TLR9-ERK-mTOR signaling is critical for autophagic cell death induced by CpG oligodeoxynucleotide 107 combined with irradiation in glioma cells

Abstract

Synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN) function as potential radiosensitizers for glioma treatment, although the underlying mechanism is unclear. It was observed that CpG ODN107, when combined with irradiation, did not induce apoptosis. Herein, the effect of CpG ODN107 + irradiation on autophagy and the related signaling pathways was investigated. In vitro, CpG ODN107 + irradiation induced autophagosome formation, increased the ratio of LC3 II/LC3 I, beclin 1 and decreased p62 expression in U87 cells. Meanwhile, CpG ODN107 also increased LC3 II/LC3 I expression in U251 and CHG-5 cells. In vivo, CpG ODN107 combined with local radiotherapy induced autophagosome formation in orthotopic transplantation tumor. Investigation of the molecular mechanisms demonstrated that CpG ODN107 + irradiation increased the levels of TLR9 and p-ERK, and decreased the level of p-mTOR in glioma cells. Further, TLR9-specific siRNA could affect the expressions of p-ERK and autophagy-related proteins in glioma cells. Taken together, CpG ODN107 combined with irradiation could induce autophagic cell death, and this effect was closely related to the TLR9-ERK-mTOR signaling pathway in glioma cells, providing new insights into the investigation mechanism of CpG ODN.

Involvement of P2X7 Receptor in Proliferation and Migration of Human Glioma Cells

“…MEK/ERK pathway is a common intracellular signaling pathway related to glioma cell proliferation [ 24 ]. Our study also demonstrated the role of MEK/ERK pathway in the proliferation and migration of glioma cells induced by P2X 7 R activation.…”

“…In tumor cells, members of the MEK/ERK pathway encoding genes are often mutated and become overactivated, which causes this pathway to be important for the development of many human tumors such as breast cancer, thyroid carcinoma, and squamous cell carcinoma [ 46 , 47 ]. The MEK/ERK pathway also plays a critical role in the development of gliomas [ 24 , 48 , 49 ]. The MEK/ERK pathway is involved in purinergic receptor, such as P2X 7 R, mediated excitotoxic neuronal injury, and neuroprotection [ 50 ].…”

Stimulating Innate Immunity to Enhance Radiation Therapy–Induced Tumor Control

“…The local synergy of radiotherapy and CpG was independently verified by a second group in a glioma model 97 . Although the exact mechanism of CpG-mediated radiosensitization is not known, studies have suggested that CpG increases both mTOR activation and autophagy 102 , decreases expression of Oct-4- mediated renewal 103 , and increases NF-kB signaling and nitric oxide production 94 .…”

Crosstalk between autophagy and intracellular radiation response (Review)

“…When the stress is mild, autophagy can degrade and recycle damaged or unwanted cellular constituents in autophagolysosomal vesicles to provide additional energy supply during stress, which has an essential effect in quality control of organelles and cellular adaptation to stress (13). However, several reports demonstrate that various drugs in combination with radiation promote autophagic cell death rather than apoptosis significantly contributing to the antitumor effects of radiosensitizing treatment or radiotherapy in glioma (14). Hence, autophagy induced by radiation also functions as a pro-death mechanism.…”