<Emphasis Type="Italic">Helicobacter pylori</Emphasis> CagA protein variation associated with gastric cancer in Asia

Recent molecular analysis has provided the pathological actions of CagA on gastric epithelial cells. CagA is injected into epithelial cells via the type IV secretion system and undergoes tyrosine phosphorylation in the cells. In addition, translocated CagA forms a physical complex with SHP-2. There are two major CagA subtypes; the East Asian and the Western type. The East Asian CagA protein possesses stronger SHP-2 binding activity than the Western CagA. The grades of inflammation, activity of gastritis, and atrophy are significantly higher in gastritis patients infected with the East Asian CagA-positive strain than in gastritis patients infected with the cagA-negative or Western CagA-positive strains. The prevalence of the East Asian CagA-positive strain is associated with the mortality rate of gastric cancer in Asia. Endemic circulation of H. pylori populations carrying biologically more active CagA proteins in East Asian countries, where the mortality rate of gastric cancer is among the highest in the world, may be involved in increasing the risk of gastric cancer in these populations.     

Relationship between the diversity of the cagA gene of Helicobacter pylori and gastric cancer in Okinawa, Japan

Background Helicobacter pylori CagA protein is considered to be one of the virulence factors associated with gastric cancer. CagA is injected into gastric epithelial cells, undergoes tyrosine phosphorylation, and binds to Src homology 2 domain-containing protein-tyrosine phosphatase (SHP-2). Two major subtypes of CagA have been observed in the SHP-2-binding site, the Western and East Asian types. The East Asian-type CagA binds to SHP-2 more strongly than the Western-type CagA. The diversity of CagA, which collectively determines the binding affinity of CagA to SHP-2, may be an important variable in determining the clinical outcome of infection by different H. pylori strains. Methods We investigated the relationship between the diversity of CagA and clinical outcome in Okinawa, Japan. A total 24 strains, 13 gastric cancer strains and 11 duodenal ulcer strains, were studied. We sequenced full-length cagA genes and analyzed the phylogenetic relationships between Okinawa isolates and previously characterized Western H. pylori strains. Results All isolates examined were cagA positive. The prevalence of East Asian CagA-positive strains was significantly higher in patients with gastric cancer (84.6%) than in patients with duodenal ulcer (27.3%) (χ-squared = 8.06, P = 0.011). The phylogenetic analysis showed that all gastric cancer strains with East Asian-type CagA were in the East Asian cluster, and that most duodenal ulcer strains were in the Western cluster. Conclusions The origins of H. pylori isolates are different between gastric cancer strains and duodenal ulcer strains, and East Asian CagA-positive H. pylori infection is associated with gastric cancer. The strain diversity observed in Okinawa may affect the difference in the prevalence of disease associated with H. pylori infection in Japan.     

Analysis of the 3′ Variable Region of the <Emphasis Type="Italic">cagA</Emphasis> Gene of <Emphasis Type="Italic">Helicobacter pylori</Emphasis> Isolated in Koreans

CagA protein of Helicobacter pylori is injected into epithelial cells, and it undergoes tyrosine phosphorylation, resulting in inducing cytoskeletal rearrangements. A few studies have suggested that the number of CagA tyrosine phosphorylation motifs (EPIYA) and subtypes of CagA were associated with gastric cancer. This study was performed to characterize the 3' variable regions of the cagA gene of H. pylori and to investigate whether or not there is any relationship between the diversities of cagA and the disease outcome in Korea. Seventy-nine patients (chronic gastritis, 15; duodenal ulcer, 27; benign gastric ulcer, 18; gastric cancer, 19) were enrolled. Biopsy specimens were taken from the antrum for H. pylori culture, and genomic DNA was extracted. PCR and DNA sequence analysis was carried out for the 3′ variable region of the cagA gene. Seventy-eight strains (98.8%) contained three EPIYA motifs and one strain (1.2%) isolated from a patient with duodenal ulcer contained four EPIYA motifs. Seventy-six strains (96.2%) were the East Asian type. In conclusion, there was no significant difference between the number of EPIYA motifs or CagA subtypes and various gastroduodenal diseases in Korea.     

