RESUMO
Over 100 different RNA modifications exist that are introduced posttranscriptionally by enzymes at specific nucleotide positions. Ribosomal RNA (rRNA) and transfer RNA (tRNA) exhibit the most and diverse modifications that presumably optimize their structure and function. In contrast, oxidative damage can lead to random modifications in rRNA and messenger RNA (mRNA) that strongly impair functionality. RNA modifications have also been implicated in avoiding self-RNA recognition by the immune system or immune evasion by pathogens. Here, we describe the detection of RNA modifications by HPLC analysis and competitive ELISA.
Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Ensaio de Imunoadsorção Enzimática/métodos , RNA Mensageiro/química , RNA Mensageiro/metabolismo , RNA Ribossômico/química , RNA Ribossômico/metabolismo , RNA de Transferência/química , RNA de Transferência/metabolismoRESUMO
Host protection from infection relies on the recognition of pathogens by innate pattern-recognition receptors such as Toll-like receptors (TLRs). Here, we show that the orphan receptor TLR13 in mice recognizes a conserved 23S ribosomal RNA (rRNA) sequence that is the binding site of macrolide, lincosamide, and streptogramin group (MLS) antibiotics (including erythromycin) in bacteria. Notably, 23S rRNA from clinical isolates of erythromycin-resistant Staphylococcus aureus and synthetic oligoribonucleotides carrying methylated adenosine or a guanosine mimicking a MLS resistance-causing modification failed to stimulate TLR13. Thus, our results reveal both a natural TLR13 ligand and specific mechanisms of antibiotic resistance as potent bacterial immune evasion strategy, avoiding recognition via TLR13.
Assuntos
Farmacorresistência Bacteriana Múltipla/imunologia , Eritromicina/farmacologia , RNA Ribossômico 23S/imunologia , Infecções Estafilocócicas/imunologia , Staphylococcus aureus/imunologia , Receptores Toll-Like/imunologia , Adenosina/metabolismo , Animais , Guanosina/metabolismo , Lincosamidas/farmacologia , Macrolídeos/farmacologia , Metilação , Camundongos , Staphylococcus aureus/efeitos dos fármacos , Estreptograminas/farmacologiaRESUMO
Foreign RNA serves as pathogen-associated molecular pattern (PAMP) and is a potent immune stimulator for innate immune receptors. However, the role of single bacterial RNA species in immune activation has not been characterized in detail. We analyzed the immunostimulatory potential of transfer RNA (tRNA) from different bacteria. Interestingly, bacterial tRNA induced type I interferon (IFN) and inflammatory cytokines in mouse dendritic cells (DCs) and human peripheral blood mononuclear cells (PBMCs). Cytokine production was TLR7 dependent because TLR7-deficient mouse DCs did not respond and TLR7 inhibitory oligonucleotides inhibited tRNA-mediated activation. However, not all bacterial tRNA induced IFN-α because tRNA from Escherichia coli Nissle 1917 and Thermus thermophilus were non-immunostimulatory. Of note, tRNA from an E. coli knockout strain for tRNA (Gm18)-2'-O-methyltransferase (trmH) regained immunostimulatory potential. Additionally, in vitro methylation of this immunostimulatory Gm18-negative tRNA with recombinant trmH from T. thermophilus abolished its IFN-α inducing potential. More importantly, Gm18-modified tRNA acted as TLR7 antagonist and blocked IFN-α induction of influenza A virus-infected PBMCs.