Here we systematically analysed tumour-infiltrating immune/inflammatory cells in pancreatic ductal carcinoma (PDC) and evaluated their clinicopathological impact.Methods:Using immunohistochemistry, we examined tumour-infiltrating CD68+ pan-macrophages, HLA-DR+CD68+ M1 macrophages (M1), CD163+ or CD204+ M2 macrophages (M2), CD66b+ neutrophils (Neu), CD4+ T cells (CD4+T), CD8+ T cells (CD8+T), and FOXP3+CD4+ regulatory T cells (Treg) in 212 cases of PDC, and conducted correlation and survival analyses using the Kaplan–Meier method and Cox proportional hazards model.Results:Higher levels of tumour-infiltrating pan-macrophages, M2, Neu, or the ratio of Tregs to CD4+T (%Treg) were significantly associated with shorter survival, whereas higher levels of tumour-infiltrating CD4+T, CD8+T, or the ratio of M1 to pan-macrophages (%M1) were significantly associated with longer survival. Survival analysis of pairs of these variables revealed that some of the resulting patient groups had exclusively longer survival. We then connected the apparently related factors, and two significant variables emerged: tumour-infiltrating CD4+Thigh/CD8+Thigh/%Treglow and tumour-infiltrating %M1high/M2low. Multivariate survival analysis revealed that these variables were significantly correlated with longer survival and had a higher hazard ratio.Conclusion:Tumour-infiltrating CD4+Thigh/CD8+Thigh/%Treglow and %M1high/M2low are independent prognosticators useful for evaluating the immune microenvironment of PDC.

DNA methyltransferase expression and DNA methylation of CPG islands and peri‐centromeric satellite regions in human colorectal and stomach cancers

We evaluated the significance of aberrant DNA methyltransferase expression in human carcinogenesis by examining 32 colorectal and 34 stomach cancers. Levels of mRNAs encoding DNA methyltransferases were measured by reverse transcription, followed by real‐time quantitative detection of PCR products. The DNA methylation state of CpG islands and peri‐centromeric satellite regions was examined by bisulfite modification and Southern blotting, respectively. The average level of mRNA for DNMT1 and DNMT3b in colorectal and stomach cancers was significantly higher than in corresponding non‐cancerous mucosae, whereas the average level of mRNA for DNMT2 was significantly lower in colorectal and stomach cancers than in non‐cancerous tissue. Over‐expression of DNMT3b in stomach cancer was significantly higher in cases with lymph node metastasis than in cases without. DNA hypermethylation on the p16, human Mut L homologue‐1 and thrombospondin‐1 genes and the methylated in tumor (MINT) 1, 2, 12, 25 and 31 clones was found in 23%, 27%, 9%, 23%, 20%, 23%, 20% and 10% of the colon cancers and in 9%, 19%, 30%, 25%, 34%, 19%, 81% and 3% of the stomach cancers, respectively. Criteria for identification of the CpG island methylator phenotype (CIMP) were met in 23% of colorectal cancers and 31% of stomach cancers. DNA hypomethylation on satellites 2 and 3 was detected in 0% and 8% of colorectal and stomach cancers, respectively. Over‐expression of DNMT1 mRNA was significantly associated with CIMP, whereas the level of DNMT3b mRNA was not associated with CIMP or DNA hypomethylation of peri‐centromeric satellite regions. These data suggest that both over‐expression of the maintenance DNA methyltransferase DNMT1 and over‐expression of a newly identified de novo DNA methyltransferase, DNMT3b, are involved in human carcinogenesis, probably at different stages and through different mechanisms.

Increased protein expression of DNA methyltransferase (DNMT) 1 is significantly correlated with the malignant potential and poor prognosis of human hepatocellular carcinomas

