Altered RNA 2'-O-Ribose methylation pattern increases receptor specificity
Toll like receptors (TLRs) are an integral part of our innate immune defense, as they recognize various pathogen associated molecular patterns (PAMPS). The TLR family members 7 and 8 are capable of detecting RNA molecules, actually in order to alert for viral infections. But both receptors may also be stimulated by artificial RNA molecules. A commonly known agonist of TLR7 and TLR8 is the 18s-rRNA derived oligonucleotide RNA63. It has been shown, that the receptor specificity of RNA63 is strongly dependent on the RNA 2'-O-Ribose methylation pattern. Methylation of the first Guanosine restricts the RNA’s activation potential to TLR8. Researchers of the Cluster of Excellence ImmunoSensation2 at the University Hospital Bonn now provide a detailed insight into the effect of the RNA63 2'-O-Ribose methylation pattern on receptor specificity. The study has recently been published in the International Journal of Molecular Sciences.
The ability to specifically target and activate receptors is essential for their analysis. Consequently, there is a constant effort to develop new, better agonists for laboratory use.
“It was already known, that RNA63 activates both TLR7 and TLR8, and that after a 2'-O-ribose methylation at the second guanine only TLR8 and no longer TLR7 is activated” Prof. Stephanie Jung describes the starting point of her project. “Until now, however, it was not known to what extent the position of this methylation plays a role, and whether a different, better TLR8 ligand can be generated by changing the position”.
RNA degradation products activate TLRs
Recent studies have shown, that the endosomal ribonuclease (RNase) T2 and RNase 2 play a crucial role in TLR8 activation. Short single stranded RNAs (ssRNAs), generated as RNA degradation products, bind and activate TLR8. RNA-degradation by RNases is impaired by posttranscriptional modifications such as methylations. In the case of RNA63, 2′-O-ribose methylation can shift the preferred RNA cleavage site, generating RNA degradation products with widely differing effects on TLR7 and TLR8 activity. “The aim of this study was to investigate, whether the known TLR8 ligand could be further optimized by alternating the position of the 2′-O-ribose methylation.” states PhD student Julia Steinberg. “Therefore, we methylated RNA63 at each of the first four guanosines, respectively.” The immune activity of the different oligonucleotides was tested in various cell systems. RNA63 methylated at the third guanosine turned out to provide the best TLR8 ligand.
The importance of RNA as a therapeutic agent has greatly increased in recent years. “The new insight may hence turn out usefull in the development of clinical TLR8 activators” Jung adds.
Success of junior scientists
The current article is one in a row of publications the team of Prof. Stephanie Jung has released in the last two years. Holding a junior professorship, Jung heads a small team of two PhD students and one technical assistant. The promotion of young scientists is a particular concern for her. Only one year into her PhD, it was already the second publication for Julia Steinberg. "I'm slowly feeling my way towards taking on more responsibility in the review process. For me, it was the first time that I also co-wrote the Response to the Reviewers, for example" .
"I'm very happy with the publication process because once again the collaboration went great, was very pleasant and productive" Jung closes.
Marina Nicolai, Julia Steinberg, Hannah-Lena Obermann, Francisco Venegas Solis, Eva Bartok, Stefan Bauer and Stephanie Jung: Identification of an optimal TLR8 ligand by alternating the position of 2'-O-ribose methylation, International Journal of Molecular Sciences, DOI: 10.3390/ijms231911139
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