This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ando, T. Articles by Blaser, M. J. Search for Related Content PubMed PubMed Citation Articles by Ando, T. Articles by Blaser, M. J.

A Helicobacter pylori Restriction Endonuclease-replacing Gene, hrgA, Is Associated with Gastric Cancer in Asian Strains¹

Departments of Medicine and Microbiology, New York University School of Medicine, New York, New York 10016 [T. A., R. A. A., A. I. T., M. J. B.]; First Department of Internal Medicine, Nagoya University School of Medicine, Nagoya 466-8550, Japan [T. A., K. K.]; Molecular Microbiology and Genomics Consultants, D-55576 Zotzenheim, Germany [T. M. W.]; Division of Gastroenterology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232 [R. M. P.]; Delft Diagnostic Laboratory, 2625 AD Delft, the Netherlands [L-J. v. D.]; and Department of Veterans Affairs Medical Center, New York, New York 10016 [M. J. B.]

	ABSTRACT

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The sensitivity of Helicobacter pylori chromosomal DNA to MboI digestion was investigated in 208 strains from several continents. Only 11 (5%) of strains were sensitive to MboI, and it was hypothesized that HpyIII, a type II restriction/modification enzyme with sequence homology to MboI, mediated the protection. This was confirmed by PCR analysis of the gene locus of hpyIII, normally composed of hpyIIIR and hpyIIIM. In all but one strain sensitive to MboI, no PCR product of hpyIIIR was obtained. In contrast, all strains yielded a product for hpyIIIM, independent of MboI phenotype. Further examination of the hpyIII locus in strains lacking a hpyIIIR PCR product identified a novel gene, hrgA, upstream of hpyIIIM. All 208 strains examined had either hpyIIIR or hrgA, but not both, upstream of hpyIIIM. Although hrgA has homology with a Campylobacter jejuni gene (Cj1602), its function is not known. In Western countries, hrgA was more prevalent (53%) than in Asia (25%; P < 0.0001, ²). In Asia, hrgA was more prevalent among gastric cancer patients (18 of 43; 42%) than among noncancer patients (16 of 95; 17%; P = 0.001, ²). All 143 Asian strains tested were cagA⁺, but among Western strains, hrgA was more prevalent in cagA⁺ strains (26 of 42; 62%) than in cagA^- strains (9 of 23; 39%; P = 0.04, ²). In coculture with epithelial cells, hpyIIIR and hrgA strains did not show any significant differences in interleukin-8 induction and apoptosis. Although a direct function for hrgA in virulence could not be demonstrated, our data indicate that hrgA is a strain-specific gene that might be associated with gastric cancer among H. pylori isolates from Asian patients.

	INTRODUCTION

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Helicobacter pylori are Gram-negative bacteria that colonize the human stomach and whose presence affects the risk of upper gastrointestinal tract diseases, including gastric cancer (1) . Several strain-specific factors have been identified that potentially are markers for the differential risk associated with H. pylori colonization; at present, cagA, a marker of the cag pathogenicity island, has the strongest predictive value (2, 3, 4, 5, 6) . However, in East Asia, most strains are cagA⁺ regardless of clinical outcome (7, 8, 9) . Thus, identification of bacterial factors involved in or serving as markers for the progression to ulceration or to gastric cancer remains desirable. During our study of R-M³ systems in H. pylori, we unexpectedly discovered such a potential marker that among Asian patients with cagA⁺ strains identifies those associated with gastric cancer.

H. pylori strains are highly heterogeneous in the number and nature of the type II R-M systems they carry (10, 11, 12, 13, 14, 15) . Type II R-M systems comprise two enzymes encoded by paired genes, a restriction endonuclease that cleaves DNA within a specific 4–8-bp sequence and a methyltransferase that specifically methylates the DNA at adenine or cytosine residues within the same sequence and thus protects the sequence from cleavage (16, 17, 18) . H. pylori DNA is highly methylated at both adenine and cytosine residues (10) , consistent with genomic sequence analyses that predicted 14 and 15 potential R-M systems for H. pylori strains 26695 and J99, respectively (11 , 12) . The hpyIII R-M gene locus (13, 14, 15) is homologous to the MboI R-M system of Moraxella bovis (19) , which recognizes the DNA sequence GATC, and the same recognition sequence has been confirmed for hpyIII (13 , 14) .

