Salmonella Effector AvrA Regulation of Colonic Epithelial Cell Inflammation by Deubiquitination

Department of Pathology, The University of Chicago, Chicago, Illinois, USA.
American Journal Of Pathology (Impact Factor: 4.59). 10/2007; 171(3):882-92. DOI: 10.2353/ajpath.2007.070220
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AvrA is a newly described bacterial effector existing in Salmonella. Here, we test the hypothesis that AvrA is a deubiquitinase that removes ubiquitin from two inhibitors of the nuclear factor-kappaB (NF-kappaB) pathway, IkappaBalpha and beta-catenin, thereby inhibiting the inflammatory responses of the host. The role of AvrA was assessed in intestinal epithelial cell models and in mouse models infected with AvrA-deficient and -sufficient Salmonella strains. We also purified AvrA and AvrA mutant proteins and characterized their deubiquitinase activity in a cell-free system. We investigated target gene and inflammatory cytokine expression, as well as effects on epithelial cell proliferation and apoptosis induced by AvrA-deficient and -sufficient bacterial strains in vivo. Our results show that AvrA blocks degradation of IkappaBalpha and beta-catenin in epithelial cells. AvrA deubiquitinates IkappaBalpha, which blocks its degradation and leads to the inhibition of NF-kappaB activation. Target genes of the NF-kappaB pathway, such as interleukin-6, were correspondingly down-regulated during bacterial infection with Salmonella expressing AvrA. AvrA also deubiquitinates and thus blocks degradation of beta-catenin. Target genes of the beta-catenin pathway, such as c-myc and cyclinD1, were correspondingly up-regulated with AvrA expression. Increased beta-catenin further negatively regulates the NF-kappaB pathway. Our findings suggest an important role for AvrA in regulating host inflammatory responses through NF-kappaB and beta-catenin pathways.

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    • "We utilized the following protocol to fix organoid cells: 10% formalin 30 min; 75% alcohol 5 min; 100% alcohol 10 min; xylene 5 min; xylene 10 min; and paraffin (65°C) 60 min. The paraffin sections were processed with standard techniques (Ye et al. 2007; Liu et al. 2010). "
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    09/2014; 2(9). DOI:10.14814/phy2.12147
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    • "In addition, it was reported that AvrA has deubiquitinase activity and removes ubiquitin from IκB and β-catenin, two inhibitors of NF-κB, thereby preventing their degradation by the proteasome. The resulting increase of association with NF-κB attenuates the translocation of the transcription factor to the nucleus and attenuates the inflammatory response and cellular apoptosis (Ye et al., 2007). NF-κB functions as an important cellular hub of immune responses that is preferentially targeted by many effectors. "
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    • "The role of Wnt/β-catenin in Salmonella infections has been investigated in vitro or in streptomycin pretreated mice models [7, 11–13]. From these studies it is known that infection of colon epithelial cells (CEC) with Salmonella typhimurium causes an increase in GSK3β-dependent β-catenin phosphorylation, leading to an upregulation of IL-6, IL-8, and Wnt2, via TLR5/NF-κB activation [10, 14]. "
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