BtpB, a novel Brucella TIR-containing effector protein with immune modulatory functions

Abstract

Several bacterial pathogens have TIR domain-containing proteins that contribute to their pathogenesis. We identified a second TIR-containing protein in Brucella spp. that we have designated BtpB. We show it is a potent inhibitor of TLR signaling, probably via MyD88. BtpB is a novel Brucella effector that is translocated into host cells and interferes with activation of dendritic cells. In vivo mouse studies revealed that BtpB is contributing to virulence and control of local inflammatory responses with relevance in the establishment of chronic brucellosis. Together, our results show that BtpB is a novel Brucella effector that plays a major role in the modulation of host innate immune response during infection.

Pathogenesis and Immunobiology of Brucellosis

“…24 Redundancy of TcpB/BtpA and BtpB function may explain the failure to identify these immunoregulatory genes by using simple transposon screens. Interaction between BtpA/BtpB and MyD88 may also explain the substantial increase in survival of Brucella in MyD88 À/À knockout mice in contrast to TLR4…”

A Pseudomonas aeruginosa TIR effector mediates immune evasion by targeting UBAP1 and TLR adaptors

“…As bacterial TIR proteins down‐modulate NF‐κB activation (Newman et al , 2006; Cirl et al , 2008; Salcedo et al , 2008, 2013; Spear et al , 2012; Askarian et al , 2014; Zou et al , 2014), we infected the lung carcinoma epithelial cell line A549, a well‐established cellular model for Pseudomonas infection and analysed NF‐κB translocation into the nucleus after one hour of infection by confocal microscopy. We developed an automated analysis of p65/RelA fluorescence in relation to DAPI labelling using a specific ImageJ plugin from images obtained by confocal microscopy (Fig EV1A) which allowed us to clearly differentiate between TNFα‐treated and mock‐infected cells (Figs 2A and EV1B).…”

“…Bacterial targeting of TLRs has been best described for uropathogenic E. coli TcpC (Cirl et al , 2008) and Brucella BtpA, also known as TcpB (Cirl et al , 2008; Salcedo et al , 2008), even though their molecular mode of action remains elusive. Brucella relies on an additional TIR protein, BtpB to down‐modulate inflammation during infection (Salcedo et al , 2013). TcpC was shown to interfere with MyD88‐dependent and independent pathways to down‐modulate TLR signalling and contribute to kidney pathology (Cirl et al , 2008; Yadav et al , 2010).…”

“…In the case of TcpC, internalization into host cells was observed but the export mechanism was not identified (Cirl et al , 2008), whereas no data are available regarding Salmonella , Yersinia, Staphyloccocus and Enteroccoccus . In the case of Brucella , depending on the fusion tags, translocation into host cells of BtpA/TcpB or BtpB was dependent or independent of the T4SS (Salcedo et al , 2013) whereas a separate group has proposed that BtpA/TcpB is cell permeable and may enter host cells in a passive manner (Radhakrishnan & Splitter, 2010). Unfortunately, PumA fusion with CyaA resulted in its cleavage preventing us from using this system.…”

“…In contrast, few examples of direct blocking at the level of initial receptor–adaptor complexes are known. Some bacterial pathogens rely on TIR domain‐containing proteins to perturb TIR‐dependent interactions (Newman et al , 2006; Cirl et al , 2008; Salcedo et al , 2008, 2013), essential in innate immune signalling. The growing number of bacterial TIR proteins recently identified in both Gram‐negative and Gram‐positive human pathogens (Spear et al , 2012; Askarian et al , 2014; Zou et al , 2014) highlights the importance of this immune evasion strategy in disease.…”