A179L, a new viral Bcl2 homolog targeting Beclin 1 autophagy related protein.

Autophagy is a relevant cellular defense mechanism that directly eliminates intracellular pathogens and has a crucial role for innate and adaptive immune responses. Some viruses have developed tools to counteract this cellular response. A179L, the viral Bcl2 homolog of African swine fever virus, interacts with proapoptotic Bcl2 family proteins to inhibit apoptosis. Here we report that this gene manipulates autophagy by interacting with Beclin 1 through its BH3 homology domain. At subcellular level, A179L colocalized with Beclin 1 at mitochondria and the endoplasmic reticulum. Virus infection inhibited autophagosome formation in cells; however, when autophagy was induced prior to or at the time of infection the number of infected cells was severely decreased.

The ATF6 branch of unfolded protein response and apoptosis are activated to promote African swine fever virus infection.

African swine fever virus (ASFV) infection induces apoptosis in the infected cell; however, the consequences of this activation on virus replication have not been defined. In order to identify the role of apoptosis in ASFV infection, we analyzed caspase induction during the infection and the impact of caspase inhibition on viral production. Caspases 3, 9 and 12 were activated from 16 h post-infection, but not caspase 8. Indeed, caspase 3 activation during the early stages of the infection appeared to be crucial for efficient virus exit. In addition, the inhibition of membrane blebbing reduced the release of virus particles from the cell. ASFV uses the endoplasmic reticulum (ER) as a site of replication and this process can trigger ER stress and the unfolded protein response (UPR) of the host cell. In addition to caspase 12 activation, indicators of ER stress include the upregulation of the chaperones calnexin and calreticulin upon virus infection. Moreover, ASFV induces transcription factor 6 signaling pathway of the UPR, but not the protein kinase-like ER kinase or the inositol-requiring enzyme 1 pathways. Thus, the capacity of ASFV to regulate the UPR may prevent early apoptosis and ensure viral replication.

Comparative inhibitory activity of the stilbenes resveratrol and oxyresveratrol on African swine fever virus replication.

Stilbenols are polyphenolic phytoalexins produced by plants in response to biotic or abiotic stress. These compounds have received much attention because of their significant biological effects. One of these is their antiviral action, which has previously been documented for two members of this class, namely resveratrol and oxyresveratrol. Here we tested the antiviral effect of these two compounds on African swine fever virus, the only member of the newly created family Asfarviridae and a serious limitation to porcine production worldwide. Our results show a potent, dose-dependent antiviral effect of resveratrol and oxyresveratrol in vitro. Interestingly, this antiviral activity was found for these synthetic compounds and also for oxyresveratrol extracted from new natural sources (mulberry twigs). The antiviral effect of these two drugs was demonstrated at concentrations that do not induce cytotoxicity in cultured cells. Moreover, these antivirals achieved a 98-100% reduction in viral titers. Both compounds allowed early protein synthesis but inhibited viral DNA replication, late viral protein synthesis and viral factory formation.

African swine fever virus protein p54 interacts with the microtubular motor complex through direct binding to light-chain dynein.

Dynein is a minus-end-directed microtubule-associated motor protein involved in cargo transport in the cytoplasm. African swine fever virus (ASFV), a large DNA virus, hijacks the microtubule motor complex cellular transport machinery during virus infection of the cell through direct binding of virus protein p54 to the light chain of cytoplasmic dynein (LC8). Interaction of p54 and LC8 occurs both in vitro and in cells, and the two proteins colocalize at the microtubular organizing center during viral infection. p50/dynamitin, a dominant-negative inhibitor of dynein-dynactin function, impeded ASFV infection, suggesting an essential role for dynein during virus infection. A 13-amino-acid domain of p54 was sufficient for binding to LC8, an SQT motif within this domain being critical for this binding. Direct binding of a viral structural protein to LC8, a small molecule of the dynein motor complex, could constitute a molecular mechanism for microtubule-mediated virus transport.