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Oncogenic Ras inhibits IRF1 to promote viral oncolysis

ABSTRACT: Oncolytic viruses exploit common molecular changes in cancer cells, which are not present in normal cells, to target and kill cancer cells. Ras transformation and defects in type I interferon (IFN)-mediated antiviral responses are known to be the major mechanisms underlying viral oncolysis. Previously, we demonstrated that oncogenic RAS/Mitogen-activated protein kinase kinase (Ras/MEK) activation suppresses the transcription of many IFN-inducible genes in human cancer cells, suggesting that Ras transformation underlies type I IFN defects in cancer cells. Here, we investigated how Ras/MEK downregulates IFN-induced transcription. By conducting promoter deletion analysis of IFN-inducible genes, namely guanylate-binding protein 2 and IFN gamma inducible protein 47 (Ifi47), we identified the IFN regulatory factor 1 (IRF1) binding site as the promoter region responsible for the regulation of transcription by MEK. MEK inhibition promoted transcription of the IFN-inducible genes in wild type mouse embryonic fibroblasts (MEFs), but not in IRF1−/− MEFs, showing that IRF1 is involved in MEK-mediated downregulation of IFN-inducible genes. Furthermore, IRF1 protein expression was lower in RasV12 cells compared with vector control NIH3T3 cells, but was restored to equivalent levels by inhibition of MEK. Similarly, the restoration of IRF1 expression by MEK inhibition was observed in human cancer cells. IRF1 re-expression in human cancer cells caused cells to become resistant to infection by the oncolytic vesicular stomatitis virus strain. Together, this work demonstrates that Ras/MEK activation in cancer cells downregulates transcription of IFN-inducible genes by targeting IRF1 expression, resulting in increased susceptibility to viral oncolysis.

ORGANISM(S): Mus musculus

PROVIDER: GSE49469 | GEO | 2014/11/13

SECONDARY ACCESSION(S): PRJNA213985

REPOSITORIES: GEO

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Project description:Lytic cell death, such as pyroptosis, can trigger antitumour immune response. However, cancerous cells avoid lytic cell death by various escape mechanisms acquired through evolution. Moreover, persistent uncontrolled lytic cell death may inversely cause hyperactive immune response or T-cell exhaustion. Therefore, an oncolytic system capable of breaking through natural restrictions to dissolve cancer cells in a catalytic and controllable manner is needed. Here, we established a microscale cytotoxic T-cell-inspired oncolytic system (TIOs) by which the NIR light-generated reactive oxygen species could precisely rupture the plasma membrane of cancer cells by direct lipids peroxidation. Similar as cytotoxic T cells, TIOs present antigen-based cell recognition and catalytic cell-lysis ability; thus, the TIOs can trigger significant oncolysis and immune response in vivo. The TIOs exhibited exceptional tumour targeting and penetration without any inflammatory risk. We applied TIOs to antitumour therapies, which showed kinds of tumour models could be cleared efficiently with negligible injuries to major organs. Tumour regression was correlated with oncolysis-mediated inflammation and T-cell-based antitumor immune response. Owing to the tuneability of TIOs-mediated oncolysis, we further revealed that though the T-cell recruitment was comparable, the high-intense oncolysis induced acute inflammation in initial stage was crucial for potent antitumour immunity and immune memory effects, and low-intense oncolysis resulted in T-cell exhaustion and tumour progression. To the mice received low-intense oncolysis, although synergizing with anti-PD-1 therapies or STING activation rescued the immune dysfunction, STING activation released a more powerful boost to durative antitumour immunity by reshaping the stemness of CD8+ T cells. Our study provides new insights to design the oncolytic systems for antitumour immunity. Moreover, our application suggests that the intensity of initial inflammation plays a decisive role in maintaining oncolysis-induced antitumour immune function and STING activation holds promise for reversal of immune dysfunction due to T-cell exhaustion.

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Oncogenic Ras inhibits IRF1 to promote viral oncolysis

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