Differential expression and functional impact of the alternatively spliced transcripts of Extracellular matrix protein 1 in esophageal squamous cell carcinoma

Abstract

BACKGROUND: Esophageal squamous cell carcinoma (ESCC) has an especially high incidence in China, with five-year survival rates in Hong Kong being of ∼14%. An oligonucleotide microarray was utilized to identify differentially-expressed genes in ESCC using 31 pairs of matched normal/tumor samples from Hong Kong and Henan, China. Extracellular matrix protein 1 (ECM1) was among the top down-regulated genes, indicating a potential tumor-suppressive role. Public cDNA microarray data also shows significant down-regulation of ECM1 expression in ESCC. Interestingly, this gene has been extensively studied in breast cancer and thyroid cancer for its oncogenic role. There are three alternatively-spliced variants of ECM1. Therefore, this gene was selected for further variant expression and functional analysis in ESCC. RESULTS: RNA sequencing analysis of matched normal/ESCC samples showed that ECM1b (NM_022664) is the dominant expressed variant in esophagus, followed by ECM1a (NM_004425). In tumor samples, the expression of ECM1a is down-regulated and that of ECM1b is down-regulated or lost, as compared to normal counterparts. Expression of ECM1c (NM_001202858) is not detected in either normal or tumor samples. Quantitative PCR using variant-specific primer sets confirms the findings of microarray and RNA sequencing analyses. When re-expressed in ESCC cell lines after lentiviral transduction, ECM1b expression shows a trend of tumor suppression in the orthotopic ESCC mouse tumorigenicity model; ECM1a shows no tumor-suppressive effect in either. ECM1b expression also shows a metastasis inhibitory effect in a tail vein experimental metastasis model. Immunohistochemical staining shows E-cadherin up-regulation in orthotopic tumors re-expressing ECM1b. CONCLUSIONS: These results suggest differential roles of variants of ECM1 in ESCC. Unlike the cases in other types of cancer, both expression of ECM1a and ECM1b is down-regulated in ESCC compared to normal esophageal tissues. ECM1b represents the dominantly expressed variants in esophagus epithelium, and its expression is highly reduced in esophageal carcinoma. ECM1b plays a potential suppressive role in tumorigenesis and metastasis.