Role of vacA and cagA in Helicobacter pylori inhibition of mucin synthesis in gastric mucous cells

Gut Bacteria Provide Genetic and Molecular Reporter Systems to Identify Specific Diseases

With genetic information gained from next-generation sequencing (NGS) and genome-wide association studies (GWAS), it is now possible to select for genes that encode reporter molecules that may be used to detect abnormalities such as alcohol-related liver disease (ARLD), cancer, cognitive impairment, multiple sclerosis (MS), diabesity, and ischemic stroke (IS). This, however, requires a thorough understanding of the gut-brain axis (GBA), the effect diets have on the selection of gut microbiota, conditions that influence the expression of microbial genes, and human physiology. Bacterial metabolites such as short-chain fatty acids (SCFAs) play a major role in gut homeostasis, maintain intestinal epithelial cells (IECs), and regulate the immune system, neurological, and endocrine functions. Changes in butyrate levels may serve as an early warning of colon cancer. Other cancer-reporting molecules are colibactin, a genotoxin produced by polyketide synthetase-positive Escherichia coli strains, and spermine oxidase (SMO). Increased butyrate levels are also associated with inflammation and impaired cognition. Dysbiosis may lead to increased production of oxidized low-density lipoproteins (OX-LDLs), known to restrict blood vessels and cause hypertension. Sudden changes in SCFA levels may also serve as a warning of IS. Early signs of ARLD may be detected by an increase in regenerating islet-derived 3 gamma (REG3G), which is associated with changes in the secretion of mucin-2 (Muc2). Pro-inflammatory molecules such as cytokines, interferons, and TNF may serve as early reporters of MS. Other examples of microbial enzymes and metabolites that may be used as reporters in the early detection of life-threatening diseases are reviewed.

Role of the gut microbiota in anticancer therapy: from molecular mechanisms to clinical applications

In the past period, due to the rapid development of next-generation sequencing technology, accumulating evidence has clarified the complex role of the human microbiota in the development of cancer and the therapeutic response. More importantly, available evidence seems to indicate that modulating the composition of the gut microbiota to improve the efficacy of anti-cancer drugs may be feasible. However, intricate complexities exist, and a deep and comprehensive understanding of how the human microbiota interacts with cancer is critical to realize its full potential in cancer treatment. The purpose of this review is to summarize the initial clues on molecular mechanisms regarding the mutual effects between the gut microbiota and cancer development, and to highlight the relationship between gut microbes and the efficacy of immunotherapy, chemotherapy, radiation therapy and cancer surgery, which may provide insights into the formulation of individualized therapeutic strategies for cancer management. In addition, the current and emerging microbial interventions for cancer therapy as well as their clinical applications are summarized. Although many challenges remain for now, the great importance and full potential of the gut microbiota cannot be overstated for the development of individualized anti-cancer strategies, and it is necessary to explore a holistic approach that incorporates microbial modulation therapy in cancer.

Chronic in vivo exposure to Helicobacter pylori VacA: Assessing the efficacy of automated and long-term intragastric toxin infusion

Helicobacter pylori (Hp) secrete VacA, a diffusible pore-forming exotoxin that is epidemiologically linked to gastric disease in humans. In vitro studies indicate that VacA modulates gastric epithelial and immune cells, but the in vivo contributions of VacA as an important determinant of Hp colonization and chronic infection remain poorly understood. To identify perturbations in the stomachs of C57BL/6 or BALB/C mice that result specifically from extended VacA exposure, we evaluated the efficacy of administering purified toxin using automated infusion via surgically-implanted, intragastric catheters. At 3 and 30 days of interrupted infusion, VacA was detected in association with gastric glands. In contrast to previously-reported tissue damage resulting from short term exposure to Hp extracts administered by oral gavage, extended infusion of VacA did not damage stomach, esophageal, intestinal, or liver tissue. However, several alterations previously reported during Hp infection were detected in animals infused with VacA, including reduction of the gastric mucus layer, and increased vacuolation of parietal cells. VacA infusion invoked an immune response, as indicated by the detection of circulating VacA antibodies. These foundational studies support the use of VacA infusion for identifying gastric alterations that are unambiguously attributable to long-term exposure to toxin.

