Allelotype analysis of adenocarcinoma of the gastric cardia

Decreased expression of the long non-coding RNA MLLT4 antisense RNA 1 is a potential biomarker and an indicator of a poor prognosis for gastric cancer

In recent years, the identification of long non-coding RNAs (lncRNAs) led to the analysis of their characteristics in cancer biology. However, the expression of lncRNAs in cancer and their clinical significance remain unclear. In the present study, an investigation of lncRNAs that may be involved in the regulation of metastasis using microarray and polymerase chain reaction analyses resulted in the identification of MLLT4 antisense RNA 1 (MLLT4-AS1) as a significantly downregulated lncRNA in gastric cancer tissue compared with normal adjacent tissue (P=0.006). Furthermore, the downregulation of MLL4-AS1 was significantly associated with advanced Tumor-Node-Metastasis stage (P=0.007) and lymph node metastasis (P=0.008). Cox regression analysis showed that MLLT4-AS1 expression was an independent predictor for overall survival (hazard ratio, 13.136; 95% confidence interval, 5.065–34.068; P<0.001). These data suggest that the decreased expression of MLLT4-AS1 is a potential biomarker and a predictor of a poor prognosis for gastric cancer.

MicroRNA-212 displays tumor-promoting properties in non-small cell lung cancer cells and targets the hedgehog pathway receptor PTCH1

Overexpression of microRNA-212 promoted cell cycle progression and cell proliferation, migration, and invasion in non–small cell lung cancer cells. PTCH1, a receptor of hedgehog pathway, is a functional target of miR-212. The role of miR-212 in cell proliferation may be mediated by PTCH1.

Dysexpression of microRNAs has been found in many tumors, including lung cancer. The hedgehog (Hh) signaling pathway plays an important role during normal development, and the abnormal regulation of its members has also been related to many tumors. However, little is known about the relationship between microRNA and the Hh pathway. In this paper, we report microRNA-212 (miR-212) playing a role in non-small cell lung cancer (NSCLC) and targeting PTCH1, a receptor of the Hh pathway. We found that miR-212 was up-regulated when cells were treated with 4ß-12-O-tetradecanoylphorbol-13-acetate (TPA). We ectopically expressed miR-212 in NSCLC cell lines to examine the influence of miR-212 overexpression. The results showed that overexpression of miR-212 in NSCLC cells promoted cell cycle progression and cell proliferation, migration, and invasion. The promoting effects of miR-212 on cell proliferation, migration, and invasion were partially reversed by the miR-212 inhibitor anti-miR-212. These results suggested that miR-212 might have tumor-promoting properties. Potential targets of miR-212 were predicted, and we showed tumor suppressor PTCH1 was a functional target of miR-212. PTCH1 may be responsible for the effect of miR-212 on cell proliferation. Altogether, our results indicated that miR-212 was involved in tumorigenesis, and the oncogenic activity of miR-212 in NSCLC cells was due, in part, to suppression of PTCH1.

Anticancer activity of PDSS2, prenyl diphosphate synthase, subunit 2, in gastric cancer tissue and the SGC7901 cell line

The aim of this study was to assess whether PDSS2 (prenyl diphosphate synthase, subunit 2), a candidate tumor suppressor protein, has a potential anticancer role in human gastric cancer tissue and the SGC7901 gastric cell line. A PDSS2 eukaryotic expression vector was constructed and introduced into SGC7901 cells. The relationship between PDSS2 expression and cell proliferation, cell cycle distribution, and apoptosis in tumor cells was analyzed by RT-PCR, western blotting, the MTT colorimetric assay, flow cytometry, and immunohistochemistry. Increased exogenous PDSS2 expression in vitro is associated with decreased cellular proliferation of the gastric cancer cell line SGC7901. PDSS2 also induced apoptosis in SGC7901 cells by causing cell cycle arrest in the G0/G1 phase. Moreover, a significantly low expression level of PDSS2 protein was found in gastric cancer. Decreased or absent expression of PDSS2 was showed in the gastric tumor biopsy samples analyzed, correlating with cancer differentiation. PDSS2 has potent anticancer activity in gastric cancer tissues and the SGC7901 cell line and is possibly involved in apoptosis in SGC7901 cells.