Alteration of DNA methylation is one of the most consistent epigenetic changes in human cancers. DNA methyltransferase (DNMT) 1 is a major enzyme involved in establishing genomic methylation patterns. Most of the studies concerning DNMT1 expression in human cancers have been performed only at the mRNA level. To directly examine DNMT1 protein expression levels during human hepatocarcinogenesis, 16 histologically normal liver tissues, 51 noncancerous liver tissues exhibiting chronic hepatitis or cirrhosis, which are considered to be precancerous conditions, and 53 hepatocellular carcinomas (HCCs) were subjected to immunohistochemic examination. If more than 20% of the cells exhibited nuclear DNMT1 staining, the tissue sample was considered to be DNMT1‐positive. DNMT1 immunoreactivity was observed in 23 (43%) of the HCCs, but in none (0%) of the histologically normal liver or noncancerous liver tissues exhibiting chronic hepatitis or cirrhosis. The incidence of increased DNMT1 protein expression in HCCs correlated significantly with poor tumor differentiation (p = 0.0006) and portal vein involvement (p = 0.0002). Moreover, the recurrence‐free (p = 0.0001) and overall (p < 0.0001) survival rates of patients with HCCs exhibiting increased DNMT1 protein expression were significantly lower than those of patients with HCCs that did not exhibit increased expression. Increased DNMT1 protein expression may play a critical role in the malignant progression of HCCs and be a biologic predictor of both HCC recurrence and a poor prognosis in HCC patients.

Overexpression of a splice variant of DNA methyltransferase 3b, DNMT3b4, associated with DNA hypomethylation on pericentromeric satellite regions during human hepatocarcinogenesis

DNA hypomethylation on pericentromeric satellite regions is an early and frequent event associated with heterochromatin instability during human hepatocarcinogenesis. A DNA methyltransferase, DNMT3b, is required for methylation on pericentromeric satellite regions during mouse development. To clarify the molecular mechanism underlying DNA hypomethylation on pericentromeric satellite regions during human hepatocarcinogenesis, we examined mutations of the DNMT3b gene and mRNA expression levels of splice variants of DNMT3b in noncancerous liver tissues showing chronic hepatitis and cirrhosis, which are considered to be precancerous conditions, and in hepatocellular carcinomas (HCCs). Mutation of the DNMT3b gene was not found in HCCs. Overexpression of DNMT3b4, a splice variant of DNMT3b lacking conserved methyltransferase motifs IX and X, significantly correlated with DNA hypomethylation on pericentromeric satellite regions in precancerous conditions and HCCs (P = 0.0001). In particular, the ratio of expression of DNMT3b4 to that of DNMT3b3, which is the major splice variant in normal liver tissues and retains conserved methyltransferase motifs I, IV, VI, IX, and X, showed significant correlation with DNA hypomethylation (P = 0.009). Transfection of human epithelial 293 cells with DNMT3b4 cDNA induced DNA demethylation on satellite 2 in pericentromeric heterochromatin DNA. These results suggest that overexpression of DNMT3b4, which may lack DNA methyltransferase activity and compete with DNMT3b3 for targeting to pericentromeric satellite regions, results in DNA hypomethylation on these regions, even in precancerous stages, and plays a critical role in human hepatocarcinogenesis by inducing chromosomal instability.

MicroRNA-500 as a potential diagnostic marker for hepatocellular carcinoma

We identified that microRNA expression changed dynamically during liver development and found that miR-500 is an oncofetal miRNA in liver cancer. miR-500 was abundantly expressed in several human liver cancer cell lines and 45% of human hepatocellular carcinoma (HCC) tissue. Most importantly, an increased amount of miR-500 was found in the sera of the HCC patients. In fact, miR-500 levels in sera of the HCC patients returned to normal after the surgical treatment in three HCC patients. Our findings reveal that diverse changes of miRNAs occur during liver development and, one of these, miR-500 is an oncofetal miRNA relevant to the diagnosis of human HCC.

Chromatin remodeling at Alu repeats by epigenetic treatment activates silenced microRNA-512-5p with downregulation of Mcl-1 in human gastric cancer cells.

Epigenetic therapy using DNA methylation inhibitors and histone deacetylase (HDAC) inhibitors has clinical promise for the treatment of human malignancies. To investigate roles of microRNAs (miRNAs) on epigenetic therapy of gastric cancer, the miRNA expression profile was analysed in human gastric cancer cells treated with 5-aza-2′-deoxycytidine (5-Aza-CdR) and 4-phenylbutyric acid (PBA). miRNA microarray analysis shows that most of miRNAs activated by 5-Aza-CdR and PBA in gastric cancer cells are located at Alu repeats on chromosome 19. Analyses of chromatin modification show that DNA demethylation and HDAC inhibition at Alu repeats activates silenced miR-512-5p by RNA polymerase II. In addition, activation of miR-512-5p by epigenetic treatment induces suppression of Mcl-1, resulting in apoptosis of gastric cancer cells. These results suggest that chromatin remodeling at Alu repeats plays critical roles in the regulation of miRNA expression and that epigenetic activation of silenced Alu-associated miRNAs could be a novel therapeutic approach for gastric cancer.