Methyl 2,2'-di-O-methylstenosporate

SignificanceThe presence of RNA chemical modifications has long been known, but their precise molecular consequences remain unknown. 2'-O-methylation is an abundant modification that exists in RNA in all domains of life. Ribosomal RNA (rRNA) represents a functionally important RNA that is heavily modified by 2'-O-methylations. Although abundant at functionally important regions of the rRNA, the contribution of 2'-O-methylations to ribosome activities is unknown. By establishing a method to disturb rRNA 2'-O-methylation patterns, we show that rRNA 2'-O-methylations affect the function and fidelity of the ribosome and change the balance between different ribosome conformational states. Our work links 2'-O-methylation to ribosome dynamics and defines a set of critical rRNA 2'-O-methylations required for ribosome biogenesis and others that are dispensable.

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.

Autoimmune diseases such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic vasculitis are caused by the body's immune response to autoantigens. The pathogenesis of autoimmune diseases is complex. RNA methylation is known to play a key role in disease progression as it regulates almost all aspects of RNA processing, including RNA nuclear export, translation, splicing, and noncoding RNA processing. This review summarizes the mechanisms, molecular structures of RNA methylations and their roles in biological functions. Similar to the roles of RNA methylation in cancers, RNA methylation in RA and SLE involves "writers" that deposit methyl groups to form N6-methyladenosine (m6A) and 5-methylcytosine (m5C), "erasers" that remove these modifications, and "readers" that further affect mRNA splicing, export, translation, and degradation. Recent advances in detection methods have identified N1-methyladenosine (m1A), N6,2-O-dimethyladenosine (m6Am), and 7-methylguanosine (m7G) RNA modifications, and their roles in RA and SLE need to be further studied. The relationship between RNA methylation and other autoimmune diseases has not been reported, and the roles and mechanisms of RNA modifications in these diseases need to be explored in the future.