Cytogenetic and molecular aspects of gastric cancer: clinical implications

Gastric cancer is of major importance world-wide being the second most common cause of cancer-related death in the world. According to Lauren's histological classification gastric cancer is divided in two groups, the better differentiated intestinal carcinomas and the poorly differentiated diffuse-type cancers. The genetic changes underlying the initiation and progression of gastric cancer are not well defined. Gastric carcinogenesis is a multistep process involving a number of genetic and epigenetic factors. Although it has been proposed that different genetic pathways exist for differentiated and undifferentiated carcinomas, the two histological subtypes of gastric cancer share some common genetic alterations. Currently, tumor histology and pathologic stage are the major prognostic variables used in the clinical practice for gastric cancer patients. However, it is known that tumors with similar morphology may differ in biological aggressiveness, prognosis and response to treatment. Molecular genetic analysis of gastric cancer revealed a number of associations of certain genetic changes with pathological features, tumor biological behavior and prognosis of gastric cancer patients, suggesting that these genetic abnormalities might play an important role in gastric tumorigenesis. Increasing evidence suggests that the molecular genetic changes could be helpful in the clinical setting, contributing to prognosis and management of patients. Regarding epigenetic events in gastric tumorigenesis, a number of methylating markers have been proposed for risk assessment, prognostic evaluation and as therapeutic targets. However, further research is required in order to systematically investigate the genetic changes in gastric cancer estimating also their usefulness in the clinical practice. A good understanding of the genetic changes underlying gastric carcinogenesis may provide new perspectives for prognosis and screening of high risk individuals. Some of the genetic alterations could definitely improve tumor classification and management of gastric cancer patients. Also, based on molecular data identified in gastric cancer novel therapeutics might help to improve the treatment of this disease.

High polymorphism in the trisomic portion of a gastric cancer cell line

BACKGROUND

Genetic instability is a hallmark of malignancy, and microsatellite instability is a widely appreciated mechanism of generating genetic changes. We have recently observed four markers clustered on chromosome 20 that showed the effects of microsatellite instability in the gastric adenocarcinoma cell line SNU-1. Each affected marker had alleles of three different sizes. The aim of this study was to investigate the origin for this high-density polymorphism on a single chromosome.

METHODS

The high polymorphism located on chromosome 20 was confirmed using 37 additional markers. To further evaluate this finding, 15 clones of the cell line were generated and then assayed with the triallelic markers.

RESULTS

All told, almost a third of the markers on chromosome 20 had triallelic patterns, but only 0.3% of the markers not on chromosome 20 showed this result. The number of clones showing allelic variation was an average of 50% greater for chromosome 20 markers than for markers elsewhere. A karyotype analysis showed that the progenitor cell line of SNU-1 was trisomic for chromosome 20, and the high polymorphism on that chromosome is almost certainly due to the trisomy.

CONCLUSIONS

Not only are there more chromosome copies and therefore more gene copies subject to mutation in cells containing trisomy, but also more mutations may be passed on to the progeny. This elevated polymorphism increases the repertoire of genetic changes that could affect cellular growth, and may independently increase genomic instability.

Hath1 up-regulates gastric mucin gene expression in gastric cells

The Notch signaling pathway is known to mediate the differentiation and fate specification of cells in embryonic stage and adult tissues. Several tumors exhibit aberrant expression of Notch signaling component genes, such as Notch1/2/3 and Hath1. In this study, we investigated the mRNA expression of seven Notch-related genes, Notch1/2/3, Hes1/2/3, and Hath1, and then compared it with the expression of gastric mucin genes, MUC5AC and MUC6, in eight gastric cancer (GC) cell lines. Notch1/2/3 and Hes1 were expressed in most GC cell lines as well as normal gastric mucosae, while Hes2/3 were expressed in neither these cell lines nor the normal stomach. As for Hath1, five GC cell lines exhibited undetectable levels, while normal gastric mucosa expressed Hath1. The expression patterns of Hath1 and MUC6 were closely related in most GC cell lines. Many MUC5AC-positive cases also tended to show Hath1 expression. Over-expression of Math1, a mouse Hath1 homolog, in the GC cells strongly enhanced both the MUC6 and MUC5AC mRNA levels. Moreover, knockdown of Hath1 by means of RNA interference significantly decreased the expression of both mucin genes. These data indicate that Hath1 is one of the transcriptional regulators for MUC6 and MUC5AC in GC cells. It is also possible that loss of Hath1 expression may play a role in gastric carcinogenesis.

