論文

Aberrant tyrosine phosphorylation of β-catenin inactivates the E-cadherin-mediated cell adhesion and invasion suppressor system in cancer cells. Elucidation of the association between β-catenin and c-erbB-2 protein prompted us to investigate whether interference with this interaction can change the invasive phenotype. In a human gastric cancer cell line, TMK-1, N-terminally deleted β-catenin, which binds to c-erbB-2 but not to cadherin, inhibited the association between endogenous β-catenin and c-erbB-2 protein, and suppressed the tyrosine phosphorylation of β-catenin. Cells expressing truncated β-catenin exhibited markedly reduced invasiveness in vitro and peritoneal metastasis in vivo, and developed an epithelial morphology. These results suggest that tyrosine phosphorylation of β-catenin regulated by c-erbB-2 protein may play an important role in the invasion, metastasis and morphogenesis of cancer cells and that inhibition of the aberrant tyrosine phosphorylation of β-catenin effectively prevents invasion and metastasis of cancer cells.

To clarify the significance of E-cadherin gene alterations in the development of diffuse-type adenocarcinoma of the stomach, we analyzed mutations of the E-cadherin gene using the polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) method followed by direct sequencing. Twenty-two signet ring cell carcinomas of the stomach (10 intramucosal and 12 advanced cancers) were examined. Genomic DNA was extracted separately from cancerous and non-cancerous tissues and PCR-SSCP analysis was performed on exons 5 to 9 and the adjacent 30- to 40 base pair intron sequences of the E-cadherin gene. Mobility shifts were found in 2 of the 10 intramucosal cancers. In 2 of the 12 advanced cancers, abnormalities of the E-cadherin gene were observed in intramucosal lesions as well as in deeply invaded areas. These results indicated that E-cadherin gene mutations are an early event in the development of signet ring cell carcinoma of the stomach. Direct sequencing revealed that the locations of mutations of the E-cadherin gene included the branch point sequence in the intron which is responsible for RNA splicing. Reverse transcriptase-PCR demonstrated aberrant RNA splicing in a case with a branch point mutation, suggesting that branch point mutations play an important role in functional modifications of E-cadherin in signet ring cell carcinoma of the stomach.

Reduced expression of E-cadherin has been regarded as one of the main molecular events involved in dysfunction of the cell-cell adhesion system, triggering cancer invasion and metastasis. However, even with a sufficient amount of E-cadherin, cell-cell adhesion is sometimes lost in 'diffusely invasive' human carcinomas. Ten human cancer cell lines, showing growth characterized morphologically by loose cell-cell adhesion, were analyzed for possible structural abnormalities of their expressed E-cadherin. Four of the cell lines showed strong mRNA and protein expression with no nucleotide sequence abnormalities, and mRNA was absent in four other cell lines. mRNA sequence was abnormal in the remaining two gastric carcinoma cell lines. In MKN45 (poorly differentiated adenocarcinoma), this involved a 12-bp in-frame deletion with strong expression of mRNA and protein. In KATO-III (signet ring cell carcinoma), there were four mRNA species with insertions of different sizes, among which the major transcripts (with a 7-bp insertion) caused a frameshift, and expression of both mRNA and protein was markedly reduced. In these two cell lines, DNA mutations were detected around exon-intron junctions, revealing that aberrant RNA splicing was the cause of the mRNA abnormalities. In addition, the wild-type allele of the E-cadherin locus was lost, suggesting that the E-cadherin gene had been inactivated by two hits (mutation and allele loss), similar to the mechanism for inactivation of tumor suppressor genes.

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 DNMTI 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 DNMTI mRNA was significantly associated with CIMP, whereas the level of DNMT3b mRNA was not associated with CIMP or DNA hypomethylation of pericentromeric satellite regions. These data suggest that both over-expression of the maintenance DNA methyltransferase DNMTI 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. © 2001 Wiley-Liss, Inc.

