cGAS/STING-mediated upregulation of NKG2D ligands in LSCs contributes to enhanced sensitivity to NK cells

Introduction: Natural killer (NK) cells-mediated immune surveillance is essential role for tumor recognition and elimination. The binding of NK group 2 member D (NKG2D) ligands to NKG2D receptor is sufficient to activate the NK cells' cytotoxicity against targeted cells. Here we reported that the inhibition of poly (ADP-ribose) polymerase 1 (PARP1) in leukemia stem cells (LSCs) induced the expression of NKG2D ligands through the activation of DNA damage response. Methods: Flow cytometry and Quantitative real-time RT-PCR were used to detect the expression levels of NKG2D ligands on cell surface and mRNA levels in leukemia cells, respectively. Cytotoxicity assay was applied to examine the cytotoxic activity of NK cells against leukemia cells. Dual luciferase reporter (DLR) assay was employed to detect the promoter activation of NKG2D ligands. Western blotting was conducted to check the protein expression level. Results: Activated ataxia-telangiectasia mutated proteins (ATM) and ɣH2AX foci accumulation were observed under the treatment of PARP inhibitor, leading to the accumulation of damaged DNA. Subsequently, cyclic GMP-AMP synthase (cGAS) was activated, and stimulator of interferon gene (STING) was recruited to promote the downstream signal transduction via TANK-binding kinase-1 (TBK1) and transcription regulatory factor 3 (IRF3). However, the NKG2D ligands induced by PARP inhibitor was reduced in STING or IRF3-knockdown LSCs, indicating that STING and IRF3 were necessary for the regulation of NGK2D ligands in LSCs upon the DNA damage response. Discussion: These data indicated that the DNA damage response-mediated cGAS/STING/TBK1/IRF3 signalling pathway played an essential role in modulating NKG2D ligands expression in LSCs.