Genetic Analysis of cagA and vacA Genes in Helicobacter Pylori Isolates and Their Relationship with Gastroduodenal Diseases in the West of Iran

Background

Helicobacter pylori have different virulence factors which are associated with several gastroduodenal diseases; however, this association is variable in different geographical regions. Data of genotypes of Iranian H. pylori isolates are few.

Objectives

The aim of the current study was to investigate the cagA/vacA genotypes of Helicobacter pylori isolates and determine the relationship between these genotypes with respect to different gastric disorders in patients of Chaharmahalo Bakhtiarian.

Materials and Methods

In this cross-sectional study, gastric biopsies were taken from 200 patients with gastrodoudenal diseases. Histopathological features were recognized by specialist. The samples were subjected to PCR for detection and identification of ureC, cagA and vacA genes.

Results

The frequency of the vacA genotypes, sa1/m1, s1a/m1b, s1a/m2, s1b/m1a, s1b/m1b, s1b/m2, s1c/m1a, s1c/m1b, s1c/m2, s2/m1a, s2/m1b and s2/m2 were 27(6.6%), 8(4.3%), 45(28.04%), 7(3.7%), 5(2.5%), 10 (6.1%), 12 (7.4%), 4 (2.5%), 18(11%), 6(3.7%), 0 and 22(13.5%) respectively. The cagA gene was detected in 92% of strains. Based on our findings, it seemed that cagPAI and vacA s1 genotypes were associated with some gastric disorders in patients with H. pylori. In this region, the isolates carrying s1a/m2 were the most prevalent.

Conclusions

We found considerable relationship between s1a/m1a, s1a/m2, s2/m2 and s1c/m1a and some gastric disorders. Further studies about the role of H. pylori virulence factors and gastric disorders were recommended.

Comparison of the virulence factors of Helicobacter pylori isolated in stomach and saliva in Iran

INTRODUCTION

Helicobacter pylori is a microaerophilic, spiral-shaped motile bacterium that is strongly associated with gastroduodenal diseases, but recently, dental plaque and saliva have been implicated as possible sources of H pylori infection. Two virulence factors that are expressed by the alleles of the cytotoxin genes, cagA and vacA, have been identified. The aim of this study was to compare cagA and vacA genotypes of H pylori between stomach and saliva in a same patient.

METHODS

This study was performed on antrum gastric biopsy specimens and saliva samples, which were obtained from 250 patients undergoing upper gastrointestinal tract endoscopy in Hagar Hospital of Shahrekord Township in Iran. Initially, H pylori strains were identified by rapid urease test; then, we applied polymerase chain reaction assay to analyze cagA and vacA genotypes of H pylori from both gastric and saliva specimens.

RESULTS

One hundred eighty-nine (75.6%) and 36 (14.4%) samples were H pylori positive in gastric and saliva samples, respectively. Evaluation of virulence factors in the 36 patients whose saliva and gastric samples were both positive for H pylori showed a great deal of cytotoxin genotypic diversity between stomach and saliva in the same patient; in fact, 14 patients (38.8%) had different H pylori strains in their saliva and gastric samples.

CONCLUSIONS

The data suggest that >1 H pylori strain may exist in stomach and saliva in the same patient.

Modification of gastric mucin oligosaccharide expression in rhesus macaques after infection with Helicobacter pylori

BACKGROUND & AIMS

Helicobacter pylori attaches to mucin oligosaccharides that are expressed on host gastric epithelium. We used the rhesus macaque model to characterize the effect of H. pylori infection on gastric mucin oligosaccharides during acute and chronic infection.

METHODS

Specific pathogen (H. pylori)-free rhesus macaques were inoculated with H. pylori J166. Biopsy specimens of the gastric antrum were obtained 2 and 4 weeks before and 2, 8, and 24 weeks after infection with H. pylori. O-linked mucin oligosaccharides were released from gastric biopsy samples by beta-elimination and profiled by matrix-assisted laser desorption/ionization mass spectrometry. Similar studies were performed on gastric biopsy samples from H. pylori-infected and uninfected humans. Formalin-fixed, paraffin-embedded sections of rhesus antrum biopsy samples were stained with H&E, periodic acid-Schiff stain, and antibody to MUC5AC, the predominant mucin expressed in the stomach.

