Precise identification of an RNA methyltransferase's substrate modification site.

Here we report a simple and nonradioactive biochemical assay which is capable of accurately determining the substrate methylation sites of human RNA N6-methyladenosine methyltransferases METTL3/METTL14 and METTL16. This method employs enzyme-assisted chemical labelling of a specific base in an RNA substrate with the assistance of an allyl-substituted methyltransferase cofactor, and enables precise identification of the labelling site by a mutation signal from standard nucleic acid sequencing. Our method provides a platform to investigate the enzymatic methylations of long and structurally complex RNA substrates, and facilitates the discovery of new methyltransferases.

A metabolic labeling method detects m6A transcriptome-wide at single base resolution.

Transcriptome-wide mapping of N6-methyladenosine (m6A) at base resolution remains an issue, impeding our understanding of m6A roles at the nucleotide level. Here, we report a metabolic labeling method to detect mRNA m6A transcriptome-wide at base resolution, called 'm6A-label-seq'. Human and mouse cells could be fed with a methionine analog, Se-allyl-L-selenohomocysteine, which substitutes the methyl group on the enzyme cofactor SAM with the allyl. Cellular RNAs could therefore be metabolically modified with N6-allyladenosine (a6A) at supposed m6A-generating adenosine sites. We pinpointed the mRNA a6A locations based on iodination-induced misincorporation at the opposite site in complementary DNA during reverse transcription. We identified a few thousand mRNA m6A sites in human HeLa, HEK293T and mouse H2.35 cells, carried out a parallel comparison of m6A-label-seq with available m6A sequencing methods, and validated selected sites by an orthogonal method. This method offers advantages in detecting clustered m6A sites and holds promise to locate nuclear nascent RNA m6A modifications.

Design, synthesis, and biological evaluation of novel tetrahydroisoquinoline derivatives as potential antitumor candidate.

A novel class of tetrahydroisoquinoline derivatives was designed and synthesized as antitumor agents and evaluated for their in vitro and in vivo biological activities. The antiproliferative activities of all the target compounds on HUVEC, MCF-7, and HT-29 were evaluated. Compared with colchicine (1.04 × 10-2  µm), 17d and 17e exhibited outstanding activity on MCF-7 with IC50 values 0.26 × 10-2  µm and 0.89 × 10-3 µm in cell cytotoxicity assay. The tubulin polymerization assay demonstrated that 17d and 17e exhibited better inhibition rate. In the MCF-7-xenograft mouse model that was treated with 17d and 17e by intraperitoneal injection, the tumor weight was decreased at same rate with tamoxifen, and relative tumor proliferation rates were 59.48% and 41.33%, while tamoxifen was 45.08% with a daily dose of 20 mg/kg, which were demonstrated potent in vivo efficacy.