Vaccinia virus protein A52R activates p38 mitogen-activated protein kinase and potentiates lipopolysaccharide-induced interleukin-10

Viral Immune Evasion Group, School of Biochemistry and Immunology, Trinity College Dublin, Dublin 2, Ireland.
Journal of Biological Chemistry (Impact Factor: 4.57). 10/2005; 280(35):30838-44. DOI: 10.1074/jbc.M501917200
Source: PubMed

ABSTRACT Vaccinia virus (VV) has many mechanisms to suppress and modulate the host immune response. The VV protein A52R was previously shown to act as an intracellular inhibitor of nuclear factor kappaB (NFkappaB) signaling by Toll-like receptors (TLRs). Co-immunoprecipitation studies revealed that A52R interacted with both tumor necrosis factor receptor-associated factor 6 (TRAF6) and interleukin-1 receptor-associated kinase 2 (IRAK2). The effect of A52R on signals other than NFkappaB was not determined. Here, we show that A52R does not inhibit TLR-induced p38 or c-Jun amino N-terminal kinase (JNK) mitogen activating protein (MAP) kinase activation. Rather, A52R could drive activation of these kinases. Two lines of evidence suggested that the A52R/TRAF6 interaction was critical for these effects. First, A52R-induced p38 MAP kinase activation was inhibited by overexpression of the TRAF domain of TRAF6, which sequestered A52R and inhibited its interaction with endogenous TRAF6. Second, a truncated version of A52R, which interacted with IRAK2 and not TRAF6, was unable to activate p38. Because interleukin 10 (IL-10) production is strongly p38-dependent, we examined the effect of A52R on IL-10 gene induction. A52R was found to be capable of inducing the IL-10 promoter through a TRAF6-dependent mechanism. Furthermore, A52R enhanced lipopolysaccharide/TLR4-induced IL-10 production, while inhibiting the TLR-induced NFkappaB-dependent genes IL-8 and RANTES. These results show that although A52R inhibits NFkappaB activation by multiple TLRs it can simultaneously activate MAP kinases. A52R-mediated enhancement of TLR-induced IL-10 may be important to virulence, given the role of IL-10 in immunoregulation.

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    • "Currently, there is no crystal or NMR structure of a complex between A52 and a cellular target. However it has been reported that p38 MAP kinase activation is enhanced by interaction of A52 with the TRAF domain of TRAF6 (Harte et al., 2003; Maloney et al., 2005). It is also known that a peptide mimic of a surface loop (residues D125–I135) linking helices a4 and a5 inhibits NF-jB activation (McCoy et al., 2005). "
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    • "A52 acts further downstream and inhibits NF-kB activation by targeting IRAK2 (Harte et al., 2003; Keating et al., 2007; Maloney et al., 2005). In addition, binding of A52 to TRAF6 mediates p38 MAP kinase activation and enhances TLR-mediated activation of the anti-inflammatory cytokine IL-10 (Maloney et al., 2005). VACV protein K7 has 20% overall sequence identities to A52. "
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    • "Second, a truncated version of A52, which interacted with IRAK-2 and not TRAF6, was unable to activate p38 (Keating and others 2007). Thus, A52 inhibits the expression of NF-κB-dependent genes, such as IL-8 and RANTES, and enhances the production of IL-10 (Maloney and others 2005), which might contribute to the role of A52 in VACV virulence (a virus deletion mutant lacking the A52R gene was attenuated in a murine intranasal model of infection; Harte and others 2003). K7 (early): K7 is a 17.5 kDa protein that shares signifi cant sequence similarity to A52 and whose NMR solution structure has been recently determined (Kalverda and others 2009). "
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