Association between diversity in the Src homology 2 domain--containing tyrosine phosphatase binding site of Helicobacter pylori CagA protein and gastric atrophy and cancer

We investigated the relationship between the diversity of Helicobacter pylori CagA protein and clinical outcome. The cagA gene was sequenced in 115 clinical isolates. The binding affinity of CagA to Src homology 2 domain-containing tyrosine phosphatase (SHP-2) was examined by in vitro infection. Two major CagA subtypes were observed--the East Asian and the Western type. The grades of inflammation, activity of gastritis, and atrophy were significantly higher in patients with gastritis infected with the East Asian CagA-positive strain than in patients with gastritis infected with cagA-negative or Western CagA-positive strains. All strains isolated from patients with gastric cancer were East Asian CagA positive. East Asian CagA exhibited stronger SHP-2-binding activity than did Western CagA. These findings suggest that infection with East Asian CagA-positive H. pylori is associated with atrophic gastritis and gastric cancer and that persistent active inflammation induced by the East Asian CagA-positive strain may play a role in the pathogenesis of disease.     

Discovery of unique African Helicobacter pylori CagA-multimerization motif in the Dominican Republic

BACKGROUND Helicobacter pylori (H. pylori) colonizes the human stomach and is a major cause of peptic ulcer disease and gastric cancer. However, although the prevalence of H. pylori is high in Africa, the incidence of gastric cancer is low, and this phenomenon is called to be African enigma. The CagA protein produced by H. pylori is the most studied virulence factor. The carcinogenic potential of CagA is associated with the Glu-Pro-Ile-Tyr-Ala (EPIYA) patterns and CagA-multimerization (CM) motifs.AIMTo better understand the EPIYA patterns and CM motifs of the cagA gene.METHODSGastric mucosal biopsy specimens were obtained from 258 patients with dyspepsia living in the Dominican Republic, from which 120 H. pylori strains were cultured. After the bacterial DNA extraction, the EPIYA pattern and CM motif genotypes were determined using a polymerase chain reaction-based sequencing. The population structure of the Dominican Republic strains was analyzed using multilocus sequence typing (MLST). Peptic ulcer disease and gastric cancer were identified via endoscopy, and gastric cancer was confirmed by histopathology. Histological scores of the gastric mucosa were evaluated using the updated Sydney system.RESULTSAll CagA-positive strains carried the Western-type CagA according to the identified EPIYA patterns. Twenty-seven kinds of CM motifs were observed. Although the typical Western CM motif (FPLKRHDKVDDLSKVG) was observed most frequently, the typical East Asian CM motif (FPLRRSAAVNDLSKVG) was not observed. However, “FPLRRSAKVEDLSKVG”, similar to the typical East Asian CM motif, was found in 21 strains. Since this type was significantly more frequent in strains classified as hpAfrica1 using MLST analysis (P = 0.034), we termed it Africa1-CM (Af1-CM). A few hpEurope strains carried the Af1-CM motif, but they had a significantly higher ancestral Africa1 component than that of those without the Af1-CM motif (P = 0.030). In 30 cagA-positive strains, the "GKDKGPE" motif was observed immediately upstream of the EPIYA motif in the EPIYA-A segment, and there was a significant association between strains with the hpAfrica1 population and those containing the “GKDKGPE” motif (P = 0.018). In contrast, there was no significant association between the CM motif patterns and histological scores and clinical outcomes.CONCLUSIONWe found the unique African CM motif in Western-type CagA and termed it Africa1-CM. The less toxicity of this motif could be one reason to explain the African enigma.     

The significance of virulence factors in Helicobacter pylori

Helicobacter pylori (H. pylori) infection is linked to various gastroduodenal diseases; however, only a small fraction of these patients develop associated diseases. Despite the high prevalence of H. pylori infection in Africa and South Asia, the incidence of gastric cancer in these areas is much lower than those in other countries. The incidence of gastric cancer tends to decrease from north to south in East Asia. Such geographical differences in the pathology can be explained, at least in part, by the presence of different types of H. pylori virulence factors in addition to host and environmental factors. Virulence factors of H. pylori, such as CagA, VacA, DupA, IceA, OipA and BabA, have been demonstrated to be the predictors of severe clinical outcomes. Interestingly, a meta‐analysis showed that CagA seropositivity was associated with gastric cancer compared with gastritis, even in East Asian countries where almost the strains possess cagA. Another meta‐analysis also confirmed the significance of vacA, dupA and iceA. However, it is possible that additional important pathogenic genes may exist because H. pylori consists of approximately 1600 genes. Despite the advances in our understanding of the development of H. pylori infection‐related diseases, further work is required to clarify the roles of H. pylori virulence factors.     

