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Activation of the unfolded protein response is required for defenses against bacterial pore-forming toxin in vivo.

Bischof LJ, Kao CY, Los FC, Gonzalez MR, Shen Z, Briggs SP, van der Goot FG, Aroian RV - PLoS Pathog. (2008)

Bottom Line: We find here that the UPR is one of the key downstream targets of the p38 MAPK pathway in response to PFT since loss of a functional p38 MAPK pathway leads to a failure of PFT to properly activate the ire-1-xbp-1 arm of the UPR.The UPR-mediated activation and response to PFTs is distinct from the canonical UPR-mediated response to unfolded proteins both in terms of its activation and functional sensitivities.These data demonstrate that the UPR, a fundamental intracellular pathway, can operate in intrinsic cellular defenses against bacterial attack.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America.

ABSTRACT
Pore-forming toxins (PFTs) constitute the single largest class of proteinaceous bacterial virulence factors and are made by many of the most important bacterial pathogens. Host responses to these toxins are complex and poorly understood. We find that the endoplasmic reticulum unfolded protein response (UPR) is activated upon exposure to PFTs both in Caenorhabditis elegans and in mammalian cells. Activation of the UPR is protective in vivo against PFTs since animals that lack either the ire-1-xbp-1 or the atf-6 arms of the UPR are more sensitive to PFT than wild-type animals. The UPR acts directly in the cells targeted by the PFT. Loss of the UPR leads to a normal response against unrelated toxins or a pathogenic bacterium, indicating its PFT-protective role is specific. The p38 mitogen-activated protein (MAPK) kinase pathway has been previously shown to be important for cellular defenses against PFTs. We find here that the UPR is one of the key downstream targets of the p38 MAPK pathway in response to PFT since loss of a functional p38 MAPK pathway leads to a failure of PFT to properly activate the ire-1-xbp-1 arm of the UPR. The UPR-mediated activation and response to PFTs is distinct from the canonical UPR-mediated response to unfolded proteins both in terms of its activation and functional sensitivities. These data demonstrate that the UPR, a fundamental intracellular pathway, can operate in intrinsic cellular defenses against bacterial attack.

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Intestinal specific expression of xbp-1 is sufficient to rescue sensitivity to the PFT.Sensitivity to Cry5B was compared among wild-type N2, xbp-1(zc12), xbp-1(zc12) transformed with app-1::GFP, and xbp-1(zc12) transformed with app-1::xbp-1 animals using a plate feeding assay. (A) The health of the worms (details in Materials and Methods) was evaluated after 72 hours on 25% Cry5B-expressing E. coli. Three and six independent lines of app-1::GFP and app-1::xbp-1 were used, respectively. Data are mean and standard deviation of three experiments. (B) Images comparing the health of wild-type N2, xbp-1(zc12), xbp-1(zc-12) app-1::GFP, and xbp-1(zc-12) app-1::xbp-1 animals on 25% Cry5B plates for 72 h. Scale bar is 0.2 mm.
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ppat-1000176-g003: Intestinal specific expression of xbp-1 is sufficient to rescue sensitivity to the PFT.Sensitivity to Cry5B was compared among wild-type N2, xbp-1(zc12), xbp-1(zc12) transformed with app-1::GFP, and xbp-1(zc12) transformed with app-1::xbp-1 animals using a plate feeding assay. (A) The health of the worms (details in Materials and Methods) was evaluated after 72 hours on 25% Cry5B-expressing E. coli. Three and six independent lines of app-1::GFP and app-1::xbp-1 were used, respectively. Data are mean and standard deviation of three experiments. (B) Images comparing the health of wild-type N2, xbp-1(zc12), xbp-1(zc-12) app-1::GFP, and xbp-1(zc-12) app-1::xbp-1 animals on 25% Cry5B plates for 72 h. Scale bar is 0.2 mm.

Mentions: To directly demonstrate the role of xbp-1 in protecting intestinal cells against Cry5B, the intestinal specific app-1 promoter [17] was used to drive expression of xbp-1 in xbp-1(zc12) mutant animals to determine if expression in the intestine is sufficient to rescue the Hpo phenotype. As a negative control, GFP was similarly expressed under control of the app-1 promoter in xbp-1(zc12) mutant animals. In control animals, expression of the GFP solely in intestinal cells was confirmed (data not shown). As expected, the majority of wild-type N2 animals showed only a low-modest degree of intoxication upon exposure to 25% Cry5B-expressing E. coli (Figure 3A, B; they were smaller and somewhat paler than the wild-type worms on control plates but were still quite active). Also as predicted, both xbp-1(zc12) mutant animals and xbp-1(zc12) mutant animals transformed with app-1::GFP were Hpo and intoxicated to similar extents (Figure 3A, B; most animals were very pale, small, and inactive). In contrast, xbp-1(zc12) worms expressing xbp-1 under the app-1 promoter were significantly healthier than either untransformed or app-1::GFP transformed xbp-1(zc12) animals fed with Cry5B (Figure 3A, B). However, these app-1::xbp-1-transformed xbp-1(z12) worms were not as healthy as wild-type N2 under the same conditions. This partial rescue could indicate the expression of the artificial xbp-1 transgenes did not fully recapitulate wild-type xbp-1 expression levels and/or that there is some role for the ire-1 – xbp-1 pathway in other cell types. Nonetheless, our results support a significant protective function for xbp-1 within the cells targeted by Cry5B.


