Radiosensitization Effect of Overexpression of Adenovirus- mediated SIRT6 on A549 Non-small Cell Lung Cancer Cells

Objective: To explore the radiosensitization effect of overexpression of silent information regulator 6 (SIRT6)
on A549 non-small cell lung cancer (NSCLC) cells.
Methods: Adenovirus vector Ad-SIRT6 causing overexpression
of SIRT6 was established. Western blotting and MTT assay were adopted to detect the level of SIRT6 protein
and the inhibitory rate of A549 cell proliferation after different concentrations of adenovirus transduction (0,
25, 50, 100, 200, and 400 pfu/cell) for 24 h. Control group, Ad-null group and Ad-SIRT6 group were designed in
this experiment and virus concentration of the latter two groups was 200 pfu/cell. Colony formation assays were
employed to test survival fraction (SF) of the 3 groups after 0, 2, 4, 6, 8, 10 X-ray irradiation. Flow cytometry
was used to detect the status of cell cycle of 3 groups after 48 h of 4Gy X-ray irradiation and Western blotting
was used to determine the expression of apoptosis-related genes of 3 groups after 48 h of 4GyX-ray irradiation.

Results: In the range of 25~400 pfu/cell, the inhibitory rate of A549 cell proliferation increased as adenovirus
concentration raised. The inhibitory rates under the concentrations of 0, 25, 50, 100, 200, and 400 pfu/cell were
0%, 4.23±0.34%, 12.7±2.57%, 22.6±3.38%, 32.2±3.22% and 47.8±5.58% and there were significantly differences
among groups (P<0.05). SF in Ad-SIRT6 group was lower than Ad-null and control groups after 4~10Gy X-ray
irradiation (P<0.05) and the sensitization enhancement ratio (SER) was 1.35 when compared with control group.
Moreover, after 48 h of 4Gy X-ray irradiation, there appeared a significant increase in G1-phase cell proportion,
up-regulated expression of the level of apoptosis-promoting genes (Bax and Cleaved caspase-3), but a obvious
decline in S-phase and G2-phase cell proportion and a significant decrease of the level of apoptosis-inhibiting
gene (Bal-2) in the Ad-SIRT6 group (P<0.05).
Conclusion: The over-expression of adenovirus-mediated SIRT6,
which has radiosensitization effect on A549 cells of NSCLC, can inhibit the proliferation of A549 cells and cause
G0/G1 phase retardation as well as induce apoptosis of cells.