AIM: To determine the expression and function of epithelial membrane protein 1 (EMP1) in colorectal carcinoma. METHODS: Colorectal samples were taken from cancer lesions and adjacent normal tissue in colorectal cancer patients immediately after endoscopic biopsy. A portion of the sample was either fixed in 4% paraformaldehyde and embedded in paraffin for immunohistochemistry or stored in liquid nitrogen for Western blot. In order to determine protein expression of EMP1 in colorectal cancer (n = 63) and normal tissue (n = 31), semi-quantitative immunohistochemistry and Western blot were utilized. For in vitro studies, the human colorectal cancer cell line SW-480 was maintained in RPMI-1640 medium supplemented with 10% fetal bovine serum. Recombinant lentivirus mediated over-expression of EMP1 in SW-480 cells was quantified by real-time reverse transcription-polymerase chain reaction and Western blot. Control SW-480 cells were transfected with an empty vector. To further study the effect of EMP1 overexpression in SW-480 cells, cell proliferation, apoptosis, migration and invasion assays were conducted. RESULTS: Expression of EMP1 was significantly lower in colorectal cancer tissue than in normal tissue using both immunohistochemistry (39.7% vs 90.3% of tissues, P < 0.05) and Western blot (0.126 +/- 0.022 vs 0.632 +/- 0.053, P < 0.05). The level of EMP1 protein expression was not correlated with gender, age, or tumor location. Decreased expression of EMP1 was significantly correlated with T stage, lymph node metastasis, clinic stage, and histological grade in patients with colorectal cancer (P < 0.05). According to Kaplan-Meier analysis, low EMP1 expression correlated significantly with poor overall five-year survival (34.2% vs 64.0% survival, P < 0.05). SW-480 cells transfected with EMP1 had a lower survival fraction, higher cell apoptosis (12.1% +/- 1.3% vs 3.1% +/- 0.6%, P < 0.05), a significant decrease in migration and invasion (124.0 +/- 17.0 and 87.0 +/- 12.0, respectively vs 213.0 +/- 29.0 and 178.0 +/- 21.0, respectively, P < 0.05), higher caspase-9 (0.635 +/- 0.063 vs 0.315 +/- 0.032, P < 0.05), and lower VEGFC protein expression (0.229 +/- 0.021 vs 0.519 +/- 0.055, P < 0.05) relative to cells not transfected with EMP1. CONCLUSION: Low EMP1 expression in colorectal cancer is associated with increased disease severity, suggesting that EMP1 may be a negative regulator of colorectal cancer. (C) 2014 Baishideng Publishing Group Co., Limited. All rights reserved.