K.Z.). Conflict of interest: The authors declare no financial or Navitoclax concentration commercial conflicts of interest. Disclaimer: Supplementary materials have been peer-reviewed but not copyedited. “
“Toll-like receptor (TLR) signalling pathways constitute an evolutionarily conserved component of the host immune response to pathogenic infection. Here, we describe the ability of a virally encoded form of the Pellino protein to inhibit Toll- and TLR-mediated activation of downstream Rel family transcription factors. In addition to inhibiting drosomycin promoter activation by Spätzle
in Drosophila melanogaster cells, viral Pellino attenuates the activation of NF-κB by TLR signalling components and by the TLR4 ligand, LPS, in human cells. We propose that viral Pellino, like mammalian Pellinos, contains a forkhead-associated domain but differs from the mammalian forms in that it lacks a complete and functional RING-like domain. We produce a Everolimus clinical trial homology model and present experimental data to support this model by demonstrating that, like mammalian Pellinos, viral Pellino can interact with IRAK-1 via its forkhead-associated domain, whereas unlike its
mammalian counterparts, it fails to post-translationally modify IRAK-1. Furthermore, we demonstrate that viral Pellino can functionally antagonise the activity of human Pellino3S. Thus, our findings identify potential immunoevasive capabilities possessed by a poxviral homolog of the Pellino protein and add growing evidence for a likely role for Pellino proteins in Toll and TLR ROS1 signalling. Chief among innate immune signalling pathways is Toll-like receptor (TLR) signalling to NF-κB, which controls expression of regulatory molecules that co-ordinate humoral and cell-mediated immunity 1. Many details of this axis were unravelled based on the evolutionary conservation with the parallel immune defence response in Drosophila,
where the Spätzle/Toll/Pelle/Cactus axis regulates induction of antimicrobial peptides 2. Upon ligand binding, all TLRs except TLR3 recruit the adaptor protein MyD88 and the kinases IRAK-1 and IRAK-4 3. TLR2 and -4 signalling require the adaptor Mal to bridge the receptor and MyD88 4. IRAK-4 phosphorylates IRAK-1, leading to IRAK-1 autophosphorylation 5. The kinases then leave the receptor to interact with TRAF6. Next, TRAF6 promotes the generation of unanchored lysine 63 polyubiquitin chains 6, leading to activation of the downstream kinase TAK-1 7, 8. This in turn can lead to activation of MAPK signalling, as well as stimulation of IKK activity. IKKβ phosphorylates IκB proteins, leading to their ultimate degradation and the ensuing liberation of NF-κB 9. An emerging aspect of control in TLR signalling is the role of Pellino proteins 10, 11. Pellino was first identified in Drosophila as a binding partner of Pelle, a Drosophila homolog of IRAK 12.