Frequent loss of heterozygosity on chromosome 17 at 17q11.2-q12 in Barrett's adenocarcinoma

SPT6 loss permits the transdifferentiation of keratinocytes into an intestinal fate that resembles Barrett's metaplasia

Transient depletion of the transcription elongation factor SPT6 in the keratinocyte has been recently shown to inhibit epidermal differentiation and stratification; instead, they transdifferentiate into a gut-like lineage. We show here that this phenomenon of transdifferentiation recapitulates Barrett's metaplasia, the only human pathophysiologic condition in which a stratified squamous epithelium that is injured due to chronic acid reflux is trans-committed into an intestinal fate. The evidence we present here not only lend support to the notion that the keratinocytes are potentially the cell of origin of Barrett's metaplasia but also provide mechanistic insights linking transient acid exposure, downregulation of SPT6, stalled transcription of the master regulator of epidermal fate TP63, loss of epidermal fate, and metaplastic progression. Because Barrett's metaplasia in the esophagus is a pre-neoplastic condition with no preclinical human models, these findings have a profound impact on the modeling Barrett's metaplasia-in-a-dish.

Overview of major molecular alterations during progression from Barrett's esophagus to esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) develops in the sequential transformation of normal epithelium into metaplastic epithelium, called Barrett's esophagus (BE), then to dysplasia, and finally cancer. BE is a common condition in which normal stratified squamous epithelium of the esophagus is replaced with an intestine-like columnar epithelium, and it is the most prominent risk factor for EAC. This review aims to impartially systemize the knowledge from a large number of publications that describe the molecular and biochemical alterations occurring over this progression sequence. In order to provide an unbiased extraction of the knowledge from the literature, a text-mining methodology was used to select genes that are involved in the BE progression, with the top candidate genes found to be TP53, CDKN2A, CTNNB1, CDH1, GPX3, and NOX5. In addition, sample frequencies across analyzed patient cohorts at each stage of disease progression are summarized. All six genes are altered in the majority of EAC patients, and accumulation of alterations correlates well with the sequential progression of BE to cancer, indicating that the text-mining method is a valid approach for gene prioritization. This review discusses how, besides being cancer drivers, these genes are functionally interconnected and might collectively be considered a central hub of BE progression.

Exploration of tumor-suppressive microRNAs silenced by DNA hypermethylation in oral cancer

In the last few years, microRNAs (miRNA) have started a revolution in molecular biology and emerged as key players in the carcinogenesis. They have been identified in various tumor types, showing that different sets of miRNAs are usually deregulated in different cancers. To identify the miRNA signature that was specific for oral squamous cell carcinoma (OSCC), we first examined expression profiles of 148 miRNAs in a panel of 18 OSCC cell lines and the immortalized oral keratinocyte line RT7 as a control. Compared with RT7, the expression of 54 miRNAs (36.5%) was frequently down-regulated in OSCC lines (<0.5-fold expression, >or=66.7% of 18 lines). Among these 54 miRNAs, we further analyzed four of these miRNAs (i.e., miR-34b, miR-137, miR-193a, and miR-203), located around CpG islands, to identify tumor-suppressive miRNAs silenced through aberrant DNA methylation. The expression of those four genes was restored by treatment with 5-aza-2'-deoxycytidine in OSCC cells lacking their expression. In addition, expression levels of the four miRNAs were inversely correlated with their DNA methylation status in the OSCC lines. In primary tumors of OSCC with paired normal oral mucosa, down-regulation of miRNA expression through tumor-specific hypermethylation was more frequently observed for miR-137 and miR-193a than for miR-34b and miR-203. Moreover, the ectopic transfection of miR-137 or miR-193a into OSCC lines lacking their expressions significantly reduced cell growth, with down-regulation of the translation of cyclin-dependent kinase 6 or E2F transcription factor 6, respectively. Taken together, our results clearly show that miR-137 and miR-193a are tumor suppressor miRNAs epigenetically silenced during oral carcinogenesis.

