Down-regulation of PCK2 enhanced the radioresistance phenotype of nasopharyngeal carcinoma.

Purpose: Radiotherapy is the main treatment for non-distant metastatic nasopharyngeal carcinoma (NPC). However, about 15% of NPC patients still experience local tumor recurrence after radiotherapy. The mechanisms underlying the radioresistance of NPC have not been fully understood. This study explored the role of phosphoenolpyruvate carboxykinase2 (PCK2) in NPC radiosensitivity.

Methods: Two NPC cell lines, SUNE-1 and 5-8 F, were enrolled in this research, and their radioresistant counterparts, SUNE-1R and 5-8FR were obtained by long-term exposure to γ-ray (2 Gy*30 times). Cells response to ionizing radiation (IR) was determined by colony formation assay (C.F.A). Immunofluorescence, microsphere formation assay and ferroptosis test were adopted to compare the difference of DNA damage repair, stemness and cell death between sensitive and resistant NPC cells. The biological functions of PCK2 were investigated by knocking down the endogenous PCK2 in vitro and in vivo. In addition, the tumor morphology and related markers were observed by HE staining and immunohistochemistry assay, respectively.

Results: Intracellular PCK2 is transiently upregulated after a single irradiation in both SUNE-1 and 5-8 F cells. However, PCK2 was significantly reduced in radiation-tolerant cells that survived from multiple irradiations. Further work showed that PCK2 down-regulation prevented SUNE-1R and 5-8FR cells from IR-induced ferroptosis, accompanied by increased cell ability of DNA damaged repair and enhanced phenotypes of tumor stem cells.

Conclusions: Our findings indicate that low expression of PCK2 is an important phenotypic feature of radioresistant NPC cells. It could be a result of PCK2 involved in regulating radiation-induced ferroptosis. Regulating the expression of PCK2 may provide new strategies for improving NPC radiation sensitivity.