Background & objective: Adenovirus type 5 early region 1A (E1A) gene has been found to be a tumor suppression gene recently. The protein of E1A gene regulates the expression of many cellular genes positively or negatively, and possesses the activities of inducing differentiation of tumor cell, reversing of malignant phenotype, anti-carcinogenesis and anti-metastasis. Study of E1A protein on the treatment of lymph node metastasis of human head and neck squamous cell carcinoma (HNSCC) was not reported. This study was designed to investigate the growth inhibition and radiochemosensitivity of E1A gene on human lymph node metastasis cell line 686LN-1 derived from the patient with human tongue squamous cell carcinoma in vitro and its mechanism.
Methods: The pcDNA3-E1A recombinant plasmid, designed for high-level expression of E1A gene in a variety of eukaryotic cell lines,was transfected into 686LN-1 cells mediated by lipofectamine. To observe the growth inhibition of E1A gene on the cells, the growth curve and doubling time were investigated. Cells before and after transfection were treated with cisplatin, paclitaxel, bleomycin, and 5-fluorouracil (5-FU) for 24 hours or irradiation, respectively, then the changes of sensitivity were tested by MTT assay. The redistributions of cell cycle were analyzed by flow cytometry. Immunocytochemical staining was used to detect the expression of p53 and HER-2/neu.
Results: Compared with the vector-transfected cells (686LN-1-vect cells), the E1A-transfected cells (686LN-1-E1A cells) grew slowly, and the doubling time elongated (1.41-fold). 686LN-1-E1A cells showed distinct sensitivity to the anticancer drugs and irradiation. According to the IC(50) value, the sensitivity of 686LN-1-E1A cells increased approximately 8-fold to cisplatin, 20-fold to bleomycin, 10-fold to paclitaxel, 1-fold to irradiation compared with 686LN-1-vect cells. However, the sensitivity to 5-FU did not change. The cell cycle was dramatically arrested at G(2)/M phase in the 686LN-1-E1A cells. E1A gene remarkably suppressed the expression of HER-2/neu gene in 686LN-1-E1A cells.
Conclusion: E1A gene can significantly inhibit the growth rate of lymph node metastasis cell line 686LN-1 of HNSCC. Moreover, it also slightly enhance the cell sensitivity to antitumor drugs and irradiation. These functions of E1A gene may be associated with its ability to suppress the HER-2/neu expression and to arrest the cell at G(2)/M phase.