Spermine oxidase, a polyamine catabolic enzyme that links Helicobacter pylori CagA and gastric cancer risk

We have recently reported that Helicobacter pylori strains expressing the virulence factor cytotoxin-associated gene A (CagA) stimulate increased levels of spermine oxidase (SMO) in gastric epithelial cells, while cagA^– strains did not. SMO catabolizes the polyamine spermine and produces H₂O₂ that results in both apoptosis and DNA damage. Exogenous overexpression of CagA confirmed these findings, and knockdown or inhibition of SMO blocked CagA-mediated apoptosis and DNA damage. The strong association of SMO, apoptosis, and DNA damage was also demonstrated in humans infected with cagA⁺, but not cagA^– strains. In infected gerbils and mice, DNA damage was CagA-dependent and only present in epithelial cells that expressed SMO. We also discovered SMO^high gastric epithelial cells from infected animals with dysplasia that are resistant to apoptosis despite high levels of DNA damage. Inhibition of polyamine synthesis or SMO could abrogate the development of this cell population that may represent precursors for neoplastic transformation.     

Association of the CagA status of Helicobacter pylori and serum levels of interleukin (IL)‐17 and IL‐23 in duodenal ulcer patients

OBJECTIVE: It has been reported that the cytotoxin‐associated gene A (cagA+) H. pylori strains induce severe gastric mucosal inflammation. The aim of this study was to investigate the association of the virulence factor CagA with IL‐17 and IL‐23 serum levels in duodenal ulcer (DU) patients and H. pylori‐infected asymptomatic (AS) carriers. METHODS: In total, 45 H. pylori‐infected DU patients were enrolled to study: 23 tested positive for the anti‐CagA antibody (anti‐CagA+) and 22 tested negative for the anti‐CagA antibody (anti‐CagA‐), 30 were AS carriers (15 were anti‐CagA+ and 15 were anti‐CagA‐) and 15 were healthy uninfected participants (as a control group). The IL‐17 and IL‐23 serum levels of participants were measured by enzyme‐linked immunosorbent assay method. RESULTS: The mean IL‐17 levels in DU patients were significantly higher than those in AS and control groups (P < 0.001 and P < 0.0001 respectively). In the DU group, the mean IL‐17 levels in participants testing positive for anti‐CagA (10.84 ± 5.79 pg/mL) were significantly higher than those observed in participants testing negative for anti‐CagA (7.65 ± 4.74 pg/mL; P < 0.05). The mean IL‐23 levels in the DU and AS groups were significantly higher than in the control group (P < 0.02 and P < 0.03 respectively) but were not significantly different in participants testing positive and negative for anti‐CagA. CONCLUSION: These results showed higher IL‐17 and IL‐23 serum levels in H. pylori‐infected participants than in the control group. In the DU group the expression of IL‐17 was influenced by the CagA factor.     

Augmented levels of gastric mucosal leucocyte activation by infection with cagA gene-positive Helicobacter pylori

The possession of the cytotoxin-associated gene (cagA) of Helicobacter pylori is thought to be highly associated with peptic ulcer disease. However, the pathogenic role of cagA is still unknown. We have emphasized the importance of the interrelationship between H. pylori-derived ammonia and oxygen radicals from in?ltrated leucocytes. The aim of the present study was to explore the relationship between oxygen radical production and H. pylori strain diversity based on cagA possession. An endoscopic examination and gastric mucosal biopsy were performed in 30 H. pylori-infected patients with gastric ulcer. Myeloperoxidase (MPO) content and the luminol-dependent chemiluminescence value in the biopsied gastric specimens were measured as an index for leucocyte in?ltration and oxygen radical production. From the precipitates of cultured bacterial isolates of biopsied specimens, bacterial DNA was puri?ed and analysed by polymerase chain reaction to characterize the possession of cagA. While all patients had ureC-positive strains, 22 had cagA-positive and eight had cagA-negative strains. In patients with cagA-positive strains, MPO contents as well as chemiluminescence values in the gastric corpus were signi?cantly higher than those in patients with cagA-negative strains. Gastric mucosal leucocyte recruitment and activation are suggested to be enhanced by cagA gene-positive H. pylori infection.     

