Intact cag pathogenicity island of Helicobacter pylori without disease association in Kolkata, India
Introduction
Helicobacter pylori, a Gram-negative microaerophilic bacterium, chronically infects the gastric epithelium, and infection is associated with several gastroduodenal diseases such as chronic gastritis, peptic ulcer, and gastric cancer (Correa, 1992, NIH Consensus Conference, 1994, Parsonnet, 1999). Although more than half of the human population carries the infection, only ∼10–15% of the infected individuals develop such gastroduodenal diseases and hence, strain-specific genetic traits could be involved in H. pylori-related pathogenesis. The cagA gene, which encodes a protein of ∼128 kDa (CagA), the CagA protein is one of the most well-studied virulence markers of H. pylori (Covacci et al., 1993, Tummuru et al., 1993). cagA along with several other virulence-associated genes constitute the ∼40-kb cag pathogenicity island (cag PAI) and is present in ∼50–70% and ∼90% of the western and Asian H. pylori strains, respectively (Covacci et al., 1993, Ito et al., 1997, van Doorn et al., 1999). Vacuolating cytotoxin (VacA), a protein that can cause severe cytotoxicity in cell lines as well as in gastric mucosa, is coded by the vacA gene, which could be present in several allelic combinations (Cover et al., 1994, Atherton et al., 1995). H. pylori strains that carry s1m1-allelic combination are significantly more cytotoxic than strains that carry s1m2-allelic combination while strains that carry s2m2-allelic combination are a non-vacuolating form of VacA (Atherton et al., 1995, Atherton et al., 1997). Interestingly, strains that carry cag PAI (cag+) are more likely to carry the s1m1-allelic combination of the vacA gene as compared to strains that lack cag PAI (cag−) (Atherton et al., 1995, Atherton et al., 1997). In western countries, strains that carry s1m1cagA are significantly associated with H. pylori-related gastroduodenal diseases, although such association is not apparent in the Indian context (Cover et al., 1994, Atherton et al., 1997, Mukhopadhyay et al., 2000, Chattopadhyay et al., 2002, Datta et al., 2003). Moreover, expression of babA gene product, which governs adherence to Lewisb (histo-blood group antigen) on gastric epithelial cells and expression of Lewis antigens as part of their lipopolysaccharide, is also strongly associated with cag+ strains (Ilver et al., 1998). Therefore, it appears that cag+ and cag− strains probably have different requirements for their colonization in gastric epithelium.
The cag PAI, which contains a different GC content than the H. pylori genome, probably entered the genome after the bacterium had evolved as a species (Tomb et al., 1997). It contains 27 genes, 6 of which are thought to encode a putative type IV secretion system, responsible for the translocation of the CagA into the host cell (Covacci et al., 1999, Stein et al., 2002). The CagA, after being translocated to the host cell, becomes phosphorylated on tyrosine residues by Src family kinases, and the phosphorylated CagA interacts with the SH2 domain of the SHP-2 (Higashi et al., 2002a, Higashi et al., 2002b). This interaction leads to an altered cellular morphology and may eventually lead to gastric carcinoma (Asahi et al., 2000, Segal et al., 1999, Odenbreit et al., 2000, Stein et al., 2000, Higashi et al., 2002a).
An intact cag PAI may be responsible for the proinflammatory nature of H. pylori leading to gastroduodenal diseases like duodenal ulcer, gastric atrophy, and gastric cancer. The presence of intact cag PAI strains was found more frequently in patients with severe gastroduodenal disease (Nilsson et al., 2003). Partial deletions of the cag PAI appear to be sufficient to render the organism less pathogenic (Ali et al., 2005, Nilsson et al., 2003). The cag PAI is involved in the induction of interleukin-8 (IL-8) secretion, which is implicated in the inflammatory response of the gastric mucosa to H. pylori infection. However, the existence of strains inducing IL-8 secretion regardless of the cag PAI structure suggests that this region is not the only prerequisite for the IL-8 secretion (Audibert et al., 2001, Hsu et al., 2002). Furthermore, the cag PAI status did not affect the attachment of the bacterium to the gastric epithelial cells. In some populations, cagA-related genes are associated with an abrogated apoptotic response, whereas other studies showed that apoptosis was increased in the antrum and body (of the stomach) only in patients with cagA-positive H. pylori strains (Peek et al., 1997, Moss et al., 2001). Moreover, cag PAI-positive H. pylori strains induce apoptosis more rapidly than cag PAI-negative mutant strains, suggesting that the H. pylori binding and subsequent apoptosis are differentially regulated with regard to bacterial properties (Minohara et al., 2007). The cagA sequences of H. pylori strains isolated from Kolkata, India, are clustered with the cagA sequences of strains isolated from western countries and differed significantly from cagA sequences of strains isolated from East Asia (China or Japan) (Mukhopadhyay et al., 2000, Datta et al., 2003, Chattopadhyay et al., 2004). There is also a distinct polymorphic site at the right end of the cag PAI of Kolkata H. pylori strains (Kersulyte et al., 2000). It has also been observed that the presence of the IS605 element both in cagA+ and cagA− strains did not systematically modify the severity of associated disease in the study population (Owen et al., 2001).
