A ribosomal RNA fragment with 2',3'-cyclic phosphate and GTP-binding activity acts as RIG-I ligand.

The RNA helicase RIG-I plays a key role in sensing pathogen-derived RNA. Double-stranded RNA structures bearing 5'-tri- or diphosphates are commonly referred to as activating RIG-I ligands. However, endogenous RNA fragments generated during viral infection via RNase L also activate RIG-I. Of note, RNase-digested RNA fragments bear a 5'-hydroxyl group and a 2',3'-cyclic phosphate. How endogenous RNA fragments activate RIG-I despite the lack of 5'-phosphorylation has not been elucidated. Here we describe an endogenous RIG-I ligand (eRL) that is derived from the internal transcribed spacer 2 region (ITS2) of the 45S ribosomal RNA after partial RNase A digestion in vitro, RNase A protein transfection or RNase L activation. The immunostimulatory property of the eRL is dependent on 2',3'-cyclic phosphate and its sequence is characterized by a G-quadruplex containing sequence motif mediating guanosine-5'-triphosphate (GTP) binding. In summary, RNase generated self-RNA fragments with 2',3'-cyclic phosphate function as nucleotide-5'-triphosphate binding aptamers activating RIG-I.

Identification of an Optimal TLR8 Ligand by Alternating the Position of 2'-O-Ribose Methylation.

Recognition of RNA by receptors of the innate immune system is regulated by various posttranslational modifications. Different single 2'-O-ribose (2'-O-) methylations have been shown to convert TLR7/TLR8 ligands into specific TLR8 ligands, so we investigated whether the position of 2'-O-methylation is crucial for its function. To this end, we designed different 2'-O-methylated RNA oligoribonucleotides (ORN), investigating their immune activity in various cell systems and analyzing degradation under RNase T2 treatment. We found that the 18S rRNA-derived TLR7/8 ligand, RNA63, was differentially digested as a result of 2'-O-methylation, leading to variations in TLR8 and TLR7 inhibition. The suitability of certain 2'-O-methylated RNA63 derivatives as TLR8 agonists was further demonstrated by the fact that other RNA sequences were only weak TLR8 agonists. We were thus able to identify specific 2'-O-methylated RNA derivatives as optimal TLR8 ligands.

Dissecting the role of toll-like receptor 7 in pancreatic cancer.

BACKGROUND: Toll-like receptors (TLRs) are gaining attention for their potential to influence tumor biology both on the level of the tumor cells as well as on the level of the surrounding inflammatory stroma. Previous studies resulted in partly conflicting data on the expression of TLR7 in healthy and neoplastic pancreatic tissues as well as its role in pancreatic tumor biology. METHODS: We used qRT-PCR and immunohistochemistry to asses TLR7 expression in primary patient material and cell lines. Cell viability was analyzed by MTT assay upon incubation with TLR7 agonist/antagonist. Mouse models were used to investigate the role of TLR7 in vivo. RESULTS: TLR7 is overexpressed in more than 50% of primary human pancreatic ductal adenocarcinoma (PDAC). High TLR7 expression was associated with shorter patient survival, and TLR7 inhibition in cell lines reduced viability in a dose-dependent manner. In contrast, global TLR7 deficiency did not alter survival or overall histopathological tumor features in genetic mouse models of PDAC. CONCLUSIONS: TLR7 may have opposing functions in tumor versus stroma cells. Further work is required to more precisely dissect the roles of TLR7 and its ligands in different populations of epithelial and stromal cells and to understand their relative contributions to tumor progression.

Extracellular Ribosomal RNA Acts Synergistically with Toll-like Receptor 2 Agonists to Promote Inflammation.

Self-extracellular RNA (eRNA), which is released under pathological conditions from damaged tissue, has recently been identified as a new alarmin and synergistic agent together with toll-like receptor (TLR)2 ligands to induce proinflammatory activities of immune cells. In this study, a detailed investigation of these interactions is reported. The macrophage cell line J774 A.1 or C57 BL/6 J wild-type mice were treated with 18S rRNA and different TLR2 agonists. Gene and protein expression of tumor necrosis factor (Tnf)-α; interleukin (Il)-1ß, Il-6; or monocyte chemoattractant protein (Mcp)-1 were analyzed and furthermore in vitro binding studies to TLR2 were performed. The TLR2/TLR6-agonist Pam2 CSK4 (Pam2) together with 18S rRNA significantly increased the mRNA expression of inflammatory genes and the release of TNF-α from macrophages in a TLR2- and nuclear factor kappa B (NF-κB)-dependent manner. The injection of 18S rRNA/Pam2 into mice increased the cytokine levels of TNF-α, IL-6, and MCP-1 in the peritoneal lavage. Mechanistically, 18S rRNA built complexes with Pam2 and thus enhanced the affinity of Pam2 to TLR2. These results indicate that the alarmin eRNA, mainly consisting of rRNA, sensitizes TLR2 to enhance the innate immune response under pathological conditions. Thus, rRNA might serve as a new target for the treatments of bacterial and viral infections.

Effect of naturally occurring α-synuclein-antibodies on toxic α-synuclein-fragments.

Alpha-synuclein (α-Syn) is a soluble protein primarily expressed in presynaptic terminals in the central nervous system (CNS). Aggregates of fibrillated α-Syn are the major component of Lewy bodies (LB), a pathologic hallmark of idiopathic Parkinson's disease (PD). Recently, naturally occurring autoantibodies against human α-Syn (nAbs α-Syn) were detected in the peripheral blood of PD patients and controls. Here, we investigated the inhibitory effects of nAbs α-Syn on distinct α-Syn fragments, as well as inflammatory responses and cytotoxicity evoked by nAbs α-Syn in primary microglia. All α-Syn fragments induced the release of the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) from microglia in primary culture. Cotreatment with nAbs α-Syn alleviated the release of pro-inflammatory cytokines induced by α-Syn fragments α-Syn 1-95, α-Syn 61-140, α-Syn 96-140 and α-Syn 112. Treatment with the α-Syn fragments α-Syn 1-95, α-Syn 61-140 and α-Syn 112 impaired the viability of primary microglia. This effect could not be counteracted by cotreatment with nAbs α-Syn. Data suggest an important role of nAbs α-Syn in the α-Syn-induced inflammation cascade, and indicate the potential importance of nAbs in the pathogenesis of PD. This could provide an experimental therapeutic target for patients with PD.