RNA interference (RNAi) functions as a potent antiviral immunity in plants and invertebrates; however, whether RNAi plays antiviral roles in mammals remains unclear. Here, using human enterovirus 71 (HEV71) as a model, we showed HEV71 3A protein as an authentic viral suppressor of RNAi during viral infection. When the 3A-mediated RNAi suppression was impaired, the mutant HEV71 readily triggered the production of abundant HEV71-derived small RNAs with canonical siRNA properties in cells and mice. These virus-derived siRNAs were produced from viral dsRNA replicative intermediates in a Dicer-dependent manner and loaded into AGO, and they were fully active in degrading cognate viral RNAs. Recombinant HEV71 deficient in 3A-mediated RNAi suppression was significantly restricted in human somatic cells and mice, whereas Dicer deficiency rescued HEV71 infection independently of type I interferon response. Thus, RNAi can function as an antiviral immunity, which is induced and suppressed by a human virus, in mammals.

RNA helicases and chaperones are the two major classes of RNA remodeling proteins, which function to remodel RNA structures and/or RNA-protein interactions, and are required for all aspects of RNA metabolism. Although some virus-encoded RNA helicases/chaperones have been predicted or identified, their RNA remodeling activities in vitro and functions in the viral life cycle remain largely elusive. Enteroviruses are a large group of positive-stranded RNA viruses in the Picornaviridae family, which includes numerous important human pathogens. Herein, we report that the nonstructural protein 2CATPase of enterovirus 71 (EV71), which is the major causative pathogen of hand-foot-and-mouth disease and has been regarded as the most important neurotropic enterovirus after poliovirus eradication, functions not only as an RNA helicase that 3′-to-5′ unwinds RNA helices in an adenosine triphosphate (ATP)-dependent manner, but also as an RNA chaperone that destabilizes helices bidirectionally and facilitates strand annealing and complex RNA structure formation independently of ATP. We also determined that the helicase activity is based on the EV71 2CATPase middle domain, whereas the C-terminus is indispensable for its RNA chaperoning activity. By promoting RNA template recycling, 2CATPase facilitated EV71 RNA synthesis in vitro; when 2CATPase helicase activity was impaired, EV71 RNA replication and virion production were mostly abolished in cells, indicating that 2CATPase-mediated RNA remodeling plays a critical role in the enteroviral life cycle. Furthermore, the RNA helicase and chaperoning activities of 2CATPase are also conserved in coxsackie A virus 16 (CAV16), another important enterovirus. Altogether, our findings are the first to demonstrate the RNA helicase and chaperoning activities associated with enterovirus 2CATPase, and our study provides both in vitro and cellular evidence for their potential roles during viral RNA replication. These findings increase our understanding of enteroviruses and the two types of RNA remodeling activities.

Severe acute respiratory syndrome (SARS) is an emerging infectious disease. Its etiological agent has been convincingly identified as a new member of family Coronaviridae (SARS-CoV). It causes serious damage to the respiratory system yet the mechanism is not clear. Infection-induced apoptosis or necrosis is suspected but no direct evidence for this yet exists. To date, Vero E6 cells are the only cell line that could be used to replicate the virus with obvious CPE (cytopathic effect) in vitro. It is known for some viruses (including members of family Coronaviridae) that CPE can be caused either by virus-induced apoptosis (active death) or cell necrosis (passive death). In this study, we examined the apoptosis in the SARS-CoV infected Vero E6 cells. Indeed, the results do show that the CPE was induced by apoptosis rather than necrosis, shown by typical DNA fragmentation, through the existence of apoptotic bodies and swollen mitochondria. This observation has some implications for the SARS-CoV pathogenicity: SARS-CoV does induce apoptosis in cell cultures and might have the same effect in vivo, responsible for the severe damage of the respiratory system.

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The present study investigated whether TLR3 is required for neonatal heart repair and regeneration following myocardial infarction (MI). TLR3 deficient neonatal mice exhibited impaired cardiac functional recovery and a larger infarct size, while wild type neonatal mice showed cardiac functional recovery and small infarct size after MI. The data suggest that TLR3 is essential for the regeneration and repair of damaged neonatal myocardium. In vitro treatment of neonatal cardiomyocytes with a TLR3 ligand, Poly (I:C), significantly enhances glycolytic metabolism, YAP1 activation and proliferation of cardiomyocytes which were prevented by a glycolysis inhibitor, 2-deoxyglucose (2-DG). Administration of 2-DG to neonatal mice abolished cardiac functional recovery and YAP activation after MI, suggesting that TLR3-mediated regeneration and repair of the damaged neonatal myocardium is through glycolytic-dependent YAP1 activation. Inhibition of YAP1 activation abolished Poly (I:C) induced proliferation of neonatal cardiomyocytes. Interestingly, activation of YAP1 increases the expression of miR-152 which represses the expression of cell cycle inhibitory proteins, P27kip1 and DNMT1, leading to cardiomyocyte proliferation. We conclude that TLR3 is required for neonatal heart regeneration and repair after MI. The mechanisms involve glycolytic-dependent YAP1 activation, resulting in miR-152 expression which targets DNMT1/p27kip1.

Anillin (ANLN), an actin-binding protein, is required for cytokinesis. Recently, ANLN has been identified as a biomarker in diverse human cancers; however, the precise role of ANLN in breast cancer remains unclear. In this study, we firstly detected the expression of ANLN in 71 patients with breast cancer by immunohistochemistry, and found ANLN was highly expressed in breast cancer tissues. To evaluate the function of ANLN in breast cancer cells, we employed lentivirus-mediated RNA interference to knock down ANLN expression in two human breast cancer cell lines, MDA-MB-231, and ZR-75-30. Knockdown of ANLN remarkably inhibited the proliferation rate and colony formation ability of both breast cancer cell lines. Moreover, flow cytometry analysis showed that depletion of ANLN in MDA-MB-231 cells blocked the cell cycle progression, with more cells delayed at G2/M phase, due to phosphorylation of Cdc2 and suppression of Cyclin D1. Furthermore, knockdown of ANLN strongly suppressed the migration of breast cancer cells, strengthening the evidence that ANLN could be involved in breast cancer progression. Our results may suggest ANLN as a potential target candidate in breast cancer.

Myocardial infarction (MI) dampens heart function and poses a great health risk. The class III deacetylase sirtuin 1 (SIRT1) is known to confer cardioprotection. SIRT1 expression is downregulated in the heart by a number of stress stimuli that collectively drive the pathogenesis of MI, although the underlying mechanism remains largely obscure. Here we show that in primary rat neonatal ventricular myocytes (NRVMs), ischaemic or oxidative stress leads to a rapid upregulation of SUV39H, the mammalian histone H3K9 methyltransferase, paralleling SIRT1 downregulation. Compared to wild-type littermates, SUV39H knockout mice are protected from MI. Likewise, suppression of SUV39H activity with chaetocin attenuates cardiac injury following MI. Mechanistically, SUV39H cooperates with heterochromatin protein 1 gamma (HP1γ) to catalyse H3K9 trimethylation on the SIRT1 promoter and represses SIRT1 transcription. SUV39H augments intracellular ROS levels in a SIRT1-dependent manner. Our data identify a previously unrecognized role for SUV39H linking SIRT1 trans-repression to myocardial infarction.