Study of expression of candidate genes located in chromosome 5p of human esophageal squamous cell carcinoma

Abstract

Esophageal squamous cell carcinoma (ESCC) is a human cancer that is characterized by a high mortality rate and geographic differences in incidence. Previous studies of comparative genomic hybridization (CGH) showed that chromosome 5p is frequently amplified in cell lines and primary tumors of ESCC which are of Hong Kong Chinese origin. In the present study, we investigated the expression level of two novel genes located in 5pl5.2 and are 5' upstream to delta catenin gene, named as JS-1 and JS-2, in cell lines and primary tumors of ESCC and also studied the transforming capacity of the two genes in normal cells. ESCC cell lines and patient cases with their matched non-tumor epithelial tissues were analyzed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) for the overexpression of JS-1 and JS-2. The transforming capacity of JS-1 and JS-2 was also investigated by transfecting NIH 3T3 cells with their full coding sequences cloned into the expression vector pcDNA3.1 (-) and followed by the study of foci formation under confluence growth and soft agar assay for investigating the anchorage independent growth property of the transfected cells. The JS-1 transfected cells with overexpression were also assessed for tumorigenicity in athymic nude mice. Fourty-five percent (5/11) and 18% (2/11) of the ESCC cell lines showed overexpression of JS-1 and JS-2 respectively, while 56% (15/27) and 14% (3/22) of primary ESCC cases showed overexpression of JS-1 and JS-2 respectively. JS-1 overexpression was found in 26% (7/27) of patient cases with stage II tumors, 18% (5/27) cases with stage III tumors, 7% (2/27) cases with stage IV tumors and 4% (1/27) case with dysplasia, whereas JS-2 was only overexpressed in a case with dysplastic lesion (1/22; 4.5%) and in 9% (2/22) of patients with stage III tumors. Overexpression of JS-1 in NIH-3T3 cells also caused foci formation in confluence growth and colony formation in soft agar but not for JS-2. Subcutaneous tumor was formed in all nude mice tested when NIH 3T3 cells overexpressing JS-1 were injected subcutaneously into five athymic nude mice. Our results thus indicate that the frequent overexpression of JS-1 in ESCC and its transforming capacity in normal cells may play a critical role in the molecular pathogenesis of ESCC. The present study also forms the ground work on the further identification of novel mechanisms of molecular carcinogenesis in ESCC and other cancers.