Helicobacter pylori CagA status associated with gastric cancer incidence rate variability in Costa Rican regions

Background We evaluated several risk factors for gastric cancer in Costa Rican regions having contrasting gastric cancer incidence rates, despite the small dimensions of the country. Methods A total of 180 dyspeptic patients were classified into two groups according to the gastric cancer incidence (GCI) rate in their Costa Rican region: group A, with a high GCI rate (n = 91) and group B, with a low GCI rate (n = 89). Helicobacter pylori infection was detected by rapid urease test, Gram staining, and histological observation. Antral and corpus specimens were obtained to assess the grade of inflammation, topography of gastritis, gastric atrophy, and intestinal metaplasia by histological examination. Serum CagA antibody was measured by an antigen-specific enzyme-linked immunosorbent assay. Results There was no significant difference in H. pylori prevalence between groups A (73%) and B (63%); however, serum CagA antibody was more frequently detected in group A (79%) than in group B (54%) [P = 0.02; odds ratio (OR), 2.68]. Among patients under 60 years of age, serum CagA antibody was even more frequently detected in group A (81%) than in group B (49%) (P < 0.01; OR, 4.50). The prevalence of corpus-predominant gastritis, atrophic gastritis, and moderate/severe grades of neutrophilic infiltration was higher in serum CagA antibody-positive patients than in CagA antibody-negative patients (P = 0.003, 0.04, and 0.002, respectively). Conclusions Infection with H. pylori possessing the cagA gene is associated with the development of severe gastric damage such as gastric atrophy, leading to gastric cancer, and probably influences the differences in GCI between Costa Rican regions.     

Association of Helicobacter pylori infection with esophageal adenocarcinoma and squamous cell carcinoma: a meta‐analysis

To evaluate the relationship of Helicobacter pylori and cytotoxin‐associated gene A (CagA) positive strains with esophageal neoplasm, including esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC), the authors conducted a meta‐analysis using a predefined protocol. PubMed, Web of Science, China biology medical literature database, Wanfang, and China National Knowledge Infrastructure were searched for relevant articles from the first available year to April 8, 2013. The fixed or random effect pooled measure was selected based on heterogeneity among studies, which was evaluated using Q test and the I² of Higgins and Thompson. Metaregression was used to explore the sources of between‐study heterogeneity. Publication bias was analyzed by Begg's funnel plot and Egger's regression test. The association was assessed by odds ratio (OR) with 95% confidence interval (CI). A total of 28 eligible studies were included in the meta‐analysis. There was a significant inverse association between H. pylori infection (pooled OR, 0.57; 95% CI, 0.44–0.73) and EAC; CagA‐positive H. pylori strains were less likely to be associated with EAC compared with CagA‐negative strains (pooled OR, 0.64; 95% CI, 0.52–0.79). However, there was no statistically significant association between H. pylori/CagA‐positive H. pylori strains infection and ESCC, and the pooled ORs were 1.16 (95% CI, 0.83–1.60) and 0.97 (95% CI, 0.79–1.19). But significant associations between CagA‐positive H. pylori strains infection and ESCC risk were found in the stratified analysis of the study location (Asian and non‐Asian), and the summary ORs were 0.74 (95% CI, 0.57–0.97) and 1.41 (95% CI, 1.02–1.94). H. pylori infection and CagA‐positive strains are associated with decreased risk of EAC in the overall population. No significant association was found between H. pylori infection/CagA‐positive strains and ESCC. But CagA‐positive strains might have a positive association with ESCC in non‐Asian population and an inverse association in Asian population.     

Functional Dyspepsia is Associated with cagA-positive Helicobacter pylori Strains