RESULTS

H. pylori-induced gastritis was accompanied by an acute and dramatic decrease in diversity and relative abundance of O-linked mucin oligosaccharides in the rhesus stomach, which largely recovered during the 24-week observation period. These variations in oligosaccharide abundance detected by mass spectrometry were reflected by changes in periodic acid-Schiff-positive material and expression of MUC5AC over time. Relatively few differences were seen in gastric mucin oligosaccharide composition between H. pylori-infected and uninfected patients, which is consistent with the results in rhesus macaques because infection occurs in childhood.

CONCLUSIONS

Acute H. pylori infection is accompanied by a dramatic but transient loss in mucin oligosaccharides that may promote colonization and persistence.

Effects of Helicobacter pylori Infection on gastric mucin expression

AIMS

This study was performed to determine the gastric distributions of MUC5AC and MUC6 depending on Helicobacter pylori (H. pylori) infection, and to evaluate whether the expressions of MUC5 and MUC6 change in H. pylori-associated gastroduodenal diseases. In addition, MUC5AC and MUC6 expressional changes were investigated before and after H. pylori eradication.

METHODS

In the 224 individuals (136 H. pylori-positive and 88 H. pylori-negative) who came from control (N=48), duodenal ulcer (N=35), benign gastric ulcer (N=61), dysplasia plus stomach cancer (N=80) groups, MUC5AC and MUC6 expressions were determined by immunohistochemical staining in the antrum and body, respectively. This staining for MUC5AC and MUC6 were reperformed in 113 of the 136 H. pylori-positive patients after successful H. pylori eradication by proton pump inhibitor-based triple therapy.

RESULTS

(1) No difference was found between the H. pylori-positive and negative groups in terms of MUC5AC expression. In contrast, MUC6 expression was significantly lower in the H. pylori-positive group than in the H. pylori-negative group in the gastric body. Moreover, reduced MUC6 expression increased to the H. pylori-negative level after eradication. (2) Expressions of MUC5AC and MUC6 were significantly lower in the dysplasia plus cancer group than those of control in case of H. pylori positive. Similarly, MUC5AC and MUC6 expressions were significantly lower in the presence of atrophic gastritis with intestinal metaplasia in case of H. pylori positive. (3) Aberrant expressions of MUC6 in foveolar cells were observed in both antrum (11.3%) and body (5.3%) only in the H. pylori-positive group, but this reverted to normal after H. pylori eradication.

CONCLUSION

These results suggest that H. pylori infection causes alterations of mucin expression, closely related with the development of gastric atrophy with intestinal metaplasia, probably contributing to carcinogenesis.

Higher gastric mucin secretion and lower gastric acid output in first-degree relatives of gastric cancer patients

BACKGROUND

Patients infected by Helicobacter pylori who have first-degree relatives with gastric cancer have an 8-fold increased risk of developing gastric cancer themselves. Mucins are high-molecular-weight glycoproteins that play a cardinal role in the protective mechanism of the gastric epithelium.

AIM

To study gastric acid and mucin secretion in dyspeptic patients with and without a family history of gastric cancer and H. pylori infection.

MATERIALS AND METHODS

Twenty-six dyspeptic patients underwent esophago-gastro-duodenoscopy, gastric biopsies, and acid and mucin secretory tests. The sample was divided by family history of gastric cancer and H. pylori status.

RESULTS

Patients who were infected by H. pylori had a significantly higher degree of inflammation than those who were not. H. pylori-positive patients with a positive family history had a lower basal and maximal gastric acid output than infected patients with no family history and noninfected controls, and a higher basal and maximal mucin output than infected patients with no family history. MUC5AC was the major mucin species expressed in gastric juice.

CONCLUSIONS

In patients with relatives with gastric cancer, H. pylori infection is associated with a more severe inflammatory reaction consisting of decreased gastric acid secretion and increased mucin secretion.

Oxidative stress in Helicobacter pylori-induced gastric cell injury

Oxygen radicals are supposed to be involved in inflammation and cell proliferation. Helicobacter pylori induces decrease in antioxidant defense factors, such as GSH, mucus and constitutive nitric oxide (NO), gastric mucosal injury and inflammation. Inflammation and injury might be caused by oxidant-mediated expression of inflammatory cytokine interleukin-8 (IL-8) and inflammatory enzymes such as cyclooxtgenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), which were mediated by oxidant-sensitive transcription factors such as nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), possibly with mitogen activated protein kinase (MAPK) activation. H. pylori-induced alterations in protein expression demonstrate the involvement of oxidative stress in the pathogenesis of H. pylori-induced gastric diseases. The differentially expressed genes and proteins may be useful as prognostic indices for gastric diseases associated with H. pylori infection. In conclusion, oxygen radicals are produced in gastric epithelial cells infected with H. pylori, which may reduce the antioxidant defense mechanism and turn on the expression of inflammatory genes, adhesion molecules and mediators stimulating cell proliferation, as well as defensive molecular chaperones in gastric epithelial cells.

