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J Exp Med. 2011 Jan 17;208(1):195-212. doi: 10.1084/jem.20100717. Epub 2011 Jan 3.

Strain-specific activation of the NF-kappaB pathway by GRA15, a novel Toxoplasma gondii dense granule protein.

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  • 1Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Abstract

NF-κB is an integral component of the immune response to Toxoplasma gondii. Although evidence exists that T. gondii can directly modulate the NF-κB pathway, the parasite-derived effectors involved are unknown. We determined that type II strains of T. gondii activate more NF-κB than type I or type III strains, and using forward genetics we found that this difference is a result of the polymorphic protein GRA15, a novel dense granule protein which T. gondii secretes into the host cell upon invasion. A GRA15-deficient type II strain has a severe defect in both NF-κB nuclear translocation and NF-κB-mediated transcription. Furthermore, human cells expressing type II GRA15 also activate NF-κB, demonstrating that GRA15 alone is sufficient for NF-κB activation. Along with the rhoptry protein ROP16, GRA15 is responsible for a large part of the strain differences in the induction of IL-12 secretion by infected mouse macrophages. In vivo bioluminescent imaging showed that a GRA15-deficient type II strain grows faster compared with wild-type, most likely through its reduced induction of IFN-γ. These results show for the first time that a dense granule protein can modulate host signaling pathways, and dense granule proteins can therefore join rhoptry proteins in T. gondii's host cell-modifying arsenal.

Comment in

PMID:
21199955
[PubMed - indexed for MEDLINE]
PMCID:
PMC3023140
Free PMC Article

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