Background: The antigen CagA can be used as a marker for virulence of Helicobacter pylori. It is tempting to assume that H. pylori strains positive for cytotoxin-associated gene A (cagA) could be responsible for functional dyspepsia. A cross-sectional study was performed in patients presenting with functional dyspepsia to correlate the clinical presentation with the presence of cagA-positive and -negative H. pylori strains. Methods: Consecutive patients referred for endoscopy were studied. An inclusion criterion was the absence of any endoscopic abnormality. Biopsy specimens were obtained from the gastric antrum for HE and immunoperoxidase stain, rapid urease test, and culture. A serum sample was taken for detection of IgG antibodies against H. pylori as well as CagA. A validated questionnaire of 14 questions regarding the upper gastrointestinal tract was used for assessment of the clinical presentation. Nine questions were scored on a 5-point Likert scale. Results: 422 patients were included, 222 were H. pylori-positive, the remaining 200 were H. pylori-negative. Mean symptom score in patients with cagA-positive strains was significantly higher than in patients with cagA-negative strains. No difference was present if cagA-negative patients were compared with H. pylori-negative dyspeptics. Four different complaints were more prevalent in the cagA-positive patients compared with cagA-negatives. When cagA-positive patients were compared with H. pylori-negative dyspeptics, seven complaints were significantly more prevalent in cagA-positives; when cagA-negatives were compared this number was only two. Conclusions: Functional dyspeptics with cagA-positive H. pylori strains have more dyspeptic symptoms and higher symptom scores than patients with cagA-negative H. pylori strains as well as H. pylori-negative functional dyspeptics.     

Heterogeneity found in the cagA gene of Helicobacter pylori from Japanese and non-Japanese isolates

We analyzed cagA genes from Helicobacter pylori strains isolated from Japanese and non-Japanese individuals for differences that could be associated with variations in virulence. The cagA genes from Japanese isolates (n = 12) and non-Japanese American Type Culture Collection (ATCC) strains (n = 4) were sequenced and compared with three published sequences. Phylogenetic analysis resolved two distinct clusters with a genetic distance of 0.1602. Similarity plot analysis of the amino acid sequences identified two highly variable regions of which each was unique to the Japanese and non-Japanese isolates, respectively. Furthermore, nucleic acid sequence analysis revealed that the multiple repeated sequences present in cagA may have been generated by homologous recombination and/or misaligned replication to promote variation in the cagA gene products. Our data indicate that alleic variations in the H. pylori genome exist between isolates from Japanese and non-Japanese subjects and that distinct H. pylori populations may be circulating in different geographical regions. Phylogenetic analysis did not reveal any association of a specific CagA type with a particular disease. Although extensive alterations were found in the cagA gene, none of the isolates contained a prematurely terminated CagA protein. The cagA gene may be advantageous to H. pylori, possibly by aiding its escape from host immune recognition by antigen modulation. Thus, this ability to elude the host immune system may contribute to an increased risk for gastric disease. Received: March 2, 2000 / Accepted: July 7, 2000     

Helicobacter pylori and CagA under conditions of iron deficiency

Iron deficiency is the most common nutritional deficiency worldwide and compelling evidence has demonstrated that this condition heightens the risk of gastric cancer. Infection with Helicobacter pylori is the strongest known risk factor for the development of gastric adenocarcinoma. Recent work has demonstrated that, under conditions of iron deficiency, H. pylori-induced gastric carcinogenesis is augmented through increased formation of the strain-specific cag type IV secretion system and enhanced delivery of the bacterial oncoprotein CagA into host cells. Although CagA is a potent virulence factor that promotes oncogenic responses, additional studies have now demonstrated that CagA modulates host cell iron homeostasis in vitro and fundamental metabolic functions of the bacterial cell in vivo. Here we discuss these findings and describe working models by which CagA exerts its effects on gastric epithelial cells, with particular emphasis on its potential role in modulation of host iron homeostasis.     

Pathological development of the gastric mucosa in Helicobacter pylori‐related diseases

OBJECTIVE : To study the relationship between Helicobacter pylori eradication and the pathological development of the gastric mucosa in H. pylori‐related diseases. METHODS : One hundred and ninety‐one H. pylori‐infected patients were randomly given anti‐H. pylori or non‐anti‐H. pylori medications. Endoscopic examination was carried out 1 year after treatment. Pathological classifications followed the Sydney System. RESULTS : Of the 191 patients, those with chronic inflammation of the gastric mucosa improved (P < 0.05), as did those with atrophy and intestinal metaplasia (P < 0.05). Helicobacter pylori was eradicated in 107 patients, but not in 84 patients. Compared with those patients in whom H. pylori was not eradicated, those with H. pylori eradicated had ameliorated chronic inflammation of the gastric mucosa (P < 0.05) and active inflammation reduced in some cases (P < 0.05). Notwithstanding a stratification of different gastric diseases and different treatments, patients with H. pylori eradicated showed a more marked improvement in mucosal chronic inflammation than did patients in whom H. pylori was not eradicated (P < 0.05). CONCLUSIONS : These results suggest that H. pylori infection is closely related to active inflammation of the gastric mucosa. Helicobacter pylori eradication is beneficial in improving chronic inflammation of the gastric mucosa.     

