Radioresistance in a human laryngeal squamous cell carcinoma cell line is associated with DNA methylation changes and topoisomerase II α

Abstract

Accumulating evidence suggests that changes in methylation patterns may help mediate the sensitivity or resistance of cancer cells to ionizing radiation. The present study provides evidence for the involvement of radioresistance-induced DNA methylation changes in tumor radioresistance. We established radioresistant laryngeal cancer cells via long-term fractionated irradiation, and examined differences in DNA methylation between control and radioresistant laryngeal cancer cells. Interestingly, we found that the promoter-CpG islands of 5 previously identified radioresistance-related genes (TOPO2A, PLXDC2, ETNK2, GFI1, and IL12B) were significantly altered in the radioresistant laryngeal cancer cells. Furthermore, the demethylation of these gene promoters with a DNA methyltransferase inhibitor (5-aza-2'-deoxycytidine) increased their transcription levels. Treatment with 5-aza-2'-deoxycytidine also sensitized the radioresistant laryngeal cancer cells to irradiation, indicating that changes in DNA methylation contributed to their radioresistance. Of the tested genes, the expression and activity levels of TOPO2A were tightly associated with the radioresistant phenotype in our system, suggesting that the hypermethylation of TOPO2A might be involved in this radioresistance. Collectively, our data suggest that radiation-induced epigenetic changes can modulate the radioresistance of laryngeal cancer cells, and thus may prove useful as prognostic indicators for radiotherapy.

Keywords:

• Human laryngeal squamous cell carcinoma
• Methylation
• Pyrosequencing
• Radioresistance
• TOPO2A

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Funding

This work was supported by Basic Science research Program (Grant no. 2014R1A1A2053524) and the Nuclear Research and Development Program through a National Research Foundation of Korea (NRF; 2012M2B2B1055642 and 2012M2A2A7012494) grant funded by the Korean government.