Over-expression of eukaryotic translation initiation factor 4 gamma 1 correlates with tumor progression and poor prognosis in nasopharyngeal carcinoma

Abstract

Background: The aim of the present study was to analyze the expression of eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) in nasopharyngeal carcinoma (NPC) and its correlation with clinicopathologic features, including patients' survival time.

Methods: Using real-time PCR, we detected the expression of EIF4G1 in normal nasopharyngeal tissues, immortalized nasopharyngeal epithelial cell lines NP69, NPC tissues and cell lines. EIF4G1 protein expression in NPC tissues was examined using immunohistochemistry. Survival analysis was performed using Kaplan-Meier method. The effect of EIF4G1 on cell invasion and tumorigenesis were investigated.

Results: The expression levels of EIF4G1 mRNA were significantly greater in NPC tissues and cell lines than those in the normal nasopharyngeal tissues and NP69 cells (P < 0.001). Immunohistochemical analysis revealed that the expression of EIF4G1 protein was higher in NPC tissues than that in the nasopharyngeal tissues (P < 0.001). In addition, the levels of EIF4G1 protein in tumors were positively correlated with tumor T classification (P = 0.039), lymph node involvement (N classification, P = 0.008), and the clinical stages (P = 0.003) of NPC patients. Patients with higher EIF4G1 expression had shorter overall survival time (P = 0.019). Multivariate analysis showed that EIF4G1 expression was an independent prognostic indicator for the overall survival of NPC patients. Using shRNA to knock down the expression of EIF4G1 not only markedly inhibited cell cycle progression, proliferation, migration, invasion, and colony formation, but also dramatically suppressed in vivo xenograft tumor growth.

Conclusion: Our data suggest that EIF4G1 can serve as a biomarker for the prognosis of NPC patients.

Figure 1

The increased expression levels of EIF4G1 mRNA and protein in NPC tumor tissue and cell lines and their association with the overall survival of NPC patients. A. EIF4G1 mRNA expression in NPC cell lines, tumor tissues, and non-cancerous nasopharyngeal (NP) tissues. EIF4G1 mRNA level was relatively high in NPC tissue, NPC cell lines (except 6-10B cells) comparing to nasopharyngeal tissue and NP69 cells. B. EIF4G1 protein expression in NPC and nasopharyngeal tissues.(1) Negative control; (2) Weak expression of EIF4G1 in nasopharyngeal tissues; (3-5) Strong expression of EIF4G1 in NPC tissues (magnification 400×). C. Kaplan--Meier survival analysis of the overall survival time in 107 NPC patients based on the levels of EIF4G1 protein expression. The log-rank test was used.

Figure 2

Reduced expression of EIF4G1 inhibited cell proliferation. A. Western blotting assay shows significantly decreased protein expression of EIF4G1 in shRNA-EIF4G1 cells comparing to shRNA-Ctr and the parental 5-8F cells. β-actin was used as the internal control. B. The cell growth of parental 5-8F cells and their stable derivatives, shRNA-Ctrl and shRNA-EIF4G1, were examined by MTT assay over a seven-day period. *P < 0.05, as compared to 5-8F and shRNA-Ctrl cells.

Figure 3

Reduced EIF4G1 expression inhibited cell migration, invasion and cell cycle progression. A. Cell cycle was determined by FACS Caliber Cytometry. Cell migration (B) and invasion (C) capabilities of parental 5-8F cells and their stable derivatives, shRNA-Ctrl and shRNA-EIF4G1, were examined using transwell assay. Data were presented as mean ± SD for three independent experiments. *P < 0.05, as compared to shRNA-Ctrl and 5-8F cells.

Figure 4

Reduced EIF4G1 expression inhibited cell colony formation and xenograft tumor growth in vivo. A. The cell clone ability of parental 5-8F cells and their stable derivatives, shRNA-Ctrl and shRNA-EIF4G1, were examined by plate colony formation assay. *P < 0.05, as compared to 5-8F and shRNA-Ctrl cells. B. 5-8F cells containing shRNA-Ctrl or shRNA-EIF4G1 lentiviral vectors were injected into nude mice (n = 6 for each group). After 25 d, tumors were harvested and weighted. Data are presented as mean ± SD. *P < 0.05 as compared to shRNA-EIF4G1 cells. C. EIF4G1 protein expression was markedly decreased in xenograft tumors induced by shRNA-EIF4G1 cells comparing to that induced by shRNA-Ctrl cells.

Figure 5

Reduced EIF4G1 expression activated the expression of PDCD4 protein. A. Protein expression of PDCD4 was increased in shRNA-EIF4G1 cells compared to shRNA-Ctrl cells and the parental 5-8F cells. Data were presented as mean ± SD. *P < 0.05.