Helicobacter pylori CagA-positive Strains Affect Oxygen Free Radicals Generation by Gastric Mucosa

Background: Helicobacter pylori plays a key role in production of reactive oxygen metabolites (ROMs). However, the importance of virulent CagA-positive H. pylori strains remains to be determined. The aim of this study was to assess ROMs production in gastric biopsies of patients infected by H. pylori. Results were correlated to CagA status and acute inflammatory infiltration. Methods: Patients undergoing gastroscopy were enrolled. H. pylori infection was assessed by histology and ¹³C urea breath test. CagA status was assessed through serology. ROMs were assayed in gastric biopsies by luminol-enhanced chemiluminescence (CLS). Gastric mucosal inflammation was histologically graded and neutrophils were individually counted. Macroscopical damage was scored according to a modified Lanza score. Results: 40 out of 60 patients evaluated were H. pylori (HP) positive. Of the 40 infected patients, 24 were CagA-positive. CLS emission was significantly higher in HP-CagA-positive patients than in HP-CagA-negatives and uninfected. ROMs production showed a significant correlation to neutrophil infiltrate in all groups. Conclusions: Gastric mucosa of patients infected by HP-CagA-positive strains is characterized by a higher generation of ROMs and by greater neutrophil counts than that observed in HP-CagA-negative subjects. Since ROMs production is associated with DNA oxidative damage, a long-term stimulation by these strains might be relevant in the pathogenesis of gastric malignancies. Assessment of CagA status might be useful to discriminate patients in which H. pylori eradication is advisable.     

Gastric mucosal cytokine levels in relation to host interleukin-1 polymorphisms and Helicobacter pylori cagA genotype

Objective The outcome of a Helicobacter pylori infection is related in part to interrelationships among H. pylori virulence factors and the H. pylori-induced mucosal response. The host inflammatory response is partly governed by polymorphisms in pro-inflammatory genes.

Material and methods Cytokine levels (interleukin (IL)-1β, IL-6 and IL-8) were examined in H. pylori-infected and uninfected normal-appearing mucosa from patients with non-ulcer dyspepsia (NUD), margins of gastric ulcers and cancer tissues. Cytokine levels were compared with cagA genotypes and host interleukin (IL)-1 polymorphisms.

Results The study comprised 168 Thai patients. All infected patients possessed anti-CagA antibody. Gastric mucosal IL-8 levels were significantly higher in H. pylori-positive cases than in -negative cases in all three tissue types (e.g. 1115 versus 217?pg/mg protein for NUD) (p<0.001). Normal-appearing but H. pylori-infected antral mucosa of patients with cagA type 1a strains had higher IL-8 levels than those with type 2a strains (2632 versus 1036 pg/mg protein) (p<0.005). IL-1B-511T/T carriers had higher antral mucosal IL-1β levels versus non-carriers (pg/mg protein) (T/T=221, T/C=178, C/C=70) (p=0.005). IL-1B-511T/T carriers also had higher IL-1β levels versus non-carriers in H. pylori-negative patients.

Conclusions It was found that both the host factors (IL-1 polymorphisms) and bacterial factors (cagA type 1a versus type 2a) influenced gastric mucosal cytokine levels. Future studies should concentrate on interactions among host factors (e.g. genetics and tissue responses) and bacterial and environmental factors.     

Helicobacter pylori and gastric carcinogenesis

Gastric carcinoma is the second leading cause of cancer-related deaths in the world, accounting for more than 700,000 deaths each year. Recent studies have revealed that infection with cagA-positive Helicobacter pylori plays an essential role in the development of gastric carcinoma. The cagA-encoded CagA protein is delivered into gastric epithelial cells via the bacterial type IV secretion system, where it undergoes tyrosine phosphorylation by Src and Abl kinases. Tyrosine-phosphorylated CagA then acquires the ability to interact with and deregulate SHP-2 phosphatase, a bona-fide oncoprotein, deregulation of which is involved in a variety of human malignancies. CagA also binds to and inhibits PAR1b/MARK2 polarity-regulating kinase to disrupt tight junctions and epithelial apical-basolateral polarity. These CagA activities may collectively contribute to the transformation of gastric epithelial cells. Indeed, transgenic expression of CagA in mice results in the development of gastrointestinal and hematological malignancies, indicating that CagA is the first bacterial oncoprotein that acts in mammalian cells. The oncogenic potential of CagA may be further potentiated in the presence of chronic inflammation, which aberrantly induces activation-induced cytidine deaminase (AID), a member of the DNA/RNA-editing enzyme family. Ectopically expressed AID may contribute to H. pylori-initiated gastric carcinogenesis by increasing the risk of likelihood of epithelial cells acquiring mutations in cancer-related genes.     

