Structural basis of CRISPR-SpyCas9 inhibition by an anti-CRISPR protein.

CRISPR-Cas9 systems are bacterial adaptive immune systems that defend against infection by phages. Through the RNA-guided endonuclease activity of Cas9 they degrade double-stranded DNA with a protospacer adjacent motif (PAM) and sequences complementary to the guide RNA. Recently, two anti-CRISPR proteins (AcrIIA2 and AcrIIA4 from Listeria monocytogenes prophages) were identified, both of which inhibit Streptococcus pyogenes Cas9 (SpyCas9) and L. monocytogenes Cas9 activity in bacteria and human cells. However, the mechanism of AcrIIA2- or AcrIIA4-mediated Cas9 inhibition remains unknown. Here we report a crystal structure of SpyCas9 in complex with a single-guide RNA (sgRNA) and AcrIIA4. Our data show that AcrIIA2 and AcrIIA4 interact with SpyCas9 in a sgRNA-dependent manner. The structure reveals that AcrIIA4 inhibits SpyCas9 activity by structurally mimicking the PAM to occupy the PAM-interacting site in the PAM-interacting domain, thereby blocking recognition of double-stranded DNA substrates by SpyCas9. AcrIIA4 further inhibits the endonuclease activity of SpyCas9 by shielding its RuvC active site. Structural comparison reveals that formation of the AcrIIA4-binding site of SpyCas9 is induced by sgRNA binding. Our study reveals the mechanism of SpyCas9 inhibition by AcrIIA4, providing a structural basis for developing 'off-switch' tools for SpyCas9 to avoid unwanted genome edits within cells and tissues.

CircRNA hsa_circ_0030018 regulates the development of glioma via regulating the miR-1297/RAB21 axis.

Circular RNAs (circRNAs) play a crucial role in tumor occurrence and progression. And the dysregulated circRNAs are reported to be relevant to glioma development. Nevertheless, the function and regulatory mechanism of hsa_circ_0030018 in glioma progression are largely indistinct. The abundances of hsa_circ_0030018, miR-1297, and RAB21 were detected using quantitative real-time polymerase chain reaction or western blot. Cell proliferation was assessed via colony formation assay and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay. Cell apoptosis and cell cycle progression were evaluated by flow cytometry. Cell migration and invasion were examined using transwell assay and wound healing assay. The protein levels were measured by western blot. The interaction between miR-1297 and hsa_circ_0030018 or RAB21 was validated via dual-luciferase reporter analysis, RNA immunoprecipitation (RIP), and RNA pull-down assays. A xenograft model experiment was performed to analyze the function of hsa_circ_0030018 on tumor growth in vivo. hsa_circ_0030018 and RAB21 levels were enhanced, and the miR-1297 level was reduced in glioma tissues and cells. The silence of hsa_circ_0030018 or overexpression of miR-1297 impeded cell proliferation, metastasis, and expedited cell apoptosis and cycle arrest in glioma cells. Furthermore, hsa_circ_0030018 modulated glioma malignant behaviors via sponging miR-1297, and miR-1297 suppressed glioma development via targeting RAB21. Moreover, hsa_circ_0030018 knockdown inhibited tumor growth in vivo. The hsa_circ_0030018 knockdown repressed glioma progression by mediating the miR-1297/RAB21 pathway, providing potential therapeutic targets for glioma treatment.

Circ-CREBBP promotes cell tumorigenesis and glutamine catabolism in glioma by regulating miR-375/glutaminase axis.

Circular RNA CREB-binding protein (circ-CREBBP) has been reported to involve in the tumorigenesis of glioma. However, the role and underlying molecular mechanism of circ-CREBBP in glioma glutamine catabolism remain unclear. The expression of circ-CREBBP, microRNA (miR)-375 and glutaminase (GLS) was detected using quantitative real-time polymerase chain reaction and western blot. The 3­(4, 5­dimethylthiazol­2­y1)­2, 5­diphenyl tetrazolium bromide (MTT), colony formation, flow cytometry and transwell assays were used to determine the effects of them on glioma cell malignant biological behaviors in vitro. Glutamine metabolism was analyzed using assay kits. Murine xenograft model was established to investigate the role of circ-CREBBP in vivo. The binding interactions between miR-375 and circ-CREBBP or GLS were confirmed by the dual-luciferase reporter assay. Circ-CREBBP was highly expressed in glioma tissues and cells, and high expression of circ-CREBBP predicted poor prognosis. Circ-CREBBP knockdown suppressed cell proliferation, migration, invasion and glutamine metabolism while expedited cell apoptosis in glioma in vitro, as well as impeded tumor growth in vivo. Circ-CREBBP directly targeted miR-375, which was demonstrated to restrain glioma cell growth, motility and glutamine metabolism. Moreover, miR-375 inhibition reverted the anticancer effects of circ-CREBBP knockdown on glioma cells. GLS was a target of miR-375, GLS silencing or the treatment of GLS inhibitor bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) impaired glioma cell malignant phenotypes and glutamine metabolism. Importantly, GLS up-regulation weakened the tumor-suppressive functions of miR-375 on glioma cells. Mechanistically, circ-CREBBP indirectly regulated GLS expression through sponging miR-375. In all, circ-CREBBP expedited glioma tumorigenesis and glutamine metabolism through miR-375/GLS axis, suggesting a promising target for combined glioma therapy.

UPLC-MS/MS Assay for Quantification of Wedelolactone and Demethylwedelolactone in Rat Plasma and the Application to a Preclinical Pharmacokinetic Study.