Topographic expression of MUC5AC and MUC6 in the gastric mucosa infected by Helicobacter pylori and in associated diseases

We investigated the topographic expression of MUC5AC and MUC6 in relationship with gastric diseases. The immunoexpression of MUC5AC and MUC6 was evaluated in 75 adults presenting Helicobacter pylori gastritis (n = 22; 11 cagA positive), duodenal ulcer (DU, n = 11), gastric ulcer (GU, n = 9), gastric carcinoma (GC, n = 20), and normal mucosa (H. pylori negative, n = 13). Five gastric areas (antral and corporeal lesser and greater curvatures and incisura) were studied. H. pylori was detected by carbolfuchsin, urease, and culture; cagA was determined by PCR. All patients with DU (eight with GU and 13 with GC) were H. pylori-positive. In H. pylori gastritis, MUC5AC expression was higher in the antrum than in the corpus; no difference was observed with respect to cagA status. MUC5AC expression was higher in the antrum of gastritis than in DU, and it was lower in the incisura among GU patients compared to DU. MUC6 expression was higher in the antrum of H. pylori gastritis compared to DU and to uninfected patients. No difference was observed in the topographic pattern of expression of MUC5AC and MUC6 among GC cases. The topographic over- and under-expression of mucins in H. pylori-associated gastritis and peptic disease suggest a role for these mucins in the pathogenesis of H. pylori infection and associated diseases.

The effect of p38 mitogen-activated protein kinase on mucin gene expression and apoptosis in Helicobacter pylori-infected gastric epithelial cells

The loss of mucus coat continuity and apoptosis have been shown in Helicobacter pylori (H. pylori)-infected gastric tissues. Blockade of p38 mitogen-activated kinase (MAPK) produced reversal in the LPS-induced reduction in mucin synthesis and apoptosis in gastric epithelial cells. This study investigates whether H. pylori induces apoptosis, alterations in mucin gene (MUC) expression, and p38 MAPK activation in human gastric epithelial AGS cells. After treatment of AGS cells with H. pylori at the ratio of 1:300, apoptosis was determined by DNA fragmentation and DNA laddering. MUC expression was assessed by RT-PCR. p38 MAPK activation and mucin protein level, using anti-mucin antibody for MUC5/6, were determined by Western blot analysis. As a result, H. pylori induced apoptosis and loss of mucin, which was supported by reduced mRNA expression of MUC5AC by H. pylori in AGS cells. MUC7/8 expression and p38 MAPK activation were induced in H. pylori-infected AGS cells. In conclusion, H. pylori induces p38 MAPK activation, wh3.ich may be the underlying mechanism of alterations in MUC expression and apoptosis in gastric epithelial cells.

Cardiac heart disease in the era of sucrose polyester, Helicobacter pylori and Chlamydia pneumoniae

Recent evidence associates inflammatory mediators with coronary heart disease. Elevation of acute-phase reaction (APR) proteins such as serum amyloid A, fibrinogen, CRP and haptoglobin in response to Helicobacter pylori (H. pylori) infection was shown to initiate gastritis and ischemic heart disease. Positive Chlamydia pneumoniae (C. pneumoniae) serology is associated with increased levels of inflammatory cytokines and tumor necrosis factor-alpha (TNF-alpha), which stimulates endothelial cell activation, procoagulant activity and angiogenesis in patients with coronary heart disease. As a final example, interleukin-6 (IL-6) has been proposed to mediate cardiovascular disorders. Public awareness of risks of excessive body weight and high levels of serum cholesterol propelled the development of synthetic dietary components such as sucrose polyester (SPE) to substitute for natural lipids. SPE is a synthetic lipid whose physical properties are similar to a natural triacylglycerol with a similar assortment of fatty acids and is resistant to lipolysis by gastric and pancreatic enzymes. Intake of SPE in lieu of natural lipids is expected to decrease absorption of essential fatty acids (EFA) and fat-soluble vitamins among other essentials. Deficiency of EFA leads to the formation of faulty cellular membranes, which is manifested as skin lesions, growth failure, erythrocyte fragility, impairment of fertility and uncoupling of oxidation and phosphorylation. Possibilities of absorption of these synthetic lipids into the circulation may represent an unexpected health hazard. We have shown that subcutaneous (sc) administration to rabbits of a range of lipolysis-resistant lipid-like sorbitol, mannitol and arabitol esters of palmitic (P) and lauric (L) acids was found to evoke a mild APR, which in humans could contribute to CHD incidence. We suggest a reversal in the commonly accepted role of SPE as a sequestor of dietary lipid: SPE may be the lipophilic solute contained within the dietary lipid solvent micelle. An alternative conclusion regarding the biological effects of excessive dose of SPE in human and pig for a short time span should be considered.

