Stimulator of Interferon Genes Signal in Lung Cancer Regulates Differentiation of Myeloid-Derived Suppressor Cells in the Tumor Microenvironment Via the Interferon Regulatory Factor 3/NF-κB Pathway

<b><i>Background:</i></b> This study was designed to explore the action mechanism of stimulator of interferon genes (STING) on the differentiation of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment of lung cancer. <b><i>Methods:</i></b> Bioinformatics analysis yielded a potential pathway for STING to regulate MDSC differentiation, the interferon regulatory factor 3 (IRF3)/NF-κB axis. The transfection efficiency of STING overexpression plasmid and small interfering RNA against IRF3 (siIRF3) was examined by quantitative real-time polymerase chain reaction (qRT-PCR). After transfection, A9 cells were co-cultured with extracted bone marrow cells (BMCs). MDSC differentiation, protein expression of the IRF3/NF-κB pathway, and changes in nuclear translocation of NF-κB were analyzed by flow cytometry, Western blot, and immunofluorescence staining experiments. A transplanted tumor mouse model was used for <i>in vivo</i> experiments. After cyclic diadenyl monophosphate (CDA; STING agonist) treatment, changes in MDSC differentiation and protein expression of the IRF3/NF-κB axis in transplanted tumors were verified by immunohistochemical staining, qRT-PCR, and Western blot. <b><i>Results:</i></b> Coculture of A9 cells and BMCs promoted MDSC differentiation, inhibited activation of IRF3/NF-κB signal in A9 cells, and boosted nuclear translocation of NF-κB. However, after the upregulation of STING, IRF3/NF-κB signal was activated, while MDSC differentiation and nuclear translocation of NF-κB were inhibited. SiIRF3 reversed the effects of STING overexpression. <i>In vivo</i>, CDA dampened MDSC differentiation and promoted protein expression of the IRF3/NF-κB axis. <b><i>Conclusion:</i></b> STING signal in lung cancer cells inhibits MDSC differentiation through activation of the IRF3/NF-κB pathway.