Characterization of CagI in the cag pathogenicity island of Helicobacter pylori

The type IV secretion system in Helicobacter pylori

Helicobacter pylori (H. pylori) has an essential role in the pathogenesis of gastritis, peptic ulcer disease, mucosa-associated lymphoid tissue lymphoma and gastric cancer. The severity of the host inflammatory responses against the bacteria have been straightly associated with a special bacterial virulence factor, the cag pathogenicity island, which is a type IV secretion system (T4SS) to deliver CagA into the host cells. Besides cag-T4SS, the chromosomes of H. pylori can encode another three T4SSs, including comB, tfs3 and tfs4. In this review, we systematically reviewed the four T4SSs of H. pylori and explored their roles in the pathogenesis of gastroduodenal diseases. The information summarized in this review might provide valuable insights into the pathogenic mechanism for H. pylori.

The Helicobacter pylori Cag Pathogenicity Island Protein Cag1 is Associated with the Function of T4SS

The human pathogen Helicobacter pylori is involved in gastric diseases ranging from gastritis to gastric cancer. Virulent strains harboring the cag pathogenicity island (cag PAI) which encode a Type IV Secretion System (T4SS) can induce pro-inflammatory cytokines such as interleukin-8 and deliver their major effector proteins CagA into the gastric cells. While a subset of cag PAI genes have been identified to be the homologues of T4SS genes from Agrobacterium tumefaciens, a majority have unknown functions. We have identified one of such proteins, Cag1, which was predicted to be a non-classically secreted and virulent protein. Our results showed that Cag1 is a membrane-associated protein essential for the induction of multiple cytokine secretions, and cag1-deficient mutant has partial influence on CagA translocation; while the protein itself was not injected into host cells. Our data indicated that Cag1 is located in the bacterial membrane and is associated with the function of T4SS.

Intact long-type DupA protein in Helicobacter pylori is an ATPase involved in multifunctional biological activities

The function of intact long-type DupA protein in Helicobacter pylori was analyzed using immunoblotting and molecular biology techniques in the study. After cloning, expression and purification, ATPase activity of DupA protein was detected. Antibody was produced for localization and interaction proteins analysis. The dupA-deleted mutant was generated for adhesion and CagA protein translocation assay, susceptibility to different pH, IL-8 secretion assay, cytotoxicity to MKN-45 cells and proteins-involved apoptosis analysis. DupA protein exhibited an ATPase activity (129.5±17.8 U/mgprot) and located in bacterial membrane, while it did not involve the adhesion and CagA protein delivery of H. pylori. DupA protein involved the urease secretion as the interaction proteins. The wild type strain had a stronger growth in low pH than the dupA-deleted mutant (p < 0.001). IL-8 productions from GES-1 cells infected with the wild type strain were significantly higher than from those with the mutant (p < 0.001). The amounts of vital MKN-45 cells were decreased and the numbers of apoptotic cells were increased with the wild type strain, compared to those with the mutant after 12 h (p < 0.05). The increase of cleaved Caspase-3 and Bax was significantly higher and the decrease of Bcl-2 was more obvious in MKN-45 cells exposed to the wild type strain than that exposed to the mutant after 6 h. We demonstrate that intact long-type DupA protein located in membrane as ATPase is a true virulence factor associated with duodenal ulcer development involving the IL-8 induction and urease secretion, while it inhibits gastric cancer cell growth in vitro by activating the mitochondria-mediated apoptotic pathway.

Cag type IV secretion system: CagI independent bacterial surface localization of CagA

Helicobacter pylori Cag type IV secretion system (Cag-T4SS) is a multi-component transporter of oncoprotein CagA across the bacterial membranes into the host epithelial cells. To understand the role of unique Cag-T4SS component CagI in CagA translocation, we have characterized it by biochemical and microscopic approaches. We observed that CagI is a predominantly membrane attached periplasmic protein partially exposed to the bacterial surface especially on the pili. The association of the protein with membrane appeared to be loose as it could be easily recovered in soluble fraction. We documented that the stability of the protein is dependent on several key components of the secretion system and it has multiple interacting partners including a non-cag-PAI protein HP1489. Translocation of CagA across the bacterial membranes to cell surface is CagI-independent process. The observations made herein are expected to assist in providing an insight into the substrate translocation by the Cag-T4SS system and Helicobacter pylori pathogenesis.

Predicting a novel pathogenicity island in Helicobacter pylori by genomic barcoding

AIM: To apply a new, integrated technique for visualizing bacterial genomes to identify novel pathogenicity islands in Helicobacter pylori (H. pylori).

METHODS: A genomic barcode imaging method (converting frequency matrices to grey-scale levels) was designed to visually distinguish origin-specific genomic regions in H. pylori. The complete genome sequences of the six H. pylori strains published in the National Center for Biotechnological Information prokaryotic genome database were scanned, and compared to the genome barcodes of Escherichia coli (E. coli) O157:H7 strain EDL933 and a random nucleotide sequence. The following criteria were applied to identify potential pathogenicity islands (PAIs): (1) barcode distance distinct from that of the general background; (2) length greater than 10000 continuous base pairs; and (3) containing genes with known virulence-related functions (as determined by PfamScan and Blast2GO).