Association of CagA and VacA presence with ulcer and non-ulcer dyspepsia in a Turkish population

AIM: The mostly known genotypic virulence features, of H. pylori are cytotoxin associated gene A (CagA) and Vacuolating cytotoxin gene A (VacA). We investigated the association of these major virulence factors with ulcer and non-ulcer dyspepsia in our region.

METHODS: One hundred and forty two dyspeptic patients were studied (average age 44.8 ± 15.9 years, range 15-87 years, 64 males and 78 females). Antral and corpus biopsies were taken for detecting and genotyping of H. pylori. 107 patients who were H. pylori positive by histological assessment were divided into three groups according to endoscopic findings: Duodenal ulcer (DU), gastric ulcer (GU) and non-ulcer dyspepsia (NUD). The polymerase chain reaction (PCR) was used to detect CagA and VacA genes of H. pylori using specific primers.

RESULTS: H. pylori was isolated from 75.4% (107/142) of the patients. Of the 107 patients, 66 (61.7%) were CagA-positive and 82 (76.6%) were VacA-positive. CagA gene was positively associated with DU and GU (P < 0.01, P < 0.02), but not with NUD (P > 0.05). Although VacA positivity in ulcer patients was higher than that in NUD group, the difference was not statistically significant (P > 0.05).

CONCLUSION: There is a significantly positive association between CagA genes and DU and GU. The presence of VacA is not a predictive marker for DU, GU, and NUD in our patients.

Comparison of cytotoxin genotypes of Helicobacter pylori in stomach and saliva

We have previously reported a high prevalence of H. pylori DNA in saliva. In this study, the cytotoxin genotypes of H. pylori strains from both stomach and saliva were compared in 31 patients with gastritis and peptic ulcer. The cagA, vacA m1, vacA m2, and vacA s1 genotypes were analyzed by PCR. The 417 bp PCR products from three patients were also subjected to DNA sequencing analysis. There was 95% agreement between stomach H. pylori isolates and their corresponding saliva DNA in at least one cytotoxin genotype; 86% agreement with two cytotoxin genotypes; 59% agreement with three cytotoxin genotypes; and 27% agreement with all four cytotoxin genotypes studied. DNA sequencing from three patients showed 78.0%, 64.0%, and 66.9% homology of H. pylori from both sources, respectively. The data suggest that more than one H. pylori strain may exist in the stomach and saliva in the same patient.

Comparison of cytotoxin genotypes of Helicobacter pylori in stomach and saliva

We have previously reported a high prevalence of H. pylori DNA in saliva. In this study, the cytotoxin genotypes of H. pylori strains from both stomach and saliva were compared in 31 patients with gastritis and peptic ulcer. The cagA, vacA m1, vacA m2, and vacA s1 genotypes were analyzed by PCR. The 417 bp PCR products from three patients were also subjected to DNA sequencing analysis. There was 95% agreement between stomach H. pylori isolates and their corresponding saliva DNA in at least one cytotoxin genotype; 86% agreement with two cytotoxin genotypes; 59% agreement with three cytotoxin genotypes; and 27% agreement with all four cytotoxin genotypes studied. DNA sequencing from three patients showed 78.0%, 64.0%, and 66.9% homology of H. pylori from both sources, respectively. The data suggest that more than one H. pylori strain may exist in the stomach and saliva in the same patient.

