Background Viruses have evolved to evade the host’s match system. cells

Background Viruses have evolved to evade the host’s match system. cells infected with ORF4 mutant computer virus, when compared to cells infected with wt computer virus. Consistent with a role of Akt activation in initial stages of contamination, inhibition of Akt signaling in wt computer virus infected cells resulted in a phenotype resembling the phenotype of the ORF4 mutant computer virus, and activation of Akt by addition of insulin partially reversed the phenotype of the ORF4 mutant computer virus. Importantly, the homologous ORF4 of KSHV was able to rescue the phenotype of the MHV-68 ORF4 mutant, indicating that ORF4 is usually functionally conserved and that ORF4 of KSHV might have a comparable function in contamination RGS13 initiation. Conclusions/Significance In summary, our studies demonstrate that ORF4 contributes to efficient contamination by activation of the protein kinase Akt and thus reveal a novel SB 252218 function of a gammaherpesvirus RCA protein. Introduction Viruses use a variety of strategies to evade the host’s immune response [1], [2]. A host mechanism involved in innate immunity against viruses is usually the match system. Consequently, viruses have evolved to evade the actions of the match system, thereby avoiding destruction by complement-mediated mechanisms [3]C[6]. A number of viruses not only avoid inactivation and destruction by match but also use match receptors to initiate contamination. For example, EBV infects its target cell, the W cell, via match receptor type 2 (CR2) [7]. The poxviral match control protein VCP (vaccinia computer virus match control protein) can hole to match components C3b and C4b, respectively, thereby inactivating match components or blocking the formation of the C3 convertase complex [8]. Extracellular vaccinia computer virus is usually resistant to complement because of incorporation of host complement control proteins into its envelope [9]. Herpesviruses SB 252218 encode complement regulatory proteins that can block complement activation and neutralization of virus particles [3]. For example, HSV-1 glycoprotein gC prevents complement-mediated cell lysis and virus neutralization [10], [11]. The open reading frame 4 (ORF4) of gammaherpesviruses, including human herpesvirus 8 (HHV-8; KSHV), herpesvirus saimiri (HVS), murine gammaherpesvirus 68 (MHV-68) and rhesus rhadinovirus (RRV), encode homologs of host regulators of complement activation (RCA) proteins [12]C[17]. MHV-68, HVS and RRV RCA proteins inhibit complement activation at the level of C3 and C4 deposition [15], [18]C[21]. The KSHV complement control protein (KCP) accelerates the decay of classical C3 convertase and induces the degradation of activated complement factors C4b and C3b [22]. The MHV-68 RCA protein has been shown to play an important role in viral evasion of complement in acute, persistent and latent SB 252218 infection in vivo [23]. Besides complement regulation, viral RCA proteins may have additional functions. SB 252218 For example, the poxvirus B5R protein is essential for virion morphogenesis and is also involved in polymerization of actin on virions in infected cells [24]. HSV gC may play a role in infection by interacting with heparan sulfate or attaching to polarized epithelial cells [25], [26]. Similarly, the RCA proteins of the gammaherpesviruses KSHV and MHV-68 have also been shown to interact with heparan sulfate and glycosaminoglycans [27]C[29]. In addition, the MHV-68 RCA protein has very recently been shown to facilitate MHV-68 replication in primary macrophages in a complement independent manner [30]. Studies to investigate the function of KSHV ORF4 during lytic infection are limited by the lack of a cell culture system capable of supporting productive replication. In contrast, MHV-68 replicates in conventional tissue culture systems and thus provides a model to study de novo gammaherpesvirus infection. MHV-68 is a natural pathogen of wild rodents [31]. The nucleotide sequence of MHV-68 is very closely related to KSHV [14]. Therefore, the functional roles of conserved gammaherpesvirus proteins can be addressed by mutagenesis of the corresponding viral genes [32]. Here, we made use of MHV-68 to study the role of ORF4 during SB 252218 infection.