Effects of over-expression of E2F transcription factor 1 on radiosensitivity glioma U251 cells / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To investigate the effects of over-expression of E2F transcription factor 1 (E2F1) on proliferation, invasion, apoptosis and radiosensitivity of glioma cell U251.Methods:Real-time quantitative PCR (qRT-PCR) were used to detect the differential expression of E2F1 mRNA in glioma cells LN18, SW1088, U251 and normal brain glial cells. The stable over-expression of E2F1 plasmid was constructed and transfected into U251 cells. qRT-PCR and Western blot test were used to detect the expression of E2F1, pituitary tumor transforming gene 1(PTTG1), C-Myc, B-cell lymphoma-2 (Bcl-2), Bcl2-associated X (Bax) mRNA and protein expression in the control group and E2F1 over-expression group.U251 cells were divided into control group(no X-ray irradiation), irradiation group(6 Gy dose of X-ray), and irradiation + E2F1 over-expression group(transfected with E2F1 first, then irradiated by 6 Gy of X-ray). Cell proliferation ability was detected by cell counting Kit-8(CCK-8) cell viability detection reagent, and cell invasion and migration ability were detected by Transwell chamber. Apoptosis and cell cycle were detected by flow cytometry.GraphPad Prism 8.0 was used for data analysis.The statistical methods were one-way ANOVA and independent sample t-test. Results:qRT-PCR showed that there was statistical difference in the mRNA levels of E2F1( F=201.92, P<0.05) in different cell lines.The expression levels of E2F1 mRNA in LN18(4.04±0.29), SW1088(3.19±0.16)and U251(4.66±0.20) cells were higher than those in HEB(1.02±0.07)cells ( q=27.00, 19.40, 32.52, all P<0.05). After successfully constructing U251 cells with stable over-expression of E2F1 plasmid, qRT-PCR and Western blot detection results showed that the mRNA and protein levels of E2F1, PTTG1, C-Myc and Bcl-2 in E2F1 over-expression group were higher than those in control group ( t=77.16, 57.88, 4.63, 51.13, 7.50, 70.85, 8.38, 48.81, all P<0.05). Bax mRNA(0.20±0.01) and protein(0.66±0.01) levels were lower than those in control group((1.00±0.02), (0.94±0.01)), and the differences were statistically significant ( t=1.74, 54.65, both P<0.05). After X-ray irradiation (6 Gy), CCK8 detection results showed the proliferation ability of the three groups at 24, 48, 72 and 96 h were significantly different ( F=95.41, 187.53, 1 158.49, 7 883.78, all P<0.05). The proliferation capacity of the irradiation group were lower than those of the control group at 24, 48, 72 and 96 h ( q=19.51, 27.20, 66.60, 174.9, all P<0.05). The proliferation capacity of irradiation + E2F1 over-expression group at 24, 48, 72 and 96 h were higher than those of irradiation group ( q=10.63, 10.81, 21.11, 60.90, all P<0.05). Transwell assay results showed that there were significant differences in cell invasion and migration ability among the three groups ( F=315.38, 681.10, both P<0.05). The invasion and migration ability of cells in the irradiation group were lower than those in the control group ( q=35.09, 12.76, both P<0.05), and the invasion and migration ability of cells in the irradiation + E2F1 over-expression group were higher than those in the irradiation group ( q=52.06, 22.81, both P<0.05). Flow cytometry showed that there were significant differences in apoptosis rate and percentage of cells in each cycle among the three groups ( F=667.63, 3 213.30, 3 011.26, 861.98, all P<0.05). The percentage of the apoptosis rate, S phase and G2 phase cells in the irradiation group were higher than those in the control group ( q=51.10, 89.39, 51.82, all P<0.05), while the percentage of G1 phase cells in the irradiation group was lower than that in the control group ( q=141.2, P<0.05). The apoptosis rate and percentage of S phase and G2 phase cells in the irradiation + E2F1 over-expression group were lower than those in the irradiation group ( q=18.87, 41.42, 29.31, all P<0.05), while the number of G1 phase cells in the irradiation + E2F1 over-expression group was lower than that in the irradiation group ( q=70.73, P<0.05). Conclusion:Over-expression of E2F1 can reduce the radiosensitivity of glioma U251 cells by regulating the expression of mRNA and protein of genes related to cell cycle and apoptosis, and E2F1 may be involved in the radioresistance of glioma cells.