Distinct repeat motifs at the C-terminal region of CagA of Helicobacter pylori strains isolated from diseased patients and asymptomatic individuals in West Bengal, India

Background

Infection with Helicobacter pylori strains that express CagA is associated with gastritis, peptic ulcer disease, and gastric adenocarcinoma. The biological function of CagA depends on tyrosine phosphorylation by a cellular kinase. The phosphate acceptor tyrosine moiety is present within the EPIYA motif at the C-terminal region of the protein. This region is highly polymorphic due to variations in the number of EPIYA motifs and the polymorphism found in spacer regions among EPIYA motifs. The aim of this study was to analyze the polymorphism at the C-terminal end of CagA and to evaluate its association with the clinical status of the host in West Bengal, India.

Results

Seventy-seven H. pylori strains isolated from patients with various clinical statuses were used to characterize the C-ternimal polymorphic region of CagA. Our analysis showed that there is no correlation between the previously described CagA types and various disease outcomes in Indian context. Further analyses of different CagA structures revealed that the repeat units in the spacer sequences within the EPIYA motifs are actually more discrete than the previously proposed models of CagA variants.

Conclusion

Our analyses suggest that EPIYA motifs as well as the spacer sequence units are present as distinct insertions and deletions, which possibly have arisen from extensive recombination events. Moreover, we have identified several new CagA types, which could not be typed by the existing systems and therefore, we have proposed a new typing system. We hypothesize that a cagA gene encoding higher number EPIYA motifs may perhaps have arisen from cagA genes that encode lesser EPIYA motifs by acquisition of DNA segments through recombination events.     

Clinical Relevance of CagA-specific Antibodies Related to CagA Status of Heliobacter pylori Isolates Using Immunofluorescence Test and PCR

Background: The cagA (cytotoxin-associated gene A) protein is found in about 50% of Helicobacter pylori strains; its clinical relevance in gastroduodenal disease is uncertain. Patients and Methods: The frequency of IgG antibodies to cagA was studied by using a commercial Western blot assay in sera of 189 patients with endoscopically and histologically confirmed gastroduodenal disease. In addition, 38 H. pylori strains isolated from biopsies were analyzed by immunofluorescence test (IFT) and PCR for detection of cagA protein and cagA gene sequences, respectively. Results: 54.3–60.0% of all patients with gastrointestinal diseases (chronic gastritis, gastric or duodenal ulcer and chronic duodenitis) and 28.6% with a normal mucosa were found to be positive for anti-cagA IgG antibodies. There was no significant difference in anti-cagA IgG seroprevalence between the different clinical entities. CagA-positive (cagA⁺) H. pylori strains were detected in 44.7% and 50% of the 38 isolates by PCR and IFT, respectively. 22 of 23 patients infected with cagA⁺ strains had anti-cagA antibodies. Using PCR as a gold standard, the sensitivity and specificity of the cagA IgG Western blot were 100.0% and 35.0%, respectively; the sensitivity and specificity of the cagA IFT were 76.5% and 71.4%, respectively. The incidence of the cagA⁺ H. pylori strains detected either by PCR or IFT was significantly higher (p < 0.05 and p < 0.01, respectively) in patients with chronic duodenitis, gastric or duodenal ulcer compared to patients with chronic gastritis (66.7%, 80% and 30.4%, respectively). Conclusion: In this study the cagA-specific serological status in H. pylori infections as diagnosed by IgG Western blot was of no predictive value for severity of disease. In contrast, the cagA status of H. pylori isolates, diagnosed by IFT or PCR, was a predictive marker for severe disease and, therefore, also of clinical relevance in the assessment of the virulence of the infecting strain. Received: July 21, 2000 · Revision accepted: March 2, 2001