Desuccinylation-Triggered Peptide Self-Assembly: Live Cell Imaging of SIRT5 Activity and Mitochondrial Activity Modulation.

Mimicking nature's ability to orchestrate molecular self-assembly in living cells is important yet challenging. Molecular self-assembly has found wide applications in cellular activity control, drug delivery, biomarker imaging, etc. Nonetheless, examples of suborganelle-confined supramolecular self-assembly are quite rare and research in this area remains challenging. Herein, we have presented a new strategy to program supramolecular self-assembly specifically in mitochondria by leveraging on a unique enzyme SIRT5. SIRT5 is a mitochondria-localized enzyme belonging to a family of NAD+-dependent histone deacetylases. Accumulating studies suggest that SIRT5 is involved in regulating diverse biological processes, such as reactive oxygen defense, fatty acid metabolism, and apoptosis. In this study, we designed a novel class of succinylated peptide precursors that can be transformed into self-assembling building blocks through SIRT5 catalysis, leading to the formation of supramolecular nanofibers in vitro and in living cells. The increased hydrophobicity arising from self-assembly remarkably enhanced the fluorescence of nitrobenzoxadiazole (NBD) in the nanofibers. With this approach, we have enabled activity-based imaging of SIRT5 in living cells for the first time. Moreover, SIRT5-mediated peptide self-assembly was found to depolarize mitochondria membrane potential and promote ROS formation. Coincubation of the peptide with three different chemotherapeutic agents significantly boosted the anticancer activities of these drugs. Our work has thus illustrated a new way of mitochondria-confined peptide self-assembly for SIRT5 imaging and potential anticancer treatment.

Targeting m6A modification inhibits herpes virus 1 infection.

The latent infection by herpes virus type 1 (HSV-1) may be lifelong in trigeminal ganglia and a suspected cause of Alzheimer's Disease (AD) and Amyotrophic lateral sclerosis (ALS). Whether and how N6-methyladenosine (m6A) modification of viral RNAs affects virus infection are poorly understood. Here, we report that HSV-1 infection enhanced the expression of m6A writers (METTL3, METTL14) and readers (YTHDF1/2/3) at the early infection stage and decreased their expression later on, while suppressed the erasers' (FTO, ALBKH5) expression immediately upon infection to facilitate viral replication. Inhibiting m6A modification by 3-deazaadenosine (DAA) significantly decreased viral replication and reduced viral reproduction over 1000 folds. More interestingly, depleting the writers and readers by siRNAs inhibited virus replication and reproduction; whereas depleting the erasers promoted viral replication and reproduction. Silencing YTHDF3 strikingly decreased viral replication by up to 90%, leading to reduction of up to 10-fold viral replication and over 100-fold virus reproduction, respectively. Depletion of m6A initiator METTL3 (by 60%-70%) by siRNA correlatedly decreased viral replication 60%-70%, and reduced virus yield over 30-fold. Consistently, ectopic expression of METTL3 largely increased virus yield. METTL3 knockdown suppressed the HSV-1 intermediate early and early genes (ICP0, ICP8 and UL23) and late genes (VP16, UL44, UL49 and ICP47); while ectopic expression of METTL3 upregulated these gene expression. Results from our study shed the lights on the importance for m6A modification to initiate HSV-1 early replication. The components of m6A modification machinery, particularly m6A initiator METTL3 and reader YTHDF3, would be potential important targets for combating HSV-1 infections.

Pim1 Impacts Enterovirus A71 Replication and Represents a Potential Target in Antiviral Therapy.

Enterovirus A71 (EV-A71) infection causes hand-foot-and-mouth disease (HFMD) and fatal neurological diseases, and there are no effective treatments. Host factors play key roles in establishing viral infection and determining the disease progression and outcome of antiviral therapies. In this study, we found that the expression of Pim1 was significantly upregulated in EV-A71 infection. Ectopic expression or silencing of Pim1 promoted or inhibited EV-A71 replication through two distinct mechanisms. Pim1 enhanced viral IRES activity by increasing viral 2A protease-mediated eIF4G cleavage and blocked AUF1, a suppressor of IRES, translocation from the nucleus to cytosol. More importantly, we discovered that Pim1 inhibitors (SGI-1776, AZD-1208, and CX-6258) reduced EV-A71 reproduction. Particularly, CX-6258 remarkably reduced EV-A71 reproduction more than 1,000 times, providing a potential therapeutic agent for EV-A71 treatment.

Novel HDAC5-interacting motifs of Tbx3 are essential for the suppression of E-cadherin expression and for the promotion of metastasis in hepatocellular carcinoma.

Tbx3, a transcriptional repressor, is essential in the organogenesis of vertebrates, stem cell self-renewal and differentiation, and the carcinogenesis of multiple tumor types. However, the mechanism by which Tbx3 participates in the metastasis of hepatocellular carcinoma (HCC) remains largely unknown. In this study, we show that Tbx3 was dramatically upregulated in clinical HCC samples and that elevated expression of Tbx3 promoted cancer progression. To determine the underlying mechanism, systematic glycine scan mutagenesis and deletion assays were performed. We identified two critical motifs, 585LFSYPYT591 and 604HRH606, that contribute to the repression of transcriptional activity. These motifs are also essential for Tbx3 to promote cell migration and metastasis both in vitro and in vivo via the suppression of E-cadherin expression. More importantly, Tbx3 directly interacts with HDAC5 via these motifs, and an HDAC inhibitor blocks Tbx3-mediated cell migration and the downregulation of E-cadherin in HCC. As Tbx3 is involved in the carcinogenesis of multiple types of human cancers, our findings suggest an important target for anti-cancer drug development.

Anthocyanin Cyanidin-3-Glucoside Attenuates Platelet Granule Release in Mice Fed High-Fat Diets.

Platelet granule release is considered an important target for preventing and treating cardiovascular diseases (CVDs). Cyanidin-3-glucoside (Cy-3-g) is a predominant bioactive anthocyanin compound in many edible plants and has been reported to be protective against CVDs by attenuating platelet dysfunction. However, direct evidence of the action of Cy-3-g on platelet granule secretion in purified platelets from in vivo assays is still poor. In the present study, we demonstrated that dietary supplementation of purified Cy-3-g reduces serum lipid levels and facilitates down-regulation of the platelet granule release of substances such as P-selectin, CD40L, 5-HT, RANTES and TGF-ß1 in gel-filtered platelets, in addition to attenuating serum PF4 and ß-TG levels in mice fed high-fat diets. These results provide evidence that Cy-3-g protects against thrombosis and CVDs by inhibiting purified platelet granule release in vivo.