An Argonaute from Thermus parvatiensis exhibits endonuclease activity mediated by 5' chemically modified DNA guides

In vitro characterization of a pAgo nuclease TtdAgo from Thermococcus thioreducens and evaluation of its effect in vivo

In spite of the development of genome-editing tools using CRISPR-Cas systems, highly efficient and effective genome-editing tools are still needed that use novel programmable nucleases such as Argonaute (Ago) proteins to accelerate the construction of microbial cell factories. In this study, a prokaryotic Ago (pAgo) from a hyperthermophilic archaeon Thermococcus thioreducens (TtdAgo) was characterized in vitro. Our results showed that TtdAgo has a typical DNA-guided DNA endonuclease activity, and the efficiency and accuracy of cleavage are modulated by temperature, divalent ions, and the phosphorylation and length of gDNAs and their complementarity to the DNA targets. TtdAgo can utilize 5'-phosphorylated (5'-P) or 5'- hydroxylated (5'-OH) DNA guides to cleave single-stranded DNA (ssDNA) at temperatures ranging from 30°C to 95°C in the presence of Mn²⁺ or Mg²⁺ and displayed no obvious preference for the 5'-end-nucleotide of the guide. In addition, single-nucleotide mismatches had little effects on cleavage efficiency, except for mismatches at position 4 or 8 that dramatically reduced target cleavage. Moreover, TtdAgo performed programmable cleavage of double-stranded DNA at 75°C. We further introduced TtdAgo into an industrial ethanologenic bacterium Zymomonas mobilis to evaluate its effect in vivo. Our preliminary results indicated that TtdAgo showed cell toxicity toward Z. mobilis, resulting in a reduced growth rate and final biomass. In conclusion, we characterized TtdAgo in vitro and investigated its effect on Z. mobilis in this study, which lays a foundation to develop Ago-based genome-editing tools for recalcitrant industrial microorganisms in the future.

Long Noncoding RNA XIST Promotes Resistance to Lenvatinib in Hepatocellular Carcinoma Cells via Epigenetic Inhibition of NOD2

Background. Hepatocellular carcinoma (HCC) is a severe global health issue that still lacks of effective treatments. Lenvatinib is a novel tyrosine kinase inhibitor (TKI) that has been approved for the treatment of HCC. However, drug resistance is inevitable and limits the clinical application of lenvatinib. Till now, there is still little knowledge about the mechanisms under the resistance to lenvatinib in HCC. Long noncoding RNA (lncRNA) is a group of noncoding RNAs that play essential roles in various physiological activities including the chemoresistance. In the present study, through RNA sequencing, we discovered that lncRNA XIST was upregulated in HCC cells that was insensitive to lenvatinib. Mechanically, we found that lncXIST promotes lenvatinib resistance via activation of EZH2-NOD2-ERK axis in HCC cells. Our data suggest that targeting lncXIST/EZH2/NOD2/ERK axis might be a promising strategy to enhance the efficacy of lenvatinib against HCC cells.