Activation of the unfolded protein response is required for defenses against bacterial pore-forming toxin in vivo.

Bischof LJ, Kao CY, Los FC, Gonzalez MR, Shen Z, Briggs SP, van der Goot FG, Aroian RV - PLoS Pathog. (2008)

Intestinal specific expression of xbp-1 is sufficient to rescue sensitivity to the PFT.Sensitivity to Cry5B was compared among wild-type N2, xbp-1(zc12), xbp-1(zc12) transformed with app-1::GFP, and xbp-1(zc12) transformed with app-1::xbp-1 animals using a plate feeding assay. (A) The health of the worms (details in Materials and Methods) was evaluated after 72 hours on 25% Cry5B-expressing E. coli. Three and six independent lines of app-1::GFP and app-1::xbp-1 were used, respectively. Data are mean and standard deviation of three experiments. (B) Images comparing the health of wild-type N2, xbp-1(zc12), xbp-1(zc-12) app-1::GFP, and xbp-1(zc-12) app-1::xbp-1 animals on 25% Cry5B plates for 72 h. Scale bar is 0.2 mm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2553261&req=5

ppat-1000176-g003: Intestinal specific expression of xbp-1 is sufficient to rescue sensitivity to the PFT.Sensitivity to Cry5B was compared among wild-type N2, xbp-1(zc12), xbp-1(zc12) transformed with app-1::GFP, and xbp-1(zc12) transformed with app-1::xbp-1 animals using a plate feeding assay. (A) The health of the worms (details in Materials and Methods) was evaluated after 72 hours on 25% Cry5B-expressing E. coli. Three and six independent lines of app-1::GFP and app-1::xbp-1 were used, respectively. Data are mean and standard deviation of three experiments. (B) Images comparing the health of wild-type N2, xbp-1(zc12), xbp-1(zc-12) app-1::GFP, and xbp-1(zc-12) app-1::xbp-1 animals on 25% Cry5B plates for 72 h. Scale bar is 0.2 mm.
Mentions: To directly demonstrate the role of xbp-1 in protecting intestinal cells against Cry5B, the intestinal specific app-1 promoter [17] was used to drive expression of xbp-1 in xbp-1(zc12) mutant animals to determine if expression in the intestine is sufficient to rescue the Hpo phenotype. As a negative control, GFP was similarly expressed under control of the app-1 promoter in xbp-1(zc12) mutant animals. In control animals, expression of the GFP solely in intestinal cells was confirmed (data not shown). As expected, the majority of wild-type N2 animals showed only a low-modest degree of intoxication upon exposure to 25% Cry5B-expressing E. coli (Figure 3A, B; they were smaller and somewhat paler than the wild-type worms on control plates but were still quite active). Also as predicted, both xbp-1(zc12) mutant animals and xbp-1(zc12) mutant animals transformed with app-1::GFP were Hpo and intoxicated to similar extents (Figure 3A, B; most animals were very pale, small, and inactive). In contrast, xbp-1(zc12) worms expressing xbp-1 under the app-1 promoter were significantly healthier than either untransformed or app-1::GFP transformed xbp-1(zc12) animals fed with Cry5B (Figure 3A, B). However, these app-1::xbp-1-transformed xbp-1(z12) worms were not as healthy as wild-type N2 under the same conditions. This partial rescue could indicate the expression of the artificial xbp-1 transgenes did not fully recapitulate wild-type xbp-1 expression levels and/or that there is some role for the ire-1 – xbp-1 pathway in other cell types. Nonetheless, our results support a significant protective function for xbp-1 within the cells targeted by Cry5B.

Bottom Line: We find here that the UPR is one of the key downstream targets of the p38 MAPK pathway in response to PFT since loss of a functional p38 MAPK pathway leads to a failure of PFT to properly activate the ire-1-xbp-1 arm of the UPR.The UPR-mediated activation and response to PFTs is distinct from the canonical UPR-mediated response to unfolded proteins both in terms of its activation and functional sensitivities.These data demonstrate that the UPR, a fundamental intracellular pathway, can operate in intrinsic cellular defenses against bacterial attack.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, United States of America.

ABSTRACT
Pore-forming toxins (PFTs) constitute the single largest class of proteinaceous bacterial virulence factors and are made by many of the most important bacterial pathogens. Host responses to these toxins are complex and poorly understood. We find that the endoplasmic reticulum unfolded protein response (UPR) is activated upon exposure to PFTs both in Caenorhabditis elegans and in mammalian cells. Activation of the UPR is protective in vivo against PFTs since animals that lack either the ire-1-xbp-1 or the atf-6 arms of the UPR are more sensitive to PFT than wild-type animals. The UPR acts directly in the cells targeted by the PFT. Loss of the UPR leads to a normal response against unrelated toxins or a pathogenic bacterium, indicating its PFT-protective role is specific. The p38 mitogen-activated protein (MAPK) kinase pathway has been previously shown to be important for cellular defenses against PFTs. We find here that the UPR is one of the key downstream targets of the p38 MAPK pathway in response to PFT since loss of a functional p38 MAPK pathway leads to a failure of PFT to properly activate the ire-1-xbp-1 arm of the UPR. The UPR-mediated activation and response to PFTs is distinct from the canonical UPR-mediated response to unfolded proteins both in terms of its activation and functional sensitivities. These data demonstrate that the UPR, a fundamental intracellular pathway, can operate in intrinsic cellular defenses against bacterial attack.

Show MeSH
Related in: MedlinePlus