In search of the Helicobacter pylori VacA mechanism of action

Helicobacter pylori secretes an approximately 88 kDa VacA toxin that is considered to be an important virulence factor in the pathogenesis of peptic ulcer disease. Over the past decade, research on the molecular mechanisms and biological functions of VacA has generated a complex and often puzzling scenario. VacA is secreted into the extracellular space and also is partially retained on the bacterial cell surface, exists in monomeric and oligomeric forms, and binds to multiple eukaryotic cell-surface receptors. The cellular effects induced by VacA include vacuolation, alteration of endo-lysosomal function, pore formation in the plasma membrane, apoptosis, and epithelial monolayer permeabilisation. VacA has been reported to target several different cell components, including endocytic vesicles, mitochondria, the cytoskeleton, and epithelial cell-cell junctions. It remains unclear whether VacA should be classified as an A/B type toxin, a channel-forming toxin, or both. This review is intended to summarise our current knowledge about VacA, and to orient the reader to this fascinating and challenging research area.

Comparison of genomic structures and antigenic reactivities of orthologous 29-kilodalton outer membrane proteins of Helicobacter pylori

We purified a 29-kDa Helicobacter pylori outer membrane protein (Omp29 protein) and cloned the gene encoding the protein from H. pylori strain ATCC 43504. The Omp29 gene corresponded to the reported JHP73 and the HP78-79 genes of H. pylori strains. A corresponding nucleotide fragment was detected in all 150 tested H. pylori clinical isolates by PCR or Southern blotting. The amplified Omp29-corresponding fragments were categorized into a ca. 770-bp-long group and a larger-fragment group. Sequence analysis indicated that the larger fragments were likely synthesized from the 770-bp fragments by insertion of an irrelevant fragment via 17-bp-long repeat sequences. Immunoblot analysis implies that the ca. 770-bp fragment is responsible for the protein homologous to Omp29, whereas the larger fragments are not responsible for those proteins or encoding antigenically distinct proteins. We postulate that the H. pylori outer membrane protein Omp29 can alter its antigenicity through gene modifications mediated by nucleotide transfer.

Helicobacter pylori CagA: analysis of sequence diversity in relation to phosphorylation motifs and implications for the role of CagA as a virulence factor

CagA is transported into host target cells and subsequently phosphorylated. Clearly this is a mechanism by which Helicobacter pylori could take control of one or more host cell signal transduction pathways. Presumably the end result of this interaction favors survival of H. pylori, irrespective of eventual damage to the host cell. CagA is noted for its amino acid (AA) sequence diversity, both within and outside the variable region of the molecule. The primary purpose of this review is to examine how variation in the type and number of CagA phosphorylation sites might determine the outcome of infection by different strains of H. pylori. The answer to this question could help to explain the widely disparate results obtained when H. pylori CagA status has been compared to type and severity of disease outcome in different populations, that is in different countries. Analysis of all available CagA sequences revealed that CagA contains both tyrosine phosphorylation motifs (TPMs) and cyclic-AMP-dependent phosphorylation motifs (CPMs). There are two potential CPMs near the N-terminus of CagA and at least two in the repeat region; these are not all equally well conserved. We also defined a 48-residue AA sequence, which includes the N-terminal TPM at tyrosine (Y)-122, which distinguishes between Eastern (Hong Kong-Taiwan-Japan-Thailand) H. pylori isolates and those from the West (Europe-Africa-the Americas-Australia). All 28 of the Eastern type CagA proteins have a functional N-terminal TPM whereas 11 of 47 (23.4%) of the Western type contain an inactive motif, with threonine (T) replacing the critical aspartic acid (D) residue. Only 13 of 24 (54%) known CagA sequences have an active TPM in the repeat region and only one has two TPMs in this region. The potential TPM near the C-terminus of CagA is not likely to be important since only 3 of 24 (12.5%) sequences were found to be intact. Protein database searches revealed that the AA sequence immediately following the TPM at Y-122 in CagA is homologous with a pair of PDZ domains which are common in signal transducing proteins, particularly tyrosine phosphatases. This provides a theoretical link between CagA and many of the observed responses of host cells to H. pylori. In summary, not all CagA proteins are equal in their potential for initiating host cell responses via signal transduction pathways. The degree of functional diversity of this protein depends upon which phosphorylation motifs are critical to the biological activity of CagA.