Interference Of The Host Innate Immunity By Shigella Fiexneri T3SS Effector LpaH4.5

Shigella spp. is a Gram-negative facultatively intracellular pathogen that isresponsible for bacillary dysentery in humans.Infection by this pathogen leads to anintense and acute inflammatory bowel disease that is characterized by watery diarrheawith purulent discharge. Colonic biopsies from infected patients reveal massiveinflammatory cell infiltration, tissue edema, and regions where the epithelium iscompletely destroyed. To gain entry into the colonic epithelium, Shigella spp. exploitsM cells to allow intact Shigella spp. to traverse into the underlying subepithelialpocket where macrophages reside. These macrophages engulf Shigella spp., butinstead of successfully destroying the bacteria, these cells rapidly undergo apoptosis.Before cell death, infected macrophages release IL-1b through the direct activation ofcaspase-1by Shigella spp. The proinflammatory nature of IL-1b results in therecruitment of polymorphonuclear cells that infiltrate the infected site and destabilizethe epithelium. Loss of integrity of the epithelial barrier allows more bacteria totraverse into the subepithelial space and gain access to the basolateral pole of theepithelial cells. Therefore, exploring the pathogenic mechanism of Shigella spp.infection and its interaction with host is of vital importance for effective Shigellosistherapy.Type III secretion systems (T3SS) are used by numerous Gram-negativepathogenic bacteria to deliver effector proteins into the cells of their human, animal orplant hosts. T3S systems comprise the T3S apparatus (T3SA) that form syringe-likestructures that span the bacterial envelope and extend like a needle from the bacterialsurface, translocators that transit through the T3SA and form a pore within the targetcell membrane, effectors that transit through the T3SA andthe pore into the cytosol ofhost cells, and specific chaperones and transcription regulators for secretion andtranscription of these effectors. Among the Shigella spp T3SS effectors are membersof the IpaH family, which comprises nine proteins encoded by both the chromosomeand the virulence plasmid. To better understand the function of this family of E3 ubiquitin ligases, we decided to define the functional relevance of IpaH4.5as a newtype of E3ubiquitin ligase. We present evidence that the IpaH4.5exert its pathogenicfunctions using TBK1and Nalp3as its E3substracts.1．IpaH4.5was shown to interact directly with TBK1and Nalp3both in vitro andin vivo.2. Overexpression of IpaH4.5destabilized TBK1and severely impaired IFN-β,IRF-3and NF-κB activation. The abundance of endogenous Nalp3and IL1bproduction was upregulated by overexpressed IpaH4.5.3. IpaH4.5promotes TBK1and Nalp3ubiquition both in vivo and in vitro.4. IpaH4.5is an important shigella virulence factor. IpaH4.5knockout shigellaproduces reduced TNFa and increased IL1b, accordingly, cell proliferation andinfection were affected by IpaH4.5knockout Sh. flexneri2a301, as compared withWT Sh. flexneri2a301.Taken together, here we showed that Sh. flexneri2a301IpaH4.5targets TBK1and Nalp3, which results in the induction of polyubiquitylation of TBK1and Nalp3,thereby facilitating the proteasome dependent degradation of TBK1and stabilizationof NAlp3. Consequently, IpaH4.5interfer with NF κB activation and promotes cellpyrotosis during bacterial infection, we propose that the polyubiquitylation of TBK1and Nalp3during Sh. flexneri2a301infection is a new bacterial strategy to modulatehost inflammatory responses and promote bacterial infection.