Cell Surface glycoRNA: A New Role That Subverts Traditional Biology
In the cognition of traditional biology, RNA is an "information molecule" that mainly exists in the cell nucleus and cytoplasm, and undertakes gene expression regulation, catalytic function or as a carrier of genetic information. The cell surface is generally considered to be the world of membrane proteins and glycolipids. However, a series of breakthrough discoveries in RNA research in recent years have completely overturned this classic cognition.
The earliest evidence that RNA may exist on the Cell Surface can be traced back to 1990, when scientists detected nucleolar protein nucleolin (NCL) - a classic RNA binding protein (RBP) on the surface of some specific cell types. However, this discovery did not attract much attention and was even considered to be an accidental contamination of sample preparation. It was not until 2021 that Ryan A. Flynn's team at the Stanford University published a landmark study that clearly proposed the concept of glycoRNA for the first time and provided conclusive evidence that RNA can be stably present on the surface of living cells after being modified with glycans.
This study caused a great shock in the academic community at the time. For a long time, people only knew that proteins and lipids could be glycosylated, while RNA, due to its structural characteristics and the chemical properties of nucleotides, was long considered impossible to be directly glycosylated. However, through biochemical analysis, fluorescent labeling and Mass Spectrometry, Ryan A. Flynn's team confirmed that a special modification - 3-(3-amino-3-carboxypropyl)uridine (acp3U) can be used as an attachment site for N-glycans to form glycoRNA. This discovery instantly pushed RNA modification research to a new dimension, and also turned RNA from a simple carrier of genetic information into a possible participant in cell surface signal regulation.
Fig. 1 The modified RNA base acp3U is an attachment site for N-glycans in glycoRNA. (Xie, et al., 2024)
This newly published paper in Cell went a step further on the basis of glycoRNA research and revealed for the first time a new cell surface nanostructure - glycoRNA-csRBP clusters. This discovery not only deepened our understanding of cell surface RNA, but also demonstrated the key role of RNA in regulating the entry of cell-penetrating peptides (CPP) into cells, further consolidating the status of RNA as a functional molecule on the cell surface.
Looking back at the history of RNA research, we can see that breakthroughs in this emerging field have gone through several key stages:
This development process not only witnessed the change of RNA research paradigm, but also foreshadowed the great potential of RNA in future biomedicine.
One of the most important findings of this latest study is that glycoRNA-csRBP nanoclusters on the cell surface can actually affect the entry of CPPs. CPPs are a class of short peptide molecules that can assist macromolecules such as proteins, RNA, and DNA to cross the cell membrane and enter the cell, and are widely used in Drug Delivery Systems. The TAT protein of the HIV-1 virus is one of the earliest discovered CPPs. It can directly bind to HIV-1 TAR RNA to promote the transcription of the viral genome.
Fig. 2 RNA-binding proteins and glycoRNAs form domains on the cell surface for cell-penetrating peptide entry. (Perr, et al., 2024)
This study revealed that TAT and other positively charged penetrating peptides not only enter cells through traditional glycosylated proteins, but also rely on RNA on the cell surface. Experiments show that:
This means that cell surface RNA is likely to be the key "gateway" for regulating CPP entry into cells. This discovery not only changes our understanding of viral infection and drug delivery, but also provides new ideas for the development of new biotechnology tools.
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