Clinicopathological significance of loss of heterozygosity in intestinal- and solid-type gastric carcinomas: a comprehensive study using the crypt isolation technique

The clinicopathological significance of loss of heterozygosity (LOH) in gastric carcinoma remains poorly understood. We and other researchers have previously demonstrated that LOH is fairly common in intestinal- and solid-type gastric carcinomas, but rare in diffuse-type tumors. In this study, we investigated the relationship between clinicopathological variables and LOH status in intestinal- and solid-type gastric carcinomas. The crypt isolation technique was utilized to analyze LOH at 1p36, 3p14, 4p15, 5q21-22, 8p11-12, 9p21, 13q22, 17p13.1 18q21 and 22q13.31 in 113 intestinal- and solid-type gastric carcinomas using a polymerase chain reaction assay. Immunostaining with D2-40 and Elastica van Gieson staining were used to detect lymphatic invasion and vessel invasion, respectively. High LOH rates (49-71%) were observed in all chromosomal regions tested. 1p36 loss was significantly associated with advanced tumors and lymph node metastasis. 8p11-12 loss was significantly associated with lymph node metastasis, lymphatic invasion, and vessel invasion. 17p13.1 (TP53) loss was significantly associated with vessel invasion. 22q13.31 loss was significantly associated with advanced tumors, lymph node metastasis, lymphatic invasion, vessel invasion and late TNM stage. No significant associations were observed between LOH at other chromosomal regions and aggressive behaviors. In addition, significantly higher LOH rates at 1p36, 9p21, 18q21 and 22q13.31 were observed in cardiac tumors compared with noncardiac tumors. These results suggest that in intestinal- and solid-type gastric carcinomas, LOH on 3p14, 4p15, 5q21-22, 9p21, 13q22 and 18q21 is associated with carcinogenesis, while LOH on 1p36, 8p11-12, 17p31.1 and 22q13.31 is associated with tumor progression.

Loss of Heterozygosity and Immunohistochemistry of Adenocarcinomas of the Esophagus and Gastric Cardia

PURPOSE

Adenocarcinomas of the distal esophagus and gastric cardia are two tumors that have many features in common. They have similar prognoses, treatment modalities, and patterns of dissemination. The etiology is different, with gastroesophageal reflux disease playing a major role for esophageal adenocarcinoma, in contrast to adenocarcinoma of the gastric cardia. In the present study, we investigated several genetic and immunohistochemical features of adenocarcinomas of the distal esophagus and gastric cardia.

EXPERIMENTAL DESIGN

Sixty-two resection specimens of either adenocarcinoma of the esophagus or adenocarcinoma of the gastric cardia were carefully selected. The genetic analysis included loss of heterozygosity of several tumor suppressor genes known to be involved in esophagogastric carcinogenesis. Immunohistochemical studies included the analysis of p53, c-Met, c-erbB-2, beta-catenin, and cyclooxygenase-2. In addition, a mutation analysis of the Tcf1 gene was done by direct sequencing.

RESULTS

Patients with cardiac carcinoma had a significantly worse tumor stage and poorer differentiation on histology. Loss of heterozygosity analysis did not reveal significant differences between esophageal adenocarcinoma and cardiac adenocarcinoma. Immunohistochemical analysis revealed significantly more nuclear accumulation of beta-catenin and overexpression of cyclooxygenase-2 in patients with esophageal adenocarcinoma, compared with patients with cardiac carcinoma. No mutation was found in the Tcf1 gene in either tumor type.

CONCLUSIONS

Although adenocarcinomas of the distal esophagus and gastric cardia have many features in common, we have found some evidence that they might form two different entities.

A new mixture model approach to analyzing allelic-loss data using Bayes factors

BACKGROUND

Allelic-loss studies record data on the loss of genetic material in tumor tissue relative to normal tissue at various loci along the genome. As the deletion of a tumor suppressor gene can lead to tumor development, one objective of these studies is to determine which, if any, chromosome arms harbor tumor suppressor genes.

RESULTS

We propose a large class of mixture models for describing the data, and we suggest using Bayes factors to select a reasonable model from the class in order to classify the chromosome arms. Bayes factors are especially useful in the case of testing that the number of components in a mixture model is n0 versus n1. In these cases, frequentist test statistics based on the likelihood ratio statistic have unknown distributions and are therefore not applicable. Our simulation study shows that Bayes factors favor the right model most of the time when tumor suppressor genes are present. When no tumor suppressor genes are present and background allelic-loss varies, the Bayes factors are often inconclusive, although this results in a markedly reduced false-positive rate compared to that of standard frequentist approaches. Application of our methods to three data sets of esophageal adenocarcinomas yields interesting differences from those results previously published.

CONCLUSIONS

Our results indicate that Bayes factors are useful for analyzing allelic-loss data.

