Circular Single-Stranded DNA: Discovery, Biological Effects, and Applications

The field of nucleic acid therapeutics has witnessed a significant surge in recent times, as evidenced by the increasing number of approved genetic drugs. However, current platform technologies containing plasmids, lipid nanoparticle-mRNAs, and adeno-associated virus vectors encounter various limitations and challenges. Thus, we are devoted to finding a novel nucleic acid vector and have directed our efforts toward investigating circular single-stranded DNA (CssDNA), an ancient form of nucleic acid. CssDNAs are ubiquitous, but generally ignored. Accumulating evidence suggests that CssDNAs possess exceptional properties as nucleic acid vectors, exhibiting great potential for clinical applications in genetic disorders, gene editing, and immune cell therapy. Here, we comprehensively review the discovery and biological effects of CssDNAs as well as their applications in the field of biomedical research for the first time. Undoubtedly, as an ancient form of DNA, CssDNA holds immense potential and promises novel insights for biomedical research.

G-quadruplex-enhanced circular single-stranded DNA (G4-CSSD) adsorption of miRNA to inhibit colon cancer progression

BACKGROUND

Chromosomal heterogeneity leads to the abnormal expression and mutation of tumor-specific genes. Drugs targeting oncogenes have been extensively developed. However, given the random mutation of tumor suppressor genes, the development of its targeted drugs is difficult.

METHODS

Our early research revealed that artificial circular single-stranded DNA (CSSD) can restore multiple tumor suppressor genes to inhibit tumor malignant progression by adsorbing miRNA. Here, we improved CSSD to a fully closed single-stranded DNA with G quadruplex DNA secondary structure (G4-CSSD), which made G4-CSSD with higher acquisition rate and decreased degradation. The Cancer Genome Atlas (TCGA) and Human Protein Atlas database were used to predict tumour suppressor genes in colon cancer. Cellular and animal experiments were performed to validate the role of G4-CSSD in cancer cell progression.

RESULTS

In colon cancer, we observed the simultaneous low expressions of chloride channel accessory 1 (CLCA1), UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 6 (B3GNT6) and UDP glucuronosyltransferase family 2 member A3 (UGT2A3), which indicated an favourable prognosis. After repressing miR-590-3p with G4-CSSD590, the upregulation of CLCA1, B3GNT6 and UGT2A3 inhibited the proliferation and metastasis of colon cancer cells.

CONCLUSIONS

This study may provide basis for new treatment methods for colon cancer by restoration of tumor suppressor genes.

[Geminivirus replication: rolling circle mechanism in plants]

Geminiviruses are single-stranded DNA viruses that infect most plants worldwide. They replicate through a rolling circle mechanism which allows the production of a large amount of single-stranded viral DNA. This mechanism has been studied in detail for prokaryotic replicons but has also been described for eukaryotic replicons. The viral Rep protein is the key element in this process and combines three functions essential for replication: recognition of the viral origin of replication, cleavage of the origin and production of the primer necessary to replicate the viral DNA, and a replicative helicase activity. Furthermore by associating with several host proteins Rep interferes with the cell cycle control to produce a favourable environment for the replication of the virus. Recent advances have been reported concerning the demonstration of the helicase activity of Rep protein and the tertiary structure of its N-terminal domain; our review will focus on these two aspects in relation with the rolling circle replication mechanism.