Early genetic instability of both epithelial and stromal cells in esophageal squamous cell carcinomas, contrasted with Barrett's adenocarcinomas

BACKGROUND

We have shown previously that stromal genetic alteration may make a greater contribution to early genesis of ulcerative colitis-associated tumors than sporadic colon cancers. We assessed whether similar differences in genetic alteration might exist between squamous cell carcinomas (SCCs) and Barrett's adenocarcinomas (BACs) of the esophagus.

METHODS

We investigated epithelial and stromal genetic instability with five National Cancer Institute standard (NCI), four chromosome 17 (Chr. 17), and six tumor suppressor gene (TSG) microsatellite markers in 26 SCC and 12 BAC cases and in 11 normal controls, using a novel combination of microdissection, polymerase chain reaction, and GeneScan.

RESULTS

Frequency of epithelial loss of heterozygosity (LOH) increased in the order background mucosa, to precursor lesions, to tumors with both types of carcinoma, especially for the Chr. 17 and TSG markers, while stromal LOH was relatively high but consistent from background mucosa to carcinoma. Epithelial LOH of D17S796 demonstrated a significantly higher frequency in SCCs than in BACs, without significant variation in p53 overexpression. The frequency of microsatellite instability (MSI) showed constant high levels in both epithelium and stroma of background, dysplasia, and carcinomas in the SCC series, and rather low frequencies in the BAC series. Although epithelial hMLH1 and hMSH2 expression decreased with tumor progression, no correlation was found with the individual MSI status.

CONCLUSIONS

Although epithelial LOH exists similarly in both lesion types, whereas epithelial and stromal MSI may occur in a relatively early phase of SCC development, stromal MSI is rare in BACs, strongly suggesting differences in tumorigenesis between the two types.

The pathogenesis of Barrett's esophagus

Significant progress has been made in clinicians' understanding of the molecular pathogenesis of BE, and the laboratory findings are beginning to lead to hypothesis-driven clinical studies; however, the following questions remain unanswered: (1) how can clinicians identify the persons most at risk for the development of esophageal adenocarcinoma, (2) what are the environmental gene interactions in esophageal carcinogenesis, and (3) can clinicians prevent the development of esophageal adenocarcinoma in the population at risk? As esophageal adenocarcinoma starts to reach epidemic proportions, further research in these areas is urgently required. With the advent of the genomic era and an explosion in studies in BE, significant progress can be made.

Overexpression of wild-type p53 in lichen sclerosus adjacent to human papillomavirus-negative vulvar cancer

Human papillomavirus is a risk factor for vulvar cancer, whereas human papillomavirus-negative late onset vulvar carcinoma is associated with the dermatologic condition, lichen sclerosus. Human papillomavirus E6 protein targets TP53 for degradation and by inference it has been assumed that human papillomavirus-negative vulvar cancer is dependent upon the acquisition of p53 somatic mutations and subsequent allelic loss. To investigate this, TP53 expression, loss of heterozygosity, and p53 genomic sequence were examined in 29 cases of human papillomavirus-negative vulvar carcinoma with adjacent lichen sclerosus. We examined 37 cases of lichen sclerosus without vulvar carcinoma, 10 cases of nongenital lichen sclerosus, and 12 cases of normal vulvar epithelium served as controls. TP53 was evident in 72% of vulvar carcinoma, 48% in epithelium adjacent to vulvar carcinoma, but was minimal in normal samples. When lichen sclerosus cases were selected to exclude samples with absolutely no TP53 expression through probable failed antigen retrieval or homozygous p53 loss the number of epithelial cells expressing TP53 increased progressively from nongenital lichen sclerosus to lichen sclerosus without vulvar carcinoma, then to lichen sclerosus with vulvar carcinoma (p<0.0001). These data suggest elevated TP53 is a feature of vulvar lichen sclerosus. Seventy-four percent of vulvar carcinoma had chromosome 17p-linked loss of heterozygosity, whereas 47% of adjacent lichen sclerosus featured loss of heterozygosity, but only 31% of vulvar carcinoma had p53 mutations, a frequency less than reported previously. Seven percent of adjacent lichen sclerosus had mutations, showing for the first time the presence of an identical mutation to the matched vulvar carcinoma. These data, however, implicate p53 mutations as a later event in vulvar carcinoma and in marked contrast to the original expectation, our loss of heterozygosity data are consistent with loss of another locus (not p53) on 17p operating as a tumor suppressor in lichen sclerosus destined to develop vulvar carcinoma.

