Glutamine synthetase facilitates cancer cells to recover from irradiation-induced G2/M arrest

Abstract

Resistance to radiation of cancer cells can be either intrinsic or acquired, leading to treatment failure. In response to DNA damage caused by IR, cancer cells are arrested in cell cycle showing limited proliferation and increased apoptosis. However, radiation-resistant cells are able to overcome the cell cycle block and proceed to proliferation, for which the detailed mechanism remains to be elucidated. In the present study, we showed that radioresistant cells exhibited a recoverable G2/M phase during prolonged cell cycle and manifested lower apoptosis rate and more colony formation. RNA-seq analysis revealed that glutamine synthetase (GS, GLUL) gene was highly expressed in radioresistant cancer cells in comparison with the parental cells, which was in accordance with the G2/M arrest after ionizing radiation. Knocking out of GS in radioresistant cells resulted in a delayed G2/M recovery and lowered proliferation rate after ionizing radiation treatment, which was accompanied with increased inhibitory phosphorylation of CDK1 at Y15 and downregulated Cdc25B, a dual specific phosphatase of CDK1. Moreover, there was an enhanced complex formation of CDK1 and Cyclin B1 when the cells were rescued by re-introducing GS. In vivo, knocking down of GS significantly sensitized CNE2-R xenografts to RT in mice. In this study, we demonstrate a novel role of glutamine synthetase independent of metabolic function in promoting recovery from G2/M arrest caused by ionizing radiation, thus, causing cancer cell resistance to radiotherapy.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

“…G2/M arrest prevents cells from entering the M (mitosis) phase in the presence of DSBs 224 . G2/M arrest often occurs at 0.5 to 4 h post exposure to IR in mammalian cells and then resolves 228 . The higher the IR dose, the more obvious the G2/M arrest, and the more delayed the recovery effect; sometimes recovery is impossible, and cell death occurs as a result of mechanisms such as mitotic catastrophe.…”

“…A study conducted by Wang et al 233 showed that IR increased colorectal cancer cell sensitivity to the melatonin by triggering G2/M arrest as well as downregulating the expression of ATM, a key mediator in DSB repair. Peng et al 228 showed that in response to IR, radioresistant cells exhibited a recoverable G2/M phase during a prolonged cell cycle. These data validate the potential of targeting G2/M-related proteins involved in the response to IR to control RR in cancer patients.…”

Metabolic pathways underlying GATA6 regulating Trastuzumab resistance in Gastric Cancer cells based on untargeted metabolomics

“…GLUL, which catalyzes the ATP-dependent conversion of glutamate and ammonia to glutamine, was dramatically downregulated upon GATA6 knockout in our study. A study reported that high expression of GLUL affects cellular response to irradiation in radiation-resistant cells and facilitates growth of cancer cells 40 . Thus, it might suggest that nucleotide metabolism mediated by GATA6 also contributes to trastuzumab resistance in gastric cancer cells.…”

Glutamine Synthetase as a Therapeutic Target for Cancer Treatment

“…The relationship between GS and radiation resistance has been reported in nasopharyngeal carcinoma (NPC) [ 55 , 56 ]. Radiation is a cancer treatment method that involves irradiating ionizing radiation to cancer tissue and causing DNA damage.…”

“…These results demonstrate that GS knockdown reverses cell metabolism from radiation-induced nucleotide synthesis to increased glycolysis. In addition, GS promotes radiation-induced G2/M arrest recovery, and genetic ablation of GS re-sensitizes radiation-resistant NPC cells to radiation therapy in vivo [ 56 ]. These findings indicate that GS connects glutamine metabolism with radiotherapy response through modulation of nucleotide synthesis and DNA repair…”