Double-stranded RNAs mediated antiviral signaling induces TGF-β independent epithelial-to-mesenchymal transition

Abstract

Inflammatory response protects our body by removing pathogens, repairing damaged tissues, and restoring homeostasis. However, chronic inflammation can cause tumorigenesis and metastasis. One key class of the upstream cues the inflammatory signaling can be provided by long double-stranded RNAs (dsRNAs) that are recognized by RNA sensors of the innate immune response system, such as PKR, RIG-I, and MDA5. In this context, the activation of innate immune response by dsRNAs results in the production of various cytokines that are known to trigger epithelial-to-mesenchymal transition (EMT), an essential process during metastasis. Existing EMT studies were conducted in cells grown as a 2D monolayer. However, the actual tumor grows in a 3D structure, and tumor cells communicate through the cytokine network in the 3D microenvironment, enhancing tumor growth, immune evasion, and invasive properties. Here, we employ an in-house developed 3D culture method using a polymer-coated surface to study the role of dsRNA-mediated antiviral signaling during EMT. We find that stimulation by synthetic dsRNA analog, polyinosinic-polycytidylic acid (poly (I:C)), to 3D spheroids reduces E-cadherin while inducing the expression of Vimentin, two key features of EMT. Also, we discover that this is caused by the SNAIL transcription factor. Such change is not mediated by the induction of TGF-β by poly (I:C), indicating that dsRNA-mediated EMT is different from the conventional EMT by TGF-β. Notably, the observed poly (I:C)-mediated EMT-like transition does not occur when cells are grown as a 2D monolayer. We further show that infecting cancer cells with a virus also results in the upregulation of various mesenchymal markers. Our study suggests that dsRNA-mediated antiviral signaling can induce TGF-β independent EMT and implies potential adverse effects of virus-mediated cancer therapy.