Allelic loss of chromosome 6q in gastric carcinoma

Loss of the long arm of chromosome 6 (6q) has frequently been reported in gastric carcinoma, and most gastric cancer patients have evidence of intestinal metaplasia in the stomach. However, the relationship between loss of chromosome 6q and intestinal metaplasia has not been studied. In the first part of the study, we define the critical deletion region of chromosome 6q using loss of heterozygosity technique (LOH). Seventeen microsatellite markers were used to detect loss of heterozygosity (LOH) in 37 microdissected gastric tumors. We also examined intestinal metaplasia (IM) foci of the stomach in the same cancer patient (17 cases). Losses on chromosome 6q were detected in high frequency (51%) by LOH. Two distinct regions of common allelic loss were identified: one centered on the marker D6S300 (at 6q16.1) and the second on D6S446 (at 6q27), with LOH frequency of 36% and 31.3%, respectively. The deletions fall into 2 discrete regions, suggesting the existence of at least 2 tumor suppressor genes in 6q. The losses at 6q27 were confirmed by fluorescence in situ hybridization study (FISH). In the cases with LOH in the tumor, no LOH were detected in the autologous IM areas, but losses were detected by FISH. In some cases, these genetic changes may be acquired in the transition from normal gastric mucosa to intestinal metaplasia.

Three different subsite classification systems for carcinomas in the proximity of the GEJ, but is it all one disease?

BACKGROUND AND AIM

Currently there are three different subsite classification systems for carcinomas in the region of the gastroesophaeal junction (GEJ), namely ICD-O, Munich and Liverpool. The aim of the present study was to compare clinicoepidemiological, pathological and molecular features of adenocarcinomas in the proximity of the GEJ, classified according to their position with respect to the GEJ initially, and then classified according to ICD-O, Munich and Liverpool classifications.

METHODS

Forty-seven adenocarcinomas in the proximity of the GEJ were subdivided into groups 1 (exclusively within esophagus), 2 (mainly within esophagus but extending distally across GEJ), 3 (equally present in esophagus and stomach) or 4 (mainly in stomach but extending proximally across GEJ), and analysis of their clinicoepidemiological, pathological and molecular features was performed. Molecular characterization included loss of heterozygosity (LOH) and microsatellite instability analyses.

RESULTS

Group 3 carcinomas were younger than other carcinomas in the proximity of the GEJ, but otherwise these carcinomas were similar in their clinicoepidemiological, pathological and molecular features. There were no significant differences between esophageal (groups 1 and 2) and gastric (groups 3 and 4) carcinomas as classified by ICD-O. Munich types I (groups 1 and 2), II (group 3) and III (group 4) carcinomas of the GEJ were also similar. LOH at the site of the Rb tumor suppressor gene and at 17p11.1-p12 was more common in GEJ (groups 2, 3 and 4) than lower third (group 1) esophageal carcinomas classified according to the Liverpool system.

CONCLUSION

Overall, adenocarcinomas of the lower esophagus and adenocarcinomas involving the GEJ have similar clinicoepidemiological, pathological and molecular features no matter which subsite classification is used, adding further evidence that they represent the same disease.

Primary adenocarcinomas of lower esophagus, esophagogastric junction and gastric cardia: in special reference to China

Gastric cardia adenocarcinoma (GCA) is an under-studied subject. The pathogenesis, molecular changes in the early stage of carcinogenesis and related risk factors have not been well characterized. There is evidence, however, that GCA differs from cancer of the rest of the stomach in terms of natural history and histopathogenesis. Adenocarcinomas of the lower esophagus, esophagogastric junction (EGJ) and gastric cardia have been given much attention because of their increasing incidences in the past decades, which is in striking contrast with the steady decrease in distal stomach adenocarcinoma. In China, epidemiologically, GCA shares very similar geographic distribution with esophageal squamous cell carcinoma (SCC), especially in Linzhou (formerly Linxian County), Henan Province, North China, the highest incidence area of esophageal SCC in the world. Historically, both GCA and SCC in these areas were referred to as esophageal cancer (EC) by the public because of the common syndrome of dysphagia. In Western countries, Barrett's esophagus is very common and has been considered as an important precancerous lesion of adenocarcinoma at EGJ. Because of the low incidence of Barrett's esophagus in China, it is unlikely to be an important factor in early stage of EGJ adenocarcinoma development. However, Z line up-growth into lower esophagus may be one of the characteristic changes in these areas in early stage of GCA development. Whether intestinal metaplasia (IM) is a premalignant lesion for GCA is still not clear. Higher frequency of IM observed at adjacent GCA tissues in Henan suggests the possibility of IM as a precancerous lesion for GCA in these areas. Molecular information on GCA, especially in early stage, is very limited. The accumulated data about the changes of tumor suppressor gene, such as p53 mutation, and ontogeny, such as C-erbB2, especially the similar alterations in GCA and SCC in the same patient, indicated that there might be some similar risk factors, such as nitrosamine, involved in both GCA and SCC in Henan population. The present observations also suggest that GCA should be considered as a distinct entity.

