The Salmonella type III effector SspH2 specifically exploits the NLR co-chaperone activity of SGT1 to subvert immunity.
To further its pathogenesis, S. Typhimurium delivers effector proteins into host cells, including the novel E3 ubiquitin ligase (NEL) effector SspH2. Using model systems in a cross-kingdom approach we gained further insight into the molecular function of this effector. Here, we show that SspH2 modulates innate immunity in both mammalian and plant cells. In mammalian cell culture, SspH2 significantly enhanced Nod1-mediated IL-8 secretion when transiently expressed or bacterially delivered. In addition, SspH2 also enhanced an Rx-dependent hypersensitive response in planta. In both of these nucleotide-binding leucine rich repeat receptor (NLR) model systems, SspH2-mediated phenotypes required its catalytic E3 ubiquitin ligase activity and interaction with the conserved host protein SGT1. SGT1 has an essential cell cycle function and an additional function as an NLR co-chaperone in animal and plant cells. Interaction between SspH2 and SGT1 was restricted to SGT1 proteins that have NLR co-chaperone function and accordingly, SspH2 did not affect SGT1 cell cycle functions. Mechanistic studies revealed that SspH2 interacted with, and ubiquitinated Nod1 and could induce Nod1 activity in an agonist-independent manner if catalytically active. Interestingly, SspH2 in vitro ubiquitination activity and protein stability were enhanced by SGT1. Overall, this work adds to our understanding of the sophisticated mechanisms used by bacterial effectors to co-opt host pathways by demonstrating that SspH2 can subvert immune responses by selectively exploiting the functions of a conserved host co-chaperone.
Michael Smith Laboratories, The University of British Columbia, Vancouver, British Columbia, Canada.
Amit P
AP
Bhavsar
Nat F
NF
Brown
Jan
J
Stoepel
Marcel
M
Wiermer
Dale D O
DD
Martin
Karolynn J
KJ
Hsu
Koshi
K
Imami
Colin J
CJ
Ross
Michael R
MR
Hayden
Leonard J
LJ
Foster
Xin
X
Li
Phil
P
Hieter
B Brett
BB
Finlay
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D017353:Gene Deletion; D054884:Host-Pathogen Interactions; D006801:Humans; D007113:Immunity, Innate; D016209:Interleukin-8 / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D053472:Nod Signaling Adaptor Proteins / Q000378:metabolism*; D057865:Plant Immunity; D018515:Plant Leaves / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D055550:Protein Stability; D011994:Recombinant Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000276:immunology* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination; D015854:Up-Regulation
D001426:Bacterial Proteins; C508606:CXCL8 protein, human; D018797:Cell Cycle Proteins; D016209:Interleukin-8; D008565:Membrane Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D053472:Nod Signaling Adaptor Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; C490164:SUGT1 protein, human; C094579:invasion protein B, Salmonella typhimurium; D044767:Ubiquitin-Protein Ligases