Gain of allelic gene expression for IGF-II occurs frequently in Barrett's esophagus

Barrett's esophagus: progression to adenocarcinoma and markers

The following on progression to adenocarcinoma and markers of Barrett's esophagus includes commentariess on the expression of claudin 4 in Barrett's adenocarcinoma; the role of acid and bile salts; the role of insulin-like growth factor; the value of reactive oxygen species; the importance of abnormal methylation; genetic alterations in stromal cells and genomic changes in the epithelial cells; the value of confocal laser endomicroscopy for the subsurface analysis of the mucosa; indications for statins as adjuvant chemotherapeutic agent; the sequence of molecular events in malignant progression in Barrett's mucosa; and the value of the macroscopic markers and of p53 mutations.

Expression of insulin-like growth factor II mRNA-binding protein 3 in human esophageal adenocarcinoma and its precursor lesions

CONTEXT

Insulin-like growth factor II mRNA-binding protein 3 (IMP3) is an oncofetal protein highly expressed in fetal tissue and malignant tumors but only rarely within adult benign tissues. The expression of IMP3 in esophageal adenocarcinoma (EAC) and its precursor lesions including distinctive type Barrett mucosa (BM, intestinal metaplasia) and esophageal columnar dysplasia (ECD) is largely unknown.

OBJECTIVE

To characterize the patterns of IMP3 expression in EAC and its precursor lesions.

DESIGN

Samples from 132 cases of EAC, 28 cases of ECD (16 high-grade dysplasia and 12 low-grade dysplasia cases), 28 cases of BM without dysplasia, and 138 cases of nonneoplastic esophageal mucosa without dysplasia or BM within formalin-fixed, paraffin-embedded tissue microarray blocks were examined. Tissues were stained with mouse monoclonal anti-IMP3 antibody. The intensity (1-3+) and percent (0%-100%) of positive cytoplasmic and/or membranous IMP3 staining cells were determined.

RESULTS

Most of EAC cases (93 of 132; 70%) showed cytoplasmic and membranous IMP3 staining. Poorly and moderately differentiated EAC showed statistically significant higher IMP3 expression compared with well-differentiated EAC (P < .001). A subset of ECD cases (7 of 28; 25%) was positive for IMP3, including 3 low-grade dysplasia cases (focal 1+ IMP3 staining) and 4 high-grade dysplasia cases (more diffuse 1-2+ IMP3 staining). No IMP3 staining was observed in any nonneoplastic esophageal mucosa and BM tissues without dysplasia.

CONCLUSIONS

This study suggests that IMP3 may play a role in the carcinogenesis of EAC and has diagnostic utility in differentiating neoplastic and nonneoplastic lesions of the esophagus.

Loss of imprinting of the insulin-like growth factor II (IGF2) gene in esophageal normal and adenocarcinoma tissues

To evaluate loss of imprinting (LOI) and expression of the IGF2 gene in matched esophageal normal and adenocarcinoma tissues, we studied a prospective cohort of 77 patients who underwent esophageal resection between 1998 and 2003. IGF2 imprinting status was determined by reverse transcription-polymerase chain reaction (PCR) following ApaI digestion, and quantitative PCR was used to evaluate IGF2 expression, which was correlated with clinicopathologic findings, disease-free and overall survival. In total, 32% (14/44) of informative tissues showed loss of IGF2 imprinting, with a strong correlation between the tumor and normal esophageal epithelia (Kappa = 0.89, P < 0.01). Normal epithelia with LOI had increased expression of IGF2 [median: 2.91, 95% confidence interval (CI): 0.93-5.06] compared with imprinted normal epithelia (median: 1.13, 95% CI: 0.85-1.39) (P = 0.03). In contrast, tumors with LOI had significantly reduced IGF2 expression (median: 1.87, 95% CI: 0.53-5.21) compared with normally imprinted tumors (median: 6.79, 95% CI: 3.39-15.89) (P = 0.016). Patients below the age of 65 years with normally imprinted tumors had significantly reduced 5 year disease-free survival (DFS) (24%) compared with patients whose tumors had LOI for IGF2 (55%) (P = 0.03). Cox regression analysis showed that IGF2 overexpression was associated with significantly reduced disease-free survival (P = 0.04). We conclude that in a subgroup of younger patients, loss of IGF2 imprinting was associated with improved outcome following esophageal resection. Expression of IGF2 in esophageal adenocarcinoma and normal esophageal epithelia depended on imprinting status and tissue type, suggesting novel molecular regulatory mechanisms in esophageal tumorigenesis.

An epigenetic approach to cancer etiology

The practice of clinical oncology historically has been rooted in therapy for established cancers, and over the past decade, early detection of the malignancy has occurred increasingly, allowing an increasing chance of cure by surgical intervention. Cancer prevention has been targeted largely to generic reduction of exposure to environmental carcinogens, such as smoking reduction. However, targeted identification of patients at increased risk and therapeutic tailored intervention in those patients have not taken hold in oncology, despite the enormous success of that approach in preventive cardiology. A paradigm of such a strategy for oncology may be the identification of patients with epigenetic alterations in progenitor cells and intervention before the development of the earliest identifiable neoplasms. We review studies of loss of imprinting of insulin-like growth factor 2 in colorectal cancer as an example of such a target for preventive oncology.

Loss of imprinting and cancer

Imprinting is defined as the parental allele-specific expression of a very limited set of genes (about 50-80). This regulation depends upon an epigenetic marking of parental alleles during gametogenesis. Monoallelic expression ensures that the levels of the proteins encoded by imprinted genes, important factors of embryonic growth, placental growth or adult metabolism, are assured. Without precise control of their expression, developmental abnormalities result, as is shown by a number of hereditary over-growth syndromes, including Beckwith-Wiedemann syndrome. The regulation of imprinted genes is largely dependent on methylation marks, which are laid down during embryological development of germ cells. Once in place, the methylation status of precise chromosomal regions, Imprinting Control Regions (ICRs), is read by either of two mechanisms, chromatin barrier formation or untranslated RNAs, thereby ensuring that only the maternal or paternal allele is expressed. Each imprinted gene is classified as maternal or paternal according to the expressed allele. The stability of the marked regions in somatic cells is maintained through each cellular replication by a methylation enzyme complex containing Dnmt1. Although the major reading mechanisms of imprinted status are known, chromatin boundary formation by CTCF and untranslated RNAs, the molecules elaborating the initial ICR methylation, are just being uncovered. Mis-regulation of imprinted gene expression (loss of imprinting [LOI]) is seen frequently and precociously in a large variety of human tumours, making LOI a potentially valuable tool for both diagnosis and treatment. In fact, LOI is presently considered the most abundant and most precocious alteration in cancer. The present review proposes a mechanism responsible for LOI, as well as its eventual value in tumour diagnosis and prognosis.