Molecular genetic analysis of the von Hippel-Lindau and human peroxisome proliferator-activated receptor gamma tumor-suppressor genes in adenocarcinomas of the gastroesophageal junction

We investigated whether 2 candidate tumor-suppressor genes, VHL at 3p25-26 and PPAR gamma at 3p24.2-25, are involved in GEJ adenocarcinogenesis. In 43 GEJ tumor samples from 40 patients, the entire coding sequence of the VHL gene and the 5' and part of the 3' UTR as well as exons 3 and 5 of the PPAR gamma gene were screened by PCR-SSCP analysis. LOH at 3p25-26 was analyzed with 2 polymorphic microsatellite markers and with the VHL exon 1 and intron 2 polymorphisms. The relationship between LOH and clinicopathologic parameters was assessed. Expression of VHL was investigated by immunohistochemistry with a VHL-specific antibody. PCR-SSCP analysis of VHL revealed 2 different aberrant patterns in 19 patients. Upon DNA sequencing, 1 pattern appeared to be a previously described exon 1 polymorphism. The other single aberrant pattern was an intron 2 polymorphism, not yet described. PCR-SSCP analysis of PPAR gamma showed no aberrant migration patterns. LOH analysis revealed 3p25-26 loss in 24/36 (67%) informative cases, but this was not significantly correlated with clinicopathologic parameters. By immunohistochemistry, all tumors showed expression of VHL protein. Despite the very frequent LOH of 3p in GEJ adenocarcinomas, mutations in VHL and PPAR gamma were not detected. Mutations outside the screened sequences, a gene dosage effect or involvement of another tumor-suppressor gene on 3p as the target of LOH should be considered.

Allelic gains and losses in distinct regions of chromosome 6 in gastric carcinoma

In gastric cancer, alterations in the long arm of chromosome 6 are a frequent event. Two regions of heterozygous loss have been described: 6q16.3-6q23 and 6q26-6q27. We have evaluated by microsatellite and FISH analyses the 6q status of three cell lines that we established from primary gastric carcinomas xenografted in nude mice, in order to elucidate the underlying mechanisms of 6q alterations. Alterations of the long arm of chromosome 6 were found in all three xenografts and corresponding cell lines. Allelic imbalance (AI) was found in the three cases, by microsatellite analysis. Fluorescence in situ hybridization analyses clearly demonstrated a duplication of the larger part of the 6q arm in all three cell lines. Two of the cell lines and the corresponding xenografts showed, in addition, complete loss of one of the parental alleles at the terminal part of 6q. Thus, the AI observed along the long arm of chromosome 6 is represented by gain of alleles in one distinct chromosomal segment and loss of alleles in another distinct segment.

Genetic alterations in gastric cancers from British patients

Twenty-six gastric carcinoma and matching normal tissue DNAs, which had previously been analyzed for alterations of the APC (adenomatous polyposis coli) and MCC (mutated in colorectal cancer) genes were further investigated for the following genetic alterations: mutation and loss of heterozygosity (LOH) of the p53 gene, replication error (RER) and LOH at 12 microsatellite repeat loci, and mutation of the hMSH2 gene. In addition, 9 of the 26 gastric carcinomas were analyzed for genetic alterations using comparative genomic hybridization (CGH). Somatic mutations of the p53 gene were found to be frequent being detected in 31% of gastric carcinomas while LOH at the p53 locus was observed in 37.5% of informative cases. Loss of wild type p53 allele was detected in the majority (7 of 8) tumors found to be harboring a mutation. In the hMSH2 gene, an intronic 4 base pair insertion at 31 base pairs upstream of the beginning of exon 13 was detected in both tumor and normal tissue from one gastric carcinoma case. RER was detected in 11.5% of gastric carcinomas, at one or more microsatellite repeat loci. Of the 12 microsatellite repeat loci analyzed LOH was most frequently observed at D22S351 (30% informative cases) suggesting that a tumor suppressor gene on 22q may be important in gastric carcinogenesis. In support of this, CGH analysis carried out on 9 of the gastric carcinomas identified loss of chromosome 22 in 5 of these tumors.