Mutation analyses of 268 candidate genes in human tumor cell lines

We have performed a homozygous deletion screen on 268 candidate genes in 90 human tumor cell lines derived from multiple types of cancers. Most of the candidate genes investigated have been proposed to be involved in cellular processes that are germane to cancer progression, such as cell cycle control, genome maintenance, chromatin remodeling, cell adhesion, and apoptosis. We have detected novel homozygous deletions affecting four independent loci: Brahma-related gene (SMARCA4) on chromosome 19p in the TSU-Pr1 prostate and A427 lung carcinoma lines, Map Kinase Kinase 3 (MAP2K3) on 17q in the NCI-H774 lung tumor cell line, TMPRSS2 on 21q in the Bx PC-3 pancreatic carcinoma line, and Cadherin 6 (CDH6) on 5p in the SK-LU-1 lung carcinoma line. Subsequent analyses of the coding sequences of these four genes using cDNAs from a panel of tumor cell lines revealed multiple sequence variants. The results of this mutation study serve to demonstrate the feasibility of performing high-throughput screens of candidate genes in tumor cell lines to identify genes that may be targeted for mutation during the development 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.

Malignant progression in Barrett's esophagus: pathology and molecular biology

Due to its increasing incidence, esophageal adenocarcinoma and its precursor lesions have received increasing attention in recent years. The histopathologic steps in the process of malignant progression in Barrett's esophagus are well described and include the following: (a) metaplasia of the normal esophageal squamous epithelium to a specialized intestinal glandular epithelium, (b) development of dysplasia (classified histologically as low and high grade), and (c) development of adenocarcinoma characterized by invasive and metastatic potential. Intestinal metaplasia can be identified by the presence of goblet cells, the detection of which can be aided by finding mucin stained by Alcian blue at low pH. Despite this well-characterized sequence, the timing of the development of dysplasia and the subsequent transition to carcinoma and the risk of development of carcinoma in low- and high-grade dysplasia are not precisely known. In addition, there are problems in the identification of dysplasia, including sampling error and interobserver discrepancies among pathologists. A better understanding of the mechanisms of these events would allow early identification and elimination of high-risk lesions before adenocarcinoma with its attendant poor prognosis were able to develop. In order to better understand this process and to potentially identify early markers of malignant transformation, a variety of molecular studies have been carried out in recent years on adenocarcinoma and its precursor lesions in Barrett's esophagus. On the phenotypic level, increased expression and changes in pattern of expression of proliferation marker (Mib-1) Ki-67 antigen, overexpression of p53 protein, overexpression of growth factors such as epidermal growth factor (EGF), c-erbB2, and transforming growth factor (TGF)-a, decreased and abnormal expression of the cell adhesion molecule E-cadherin, and, in carcinomas, increased expression of serine proteases have all been described. A new area of interest is the family of rab proteins, which play an important role in maintaining cell polarity in the gastrointestinal tract. Increased expression of one of these proteins, rab11, has been described in low-grade, but not high-grade dysplasia. In cytogenetic studies, an increased S-phase fraction, followed by an increased tetraploid (4N) fraction and then aneuploidy, has been described. So far, the specific genes which have been most thoroughly investigated have been p53, APC, p16, and the sites of probable tumor suppressor genes, including 3p (FHIT), 13q, and 18q. With only a few exceptions (i.e., rab11 expression, and possibly mutations of FHIT), the numerous molecular abnormalities which have been described occur late in malignant progression, which means that the best marker which presently exists to identify high-risk lesions in Barrett's esophagus is the histologic identification of dysplasia in endoscopic biopsies, especially high-grade dysplasia. We are presently beginning studies using laser microdissection and competitive genomic hybridization (CGH), which could help to identify new chromosomal areas that might contain genes that are crucial in the early phases of malignant progression in Barrett's esophagus. In the future, identification of such early molecular events which predispose to carcinoma development will allow more precise and earlier risk assessment for individual patients, therefore, enabling more effective therapy.

