We have shown that SARS-CoV E protein is a virulence factor that includes at least two virulence motifs: its ion channel (IC) activity encoded within the transmembrane domain and a PDZ binding motif (PBM) located at its carboxy-terminus. We showed that E protein pathogenicity was caused by the activation of different host signaling pathways. One of them was the activation of inflammasome, a process mediated by the conductance of Ca++ byEprotein IC activity, leading to an increased expression of IL-1beta, TNF-alpha and IL-6 levels. Another signaling pathway implied the activation of a proinflammatory response mediated by NF-kB activation. This activation was a consequence of E protein-syntenin binding mediated by PBM-PDZ interactions. This binding caused an increase of p38MAPK phosphorylation promoting the induction of acute respiratory distress syndrome (ARDS), edema and death of mice infected with a mouse adapted SARS-CoV. The relevance of p38 MAPK activation after infection with the mouse adapted SARS-CoV was confirmed by the protection of mice in the presence of an inhibitor of p38 MAPK, but not in its absence. These results illustrated the identification of an efficient coronavirus (CoV) antiviral. The presence of a virulence factor such as the PBM motif in E protein allows the virus to interact with more than 400 cell proteins containing PDZ motifs, conferring the virus the potential to control a high number of cell-signaling pathways increasing its replication and virulence. In fact, we are analyzing the proteome of the viral PBM-cellular PDZ interactions using system biology approaches. Frequently, the ARDS caused by lung infection with mild respiratory viruses is resolved before it evolves to serious edema. In contrast, after SARS-CoV infection frequently this resolution does not take place. We have shown the binding of E protein to a main mediator of edema resolution, the Na+ /K+ ATPase, and proposed that this may be one of the procedures by which edema recovery is prevented after SARS-CoV infection, either by inhibition of Na+ /K+ ATPase activity or by relocating this enzyme to another subcellular compartment. Deadly human CoVs as SARS- and MERS-CoVs have at least two viral proteins with IC activity and PBM motifs. Studies on the relevance of E and 3a SARS-CoV proteins in replication and virulence, and the interdependence among them have shown that the presence in the virus of at least E or 3a proteins was needed for virus viability. In fact, we have shown that the complementation between E and 3a proteins is mediated by the PBM motifs located at the carboxy-terminus of these proteins. Our studies on the interaction of SARS-CoV and MERS-CoV with the host, and the engineering of reverse genetics systems for each of these viruses, led us to the development of genetically stable vaccine candidates that provided full-protection against the challenge with the homologous virulent virus using mice models.

Trabajo presentado en el XIV International Nidovirus Symposium (Nido2017), celebrado en Kansas City, Missouri (Estados Unidos), del 4 al 9 de junio de 2017