In a previous study (20) , we showed that all H. pylori strains examined were resistant to NlaIII and that most (95%) were also resistant to MboI. NlaIII is homologous to hpyIR, which has been called iceA1, and MboI is homologous to hpyIIIR. In some H. pylori strains, iceA2 replaces iceA1, and strains with iceA1 have been found to be more highly associated with peptic ulcer disease (21 , 22) and gastric cancer (23) than those with iceA2. These associations prompted us to study the hpyIII R-M system in more detail to determine whether there was a similar correlation with pathogenic outcomes. We assayed a collection of strains for susceptibility to MboI. When a small minority of strains was found to be sensitive to this restriction enzyme, they were examined to detect polymorphisms in their hpyIII locus. These analyses identified a new gene, hrgA, that had replaced hpyIIIR in most MboI-sensitive strains. For most strains investigated, the patient’s clinical outcome was known, allowing investigation of correlations with hrgA/hpyIIIR status. Our findings suggest that hrgA can potentially be used as a marker for virulence in the presence of cagA.

	MATERIALS AND METHODS

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Bacterial Strains and Growth Conditions.
A total of 208 clinical isolates from different parts of the world (Table 1) were from patients with duodenal ulcers (n = 55), gastric ulcers (n = 42), gastric cancer (n = 43), and nonulcer dyspepsia (n = 62). The three Colombian strains were isolated from Hispanic persons and categorized as Western strains. For six patients (five from Thailand, one from the United States), clinical data were not available. The strains were obtained from 208 unique patients. At the time of endoscopy, two biopsy specimens were obtained from the greater curvature of the antrum, between 2 and 5 cm from the pylorus. To isolate H. pylori, biopsies were homogenized in 250 µl of saline, and 50 µl were plated onto trypticase soy agar with 5% sheep blood (BBL) and incubated for up to 9 days under microaerobic conditions. Single colonies were collected, and bacteria were identified as H. pylori by Gram’s stain morphology as well as by urease and oxidase activity. All isolates were characterized by their cagA status (positive, n = 185; negative, n = 23). Strain JP26, from which hrgA was originally isolated and sequenced, is a H. pylori strain obtained from a gastric cancer patient in Japan.

View larger version (44K): [in this window] [in a new window] [Download PPT slide]   Fig. 1. A, schematic representation of the hpyIII R-M locus in H. pylori strains. Type I represents strains containing hpyIIIR, and Type II represents strains containing hrgA. PCR primers used in the analysis of these loci are indicated by black arrows, and the sizes of obtained PCR products are shown in italics. B, representative agarose gel (26695 for type I, JP26 for type II) showing the size of PCR products obtained with the primers specific for hpyIIIR, hpyIIIM, hrgA, and the complete locus. For both types, Lane 1, hpyIIIR; Lane 2, hpyIIIM; Lane 3, the complete locus; Lane 4, hrgA.

hrgA Sequence.
For sequence analysis, the PCR product of JP26, generated with primers locf and locr, was purified using the QiaQuick PCR purification kit and the QiaQuick Gel Extraction kit. The purified PCR product was subsequently sequenced on both strands in an automated sequencer (Applied Biosystems, Inc.) in the New York University Cancer Center Core Laboratory and analyzed using Sequencer 3.1.1 (Gene Code Corp, Inc., Ann Arbor, MI). The accession no. was AF446009.

Disruption of hrgA in H. pylori strain 26695 or JP26.
A chloramphenicol resistance gene (cat) was inserted in hrgA of JP26. A PCR fragment was first generated from hrgA of strain JP26, using primers NthrgAf and XhhrgAr (Table 2) . This product was cloned into pBluescript, using Escherichia coli DH5. A unique EcoRI site was created by inverse PCR with primers hrgAinr and hrgAinf, disrupting hrgA. The cat gene of pBSC103 (26) was amplified using primers catf and catr, which added EcoRI restriction sites. This cassette was ligated into the inverse PCR product, thereby disrupting hrgA. H. pylori strain JP26 was transformed to chloramphenicol resistance with the pBSC103 vector containing the hrgA gene interrupted by cat, to create JP26-hrgA::cat. Chromosomal DNA was isolated from the transformants, and the insertion of the cat cassette within hrgA was confirmed by PCR.

