Molecular dissection of 17q12 amplicon in upper gastrointestinal adenocarcinomas

Abstract

DNA amplification at 17q is frequently detected in upper gastrointestinal adenocarcinomas (UGC; stomach and esophagus). In this study, we did fluorescence in situ hybridization on a tissue microarray that contained 304 UGCs and 89 normal stomach samples using a approximately 168-kb BAC clone (CTD-2019C10) that maps to 17q12-q21.1. This 168-kb region contains the following genes: PPP1R1B/DARPP-32, STARD3, TCAP, PNMT, PERLD1, ERBB2, C17orf37, and GRB7 as well as the first two exons of ZNFN1A3. DNA amplification (> or =5 signals) was detected in 85 of 282 (30%) of UGCs, and high-level amplification (> or =10 signals) was seen in 28 of 282 (10%) of all tumors. Adenocarcinomas of gastroesophageal junction and lower esophagus had the highest frequency of amplification (45%) compared with stomach tumors (27%; P = 0.04). On the other hand, 38% of tumors with intestinal-type morphology had amplification compared with 26% of diffuse-type tumors (P = 0.02). We further did quantitative real-time reverse transcription-PCR on 74 frozen tissue samples from UGCs for 11 genes located within or adjacent to the boundaries of this approximately 168-kb genomic region. These genes include all 9 genes that are fully or partially located inside the CTD-2019C10 clone as well as 2 additional adjacent genes (NEUROD and TOP2A). Overexpression of PPP1R1B/DARPP-32, TCAP, and TOP2A was seen in approximately half of the tumors, whereas STARD3 and ZNFN1A3 were rarely overexpressed (12%). Interestingly, there was a statistical correlation between expression of all 8 genes that map between PPP1R1B/DARPP-32 and GRB7, whereas expression of NEUROD, ZNFN1A3, and TOP2A that are partially inside or adjacent to the boundaries of the CTD-2019C10 clone did not correlate with the expression of any of these 8 genes. These data show a transcriptionally active oncogenomic region bounded by PPP1R1B/DARPP-32 and GRB7 in UGCs and provide further insight into expression levels of several critical genes.