title: Impact of host membrane pore formation by the Yersinia pseudotuberculosis type III secretion system on the macrophage innate immune response.
abstract: Type III secretion systems (T3SSs) are used by Gram-negative pathogens to form pores in host membranes and deliver virulence-associated effector proteins inside host cells. In pathogenic Yersinia, the T3SS pore-forming proteins are YopB and YopD. Mammalian cells recognize the Yersinia T3SS, leading to a host response that includes secretion of the inflammatory cytokine interleukin-1β (IL-1β), Toll-like receptor (TLR)-independent expression of the stress-associated transcription factor Egr1 and the inflammatory cytokine tumor necrosis factor alpha (TNF-α), and host cell death. The known Yersinia T3SS effector proteins are dispensable for eliciting these responses, but YopB is essential. Three models describe how the Yersinia T3SS might trigger inflammation: (i) mammalian cells sense YopBD-mediated pore formation, (ii) innate immune stimuli gain access to the host cytoplasm through the YopBD pore, and/or (iii) the YopB-YopD translocon itself or its membrane insertion is proinflammatory. To test these models, we constructed a Yersinia pseudotuberculosis mutant expressing YopD devoid of its predicted transmembrane domain (YopD(ΔTM)) and lacking the T3SS cargo proteins YopHEMOJTN. This mutant formed pores in macrophages, but it could not mediate translocation of effector proteins inside host cells. Importantly, this mutant did not elicit rapid host cell death, IL-1β secretion, or TLR-independent Egr1 and TNF-α expression. These data suggest that YopBD-mediated translocation of unknown T3SS cargo leads to activation of host pathways influencing inflammation, cell death, and response to stress. As the YopD(ΔTM) Y. pseudotuberculosis mutant formed somewhat smaller pores with delayed kinetics, an alternative model is that the wild-type YopB-YopD translocon is specifically sensed by host cells.
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California-Santa Cruz, Santa Cruz, California, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Kwuan
authors.forename: Walter
authors.initials: W
authors.lastname: Adams
authors.forename: Victoria
authors.initials: V
authors.lastname: Auerbuch
mesh_terms: D000818:Animals; D016923:Cell Death; D002460:Cell Line; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000276:immunology / Q000502:physiology; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D016133:Polymerase Chain Reaction / Q000379:methods; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D015011:Yersinia pseudotuberculosis / Q000235:genetics / Q000378:metabolism*
chemical_list: D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D053583:Interleukin-1beta; D014409:Tumor Necrosis Factor-alpha