Studies concerning the variation within the cag PAI of H. pylori infection associated with a variety of outcomes ranging from seemingly asymptomatic coexistence to peptic ulcer disease and gastric cancer showed variable results in different geographical populations (Yakoob et al., 2009). One study from southern India reported that intact cag PAI is present in only 12% of the population which correlated well with the data that 15% of the infected patients are symptomatic (Kauser et al., 2004). Another study claimed that the presence of an intact cag PAI correlated with the development of more severe pathology, and such strains were found more frequently in patients with severe gastroduodenal disease (Ali et al., 2005).
These considerations and our interest in the dynamics of genetic traits associated with H. pylori infection and disease association motivated us to conduct the present study (i) whether the Bengali population, which is different from the south Indian population, has a similarly low percentage of intact cag PAI carrying H. pylori strains, and (ii) whether the presence of intact cag PAI is correlated with the development of a more severe pathology to understand the disease process and pathogen–host interaction.
Section snippets
Patient samples
A total of 73 adult participants [duodenal ulcer (DU) patients and non-ulcer dyspepsia (NUD) or asymptomatic volunteers (AV)] of both sexes (aged between 20 and 65 years) underwent a non-sedated upper gastrointestinal endoscopy (GIF XQ 30, Olympus Optical Company, Japan) under topical lignocaine anesthesia at the hospital of the Institute of Post Graduate Medical Education and Research, Kolkata, India, during the years 2002–2004. Among the 40 DU cases (17 females and 23 males), the mean age
Results
Among 73 individuals included in the study, 40 had clinical features of DU and 33 were NUD or asymptomatic subjects. In 30 out of 40 (75%) DU and 22 out of 33 (67%) NUD or asymptomatic subjects, evidence of H. pylori infection was confirmed from the isolation of this bacterium by culture method, and these were included in the further study.
Discussion
The severity of H. pylori-related disease correlates with the presence of a cag pathogenicity island (cag PAI) in western countries. Genetic diversity within the cag PAI may have a profound effect on the pathogenic potential of the infecting strain, and the cag PAI has been studied in different H. pylori populations by various methods including PCR, Southern blotting, dot blot, and by long-distance PCR (Slater et al., 1999, Audibert et al., 2001, Ikenoue et al., 2001, Azuma et al., 2004). In
Acknowledgements
We would like to thank Mr. Manash Ray for his technical support during the preparation of the manuscript. The work was supported in part by the Indian Council of Medical Research, Government of India; the Japan Initiative for Global Research Network on Infectious Diseases, Ministry of Education, Culture, Sports, Science and Technology of Japan; and the Department of Biotechnology (No. BT/PR10407/BRB/10/604/2008). D.E. Berg was supported by grants (R21 AI078237 and R21 AI088337) from the US
References (55)
- et al.
Mosaicism in vacuolating cytotoxin alleles of Helicobacter pylori, association of specific vacA types with cytotoxin production and peptic ulceration
J. Biol. Chem.
(1995) - et al.
Clinical and pathological importance of heterogeneity in vacA, the vacuolating cytotoxin gene of Helicobacter pylori
Gastroenterology
(1997) - et al.
Divergence of genetic sequences for the vacuolating cytotoxin among Helicobacter pylori strains
J. Biol. Chem.
(1994) - et al.
Clinical presentation in relation to diversity within the Helicobacter pylori cag pathogenicity island
Am. J. Gastroenterol.
(2002) The human genetic history of South Asia
Curr. Biol.
(2010)- et al.
Molecular epidemiology of Helicobacter pylori in England, prevalence of cag pathogenicity island markers and IS605 presence in relation to patient age and severity of gastric disease
FEMS Immunol. Med. Microbiol.
(2001) - et al.
Conservation of the cag pathogenicity island of Helicobacter pylori, associations with vacuolating cytotoxin allele and IS605 diversity
Gastroenterology
(1999) - et al.
Genomic analysis of Helicobacter pylori from Andhra Pradesh, South India, molecular evidence for three major genetic clusters
Curr. Sci.
(2003) - et al.
Association between cag-pathogenicity island in Helicobacter pylori isolates from peptic ulcer, gastric carcinoma, and non-ulcer dyspepsia subjects with histological changes
World J. Gastroenterol.
(2005) - et al.
Helicobacter pylori CagA protein can be tyrosine phosphorylated in gastric epithelial cells
J. Exp. Med.
(2000)