PFAS promotes colorectal cancer progression via regulating RIG-I-mediated innate immune signalling

Phosphoribosylformylglycinamidine synthase (PFAS) is a critical enzyme in de novo synthesis of purine. Innate immunity recognizes tumor derived damage-associated molecular patterns (DAMPs) and initiates the anti-tumor adaptive responses. While the function of PFAS catalyzed de novo synthesis of purine is well proved, its effect on innate immune evasion in cancer is unclear and needs to be further explored. The purpose of this study was to investigate the specific mechanisms by which PFAS inhibits RIG-I receptor (RLR) -mediated NF-κB axis in CRC.

quantitative real-time PCR (qRT-PCR), Immunohistochemical (IHC) staining and western blotting were conducted to study the expression of PFAS in CRC tissues. Survival analysis, COX regression analysis and receiver operating characteristic (ROC) curve analysis were respectively conducted to assess correlation between the PFAS expression and clinicopathological characteristics, investigate the percent survival based on PFAS level in different clinical CRC groups, identify factors influencing the prognosis of CRC, and illustrate the diagnostic ability of PFAS in CRC patients. Furthermore, the CCK8 and transwell assays were carried out to study CRC cell function affected by PFAS. Mechanistically, plaque assay was used to assess the regulation of PFAS on innate immune signalling. The inhibition of PFAS on RIG-I-mediated innate immune signalling was further investigated by qRT-PCR and reporter assays in thepresence of lentiviral-mediated PFAS stably knocking down and stably overexpressing. Lastly, the interaction between PFAS and RIG-I was verified by co-immunoprecipitation assay.

The expression of PFAS in CRC tissue was higher than in adjacent normal colorectal tissue. The level of PFAS expression was significantly associated with stage-AJCC, regional lymph nodes metastasis and recurrence in CRC. Low expression of gene PFAS caused better survival than high expression in CRC patients. PFAS could be considered as an independent prognostic risk factor of CRC. PFAS promote cell proliferation and invasion of CRC cell lines. According to ROC curve analysis, PFAS could be used as a diagnostic biomarker in CRC. Mechanistically, PFAS inhibit interferon-β (IFN-β) gene and interferon-stimulated gene 56 (ISG56) expression. Furthermore, we confirmed that PFAS target RIG-I to inhibit RIG-I-mediated innate immune signalling.