Ubiquitination and degradation of GBPs by a Shigella effector to suppress host defence

Abstract

Interferon-inducible guanylate-binding proteins (GBPs) mediate cell-autonomous antimicrobial defences. Shigella flexneri, a Gram-negative cytoplasmic free-living bacterium that causes bacillary dysentery, encodes a repertoire of highly similar type III secretion system effectors called invasion plasmid antigen Hs (IpaHs). IpaHs represent a large family of bacterial ubiquitin-ligases, but their function is poorly understood. Here we show that S. flexneri infection induces rapid proteasomal degradation of human guanylate binding protein-1 (hGBP1). We performed a transposon screen to identify a mutation in the S. flexneri gene ipaH9.8 that prevented hGBP1 degradation. IpaH9.8 targets hGBP1 for degradation via Lys48-linked ubiquitination. IpaH9.8 targets multiple GBPs in the cytoplasm independently of their nucleotide-bound states and their differential function in antibacterial defence, promoting S. flexneri replication and resulting in the death of infected mice. In the absence of IpaH9.8, or when binding of GBPs to IpaH9.8 was disrupted, GBPs such as hGBP1 and mouse GBP2 (mGBP2) translocated to intracellular S. flexneri and inhibited bacterial replication. Like wild-type mice, mutant mice deficient in GBP1-3, 5 and 7 succumbed to S. flexneri infection, but unlike wild-type mice, mice deficient in these GBPs were also susceptible to S. flexneri lacking ipaH9.8. The mode of IpaH9.8 action highlights the functional importance of GBPs in antibacterial defences. IpaH9.8 and S. flexneri provide a unique system for dissecting GBP-mediated immunity.

Sensing of invading pathogens by GBPs: At the crossroads between cell-autonomous and innate immunity

“…Surprisingly, Feng Shao group demonstrated that in S. flexneri infected cells, hGBP1 was degraded by proteasomes over time, which was also dependent on virulence factors secreted by S. flexneri . A transposon‐insertion library screening then identified that the bacterial secreted effector IpaH9.8, a E3 ubiquitin ligase, was responsible for causing hGBP1 degradation, as well as the degradation of hGBP2, 4, and 6, as well as mGBP2, 3, 6, 7, 9, 10, and 11 . A role for IpaH9.8 in degrading hGBPs was independently confirmed by Wandel et al., who also showed that this restores actin‐dependent bacterial motility and cell‐to‐cell spread .…”

Bacterial injection machines: Evolutionary diverse but functionally convergent

“…Feng Shao (National Institute of Biological Sciences, Beijing, China) reported the interaction of the T3 effector IpaH9.8 of S. flexneri with the host immune response. IpaH9.8 suppresses host defence through ubiquitination and degradation of guanylate‐binding proteins (GBPs; Li et al, ). Lack of IpaH9.8 or its binding to GBPs provoked translocation of GBPs such as hGBP1 and mGBP2 to intracellular S. flexneri, where they inhibited bacterial replication, highlighting the functional importance of GBPs in antibacterial defences.…”

Demarcation of Viral Shelters Results in Destruction by Membranolytic GTPases: Antiviral Function of Autophagy Proteins and Interferon‐Inducible GTPases

“…In addition to their dynamin‐like function, these GTPases have more recently been appreciated to have a multitude of roles within cell‐autonomous defenses. GBPs are also known to bring various anti‐microbial effector proteins or to stunt bacterial spread by blocking bacterial association with actin . Furthermore, GBPs can enhance inflammasome formation, which produces inflammatory cytokines in response to pathogen invasion and cellular damages …”