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Functional plasticity in the type IV secretion system of Helicobacter pylori.

Barrozo RM, Cooke CL, Hansen LM, Lam AM, Gaddy JA, Johnson EM, Cariaga TA, Suarez G, Peek RM, Cover TL, Solnick JV - PLoS Pathog. (2013)

Bottom Line: CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions.Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS.We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

View Article: PubMed Central - PubMed

Affiliation: Center for Comparative Medicine, University of California Davis, Davis, California, United States of America.

ABSTRACT
Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

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Loss of the capacity to induce IL-8 in H. pylori recovered from rhesus monkeys is associated with changes in the gene encoding CagY, an essential protein in the T4SS.(A–E) H. pylori was isolated from five rhesus macaques up to 14 months after experimental infection with H. pylori WT J166. Individual colonies were co-cultured with AGS cells, and ELISA was used to measure IL-8 levels, which were normalized to the WT J166 positive control. Each data point represents the results from a single colony. The capacity to induce IL-8 decreased over time in colonies recovered from four monkeys (A–D), but was largely unchanged in one (E). PCR-RFLP analysis showed that H. pylori colonies that lost the capacity to induce IL-8 were associated with a change in cagY (open circles), while those that maintained IL-8 induction typically had cagY that was indistinguishable from WT J166 (filled circles). Animal designation is shown in the upper left corner of each panel. (F) Output strains from each monkey were analyzed by cagY PCR-RFLP and compared to WT H. pylori J166 (dark blue) and to one another. Each pie chart represents all colonies recovered from one of the five monkeys (12–24 colonies/monkey); different colors represent different cagY variants.
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ppat-1003189-g001: Loss of the capacity to induce IL-8 in H. pylori recovered from rhesus monkeys is associated with changes in the gene encoding CagY, an essential protein in the T4SS.(A–E) H. pylori was isolated from five rhesus macaques up to 14 months after experimental infection with H. pylori WT J166. Individual colonies were co-cultured with AGS cells, and ELISA was used to measure IL-8 levels, which were normalized to the WT J166 positive control. Each data point represents the results from a single colony. The capacity to induce IL-8 decreased over time in colonies recovered from four monkeys (A–D), but was largely unchanged in one (E). PCR-RFLP analysis showed that H. pylori colonies that lost the capacity to induce IL-8 were associated with a change in cagY (open circles), while those that maintained IL-8 induction typically had cagY that was indistinguishable from WT J166 (filled circles). Animal designation is shown in the upper left corner of each panel. (F) Output strains from each monkey were analyzed by cagY PCR-RFLP and compared to WT H. pylori J166 (dark blue) and to one another. Each pie chart represents all colonies recovered from one of the five monkeys (12–24 colonies/monkey); different colors represent different cagY variants.

Mentions: H. pylori strains adapted to colonization of mice frequently lose the capacity to induce IL-8 and translocate CagA into gastric epithelial cells [20], [21], which are measures of a functional T4SS. The cagPAI is retained and the mechanism is unknown [21]. Since mice are not a natural host for H. pylori, we asked whether similar changes occur during infection of rhesus macaques, which are commonly infected with H. pylori that is indistinguishable by comparative genomic hybridization from that which infects humans [22]. Five rhesus monkeys were previously challenged with a single colony of wild type (WT) H. pylori J166 that has a functional cagPAI [23]. Multiple output colonies recovered from each monkey up to 14 months post inoculation (PI) were co-cultured with AGS gastric cells to determine their capacity to induce IL-8, which was normalized to the WT control strain. IL-8 induction resembled WT in bacteria recovered early after challenge, but decreased over time in 4 of 5 monkeys (Figure 1A–D). In one monkey, all but one bacterial colony induced IL-8 at levels≥WT, even after 14 months of colonization (Figure 1E). Selected rhesus output colonies that induced low IL-8 (designated rOut1 and rOut2) or high IL-8 (rOut3) in AGS cells were also tested in KATO III gastric cells. Similar results were obtained (Figure S1A). These results demonstrate that H. pylori infection of rhesus monkeys results in a population of strains that have lost the capacity to induce the pro-inflammatory cytokine, IL-8, though there are individual differences among animals. Since loss of T4SS function occurs in macaques as well as mice, yet differs among individuals, it may represent a physiologic accommodation to the gastric environment.