Role of p53 assessment in management of Barrett's esophagus

The risk of developing gastroesophageal adenocarcinoma is increased in patients with Barrett's esophagus. The management of dysplasia in Barrett's esophagus remains controversial. Understanding of the sequence of events preceding malignancy is essential before screening protocols for early diagnosis and preventive measures can be implemented. The aim of this review is to examine the published data on the role p53 assessment may play in the management of Barrett's esophagus. Relevant papers were identified by an extensive text word search of the Medline database and a review of quoted articles. The p53 abnormality occurs more frequently in highly dysplastic epithelium than in nondysplastic epithelium. However, the retrospective nature of most of the available data could be a significant confounding factor. Our current knowledge suggests that p53 protein overexpression does not seem to predict future progression to cancer or determine disease outcome. The p53 abnormality alone can not be reliably used to predict progression of Barrett's esophagus to cancer. We must await long-term evaluation of patients to determine the percentage of patients with p53 gene abnormality, and nondysplastic Barrett's who will progress to dysplasia or carcinoma. Large randomized controlled long-term follow-up studies are much needed.

Multiple target sites of allelic imbalance on chromosome 17 in Barrett's oesophageal cancer

Twelve Barrett's adenocarcinomas have been analysed for the occurrence of allelic imbalance (LOH) on chromosome 17 using 41 microsatellite markers. This study provides evidence for 13 minimal regions of LOH, six on 17p and seven on 17q. Four of these centre in the vicinity of the known tumour suppressor genes (TSGs) TP53 (17p13.1), NFI (17q11.2), BRCA1 (17q21.1), and a putative TSG (17p13.3). The tumours all displayed relatively small regions of LOH (1-10 cM), and in several tumours extensive regions of LOH were detected. One tumour displayed only two very small regions of LOH; 17p11.2 and 17p13.1. The frequency of allelic imbalance has been calculated based on the LOH encompassing only one minimal region, and based on all the LOH observations. By both evaluations the highest LOH frequencies were found for regions II (p53), III (17p13.1 centromeric to p53), IV (17p12), V (17p11.2) and VII (NF1, 17q11.2). Our data supports the existence of multiple TSGs on chromosome 17 and challenges the view that p53 is the sole target of LOH on 17p in Barrett's adenocarcinoma.

Allelotype analysis of oesophageal adenocarcinoma: loss of heterozygosity occurs at multiple sites

Deletions of tumour-suppressor genes can be detected by loss of heterozygosity (LOH) studies, which were performed on 23 cases of adenocarcinoma of the oesophagus, using 120 microsatellite primers covering all non-acrocentric autosomal chromosome arms. The chromosomal arms most frequently demonstrating LOH were 3p (64% of tumours), 5q (45%), 9p (52%), 11p (61%), 13q (50%), 17p (96%), 17q (55%) and 18q (70%). LOH on 3p, 9p, 13q, 17p and 18q occurred mainly within the loci of the VHL, CDKN2, Rb, TP53 and DCC tumour-suppressor genes respectively. LOH on 5q occurred at the sites of the MSH3 mismatch repair gene and the APC tumour-suppressor gene. 11p15.5 and 17q25-qter represented areas of greatest LOH on chromosomes 11p and 17q, and are putative sites of novel tumour-suppressor genes. LOH on 9p was significantly associated with LOH on 5q, and tumours demonstrating LOH at both the CDKN2 (9p21) and MSH3 (5q11-q12) genes had a significantly higher fractional allele loss than those retaining heterozygosity at these sites. Six of nine carcinomas displaying microsatellite alterations also demonstrated LOH at CDKN2, which may be associated with widespread genomic instability. Overall, there are nine sites of LOH associated with oesophageal adenocarcinoma.