RESULTS: Comparison of the barcode images generated for the 26695, HPAG1, J99, Shi470, G27 and P12 H. pylori genomes with those for the E. coli and random sequence controls revealed that H. pylori genomes contained fewer anomalous regions. Among the H. pylori-specific continuous anomalous regions (longer than 20 kbp in each strain’s genome), two fit the criteria for identifying candidate PAIs. The bioinformatic-based functional analyses revealed that one of the two anomalous regions was the known pathogenicity island cag-PAI, this finding also served as proof-of-principle for the utility of the genomic barcoding approach for identifying PAIs, and characterized the other as a novel PAI, which was designated as tfs3-PAI. Furthermore, the cag-PAI and tfs3-PAI harbored genes encoding type IV secretion system proteins and were predicted to have potential for functional synergy.

CONCLUSION: Genomic barcode imaging represents an effective bioinformatic-based approach for scanning bacterial genomes, such as H. pylori, to identify candidate PAIs.

The Helicobacter pylori protein CagM is located in the transmembrane channel that is required for CagA translocation

Helicobacter pylori (H. pylori) is a human gastric pathogen that colonizes the stomach in more than 50 % of the world's human population. Infection with this bacterium can induce several gastric diseases ranging from gastritis to peptic ulcer and gastric cancer. Virulent H. pylori isolates harboring the cag pathogenicity island (cag PAI), which encodes a Type IV Secretion System (T4SS), form a pilus for the injection of its major virulence protein CagA into gastric cells. Several cag PAI genes have been identified as homologues of T4SS genes from Agrobacterium tumefaciens, while the other members in cag PAI still have no known function. We studied one of such proteins with unknown function, CagM, which was predicted to have a putative N-terminal signal sequence and at least three transmembrane helices. To determine the subcellular localization of CagM, we performed a cell fractionation procedure and produced rabbit anti-CagM polyclonal antibodies for immunoblotting assays. Furthermore, we generated an isogenic ΔcagM mutant to investigate the ability of CagA translocation compared with the wild-type NCTC 11637 strain using GES-1 and MKN-45 cell infection experiments. Our results indicated that CagM was mainly located in the bacterial membrane, partially located in the periplasm, and essential for CagA translocation both in GES-1 and MKN-45 cells, which suggested that CagM was one of the core members of Cag T4SS and localized in the transmembrane channel.

Distribution of Helicobacter pylori virulence markers in patients with gastroduodenal diseases in a region at high risk of gastric cancer

ABSTRACT BACKGROUND

Helicobacter pylori (H. pylori) is a major human pathogen that is responsible for various gastroduodenal diseases. We investigated the prevalence of H. pylori virulence markers in a region at high risk of gastric cancer.

METHODS

One hundred and sixteen H. pylori strains were isolated from patients with gastroduodenal diseases. cagA, the cagA 3' variable region, cagPAI genes, vacA, and dupA genotypes were determined by PCR, and some amplicons of the cagA 3' variable region, cagPAI genes and dupA were sequenced.

RESULTS

cagA was detected in all strains. The cagA 3' variable region of 85 strains (73.3%) was amplified, and the sequences of 24 strains were obtained including 22 strains possessing the East Asian-type. The partial cagPAI presented at a higher frequency in chronic gastritis (44.4%) than that of the severe clinical outcomes (9.7%, p < 0.001). The most prevalent vacA genotypes were s1a/m2 (48.3%) and s1c/m2 (13.8%). Thirty-six strains (31.0%) possessed dupA and sequencing of dupA revealed an ORF of 2449-bp. The prevalence of dupA was significantly higher in strains from patients with the severe clinical outcomes (40.3%) than that from chronic gastritis (20.4%, p = 0.02).

CONCLUSION

The high rate of East Asian-type cagA, intact cagPAI, virulent vacA genotypes, and the intact long-type dupA may underlie the high risk of gastric cancer in the region.

Role of Helicobacter pylori in common rosacea subtypes: a genotypic comparative study of Egyptian patients

Helicobacter pylori was incriminated as an etiological factor of rosacea. However, there is still controversy about this association. We conducted a comparative study in order to assess the role of H. pylori in rosacea patients who had dyspeptic symptoms. The study included 68 patients and 54 controls. Screening for H. pylori was performed and positive cases were referred for gastric endoscopy. The inflammatory response and bacterial density were evaluated in gastric biopsy. H. pylori vacA alleles, cagA and iceA genotypes were assessed by polymerase chain reaction. We found that 49 rosacea (72%) and 25 controls (46.3%) were infected with H. pylori. Thirty-one rosacea cases were papulopustular (PPR) while 18 were erythematotelangiectatic (ETR). Gastric ulceration was higher in PPR cases (38.7%) than ETR (11.1%) and controls (12%). A significant inflammatory reaction was observed more in PPR cases (74.2%) compared with 44.4% in ETR (P = 0.04) and 44% in controls (P = 0.02). Analysis of H. pylori genotypes revealed that vacA s1m1 was more identified in PPR cases (54.8%) compared with 22.2% in ETR (P = 0.03) and 16% in controls (P = 0.003). There was a significant elevation of cagA/vacA s1m1 positivity in PPR cases. After the eradication regimen of H. pylori, a significant improvement (P < 0.05) was observed in 15 out of 27 PPR cases (55.6%) compared with three out of 17 ETR (17.6%). We concluded that H. pylori has a significant role in rosacea patients who had dyspeptic symptoms. The PPR type is more influenced by H. pylori and this is regarded as being because of certain virulent strains that increase the inflammatory response in gastric mucosa and also in cutaneous lesions.