Krüppel-like factors (KLFs) are key transcriptional regulators of cell differentiation and proliferation. Among the KLF family, the expression of KLF4 (GKLF) and KLF5 (IKLF) is highly restricted in the epithelial cells of several organs such as the gut and skin, and it has been reported that these epithelial-type KLF genes may be involved in colon carcinogenesis. Recently we found that Klf4 and Klf5 genes were significantly expressed in the developmental bladder epithelium of mice as well. Therefore, in this report we studied the involvement of the KLF4 and KLF5 genes in bladder carcinogenesis. First, we analyzed the expression of KLF4 and KLF5 in a variety of human bladder cancer cell lines and surgical specimens by RNA blot and in situ hybridization analyses. Both genes were highly expressed in the normal bladder epithelium, whereas KLF4, but not KLF5, was frequently downregulated in bladder cancer cell lines and cancer tissues. We then transduced the KLF4 and KLF5 genes into the bladder cancer cell lines using adenoviral vectors to examine the biological activities of the genes on those cells. The transduction of KLF4, but not KLF5, suppressed cell growth and induced apoptosis. Our study suggests that inactivation of KLF4 is one of the frequent steps towards bladder carcinogenesis. © 2003 Elsevier Inc. All rights reserved.

A 34-year-old premenopausal woman developed asynchronous bilateral nonpalpable breast cancers at the age of 32 and 34 years. She had undergone amputation of her left lower leg because of osteosarcoma at the age of 16. Her mother had been diagnosed with breast cancer at the age of 45. The clinicopathological features of the two breast tumors in this patient closely resembled each other; both were nonpalpable, and detectable only by helical CT scan. Histologically, they consisted mainly of an intraductal component with small grade 3 invasive foci. In addition, both tumors estrogen receptor (ER) status was negative, and both were positive for c-erbB-2 protein on immunohistochemical staining. A missense germ line mutation of BRCA2 (exon 25 codon 3118; Met31 1 8Thr) was detected in this patient. These data may provide useful information on the carcinogenesis and biological behavior of breast cancers which develop in patients with BRCA2 germ line mutations.

We report a case of invasive breast cancer in a 62-year-old female patient with Cowden's disease. A left modified radical mastectomy was performed and histopathology of the tumor showed invasive ductal carcinoma, histological grade 3, without lymph node metastasis. The patient had a past history of endometrial cancer at 55 but did not have a family history of malignant disease. Goiter was palpable but aspiration cytology revealed no malignancy. There were several papillomas on the oral mucosa and multiple papillomatous lesions on the right femur. Barium X-ray and endoscopic examination revealed multiple, small, hyperplastic polypoid lesions on the esophagus, stomach and rectum. Histopathology of the biopsy specimens from the esophagus and stomach showed acanthotic squamous epithelium and foveolar hyperplastic polyps. The patient was followed up closely to monitor the thyroid lesions and polyposis of the digestive tract. A total of 12 breast cancer patients who also had Cowden's disease have been reported in Japan and these cases are reviewed in this report.

Association of the c-erbB-2 oncogene product with the cadherin-catenin complex has been demonstrated in human cancer cell lines. Although β-catenin and plakoglobin have been proven to be crucial for the association, no previous study has shown whether the interactions are direct or indirect. In the present study, the c-erbB-2 gene product was shown by far-Western blotting analysis to associate directly with both β-catenin and plakoglobin through its cytoplasmic domain core region, which showed extensive homology with epidermal growth factor receptor. These data suggest that c-erbB-2-induced signaling is also directly liked to the cadherin-mediated cell adhesion and "invasion-suppressor" system through β-catenin and plakoglobin in cancers. © 1995 Academic Press. All rights reserved.

Phosphorylation of β-catenin, an intracytoplasmic cadherin-binding protein, causes disruption of the cadherin-mediated cell adhesion system in cancer cells. A 185-kDa phosphorylated protein, identified as the c-erbB-2 gene product, was co-immunoprecipitated with the E-cadherin-catenin complex. Association of the c-erbB-2 gene product with the cadherin-catenin complex was proved to be mediated through β-catenin and plakoglobin using an in vitro protein-protein precipitation system. These results indicate that the c-erbB-2 gene product associates with catenins and may regulate the cell adhesion and invasive growth of cancer. © 1994 Academic Press, Inc.

