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Enteric bacterial protein AvrA promotes colonic tumorigenesis and activates colonic beta-catenin signaling pathway.

Lu R, Wu S, Zhang YG, Xia Y, Liu X, Zheng Y, Chen H, Schaefer KL, Zhou Z, Bissonnette M, Li L, Sun J - Oncogenesis (2014)

Bottom Line: In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS).Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain.Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Rush University, Chicago, IL, USA.

ABSTRACT
Salmonella infections can become chronic and increase the risk of cancer. The mechanisms by which specific Salmonella organisms contribute to cancer, however, are still unknown. Live and attenuated Salmonella are used as vectors to target cancer cells, but there have been no systematic studies of the oncogenic potential of chronic Salmonella infections in cancer models. AvrA, a pathogenic product of Salmonella, is inserted into host cells during infection and influences eukaryotic cell pathways. In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS). We confirmed Salmonella persisted in the colon for up to 45 weeks. Salmonella was identified not only in epithelial cells on the colonic luminal surface and base of the crypts but also in invading tumors. Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain. Infection with AvrA+ strain also altered tumor distribution from the distal to proximal colon that might reflect changes in the microbiome. AvrA-expressing bacteria also upregulated beta-catenin signaling as assessed by decreased beta-catenin ubiquitination, increased nuclear beta-catenin and increased phosphorylated-beta-catenin (Ser552), a marker of proliferating stem-progenitor cells. Other β-catenin targets increased by AvrA included Bmi1, a cancer stem cell marker, matrix metalloproteinase-7, and cyclin D1. In summary, AvrA-expressing Salmonella infection activates β-catenin signals and enhances colonic tumorigenesis. Our findings provide important new mechanistic insights into how a bacterial protein targets proliferating stem-progenitor cells and contributes to cancer development. Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy. Finally, these studies could suggest biomarkers (such as AvrA level in gut) to assess cancer risk in susceptible individuals and infection-related dysregulation of β-catenin signaling in cancer.

No MeSH data available.


Related in: MedlinePlus

Bacterial AvrA activates β-catenin signaling. (a) AvrA induces β-catenin signaling in HEK293 cells. HEK293 cells were transiently co-transfected with a pcmv-myc-AvrA plasmid and a pGL3-OT plasmid (TCF-responsive reporter with WT TCF binding site) or pGL3-OF (mutant TCF binding site), using lipofectin reagent according to the manufacturer's instructions. LiCl treatment (20 mmol/l) was used as the positive control. Each experiment was assayed in triplicate. N=3 independent platings *P<0.05. (b) Colonic BrdU was detected in normal mucosa and tumors in control mice (AOM/DSS alone) or mice also gavaged with the indicated bacteria 45 weeks postinfection. (c) Quantitation of BrdU staining in normal tissue and tumors from the indicated groups. *P<0.05, **P<0.01. (d) Model of AvrA regulation of β-catenin signaling in colonic tumorigenesis. In mice chronically infected with Salmonella, AvrA activates β-catenin, which upregulates its target genes to promote colonic tumorigenesis.
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fig5: Bacterial AvrA activates β-catenin signaling. (a) AvrA induces β-catenin signaling in HEK293 cells. HEK293 cells were transiently co-transfected with a pcmv-myc-AvrA plasmid and a pGL3-OT plasmid (TCF-responsive reporter with WT TCF binding site) or pGL3-OF (mutant TCF binding site), using lipofectin reagent according to the manufacturer's instructions. LiCl treatment (20 mmol/l) was used as the positive control. Each experiment was assayed in triplicate. N=3 independent platings *P<0.05. (b) Colonic BrdU was detected in normal mucosa and tumors in control mice (AOM/DSS alone) or mice also gavaged with the indicated bacteria 45 weeks postinfection. (c) Quantitation of BrdU staining in normal tissue and tumors from the indicated groups. *P<0.05, **P<0.01. (d) Model of AvrA regulation of β-catenin signaling in colonic tumorigenesis. In mice chronically infected with Salmonella, AvrA activates β-catenin, which upregulates its target genes to promote colonic tumorigenesis.

Mentions: To further investigate the role of bacterial AvrA in modulating the host signaling pathways in vitro, we transfected human HEK293 cells with AvrA and TCF lucifierase reporter plasmid. We found that AvrA could increase the β-catenin activity as assessed by increased luciferase activity in cells transfected with a PGL3-OT plasmid with WT TCF-binding site (Figure 5a). In contrast, AvrA did not increase activation of mutated PGL3-OF that is unresponsive to β-catenin–TCF transactivation.


