The Shigella flexneri effector OspG interferes with innate immune responses by targeting ubiquitin-conjugating enzymes

doi:10.1073/pnas.0504466102

The Shigella flexneri effector OspG interferes with innate immune responses by targeting ubiquitin-conjugating enzymes

^*Unité de Pathogénie Microbienne Moléculaire, Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche 389, Institut Pasteur, 28 Rue du Dr. Roux, 75015 Paris, France; and ^‡Hybrigenics, 3-5 Impasse Reille, 75014 Paris, France

Edited by Stanley Falkow, Stanford University, Stanford, CA (received for review May 30, 2005)

Abstract

Bacteria of Shigella spp. are responsible for shigellosis in humans. They use a type III secretion system to inject effector proteins into host cells and induce their entry into epithelial cells or trigger apoptosis in macrophages. We present evidence that the effector OspG is a protein kinase that binds various ubiquitinylated ubiquitin-conjugating enzymes, including UbcH5, which belongs to the stem cell factor SCF^β-TrCP complex promoting ubiquitination of phosphorylated inhibitor of NF-κB type α (phospho-IκBα). Transfection experiments indicated that OspG can prevent phospho-IκBα degradation and NF-κB activation induced by TNF-α stimulation. Infection of epithelial cells by the S. flexneri wild-type strain, but not an ospG mutant, led to accumulation of phospho-IκBα, consistent with OspG inhibiting SCF^β-TrCP activity. Upon infection of ileal loops in rabbits, the ospG mutant induced a stronger inflammatory response than the wild-type strain. This finding indicates that OspG negatively controls the host innate response induced by S. flexneri upon invasion of the epithelium.

Footnotes

↵ ** To whom correspondence should be addressed. E-mail: cparsot{at}pasteur.fr.
↵ † Present address: International Vaccine Institute, San 4-8, Bongcheon-7-dong, Kwanak-gu, Seoul 151-818, Korea.
↵ § Present address: Diatos, 3-5 Impasse Reille, 75014 Paris, France.
↵ ¶ Present address: G. W. Hooper Research Foundation, University of California, 513 Parnassus Avenue, HSW1501, Box 0552, San Francisco, CA 94143-0552.
↵ ∥ Present address: Département de Biologie Joliot-Curie, Commissariat à l'Energie Atomique, 91191 Gif-sur-Yvette, France.
Author contributions: D.W.K., P.L., and C.P. designed research; D.W.K., G.L., A.-L.P., and P.J.S. performed research; G.L. contributed new reagents/analytic tools; D.W.K., G.L., A.-L.P., P.J.S., and C.P. analyzed data; and D.W.K., P.J.S., and C.P. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: E1, ubiquitin-activating enzyme; E2, ubiquitin-conjugating enzyme; E3, ubiquitin-ligating enzyme; TTS, type III secretion; IκBα, inhibitor of NF-κB type α; hIκBα, human IκBα; mIκBα, mouse IκBα; PMN, polymorphonuclear leukocyte(s).