Molecular cytogenetic evaluation of gastric cardia adenocarcinoma and precursor lesions

Analyses of cancer incidence data in the United States and Western Europe revealed steadily rising rates over the past decades of adenocarcinomas of the esophagus and gastric cardia. Genetic information on gastric cardia adenocarcinoma and its preneoplasias is sparse. We have used comparative genomic hybridization to obtain a genome-wide overview of 20 archival gastric cardia adenocarcinomas and 10 adjacent preneoplastic lesions (4 metaplasias, 1 low-grade dysplasia, 5 high-grade dysplasias). Multiple genetic alterations were discriminated in all adenocarcinomas. Frequent loss (> or =25% of all tumors) was detected, in decreasing order of frequency, on 5q, 18q, 4q, 3p, 9p, 2q, 11q, 14q, 21q, 4p, 9q, 16q, 1p, and 8p. Frequent gain (> or =25% of all tumors) was disclosed, in decreasing order of frequency, on 20q, 7p, 8q, 1q, 7q, 20p, 17q, 13q, Xp, 6q, 8p, 19q, 5p, 6p, and Xq. Loss of the Y chromosome was found in 60% of male cases. High level amplification was frequently (>10% of all tumors) detected on 7q21, 8p22, 12p11.2, 17q12-q21, and 19q13.1-q13.2. The precursor lesions showed multiple aberrations in all high-grade dysplasias, whereas few genetic changes were discerned in LGD and metaplasias. High level amplifications were also found in high-grade dysplasias, ie, on 7q21, 8p22, and 17q12-q21. Moreover, the percentage of aberrations was not significantly different for invasive carcinomas or high-grade dysplasias. Approximately 70% of the precursor aberrations were also present in the adjacent carcinoma. Minimal overlapping regions in the preneoplasias included loss on 18q12-q21 and gains on 8q23 and 17q12-q21, suggesting involvement of genes residing in these regions. In conclusion, we have (i) created a map of genetic alterations in gastric cardia adenocarcinomas and (ii) provided evidence for the presence of a metaplasia-dysplasia-carcinoma sequence in this poorly understood type of cancer.

Molecular biology of Barrett's adenocarcinoma

OBJECTIVE

To review the current knowledge on the genetic alterations involved in the development and progression of Barrett's esophagus-associated neoplastic lesions.

SUMMARY BACKGROUND DATA

Barrett's esophagus (BE) is a premalignant condition in which the normal squamous epithelium of the esophagus is replaced by metaplastic columnar epithelium. BE predisposes patients to the development of esophageal adenocarcinoma. Endoscopic surveillance can detect esophageal adenocarcinomas when they are early and curable, but most of the adenocarcinomas are detected at an advanced stage. Despite advances in multimodal therapy, the prognosis for invasive esophageal adenocarcinoma is poor. A better understanding of the molecular evolution of the Barrett's metaplasia to dysplasia to adenocarcinoma sequence may allow improved diagnosis, therapy, and prognosis.

METHODS

The authors reviewed data from the published literature to address what is known about the molecular changes thought to be important in the pathogenesis of BE-associated neoplastic lesions.

RESULTS

The progression of Barrett's metaplasia to adenocarcinoma is associated with several changes in gene structure, gene expression, and protein structure. Some of the molecular alterations already showed promise as markers for early cancer detection or prognostication. Among these, alterations in the p53 and p16 genes and cell cycle abnormalities or aneuploidy appear to be the most important and well-characterized molecular changes. However, the exact sequence of events is not known, and probably multiple molecular pathways interact and are involved in the progression of BE to adenocarcinoma.

CONCLUSIONS

Further research into the molecular biology of BE-associated adenocarcinoma will enhance our understanding of the genetic events critical for the initiation and progression of Barrett's adenocarcinoma, leading to more effective surveillance and treatment.

