Overexpression of β-Catenin Decreases the Radiosensitivity of Human Nasopharyngeal Carcinoma CNE-2 Cells.

BACKGROUND/AIMS: Nasopharyngeal carcinoma (NPC) is rare worldwide but remains highly prevalent in endemic regions, notably in southern China. Radiotherapy remains the treatment of choice for NPC, but radioresistance has been identified as a major cause of therapeutic failure. The Wnt/β-catenin signaling has been found to be involved in NPC radioresistance; however, the effect of β-catenin overexpression on radioresistance remains unknown in NPC until now. This study aimed to examine the impact of β-catenin overexpression on the radiosensitivity of human NPC CNE-2 cells.

METHODS

Immunohistochemistry was performed to detect the β-catenin expression in normal nasopharyngeal specimens and NPC specimens. The human NPC CNE-2 cell line overexpressing β-catenin was modeled by transfection with the pcDNA3.1/Hygro(+)/β-catenin recombinant vector (transfection group), while cells transfected with the pcDNA3.1/Hygro(+) vector served as negative controls and non-transfected cells served as blank controls. The expression of key molecules of the Wnt/β-catenin signaling pathway was determined using Western blotting and qPCR assays, and the changes of radiation sensitivity were measured with a colony-formation assay. Cell viability was measured by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5 -diphenyltetrazolium bromide) assay. In addition, the cell cycle and apoptosis was detected using flow cytometry and the TCF/LEF transcriptional activity was measured with a Dual Luciferase Reporter Assay System.

RESULTS

Immunohistochemical staining showed high β-catenin expression in radioresistant NPC specimens, and low expression in radiosensitive NPC specimens and normal nasopharyngeal specimens. Western blotting and qPCR assays detected higher β-catenin expression in the transfection group than in the negative and blank controls (P < 0.01). Down-regulation of GSK-3β expression (P < 0.05) and up-regulation of Cyclin D1 expression (P < 0.01) was detected in β-catenin overexpressing NPC cells exposed to X-ray radiation relative to negative and blank controls. Colony-formation assay revealed higher D0, Dq and SF in the transfection group than in the negative and blank control groups post-radiation, and the SER in the transfection group was 0.75-fold and 0.68-fold greater than that in the blank and negative control groups, respectively. MTT assay revealed that the viability of CNE-2 cells was significantly higher in the transfection group (96% ± 8.72%) than in the negative control group (74.67 ± 7.05%) and the blank control group (75.33% ± 7.02%) 24 h post-exposure to 6 Gy X-ray radiation (P < 0.05). X-ray radiation led to a lower proportion of CNE-2 cells at the G2/M phase and a lower apoptotic rate in the transfection group than in the negative and blank control groups (P < 0.05). In addition, the TCF/LEF transcriptional activity was higher in the transfection group than in the negative and blank control groups (P < 0.01), and 6 Gy X-ray radiation elevated the TCF/LEF transcriptional activity relative to 0 Gy radiation in the transfection group (P < 0.01).

CONCLUSION

β-catenin overexpression may decrease the radiation sensitivity in NPC CNE-2 cells through activating the downstream transcriptional factors of β-catenin, and reducing G2/M arrest and cell apoptosis.