Distal chromosome 17q loss in Barrett's esophageal and gastric cardia adenocarcinomas: implications for tumorigenesis

The molecular genetic mechanisms underlying esophageal cancer are poorly understood. However, a novel gene that may be involved in esophageal carcinogenesis was recently localized by others to distal 17q by linkage analysis of kindreds with palmoplantar keratoderma and squamous cell carcinoma of the esophagus. To help determine whether a distal 17q gene may also be involved in the pathogenesis of primary Barrett's esophageal and gastric cardia adenocarcinomas, we performed loss of heterozygosity (LOH) analysis of 21 Barrett's and 18 gastric cardia adenocarcinomas at loci spanning 17q: cen-BRCA1-SSTR2-D17S2058-D17S929-D17S722-+ ++D17S937-D17S802-tel. Over 50% of the Barrett's and cardia adenocarcinomas demonstrated loss of an allele at one or more informative distal 17q markers. One common overlapping region of loss involved loci mapped to distal 17q24-proximal 17q25, which tentatively defines a potential chromosomal region distal to BRCA1 involved in the pathogenesis or progression of both types of adenocarcinomas. LOH analysis of DNA from matched microdissected sections of Barrett's metaplasia suggested that loss of D17S2058 in this region may be an early event in the malignant transformation of Barrett's metaplasia. No statistically significant correlations between 17q LOH and tumor stage or patient survival were noted. In summary, LOH mapping of 17q in Barrett's and cardia adenocarcinomas suggests the existence of at least one putative distal 17q tumor suppressor gene involved in the pathogenesis of these tumors.

Diagnostic value of p53 immunohistochemistry in Barrett's esophagus: an endoscopic study

The aim of this study was to establish the diagnostic utility of p53 immunohistochemistry in Barrett's esophagus. Three pathologists reviewed endoscopic biopsy specimens and one surgical specimen derived from 102 subjects in a prospective follow-up series. Dysplasia was graded as negative, indefinite, low grade and high grade. p53 staining was assessed as negative, weak or patchy and strong. Kappa coefficients for interobserver agreement for the three combinations of observer pairs were moderate to substantial (0.48, 0.55 and 0.68) for dysplasia and substantial to near perfect (0.77, 0.82 and 0.89) for p53 immunostaining. In the consensus grading achieved for dysplasia, strong p53 staining was recorded in 0/79 samples that were negative or indefinite for dysplasia, 5/15 (33%) examples of low grade dysplasia and 7/8 (87%) examples of high grade dysplasia. Non-dysplastic p53 positive glands were seen in specimens from two subjects harbouring dysplasia or cancer elsewhere. Two p53 positive specimens were, upon review and discussion, re-assigned from low- to high-grade dysplasia. It is concluded that p53 immunohistochemistry facilitates the interpretation of Barrett's epithelium but need only be employed to confirm a suspected diagnosis of dysplasia and assist with the distinction between low- and high-grade dysplasia.

Localization of prostate cancer metastasis-suppressor activity on human chromosome 17

BACKGROUND

Prostate cancer is the most commonly diagnosed malignancy in American men. Currently, it is difficult to accurately predict the clinical course of histologically localized prostatic cancer in the individual patient. Identification of markers for metastatic potential of prostate cancer may improve the diagnosis and treatment of this disease. We have previously demonstrated that human chromosome 17 (17pter-q23) suppresses the metastatic ability of AT6.1 rat prostatic cancer cells. In this study we report on the further localization of the metastasis suppressor activity encoded by human chromosome 17.