Cadherin and catenin compose cell adhesion complex and are indispensable for tight cell-cell adhesion. Dysfunction of this adhesion complex causes dissociation of cancer cells from primary tumor nodules, thus possibly contributing to cancer invasion and metastasis. In this report, we present the human α-caienin sequence. Human α-catenin showed extensive homology with that of mouse, i.e., 91.8% and 99.3% at the nucleic acid and amino acid levels, respectively, indicating that this molecule has been evolutionarily conserved in mammals. Characterization of the mRNA sequence of α-catenin in PC9 was also carried out, and two distinct abnormal sequences, i.e., one of 957 bp deletion resulting in a 319-amino-acid deletion and another of 761 bp deletion resulting in a frameshift, were identified. These deletions were probably produced by an error of RNA splicing, presenting one possible mechanism for the loss of intact α-catenin expression. © 1993 Academic Press, Inc.

Background: Apocrine carcinoma is rare and most of its clinicopathological features are still unknown. The purpose of this study was to identify the clinicopathological characteristics of apocrine carcinoma. Methods: We clinicopathologically analyzed apocrine breast carcinomas resected from 12 Japanese women and subclassified them histopathologically. Results: The average age of the patients at diagnosis was 60.1 years (range: 38-78). Tumor diameters ranged from 0.5 to 4.5 cm (median 2.4). Mammography revealed tumor shadows without microcalcifications in all patients. Two (17%) of the 12 patients were lymph node metastasis-positive, and lymphatic permeation by tumor cells was observed in 3 (25%). Apocrine carcinoma in this study could be classified into three subtypes according to predominant histopathological growth pattern: type I, intraductal spreading type (4 patients); type II, adenosis-associated type (3 patients); and type III, infiltrating type (5 patients). Types I and II showed no lymph node metastasis and had an excellent prognosis, whereas the infiltrating type was associated with lymph node metastasis and death from cancer. Estrogen receptors and progesterone receptors were positive in 17% (1/6) and 60% (3/5), respectively, of the tumors tested. Conclusions: In the present study, apocrine carcinoma of the breast was characterized by higher patient age and tumor shadows without microcalcifications on mammography. However, the tumors were heterogenous with regard to pattern of local spread.

In order to clarify the significance of DNA methylation in both earlier and later stages of hepatocarcinogenesis, the DNA methylation state on chromosome 16, on which loss of heterozygosity (LOH) has frequently been detected in human hepatocellular carcinomas (HCCs), was examined. DNA from primary HCCs and tissues showing chronic hepatitis and liver cirrhosis, which are considered to be precancerous conditions, was analyzed by digestion with methylation-sensitive and non-sensitive restriction enzymes. DNA hypermethylation at the D16S32, tyrosine aminotransferase (TAT) and D16S7 loci and hypomethylation at the D16S4 locus were detected in 18%, 58%, 20% and 48% of examined HCCs, respectively. Aberrant DNA methylation occurred more frequently in advanced HCCs than in early HCCs. Moreover, DNA hypermethylation at the D16S32, TAT and D16S7 loci was frequently observed in chronic hepatitis and liver cirrhosis. The incidence of DNA hypermethylation was higher than that of LOH (42% at the TAT locus). These data suggest that DNA hypermethylation might predispose the locus to allelic loss. Aberrant DNA methylation is a significant change which may participate in the early developmental stages of HCCs.

The neurofibromatosis 2 gene (NF2) mapped to chromosome 22q is a recently isolated tumor suppressor gene that participates in the tumorigenesis of cells of embryonic neural crest origin. The structural similarities between the NF2 product, merlin-schwannomin, and the band 4.1 family raise the possibility that merlin may participate in a wide range of cell activities, in which the cytoskeleton latticework has important roles to play. In order to examine the significance of NF2 in general carcinogenesis, comprehensive analyses of 68 cases of breast carcinoma, which shows frequent loss of heterozygosity at chromosome 22, and 48 hepatocellular carcinomas of different histological grade were performed. No mutation was detected by the polymerase chain reaction-single-strand conformation polymorphism method for six exons of NF2 in any of the cases examined, suggesting that NF2 may be less important in the tumorigenesis of breast and liver cancers than in that of cancers originating from the neural crest.

