A novel tumor transforming gene at 7q22, GAESCC1, is frequently amplified and overexpressed in primary esophageal squamous cell carcinomas

Abstract

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignances in China and remains a significant problem with low 5-year survival rates. Gene amplifications and overexpressions have been suggested as the major genomic aberrations involved in the pathogenesis of ESCC. Application of comparative DNA fingerprinting using inter-simple sequence repeat PCR showed that a 357bp DNA fragment was significantly amplified in a high proportion of primary ESCC. The fragment shows an exact homology to a 293bp EST sequence which has been mapped to the 7q22 region. 5’ and 3’ RACE of the EST sequence on mRNA from two morphologically normal non-tumor esophageal epithelia, followed by DNA sequencing of the RACE products and comparison of the full-length cDNA sequence with the genomic sequence, revealed that it is a part of an intronless gene with full-length sequence of 2051bp with 327bp of open reading frame (ORF) and 518bp of 5’ and 1206bp of 3’ non-coding sequences. It contains a tract of six GTG-trinucleotide repeats in its coding region and a track of four CAC trinucleotides in its 3’ non-coding region. The gene, namely GAESCC1 (Gene Amplified in Esophageal Squamous Cell Carcinoma 1), was predicted to encode a novel protein of 109 amino acids that contain target sites for phosphorylation by protein kinase C and casein kinase II. These kinases are usually involved in the signal transduction and differentiation pathways in cells. Studies by multiple-tissue expression (MTE) arrays demonstrated that GAESCC1 mRNA is expressed differentially in all normal human tissues. Similar results were observed by the screening of multiple-tissue cDNA (MTC) panels comprised of the first strand cDNAs generated from various gastrointestinal organs and other human tissues. A single-sized transcript of GAESCC1 mRNA (∼2051bp) was detected in all gastrointestinal organs by probing the multiple-tissue northern (MTN) blot for GAESCC1 mRNA, with no evidence of alternately spliced GAESCC1 mRNA. Gene amplification and overexpression of GAESCC1, studied by semi-quantitative PCR on genomic DNA and RT-PCR on cDNA, was detected in 43% and 42% of ESCC respectively. The comparison of the GAESCC1 cDNA sequences from ten tumor and corresponding non-tumor samples provided no evidence of alternately spliced GAESCC1 mRNAs or polymorphisms or somatic mutations of GAESCC1 in ESCC. Furthermore, overexpression of GAESCC1 in mouse 3T3 fibroblasts caused morphological transformation and colony formation in soft agar in vitro while the injection of GAESCC1-transfected 3T3 cells into athymic nude mice resulted in the formation of undifferentiated sarcoma. The overall results indicate that GAESCC1 is a novel and potent tumor transforming gene and suggest that it might play a crucial role in the pathogenesis of ESCC involving the signal transduction and differentiation pathways.