METHODS

A series of AT6.1-17 microcell hybrids was constructed using microcell-mediated chromosomal transfer of human chromosome 17 into highly metastatic AT6.1 cells. Hybrids which had spontaneously deleted regions of chromosome 17 were analyzed by PCR for the presence of 32 sequence-tagged sites (STS) markers as well as the prostate cancer tumor-suppressor loci reported on 17q. In addition, we examined a number of candidate genes and markers that previously have been mapped to chromosome 17. The in vivo metastatic potential of these AT6.1-17 deletion hybrids was determined.

RESULTS

We have localized metastasis-suppressor activity to a approximately 70-centiMorgan (cM) portion of chromosome 17, consisting of three distinct regions of 30 cM (D17S952-->D17S805), 6 cM (D17S930-->D17S797), and 34 cM (D17S944-->D17S784). Three of the four markers on 17p13, including HIC1 and TP53, and 12 of the 13 markers in 17q21-23, including BRCA1 (D17S855) and NM23 (NME1), were not retained in the conserved approximately 70-cM metastasis-suppressor region.

CONCLUSIONS

These results support a role for a novel metastasis-suppressor gene(s) or a novel metastasis-suppressor function on chromosome 17. Complementary candidate gene and positional cloning approaches are being used to identify the gene(s) within the approximately 70-cM conserved region responsible for metastasis suppression.

The molecular basis for carcinogenesis in metaplastic columnar-lined esophagus

A wide variety of biologic events and mechanisms appear to have roles in the development and progression of Barrett's esophagus-associated neoplastic lesions. Figure 5 is a schematic depiction of these events. This is known as an infernogram (named after Dante's Inferno) (S. Kern, unpublished presentations, 1996). Events at the bottom rings of the inferno are high-frequency mutations; nearer to the top of the inferno are the less common events. The next several years promise many further discoveries of not only high-frequency and low-frequency events, but also their application. Some of the molecular alterations already studied show promise as markers for early cancer detection or prognostication. Eventually, applications of these discoveries should yield new and more effective means of preventing and treating the deadly complications of this troublesome premalignant condition.

Epidemiology and molecular biology of Barrett's adenocarcinoma

In the United States, the incidence of esophageal adenocarcinoma has risen faster than any other malignancy in recent years, and now represents the most common histologic type of esophageal cancer observed in major institutions. The precise etiology of this malignancy, and the epidermiologic variables responsible for its dramatically rising incidence, remains obscure. Elucidation of the molecular biology of malignant transformation in Barrett's esophagus may improve the management of patients with advanced esophageal adenocarcinomas. Furthermore, appreciation of the molecular events associated with esophageal adenocarcinomas. Furthermore, appreciation of the molecular events associated with esophageal adenocarcinogenesis may facilitate early detection of occult carcinomas, and enable therapeutic interventions designed to prevent these otherwise highly lethal neoplasms.

Genetic alterations in esophageal cancer and their relevance to etiology and pathogenesis: a review

Cancer of the esophagus exists in 2 main forms with different etiological and pathological characteristics-squamous cell carcinoma (SCC) and adenocarcinoma (ADC). This review focuses on the occurrence of genetic alterations in SSC and ADC of the esophagus and on their possible implications for the elucidation of the etiology and pathogenesis of these cancers. The most common alterations found in esophageal cancers include allelic losses at chromosomes 3p, 5q, 9p, 9q, 13q, 17p, 17q and 18q, as well as mutations of p53 (mostly missense), Rb (deletions), cyclin DI (amplifications) and c-myc (amplifications). The sequence of occurrence of these alterations with respect to histopathological tumor progression is discussed. Our findings underscore the different etiology and pathogenesis of SCC vs. ADC and suggest that the genetic alterations observed may represent molecular fingerprints of critical risk involved in the development of these 2 cancers.