AIMS AND OBJECTIVE: Wedelolactone and demethylwedelolactone are the two major coumarin constituents of Herba Ecliptae. The objective of this work was to develop and validate a sensitive, rapid, and robust UPLC-MS/MS method for the simultaneous quantification of wedelolactone and demethylwedelolactone in rat plasma. MATERIALS AND METHODS: Wedelolactone and demethylwedelolactone were extracted from rat plasma by protein precipitation with acetonitrile. Electrospray ionization in negative mode and selected reaction monitoring (SRM) were used for wedelolactone and demethylwedelolactone at the transitions m/z 312.8→298.0 and m/z 299.1→270.6, respectively. Chromatographic separation was conducted on a Venusil C18 column (50 mm × 2.1 mm, 5 µm) with isocratic elution of acetonitrile-0.1% formic acid in water (55:45, v/v) at a flow rate of 0.3 mL/min. A linear range was observed over the concentration range of 0.25-100 ng/mL for wedelolactone and demethylwedelolactone. RESULTS: They reached their maximum plasma concentrations (Cmax, 74.9±13.4 ng/mL for wedelolactone and 41.3±9.57 ng/mL for demethylwedelolactone) at the peak time (Tmax) of 0.633 h and 0.800 h, respectively. The AUC0-t value of wedelolactone (260.8±141.8 ng h/mL) was higher than that of demethylwedelolactone (127.4±52.7 ng h/mL) by approximately 2-fold, whereas the terminal elimination half-life (t1/2) of wedelolactone (2.20±0.59 h) showed the approximately same as that of demethylwedelolactone (2.08±0.69 h). CONCLUSION: Based on full validation according to US FDA guidelines, this UPLC-MS/MS method was successfully applied to a pharmacokinetic study in rats.

Nm23-H1 inhibits the proliferation of glioma cells via regulation of PKC signaling pathway.

PURPOSE: To explore the influence of nm23-H1 on the proliferation and apoptosis of glioma cells and the mechanism of action. METHODS: The changes in the messenger RNA (mRNA) expression of nm23-H1 were detected via quantitative real-time-polymerase chain reaction (qRT-PCR), and the relative protein expression level of nm23-H1 was determined using immunohistochemistry. The glioma H4 cells were transfected exogenously with nm23-H1 gene (nm23-H1 group) or empty vector (Vector group), and the biological influence of the expression level of nm23-H1 on H4 cells was then assessed through in vitro functional experiments. Besides, the cells transfected with nm23-H1 were incubated with the protein kinase C (PKC) pathway inhibitor Calphostin C, and functional experiments were performed to observe the changes in the proliferation and apoptosis of cells after incubation. RESULTS: According to the immunohistochemistry and qRT-PCR results, the protein and mRNA expression levels of nm23-H1 declined notably in glioma tissues (p<0.01). The cells with up-regulated nm23-H1 expression had substantially weakened proliferation and migration abilities, but exhibited dramatically enhanced apoptosis (p<0.01). The PKC pathway inhibitor considerably potentiated the effects of nm23-H1 protein on the proliferation and apoptosis of H4 cells (p<0.05), and the protein expression level of nm23-H1 rose in the cells treated with the PKC inhibitor (p<0.01). CONCLUSIONS: Compared with normal brain tissues, nm23-H1 is lowly expressed in glioma tissues and affects the expression of PKC to influence the biological behaviors of H4 cells.

Anti-CRISPR-based biosensors in the yeast S. cerevisiae.

BACKGROUND: Anti-CRISPR proteins are expressed by phages as a reaction to the bacterial CRISPR-Cas defense system. Recently, the structures of anti-CRISPR proteins have been determined, and their diverse functions have been clarified. Anti-CRISPR proteins such as LmAcrIIA2 and LmAcrIIA4 interact with the SpCas9:gRNA system and occlude the protospacer adjacent motif (PAM) recognition site, thereby preventing SpCas9:gRNA from binding to the DNA. Hence, anti-CRISPR proteins represent a powerful means to control and modulate the activity of SpCas9 and its nuclease-deficient version dSpCas9. LmAcrIIA2 and LmAcrIIA4 have been shown to be efficient inhibitors of SpCas9 in Escherichia coli, Saccharomyces cerevisiae, and mammalian cells. To date, there have been no reports of anti-CRISPR-based synthetic gene circuits engineered into yeast cells. RESULTS: We constructed in the yeast S. cerevisiae synthetic biosensors based on the anti-CRISPR-dSpCas9:gRNA interaction. Upon induction with galactose or ß-estradiol, anti-CRISPR proteins (LmAcrIIA4, LmAcrIIA2, and StAcrIIA5) produced an enhancement in fluorescence expression by preventing the dSpCas9-Mxi1:gRNA complex from binding to the DNA. We found that LmAcrIIA2 performed as well as LmAcrIIA4 in S. cerevisiae, whereas StAcrIIA5, which had previously been tested in bacteria only, had non-negligible negative effects on yeast cell growth. The efficiency of anti-CRISPR-based biosensors was strongly dependent on the means by which the guide RNAs were produced. The best performance, as measured by the increase in fluorescence, was achieved using a "ribozyme-gRNA-ribozyme" expression cassette under the control of the yeast constitutive ADH1 promoter. CONCLUSIONS: This work demonstrates that anti-CRISPR proteins are effective dSpCas9 suppressors in yeast cells. In particular, LmAcrIIA2 and LmAcrIIA4 could be employed as new components of yeast synthetic gene circuits.