Coamplification and coexpression of GRB7 and ERBB2 is found in high grade intraepithelial neoplasia and in invasive Barrett's carcinoma

The human growth factor receptor-bound protein 7 gene (GRB7), the founding member of a family of adaptor molecules has been shown to regulate cell migration and has been implicated in tumor progression. GRB7 is localized in close proximity to the ERBB2 gene within an amplicon previously identified in Barrett's adenocarcinoma (BCA). We evaluated gene amplification and mRNA expression of GRB7 and ERBB2 in Barrett's carcinoma and its associated precursor lesions to assess their possible role in Barrett's malignant transformation. Copy number and expression levels were analyzed by Q-PCR (GRB7, ERBB2) and QRT-PCR (GRB7, ERBB2) using TaqMan technology and fluorescence in situ hybridization (ERBB2) in a series of 24 laser-microdissected samples of Barrett's carcinomas and 32 samples of associated premalignant lesions. Parallel analysis of gene copy number changes and expression levels demonstrated that GRB7 and ERBB2 displayed concomitant elevated expression levels and increased copy numbers in 32% of Barrett's carcinomas. There was a correlation between GRB7 and ERBB2 in BCA at the DNA level (r_s = 0.76, p < 0.001) and the mRNA level (r_s = 0.89, p < 0.001). Moreover, coamplification (r_s = 0.97, p < 0.001) and coexpression (r_s = 0.81, p < 0.001) of GRB7 and ERBB2 are shown to be already present in a subset of BCA associated high-grade intraepithelial neoplasia (HGIN), possibly reflecting a role of a concerted expression of GRB7 and ERBB2. No alterations, neither gene amplification nor over-expression were detected in Barrett's carcinoma associated low grade intraepithelial neoplasia (LGIN), intestinal metaplasia (IM) and squamous epithelium, indicating that alterations of GRB7 and ERBB2 are late events in the carcinogenesis of Barrett's esophagus. These findings may be of particular interest because the transition from high grade intraepithelial neoplasia to invasive carcinoma is a crucial step in malignant transformation in Barrett's carcinogenesis and might underline the putative role of GRB7 and ERBB2 in cell migration and tumor invasion.