Published online Apr 14, 2014. doi: 10.3748/wjg.v20.i14.4001
Revised: December 24, 2013
Accepted: February 17, 2014
Published online: April 14, 2014
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 overexpression 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.
Core tip: Epithelial membrane protein 1 (EMP1) has a known role in tumor development and progression, and its activity is linked to a number of biological processes including proliferation, apoptosis, invasion, and metastasis of colorectal cancer. We detected expression of EMP1 in colorectal carcinoma and analyzed the biological effect of EMP1 overexpression in a colorectal carcinoma cell line. EMP1 expression was decreased in colorectal cancer and its expression correlated significantly with T stage, lymph node metastasis, clinic stage, histological grade, and poor overall survival. Taken together, our findings suggest that EMP1 may play an important role as a negative regulator of colorectal cancer.