The E-cadherin-mediated cell adhesion system acts as an "invasion suppressor" system, which is widely considered to be inactivated when the expression of E-cadherin is reduced and/or heterogeneous. To further investigate the molecular mechanisms responsible for dysfunction of this system in cancers, we examined human carcinoma cell lines lacking tight cell-cell adhesion. In KATO-III, established from stomach cancer, a point mutation of the E-cadherin gene resulted in a mRNA splicing error and markedly reduced E-cadherin expression. In another stomach cancer cell line, MKN 45, an 18-bp deletion of the E-cadherin gene caused a mRNA splicing error and a 4-amino-acid deletion, which was considered to alter the conformation around the key Ca(2+)-binding motif. In these two cell lines, the wild-type allele of the E-cadherin locus, which was assigned to chromosome 16q, was lost. Also in vivo, we found mutation of E-cadherin in breast cancers, where allele loss on chromosome 16 has frequently been reported. Thus, dysfunction of E-cadherin could be caused by a combination of the loss of one allele and a mutation in the remaining allele. Homologous deletion of part of the alpha-catenin gene, resulting in markedly reduced expression, was observed in a human lung cancer cell line, PC9. Recently, we also found mutations of beta-catenin in human carcinoma cell lines. These findings indicate the possible involvement of genetic abnormalities of various components in inactivation of the E-cadherin-mediated "invasion suppressor system" in cancers.

The aim of this study was to examine the significance of aberrant DNA methylation, the participation of which in genetic instability is controversial, in hepatocarcinogenesis. The DNA methylation status of the region around the promoter of the E-cadherin tumor suppresser gene, which is located on 16q22.1, and the allelic status at the D16S421 locus, which is adjacent to the E-cadherin locus, were examined using microdissected liver specimens from 38 hepatocellular carcinoma (HCC) patients. Almost all of the non-cancerous liver tissues showed histological findings compatible with chronic hepatitis and cirrhosis, which are considered to be precancerous conditions. DNA hypermethylation was detected in 61% of the non-cancerous liver tissues. The incidence of DNA hypermethylation in the non-cancerous liver tissues of patients with HCCs also showing DNA hypermethylation (72%) was significantly higher than that of patients without DNA hypermethylation in their HCCs (53%, P<0.05). Loss of heterozygosity (LOH) at the D16S421 locus was detected in 35% of the non-cancerous liver tissues. The incidence of LOH in the non-cancerous liver tissues of patients with HCCs also showing LOH was 78%, whereas LOH was not detected in non-cancerous liver tissues of patients without LOH in their HCCs. Fifty-two percent of the non-cancerous liver tissues showed both or neither of DNA hypermethylation and LOH; the incidence of DNA hypermethylation alone in non-cancerous liver tissue was 41%. The incidence of LOH alone in non-cancerous liver tissue (7%) was significantly lower compared to those of the former two cases (P<0.0001). These data suggest that aberrant DNA methylation participates in the precancerous stage of hepatocarcinogenesis by preceding, or causing, LOH. Copyright (C) 2000 Elsevier Science Ireland Ltd.

The present study attempted to clarify the significance of aberrant expression of β-catenin protein and mutation of exon 3 of the β-catenin gene in renal and urothelial carcinogenesis. β-Catenin expression was examined immunohistochemically and mutation of the β-catenin gene was analyzed by polymerase chain reaction-single strand conformation polymorphism (SSCP) and direct sequencing. β-Catenin immunoreactivity was observed at the cell membrane in all 30 renal cell carcinomas (RCC) examined, and no RCC showed a mobility-shifted SSCP band. Of 46 transitional cell carcinomas (TCC) examined, there was reduced expression of β-catenin, as compared with its expression in non-cancerous transitional epithelium, in 22 cases (48%) and catenin accumulation in the nucleus in five cases (11%). Of four renal pelvis TCC examined, point mutation of exon 3 of the β-catenin gene at codon 45 resulting in amino acid substitution (Ser to Phe) was detected in one (25%). The incidence of reduced expression of β-catenin correlated significantly with the growth pattern (superficial type vs invasive type) of TCC (P < 0.05). These data indicate that: (1) aberrant β-catenin expression may be at least partly involved in urothelial carcinogenesis, but less significantly so in renal carcinogenesis, and (2) it may be associated with the progression of TCC showing invasive growth.