RNA Polymerase III Detects Cytosolic DNA and Induces Type I Interferons through the RIG-I Pathway

Abstract

Summary Type-I interferons (IFNs) are important for antiviral and autoimmune responses. Retinoic acid-induced gene I (RIG-I) and mitochondrial antiviral signaling (MAVS) proteins mediate IFN production in response to cytosolic double-stranded RNA or single-stranded RNA containing 5′-triphosphate (5′-ppp). Cytosolic B-form double-stranded DNA, such as poly(dA-dT)·poly(dA-dT) [poly(dA-dT)], can also induce IFN-β, but the underlying mechanism is unknown. Here we show that the cytosolic poly(dA-dT) DNA is converted into 5′-ppp RNA to induce IFN-β through the RIG-I pathway. Biochemical purification led to the identification of DNA-dependent RNA polymerase III (Pol-III) as the enzyme responsible for synthesizing 5′-ppp RNA from the poly(dA-dT) template. Inhibition of RNA Pol-III prevents IFN-β induction by transfection of DNA or infection with DNA viruses. Furthermore, Pol-III inhibition abrogates IFN-β induction by the intracellular bacterium Legionella pneumophila and promotes the bacterial growth. These results suggest that RNA Pol-III is a cytosolic DNA sensor involved in innate immune responses.

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

“…This is based on studies using BMD macrophages from knockout mice and knockdown of RLR pathway adaptors in human epithelial cells (46)(47)(48)(49)(50)(51)(52). In order to judge the influence of RLR signaling on L. pneumophila infection of human macrophages as well as T2S-mediated dampening of innate immunity, we examined infected U937 cells that were knocked down for receptors and adaptors in the RLR pathway.…”

Type-I-interferons in infection and cancer: Unanticipated dynamics with therapeutic implications

“…28 RNA polymerase-III (POLR3), the second cytosolic DNA sensor discovered, was reported to use ATrich and herpesvirus DNA as a template to produce 5 0 -triphosphate RNAs, which then induce Type-I-IFNs by activating RIG-I. 29 However, POLR3 could not account for DAIindependent sensing of non-AT-rich DNA suggesting the existence of additional cytosolic DNA sensors. Remarkably, an adaptor molecule referred to as stimulator of IFN genes (STING) was identified as being crucial for recognizing cytoplasmic DNA and inducing innate immune responses to a variety of DNA pathogens even including certain RNA viruses.…”

TBK1-associated Protein in Endolysosomes (TAPE) Is an Innate Immune Regulator Modulating the TLR3 and TLR4 Signaling Pathways

“…Four major families of PRRs have been identified as follows: Toll-like receptors (TLRs), RIG-Ilike receptors, NOD-like receptors, and C-type lectin receptors (1). Recently, several cytosolic nucleic acid sensors have also been found, including DAI (2), AIM-2 (3-6), RNA polymerase III (7,8), and LRRFIP1 (9). PRRs are located in discrete subcellular compartments, like the cell surface, endolysosome, and cytoplasm, to detect invading pathogens by different routes.…”