Previous studies have shown that interferon gene-stimulating protein (STING) is essential for IFN-γ-inducible protein 16 (IFI16) as the DNA sensor and RNA sensor to induce transcription of type I interferon (IFN-I) and is essential for IFI16 to synergize with DNA sensor GMP-AMP (cGAMP) synthase (cGAS) in induction of IFN-I transcription. While other and our previous studies have shown that IFI16 enhanced retinoic acid-inducible gene I (RIG-I)-, which was an RNA sensor, and mitochondrial antiviral signaling (MAVS)-, which was the adaptor protein of RIG-I, induced production of IFN-I, so we wonder whether IFI16 regulates the signal pathway of RNA-RIG-I-MAVS-IFN-I in a STING-dependent manner. We used HEK 293T cells, which did not express endogenous STING and were unable to mount an innate immune response upon DNA transfection and found that IFI16 could enhance RIG-I- and MAVS-mediated induction of IFN-I in a STING-independent way. Furthermore, we found that upregulation of the expression of NF-kappa-B essential modulator (NEMO) by IFI16 was not the mechanism that IFI16 regulated the induction of IFN-I. In conclusion, we found that IFI16 regulated the signal pathway of RNA-RIG-I-MAVS-IFN-I in a STING-independent manner.

Cervical cancer remains one of the leading causes of cancer death worldwide. Immunotherapy is the most promising cancer therapeutics in recent years and has gain positive results in several cancers in the clinic. This study was aimed to investigate the roles and mechanism of IFI16 in cervical cancer immunotherapy. We observed an abnormally high expression of Programmed cell death 1 ligand 1 (PD-L1) and Interferon-inducible 16 (IFI16) in Human papillomavirus (HPV) positive cervical cancer cells compared with HPV negative cervical cancer cells. Moreover, IFI16 promotes cervical cancer development in vitro and in vivo as the oncogenic role of PD-L1. In the subsequent mechanism investigation, we found that IFI16 activated STING-TBK1-mediated immunoregulation, and subsequently activated downstream NF-kB pathway, which interacted with the proximal region of PD-L1 promoter to facilitate PD-L1 expression. In conclusion, we found that IFI16 positively regulate PD-L1 through STING-TBK1-NF-kB pathway, thus promoting cervical cancer progression. The roles of IFI16 in cervical cancer progression deserve further investigation and hold the promise of being developed as a novel immunotherapy target in the future.