title: SseK1 and SseK3 Type III Secretion System Effectors Inhibit NF-κB Signaling and Necroptotic Cell Death in Salmonella-Infected Macrophages.
abstract: Within host cells such as macrophages,Salmonella entericatranslocates virulence (effector) proteins across its vacuolar membrane via the SPI-2 type III secretion system. Previously, it was shown that when expressed ectopically, the effectors SseK1 and SseK3 inhibit tumor necrosis factor alpha (TNF-α)-induced NF-κB activation. In this study, we show that ectopically expressed SseK1, SseK2, and SseK3 suppress TNF-α-induced, but not Toll-like receptor 4- or interleukin-induced, NF-κB activation. Inhibition required a DXD motif in SseK1 and SseK3, which is essential for the transfer ofN-acetylglucosamine to arginine residues (arginine-GlcNAcylation). During macrophage infection, SseK1 and SseK3 inhibited NF-κB activity in an additive manner. SseK3-mediated inhibition of NF-κB activation did not require the only known host-binding partner of this effector, the E3-ubiquitin ligase TRIM32. SseK proteins also inhibited TNF-α-induced cell death during macrophage infection. Despite SseK1 and SseK3 inhibiting TNF-α-induced apoptosis upon ectopic expression in HeLa cells, the percentage of infected macrophages undergoing apoptosis was SseK independent. Instead, SseK proteins inhibited necroptotic cell death during macrophage infection. SseK1 and SseK3 caused GlcNAcylation of different proteins in infected macrophages, suggesting that these effectors have distinct substrate specificities. Indeed, SseK1 caused the GlcNAcylation of the death domain-containing proteins FADD and TRADD, whereas SseK3 expression resulted in weak GlcNAcylation of TRADD but not FADD. Additional, as-yet-unidentified substrates are likely to explain the additive phenotype of aSalmonellastrain lacking both SseK1 and SseK3.
authors.affiliation: Section of Microbiology, Medical Research Council Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: Regina A
authors.initials: RA
authors.lastname: Günster
authors.affiliation: Section of Microbiology, Medical Research Council Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: Sophie A
authors.initials: SA
authors.lastname: Matthews
authors.affiliation: Section of Microbiology, Medical Research Council Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: Holden
authors.affiliation: Section of Microbiology, Medical Research Council Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom t.thurston@imperial.ac.uk.
authors.forename: Teresa L M
authors.initials: TLM
authors.lastname: Thurston
mesh_terms: D000818:Animals; D017209:Apoptosis; D001120:Arginine / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death; D002460:Cell Line; D002478:Cells, Cultured; D055786:Gene Knockout Techniques; D006031:Glycosylation; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D012475:Salmonella / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D000070584:Tripartite Motif Proteins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D000069296:Type III Secretion Systems; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D016328:NF-kappa B; C490535:SseK1 protein, Salmonella enterica; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D014409:Tumor Necrosis Factor-alpha; D000069296:Type III Secretion Systems; D001120:Arginine; C094027:TRIM32 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: NF-κB signaling; Salmonella; cell death; necroptosis