A-049

Vaccinia virus (VACV) encodes many proteins that inhibit innate immunity. For instance, protein A49 inhibits NF-κB activation by binding to β-TrCP. Here we show that A49 is phosphorylated on serine 7 and that this is necessary for binding β-TrCP and inhibition of NF-κB activation. Further, this phosphorylation occurs when the NF-κB pathway is stimulated and the kinase IKKβ is activated. Thus, A49 shows beautiful biological regulation, for activation of the pathway also activates the virus inhibitor of the pathway. The significance is seen in vivo, since VACVs expressing A49 S7A or S7E are less virulent than wild-type virus but more virulent than a virus lacking A49.

Vaccinia virus (VACV) encodes multiple proteins inhibiting the NF-κB signalling pathway. One of these, A49, targets the E3 ubiquitin ligase β-TrCP, which is responsible for the ubiquitylation and consequential proteosomal degradation of IκBα and the release of the NF-κB heterodimer. β-TrCP is a pleiotropic enzyme ubiquitylating multiple cellular substrates, including the transcriptional activator β-catenin. Here we demonstrate that A49 can activate the Wnt signalling pathway, a critical pathway that is involved in cell cycle and cell differentiation, and is controlled by β-catenin. The data presented show that the expression of A49 ectopically or during VACV infection causes accumulation of β-catenin, and that A49 triggering of Wnt signalling is dependent on binding β-TrCP. This is consistent with A49 blocking the ability of β-TrCP to recognise β-catenin and IκBα, and possibly other cellular targets. Thus, A49 targetting of β-TrCP affects multiple cellular pathways, including the NF-κB and Wnt signalling cascades.