Chromosomal alterations in paired gastric adenomas and carcinomas

Gastric adenoma is a precancerous lesion of the stomach and its malignant transformation is thought to result from accumulative series of gene alterations. The aim of this study was to determine the pattern of chromosomal changes during gastric carcinogenesis. Pairs of adenoma and carcinoma tissues from 15 gastrectomy cases containing both adenomas and carcinomas in the same (adjacent pairs, 6 cases) and different (non-adjacent pairs, 9 cases) lesions, were analyzed for chromosomal alterations of 39 non-acrocentric chromosomal arms by comparative genomic hybridization (CGH). CGH analysis identified frequent chromosomal alterations in most of the gastric adenomas (14/15, 93%) and all of the carcinomas. The mean number of chromosomal alterations was higher in carcinoma (5.5 for adenoma and 11.7 for carcinoma; P = 0.006, by nonparametric Wilcoxon's test). Losses on the short arm of chromosome 17 were most common in both adenomas (43%) and carcinomas (67%). The pattern of chromosomal alterations in paired gastric adenomas and carcinomas showed greater similarity compared to the non-case pairs and this similarity was increased in the adjacent pairs. Deletion mapping analysis on chromosome 17p also demonstrated that the conserved deletion area was more frequent in the adjacent pairs. Among these 6 adjacent pairs, all had common deletion areas. In contrast, among the 9 non-adjacent pairs, 2 (22%) had common area of deletion, 5 (56%) showed deletion only in the carcinoma, and the remaining 2 (22%) had no deletion on 17p, suggesting diverse genetic changes might be involved in the multiple tumor formation. Our results that common clonal genetic changes between adjacent pairs of gastric adenomas and carcinomas and accumulated genetic changes in the carcinomas provide evidences for the stepwise mode of gastric carcinogenesis through the accumulation of a series of genetic alterations.

Correlation of histologic subtypes and replication error phenotype with comparative genomic hybridization in gastric cancer

To characterize phenotypic and genotypic changes in gastric cancer (GC), DNA copy number aberrations (CNAs) were assessed in 53 tumors using comparative genomic hybridization (CGH) and correlated with clinicopathologic characteristics and status of TP53 and replication error (RER). The number of CNAs per tumor was 6.8 (gain 5.3, loss 1.5), and the number of changes was significantly higher in tumors with advanced stage, TP53 mutation, and without RER than in those with early stage (7.7 vs. 3.0), no TP53 mutations (12.4 vs. 4.8) or RER phenotype (8.2 vs. 2.6). Frequent abnormalities included gains on chromosomal arms 8q (43%), 6q (26%), 11q (26%), 13q (24%), 7p (23%), 17q (23%), and 20q (23%), and losses on chromosomal arms 16q (26%), 19p (23%), 5q (19%), 3p (15%), 4q(15%), and 1p (15%). Advanced GC demonstrated a higher prevalence of gains of 8q (51% vs. 10%, P < 0.05) and loss of 16q (33% vs. 0%, P < 0.05) than early GC. Gains on 8q (64% vs. 20%, P < 0.05), 17q (39% vs. 4%, P < 0.05) and losses on 3p (25% vs. 4%, P = 0.05) and 5q (32% vs. 4%, P < 0.05) were higher in intestinal GC than in diffuse GC. On the other hand, gains on 13q were more common in the diffuse type (40% vs. 11%, P < 0.05). As compared with noncardia cancer, cardia cancer showed more gains on 7p (58% vs. 12%, P < 0.05) and 20q (58% vs. 12%, P < 0.05) and more losses on 4q (50% vs. 5%, P < 0.05). The finding of histology-related aberrations and the combination of CGH and molecular data thus provide additional evidence suggesting genetic heterogeneity of GC.

Alterations and hypermethylation of the p14(ARF) gene in gastric cancer

p14(ARF), generated through an alternative splicing process that replaces the first exon, 1alpha, of p16(INK4a) with exon 1beta, located >15 kb upstream of exon 1alpha, has been shown to function as a growth suppressor. We examined 11 gastric cancer cell lines for mRNA expression, homozygous deletion, mutation, and promoter methylation of the p14(ARF) gene. No mRNA expression was detected in 5 of the 7 diffuse-type cell lines. All intestinal cell lines displayed normal levels of expression except for one with a low level of expression. Of the 5 cell lines without expression, 3 (MKN45, NUGC-2, and NUGC-4) and 1 (KATO III) displayed homozygous deletion and methylation of the p14(ARF) gene, respectively. No mutation was found in the whole coding region of the p14(ARF) gene in 8 cell lines without homozygous deletion. Our results indicate that the p14(ARF) gene is more frequently inactivated by homozygous deletion or methylation in diffuse-type gastric cancer cell lines (5/7, 71.4%) than in intestinal ones (0/4, P = 0.022). When we also analyzed 62 primary gastric cancers for the methylation status of the p14(ARF) promoter region, the methylation frequency tended to be higher in diffuse-type gastric cancers (15/33, 45.5%) than in intestinal ones (7/28, 25%). Thus, p14(ARF) alterations might be involved in diffuse-type gastric carcinogenesis.

