Different Domains of Pseudomonas aeruginosa Exoenzyme S Activate Distinct TLRs

Abstract

Some bacterial products possess multiple immunomodulatory effects and thereby complex mechanisms of action. Exogenous administration of an important Pseudomonas aeruginosa virulence factor, exoenzyme S (ExoS) induces potent monocyte activation leading to the production of numerous proinflammatory cytokines and chemokines. However, ExoS is also injected directly into target cells, inducing cell death through its multiple effects on signaling pathways. This study addresses the mechanisms used by ExoS to induce monocyte activation. Exogenous administration resulted in specific internalization of ExoS via an actin-dependent mechanism. However, ExoS-mediated cellular activation was not inhibited if internalization was blocked, suggesting an alternate mechanism of activation. ExoS bound a saturable and specific receptor on the surface of monocytic cells. ExoS, LPS, and peptidoglycan were all able to induce tolerance and cross-tolerance to each other suggesting the involvement of a TLR in ExoS-recognition. ExoS activated monocytic cells via a myeloid differentiation Ag-88 pathway, using both TLR2 and the TLR4/MD-2/CD14 complex for cellular activation. Interestingly, the TLR2 activity was localized to the C-terminal domain of ExoS while the TLR4 activity was localized to the N-terminal domain. This study provides the first example of how different domains of the same molecule activate two TLRs, and also highlights the possible overlapping pathophysiological processes possessed by microbial toxins.

Synergistic regulation of Pseudomonas aeruginosa‐induced cytokine production in human monocytes by mannose receptor and TLR2

“…TLR2 has been reported to participate in recognition of multiple P. aeruginosa ligands, including lipoproteins [23,51], alginate [42], flagellin [52], and exoenzyme S [21]. TLR2 is an endocytic receptor [53] and has been reported to recruit phagosomes containing yeasts specifically to macrophage [36].…”

“…We and others have reported that Pseudomonas aeruginosa, an opportunistic pathogen responsible for life-threatening infections in immunosuppressed patients, stimulates pro-inflammatory cytokine production mainly through TLR2 and TLR4 [21][22][23]. In murine experimental models of lung infection triggered by P. aeruginosa, TLR signaling seems redundant in the pulmonary host response [24,25], suggesting potential involvement of another receptor in the host defense against P. aeruginosa.…”

“…At the end of the 4 h incubation period the transfection mixture was discarded and cells were allowed to recover for 16 h prior to stimulation in DMEM110% FBS. Cells were then stimulated for 18 h by different stimuli, harvested, and washed twice with PBS (without Mg 21 or Ca 21 ).…”

“…In macrophages, MR is an important player in innate immunity mediating non-opsonic phagocytic uptake of a wide variety of microbes, which include yeast, fungi, protozoa, and bacteria [12]. MR also mediates the endocytosis of soluble glycoconjugates to promote uptake of ligands in macrophages and dendritic cells [13].A number of observations suggest that when engaged by microorganisms or particles, MR may act as a signal-transducing receptor, which triggers a variety of responses, including secretion of mediators [14], lysosomal enzyme secretion [15], cytokine production [16,17], and modulation of other cell surface receptors [18][19][20].We and others have reported that Pseudomonas aeruginosa, an opportunistic pathogen responsible for life-threatening infections in immunosuppressed patients, stimulates pro-inflammatory cytokine production mainly through TLR2 and TLR4 [21][22][23]. In murine experimental models of lung infection triggered by P. aeruginosa, TLR signaling seems redundant in the pulmonary host response [24,25], suggesting potential involvement of another receptor in the host defense against P. aeruginosa.…”

A Role of Toll-IL-1 Receptor Domain-Containing Adaptor-Inducing IFN-β in the Host Response to Pseudomonas aeruginosa Lung Infection in Mice

“…Recently, a number of in vitro and in vivo studies have shown that TLRs are involved in the recognition of P. aeruginosa (5)(6)(7)(8)(9)(10). TLRs are a family of pattern recognition receptors that are critical for cellular responses to microbial products (11).…”