GlycoRNA-L and glycoRNA-S mediate human monocyte adhesion via binding to Siglec-5

It was recently reported that RNAs can be glycosylated, and such glycosylated RNAs (referred to as glycoRNAs) are located on the outer cell surface. We here reported that there are two forms of glycoRNAs, named as glycoRNA-L and glycoRNA-S, robustly expressed in human monocytes. We verified that the glycoRNA-S specifically detected in human monocytes is synthesized by enzyme-catalyzed conjugation, but not artificial products of labelling probe. RNase-treatment removed both glycoRNA-L and glycoRNA-S, suggesting that they are localized on cell surface. Removing glycoRNAs significantly suppressed the interaction of human monocytes with endothelial cells, suggesting that glycoRNAs mediate human monocyte adhesion. Using flow cytometry, immunoprecipitation and northern blotting we identified Siglec-5 as the binding receptor of glycoRNAs. Siglec-5 is expressed in human endothelial cells but presented on endothelial cell surface when endothelial cells are activated. We observed that glycoRNA-L was heavily labeled with sialic acid, whereas glycoRNA-S was heavily labeled with N-acetylgalactosamine and N-acetylglucosamine. Together, these results demonstrate that two forms of glycoRNAs exist in human monocytes, which may play significant role in controlling the interaction of human monocytes and endothelial cells and contribute to the pathogenesis of inflammatory diseases.