Hijacking cellular garbage cans

The cytotoxicity of coxsackievirus B3 is associated with a blockage of autophagic flux mediated by reduced syntaxin 17 expression

Coxsackievirus B3 (CVB3) is an important human pathogen linked to cardiac arrhythmias and acute heart failure. CVB3 infection has been reported to induce the formation of autophagosomes that support the viral replication in host cells. Interestingly, our study shows that the accumulation of autophagosomes during CVB3 infection is caused by a blockage of autophagosome–lysosome fusion rather than the induction of autophagosome biogenesis. Moreover, CVB3 decreases the transcription and translation of syntaxin 17 (STX17), a SNARE (soluble N-ethylmaleimide-sensitive factor activating protein receptor) protein involved in autophagosome–lysosome fusion. Overexpression of STX17 restored the autophagic flux, alleviated the virus-induced lysosomal dysfunction, and decreased the apoptosis induced by CVB3 infection in HeLa cells. Taken together, our results suggest that CVB3 infection impairs the autophagic flux by blocking autophagosome–lysosome fusion. These findings thus point to potential new therapeutic strategies targeting STX17 or autophagosome–lysosome fusion for treating CVB3-associated diseases.

Viral proteins and Src family kinases: Mechanisms of pathogenicity from a “liaison dangereuse”

To complete their life cycle and spread, viruses interfere with and gain control of diverse cellular processes, this most often occurring through interaction between viral proteins (VPs) and resident protein partners. Among the latter, Src family kinases (SFKs), a class of non-receptor tyrosine kinases that contributes to the conversion of extracellular signals into intracellular signaling cascades and is involved in virtually all cellular processes, have recently emerged as critical mediators between the cell’s infrastructure and the viral demands. In this scenario, structural or ex novo synthesized VPs are able to bind to the different domains of these enzymes through specific short linear motifs present along their sequences. Proline-rich motifs displaying the conserved minimal consensus PxxP and recognizing the SFK Src homology (SH)3 domain constitute a cardinal signature for the formation of multiprotein complexes and this interaction may promote phosphorylation of VPs by SFKs, thus creating phosphotyrosine motifs that become a docking site for the SH2 domains of SFKs or other SH2 domain-bearing signaling molecules. Importantly, the formation of these assemblies also results in a change in the activity and/or location of SFKs, and these events are critical in perturbing key signaling pathways so that viruses can utilize the cell’s machinery to their own benefit. In the light of these observations, although VPs as such, especially those with enzyme activity, are still regarded as valuable targets for therapeutic strategies, multiprotein complexes composed of viral and host cell proteins are increasingly becoming objects of investigation with a view to deeply characterize the structural aspects that favor their formation and to develop new compounds able to contrast viral diseases in an alternative manner.

Pancreatic acinar cell-specific autophagy disruption reduces coxsackievirus replication and pathogenesis in vivo

Autophagy protects against many infections by inducing the lysosomal-mediated degradation of invading pathogens. However, previous in vitro studies suggest that some enteroviruses not only evade these protective effects but also exploit autophagy to facilitate their replication. We generated Atg5(f/f)/Cre(+) mice, in which the essential autophagy gene Atg5 is specifically deleted in pancreatic acinar cells, and show that coxsackievirus B3 (CVB3) requires autophagy for optimal infection and pathogenesis. Compared to Cre(-) littermates, Atg5(f/f)/Cre(+) mice had an ∼2,000-fold lower CVB3 titer in the pancreas, and pancreatic pathology was greatly diminished. Both in vivo and in vitro, Atg5(f/f)/Cre(+) acinar cells had reduced intracellular viral RNA and proteins. Furthermore, intracellular structural elements induced upon CVB3 infection, such as compound membrane vesicles and highly geometric paracrystalline arrays, which may represent viral replication platforms, were infrequently observed in infected Atg5(f/f)/Cre(+) cells. Thus, CVB3-induced subversion of autophagy not only benefits the virus but also exacerbates pancreatic pathology.