Helicase DHX36 plays essential roles in cell development and differentiation at least partially by resolving G-quadruplex (G4) structures. Here we report crystal structures of the Drosophila homolog of DHX36 (DmDHX36) in complex with RNA and a series of DNAs. By combining structural, small-angle X-ray scattering, molecular dynamics simulation, and single-molecule fluorescence studies, we revealed that positively charged amino acids in RecA2 and OB-like domains constitute an elaborate structural pocket at the nucleic acid entrance, in which negatively charged G4 DNA is tightly bound and partially destabilized. The G4 DNA is then completely unfolded through the 3'-5' translocation activity of the helicase. Furthermore, crystal structures and DNA binding assays show that G-rich DNA is preferentially recognized and in the presence of ATP, specifically bound by DmDHX36, which may cooperatively enhance the G-rich DNA translocation and G4 unfolding. On the basis of these results, a conceptual G4 DNA-resolving mechanism is proposed.

Pif1 is an SF1B helicase that is evolutionarily conserved from bacteria to humans and plays multiple roles in maintaining genome stability in both nucleus and mitochondria. Though highly conserved, Pif1 family harbors a large mechanistic diversity. Here, we report crystal structures of Thermus oshimai Pif1 (ToPif1) alone and complexed with partial duplex or single-stranded DNA. In the apo state and in complex with a partial duplex DNA, ToPif1 is monomeric with its domain 2B/loop3 adopting a closed and an open conformation, respectively. When complexed with a single-stranded DNA, ToPif1 forms a stable dimer with domain 2B/loop3 shifting to a more open conformation. Single-molecule and biochemical assays show that domain 2B/loop3 switches repetitively between the closed and open conformations when a ToPif1 monomer unwinds DNA and, in contrast with other typical dimeric SF1A helicases, dimerization has an inhibitory effect on its helicase activity. This mechanism is not general for all Pif1 helicases but illustrates the diversity of regulation mechanisms among different helicases. It also raises the possibility that although dimerization results in activation for SF1A helicases, it may lead to inhibition for some of the other uncharacterized SF1B helicases, an interesting subject warranting further studies.

Systemic sclerosis (SSc) is a prototypic fibrotic disease characterized by localized or diffuse skin thickening and fibrosis. Tissue fibrosis is driven by myofibroblasts, and factors affecting myofibroblast activation may also be involved in the development of SSc. In this study, we examined molecular mechanisms underlying SSc by focusing on myofibroblast activation processes. Bioinformatics analysis conducted to identify differentially expressed miRNAs (DEMs) and genes (DEGs) revealed that microRNA-16-5p (miR-16-5p) was downregulated and NOTCH2 was upregulated in SSc patients. In vitro experiments confirmed that miR-16-5p was able to bind directly to NOTCH2 and inhibit myofibroblast activation. Moreover, miR-16-5p-dependent inhibition of NOTCH2 decreased collagen and α-SMA expression. MiR-16-5p downregulation and NOTCH2 upregulation was also confirmed in vivo in SSc patients, and NOTCH2 activation promoted fibrosis progression in vitro . These results indicate that miR-16-5p suppresses myofibroblast activation by suppressing NOTCH signaling.

Purpose Resveratrol (Res) is a natural polyphenolic compound found in several plants and reported as a promising biological molecule with effective anti-fibrosis and anti-inflammatory activities. However, the underlying mechanism of Res on systemic sclerosis (SSc) remains unclear. In the study, we identified the key cellular signaling pathways involved in the Res regulatory process on SSc. Methods Res-targeted genes interaction network was constructed using the STITCH database, and the shared Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways involved in both SSc and Res-targeted genes were then identified. The top five enriched KEGG pathways were visualized by GOplot. KEGG pathways associated with Res-targeted genes were established by Pathway Builder Tool 2.0. Quantitative real-time PCR (qRT-PCR) was used to assess the expression of sirtuin 1 (SIRT1), mammalian targeted of rapamycin (mTOR), and cytokines. Results Enrichment analysis of Res-targeted genes showed 79 associated pathways, 27 of which were also involved in SSc. Particularly, SIRT1/mTOR signaling was found as one of the crucial regulatory pathways. In vitro results suggested that SIRT1-mediated mTOR degradation ameliorated bleomycin (BLM)-induced fibrosis and inflammation. Res was capable of elevating the SIRT1 level in fibroblasts and partially reversing mTOR-dependent induction of fibrosis and inflammation. Conclusion These results indicated that Res is a feasible and effective choice for SSc and therapeutic target of mTOR could be a potential alternative for treatment of SSc.

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