Genetic alterations in gastric cancer cell lines and their original tissues

To investigate the genetic changes that occur during establishment of gastric cancer cell lines, 4 gastric cancer cell lines and their original tumor tissues were examined for microsatellite instability (MSI), loss of heterozygosity (LOH), and p53 mutation. MSI status did not change during the establishment, though the cell lines gained frameshift mutation in some of the genes with polytract coding sequences. There was no difference in p53 mutation between the cell lines and the original tumors. The frequency of LOH was similar between the cell lines and each original tumor, in the range 30.8% to 85.7%. The difference in the LOH results between the cell lines and the original tumors was not greater than the difference between the different areas of the original tumors. The above results suggested that most of the genetic alterations, such as MSI, LOH, and p53 gene mutation, were sustained during the establishment of gastric cancer cell lines. Minor genetic differences between original tumor tissues and cancer cell lines could be explained as a tumor heterogeneity because separate areas of the original tumor tissues manifest similar variations.

Genome-wide detection of allelic imbalance using human SNPs and high-density DNA arrays

Most human cancers are characterized by genomic instability, the accumulation of multiple genetic alterations and allelic imbalance throughout the genome. Loss of heterozygosity (LOH) is a common form of allelic imbalance and the detection of LOH has been used to identify genomic regions that harbor tumor suppressor genes and to characterize tumor stages and progression. Here we describe the use of high-density oligonucleotide arrays for genome-wide scans for LOH and allelic imbalance in human tumors. The arrays contain redundant sets of probes for 600 genetic loci that are distributed across all human chromosomes. The arrays were used to detect allelic imbalance in two types of human tumors, and a subset of the results was confirmed using conventional gel-based methods. We also tested the ability to study heterogeneous cell populations and found that allelic imbalance can be detected in the presence of a substantial background of normal cells. The detection of LOH and other chromosomal changes using large numbers of single nucleotide polymorphism (SNP) markers should enable identification of patterns of allelic imbalance with potential prognostic and diagnostic utility.

Chromosome band 16q24 is frequently deleted in human gastric cancer

We have analysed the loss of heterozygosity (LOH) on chromosome bands 16q22-q24 in 24 primary gastric cancer tissues and found three regions of frequent allelic loss (16q22, 16q24.1-q24.3 and 16q24.3). The region for the most frequent allelic loss (63%) was in 16q24.1-q24.3. LOH of this region had no relationship with histological subtype, but a significant association between LOH and microscopic lymphangial invasion was observed. Although not significant, vascular and gastric wall invasions are also associated with LOH. The region includes the locus for the H-cadherin gene. Therefore we examined the genetic and epigenetic alterations of this gene. Markedly reduced expression was observed in gastric cancer cell lines compared with that of normal gastric mucosa. However, no mutation was found in this gene in any of the gastric cancer tissues or the gastric cancer cell lines. Furthermore, we analysed the methylation status of the 5'-flanking region of the gene, but no significant association was found. We suggest that some other tumour suppressor gene(s) in 16q24.1-q24.3 may be responsible for gastric carcinogenesis.

Genetic alterations in hepatocellular carcinomas: association between loss of chromosome 4q and p53 gene mutations

The major risk factors for hepatocellular carcinomas (HCC) in high incidence areas include infection with hepatitis B and C viruses (HBV, HCV) and exposure to aflatoxin. Genetic alterations in 24 liver resection specimens from Shanghai and Qidong were studied. Hepatitis B virus was integrated in all patient samples, and a null phenotype for the GSTM1 enzyme was present in 63% of patients. Alteration of p53 was present in 95% (23/24) of cases: mutations of the p53 gene in 12 HCC, p53 overexpression in 13 and loss of heterozygosity (LOH) of chromosome 17p in 17. All seven HCCs with a p53 mutation from Qidong and three of five from Shanghai had the aflatoxin-associated point mutation with a G to T transversion at codon 249, position 3. No HCC had microsatellite instability. LOH of chromosome 4q, 1p, 16q and 13q was present in 50%, 46%, 42% and 38%, respectively, and 4q was preferentially lost in HCCs containing a p53 mutation: LOH of 4q was present in 75% (9/12) of HCC with, but only 25% (3/12) of HCC without, a p53 gene mutation (P = 0.01). These data indicate a possible interaction between p53 gene mutation and 4q loss in the pathogenesis of HCC.