Functional plasticity in the type IV secretion system of Helicobacter pylori.

Barrozo RM, Cooke CL, Hansen LM, Lam AM, Gaddy JA, Johnson EM, Cariaga TA, Suarez G, Peek RM, Cover TL, Solnick JV - PLoS Pathog. (2013)

Loss of the capacity to induce IL-8 in H. pylori recovered from rhesus monkeys is associated with changes in the gene encoding CagY, an essential protein in the T4SS.(A–E) H. pylori was isolated from five rhesus macaques up to 14 months after experimental infection with H. pylori WT J166. Individual colonies were co-cultured with AGS cells, and ELISA was used to measure IL-8 levels, which were normalized to the WT J166 positive control. Each data point represents the results from a single colony. The capacity to induce IL-8 decreased over time in colonies recovered from four monkeys (A–D), but was largely unchanged in one (E). PCR-RFLP analysis showed that H. pylori colonies that lost the capacity to induce IL-8 were associated with a change in cagY (open circles), while those that maintained IL-8 induction typically had cagY that was indistinguishable from WT J166 (filled circles). Animal designation is shown in the upper left corner of each panel. (F) Output strains from each monkey were analyzed by cagY PCR-RFLP and compared to WT H. pylori J166 (dark blue) and to one another. Each pie chart represents all colonies recovered from one of the five monkeys (12–24 colonies/monkey); different colors represent different cagY variants.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585145&req=5

ppat-1003189-g001: Loss of the capacity to induce IL-8 in H. pylori recovered from rhesus monkeys is associated with changes in the gene encoding CagY, an essential protein in the T4SS.(A–E) H. pylori was isolated from five rhesus macaques up to 14 months after experimental infection with H. pylori WT J166. Individual colonies were co-cultured with AGS cells, and ELISA was used to measure IL-8 levels, which were normalized to the WT J166 positive control. Each data point represents the results from a single colony. The capacity to induce IL-8 decreased over time in colonies recovered from four monkeys (A–D), but was largely unchanged in one (E). PCR-RFLP analysis showed that H. pylori colonies that lost the capacity to induce IL-8 were associated with a change in cagY (open circles), while those that maintained IL-8 induction typically had cagY that was indistinguishable from WT J166 (filled circles). Animal designation is shown in the upper left corner of each panel. (F) Output strains from each monkey were analyzed by cagY PCR-RFLP and compared to WT H. pylori J166 (dark blue) and to one another. Each pie chart represents all colonies recovered from one of the five monkeys (12–24 colonies/monkey); different colors represent different cagY variants.
Mentions: H. pylori strains adapted to colonization of mice frequently lose the capacity to induce IL-8 and translocate CagA into gastric epithelial cells [20], [21], which are measures of a functional T4SS. The cagPAI is retained and the mechanism is unknown [21]. Since mice are not a natural host for H. pylori, we asked whether similar changes occur during infection of rhesus macaques, which are commonly infected with H. pylori that is indistinguishable by comparative genomic hybridization from that which infects humans [22]. Five rhesus monkeys were previously challenged with a single colony of wild type (WT) H. pylori J166 that has a functional cagPAI [23]. Multiple output colonies recovered from each monkey up to 14 months post inoculation (PI) were co-cultured with AGS gastric cells to determine their capacity to induce IL-8, which was normalized to the WT control strain. IL-8 induction resembled WT in bacteria recovered early after challenge, but decreased over time in 4 of 5 monkeys (Figure 1A–D). In one monkey, all but one bacterial colony induced IL-8 at levels≥WT, even after 14 months of colonization (Figure 1E). Selected rhesus output colonies that induced low IL-8 (designated rOut1 and rOut2) or high IL-8 (rOut3) in AGS cells were also tested in KATO III gastric cells. Similar results were obtained (Figure S1A). These results demonstrate that H. pylori infection of rhesus monkeys results in a population of strains that have lost the capacity to induce the pro-inflammatory cytokine, IL-8, though there are individual differences among animals. Since loss of T4SS function occurs in macaques as well as mice, yet differs among individuals, it may represent a physiologic accommodation to the gastric environment.

Bottom Line: CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions.Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS.We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

View Article: PubMed Central - PubMed

Affiliation: Center for Comparative Medicine, University of California Davis, Davis, California, United States of America.

ABSTRACT
Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

Show MeSH
Related in: MedlinePlus