Abstract 3074: CD95/Fas increases type I interferon expression through NF-κB activation

Abstract

Abstract CD95/Fas, an apoptosis-inducing death receptor, has also been shown to be required for the proliferation and survival of cancer cells. Chronic stimulation through CD95 enhanced formation of cancer stem cell enriched spheres and it increased expression of cancer stem cell markers and a set of genes consistent with a Type I Interferon (IFN) signature. We reported that CD95 stimulation induces upregulation of Type I IFNs that bind to both Type I receptors IFNAR1 and IFNAR2, resulting in activation of JAK kinases, activation of STAT1, and induction of a number of STAT1-regulated genes. However, the mechanism through which CD95 induces Type I IFNs and STAT1 activation is unknown. In this study we have investigated the mechanism of CD95 stimulation of Type I IFN production in the context of breast cancer. We show that knockout of CD95, FADD or Caspase-8 in MCF7 cells using the CRIPSR/Cas9 gene editing system resulted in a loss of the ability of CD95 to increase IFNα, IFNβ, STAT1, STAT2 expression and the phosphorylation of STAT1 and STAT3. The caspase-8 selective inhibitor zIETD-fmk blocked phosphorylation of STAT1 and STAT3 and blocked Type I IFN expression following CD95 stimulation. This identifies caspase-8 as a critical mediator of the Type I IFN-inducing activity of CD95. On other hand, we also showed that CD95 stimulation induced an antiviral program through RIG-I signaling, which is known to induce NF-κB and IFN signaling. RIG-1, MDA5, IRF7 expression and phosphorylation of IRF3 were increased with prolonged CD95 stimulation. Knocking down IRF3 using a siIRF3 smart pool partially reduced the phosphorylation of STAT1 and STAT3 in response to CD95 stimulation. Finally, we show that NF-κB activation is a key regulator of CD95-mediated Type I IFN expression. A NF-κB inhibitor completely blocked STAT1, STAT2 expression and phosphorylation of STAT1 and STAT3 following CD95 stimulation. Knocking out CD95, FADD or Caspase-8 or knocking down IRF3 also reduced NF-κB activation in response to CD95 stimulation. We conclude that CD95 stimulation induces Type I IFN expression through activation of caspase-8 and NF-κB and identify RIG-1 as a possible mediator of NF-κB activation during CD95 stimulation. Citation Format: Abdul Qadir Syed, Marcus Peter. CD95/Fas increases type I interferon expression through NF-κB activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3074.