STING-Dependent Interferon-λ1 Induction in HT29 Cells, a Human Colorectal Cancer Cell Line, After Gamma-Radiation

Purpose: To investigate the induction of type III interferons (IFNs) in human cancer cells by gamma-rays. Methods and Materials: Type III IFN expression in human cancer cell lines after gamma-ray irradiation in vitro was assessed by reverse transcriptionequantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Signaling pathways mediating type III IFN induction were examined by a variety of means, including immunoblotting, flow cytometry, confocal imaging, and reverse transcriptione quantitative polymerase chain reaction. Key mediators in these pathways were further explored and validated using gene CRISPR knockout or short hairpin RNA knockdown. Results: Exposure to gamma-rays directly induced type III IFNs (mainly IFNL1) in human cancer cell lines in dose-and time-dependent fashions. The induction of IFNL1 was primarily mediated by the cytosolic DNA sensorse-STING-TBK1-IRF1 signaling axis, with a lesser contribution from the nuclear factor kappa b signaling in HT29 cells. In addition, type III IFN signaling through its receptors serves as a positive feedback loop, further enhancing IFN expression via up-regulation of the kinases in the STINGeTBK1 signaling axis. Conclusions: Our results suggest that IFNL1 can be up-regulated in human cancer cell lines after gamma-ray treatment. In HT29 cells this induction occurs via the STING pathway, adding another layer of complexity to the understanding of radiation-induced antitumor immunity, and may provide novel insights into IFN-based cancer treatment. (C) 2018 Elsevier Inc. All rights reserved.