Enteric bacterial protein AvrA promotes colonic tumorigenesis and activates colonic beta-catenin signaling pathway.

Lu R, Wu S, Zhang YG, Xia Y, Liu X, Zheng Y, Chen H, Schaefer KL, Zhou Z, Bissonnette M, Li L, Sun J - Oncogenesis (2014)

Bacterial AvrA activates β-catenin signaling. (a) AvrA induces β-catenin signaling in HEK293 cells. HEK293 cells were transiently co-transfected with a pcmv-myc-AvrA plasmid and a pGL3-OT plasmid (TCF-responsive reporter with WT TCF binding site) or pGL3-OF (mutant TCF binding site), using lipofectin reagent according to the manufacturer's instructions. LiCl treatment (20 mmol/l) was used as the positive control. Each experiment was assayed in triplicate. N=3 independent platings *P<0.05. (b) Colonic BrdU was detected in normal mucosa and tumors in control mice (AOM/DSS alone) or mice also gavaged with the indicated bacteria 45 weeks postinfection. (c) Quantitation of BrdU staining in normal tissue and tumors from the indicated groups. *P<0.05, **P<0.01. (d) Model of AvrA regulation of β-catenin signaling in colonic tumorigenesis. In mice chronically infected with Salmonella, AvrA activates β-catenin, which upregulates its target genes to promote colonic tumorigenesis.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4150214&req=5

fig5: Bacterial AvrA activates β-catenin signaling. (a) AvrA induces β-catenin signaling in HEK293 cells. HEK293 cells were transiently co-transfected with a pcmv-myc-AvrA plasmid and a pGL3-OT plasmid (TCF-responsive reporter with WT TCF binding site) or pGL3-OF (mutant TCF binding site), using lipofectin reagent according to the manufacturer's instructions. LiCl treatment (20 mmol/l) was used as the positive control. Each experiment was assayed in triplicate. N=3 independent platings *P<0.05. (b) Colonic BrdU was detected in normal mucosa and tumors in control mice (AOM/DSS alone) or mice also gavaged with the indicated bacteria 45 weeks postinfection. (c) Quantitation of BrdU staining in normal tissue and tumors from the indicated groups. *P<0.05, **P<0.01. (d) Model of AvrA regulation of β-catenin signaling in colonic tumorigenesis. In mice chronically infected with Salmonella, AvrA activates β-catenin, which upregulates its target genes to promote colonic tumorigenesis.
Mentions: To further investigate the role of bacterial AvrA in modulating the host signaling pathways in vitro, we transfected human HEK293 cells with AvrA and TCF lucifierase reporter plasmid. We found that AvrA could increase the β-catenin activity as assessed by increased luciferase activity in cells transfected with a PGL3-OT plasmid with WT TCF-binding site (Figure 5a). In contrast, AvrA did not increase activation of mutated PGL3-OF that is unresponsive to β-catenin–TCF transactivation.

Bottom Line: In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS).Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain.Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Rush University, Chicago, IL, USA.

ABSTRACT
Salmonella infections can become chronic and increase the risk of cancer. The mechanisms by which specific Salmonella organisms contribute to cancer, however, are still unknown. Live and attenuated Salmonella are used as vectors to target cancer cells, but there have been no systematic studies of the oncogenic potential of chronic Salmonella infections in cancer models. AvrA, a pathogenic product of Salmonella, is inserted into host cells during infection and influences eukaryotic cell pathways. In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS). We confirmed Salmonella persisted in the colon for up to 45 weeks. Salmonella was identified not only in epithelial cells on the colonic luminal surface and base of the crypts but also in invading tumors. Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain. Infection with AvrA+ strain also altered tumor distribution from the distal to proximal colon that might reflect changes in the microbiome. AvrA-expressing bacteria also upregulated beta-catenin signaling as assessed by decreased beta-catenin ubiquitination, increased nuclear beta-catenin and increased phosphorylated-beta-catenin (Ser552), a marker of proliferating stem-progenitor cells. Other β-catenin targets increased by AvrA included Bmi1, a cancer stem cell marker, matrix metalloproteinase-7, and cyclin D1. In summary, AvrA-expressing Salmonella infection activates β-catenin signals and enhances colonic tumorigenesis. Our findings provide important new mechanistic insights into how a bacterial protein targets proliferating stem-progenitor cells and contributes to cancer development. Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy. Finally, these studies could suggest biomarkers (such as AvrA level in gut) to assess cancer risk in susceptible individuals and infection-related dysregulation of β-catenin signaling in cancer.

No MeSH data available.


Related in: MedlinePlus