AGS Cell Culture and IL-8 Assays.
AGS human gastric epithelial cells (ATCC CRL 1739) were grown in RPMI 1640 (Life Technologies, Inc., Rockville, MD) supplemented with 10% FBS and 20 µg/ml gentamicin in an atmosphere of 5% CO₂ at 37°C. For coculture experiments, H. pylori was grown in Brucella broth with 5% FBS for 48 h. Cells were harvested by centrifugation (2000 x g) and resuspended in antibiotic-free RPMI 1640 with 10% FBS to yield a final concentration of 1 x 10⁸ colony-forming units/ml. H. pylori were added to AGS cells at a bacteria:cell concentration of 1000:1 for the IL-8 assays or 100:1 for the apoptosis assays. Experiments were performed in antibiotic-free medium containing 10% FBS in T-150 flasks (Corning Costar, Cambridge, MA) or 96-well polypropylene tissue culture plates (Nunc, Roskilde, Denmark). To recapitulate events that occur in native actively replicating gastric mucosa, AGS cells were not serum starved and remained subconfluent during each assay. Levels of IL-8 (expressed as pg/ml) in culture supernatants were assayed in duplicate by specific ELISAs (Research and Development Systems, Minneapolis, MN), according to the manufacturer’s instructions.

Assessment of Apoptosis by DNA Fragmentation Assay.
DNA fragmentation was quantified using a commercially available ELISA (Boehringer Mannheim Biochemicals, Indianapolis, IN) that detects nucleosomal fragments in cytoplasmic fractions of cells undergoing apoptosis, but not necrosis. For these experiments, 5 x 10³ AGS cells/well were incubated in 96-well plates in duplicate with H. pylori (5 x 10⁵ colony-forming units/well) cells or with RPMI 1640–10% FBS alone for 48 h and lysed. Lysates were centrifuged, and supernatants were used for ELISA. Absorbance measured at 405 nm was compared between AGS cells cultured with H. pylori or with the negative control.

	RESULTS

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
MboI Digestion of H. pylori Chromosomal DNA and PCR Analysis of the hpyIII R-M Locus.
After a preliminary study involving a few H. pylori strains, chromosomal DNA from 208 strains (listed in Table 1 ) was digested with the restriction enzyme MboI. Of the 208 strains, 197 were resistant and 11 (5%) were sensitive. To determine whether the MboI digestion susceptibility was attributable to the absence or the genetic variability in the hpyIII R-M gene locus (10 , 13, 14, 15) , the presence of hpyIIIR and hpyIIIM was assessed by PCR, using primers described in Fig. 1 . With primers hpMf and hpMr, all 208 strains studied amplified a hpyIIIM PCR product of the expected size (550 bp). In contrast, with primers hpRf and hpRr, only 138 strains (66%) yielded a hpyIIIR PCR product of the expected size (420 bp). Of the 11 MboI-sensitive strains, only 1 strain (88-29) amplified a product with hpyIIIR-specific primers. To determine whether the absence of a hpyIIIR PCR product was attributable to deletion of the gene or to mutations prohibiting primer annealing, a PCR was performed using primers (locf and locr) that flank the entire hpyIII R-M locus (Fig. 1) . As expected, strains that previously showed a hpyIIIR PCR product now yielded the expected 2.1-kb product (except for strain 99-517, which yielded a product of 2.0 kb). In contrast, all strains from which hpyIIIR had not been amplified now yielded 2.3 kb products (Fig. 1B) . Sequence analysis of the 2.3-kb PCR product from a Japanese strain, JP26 (a MboI-sensitive strain that failed to amplify a hpyIIIR PCR product), revealed that another gene had replaced hpyIIIR. We named this gene hrgA (AF446009), for H. pylori restriction endonuclease-replacing gene A.

Prevalence of hrgA.
The primers hrgAf and hrgAr, derived from the JP26 hrgA sequence, were used to examine the presence of hrgA in all 208 strains included in this study. The results indicated that the presence of hrgA and hpyIIIR is mutually exclusive in all strains tested (Table 3) . Using PCR primer pairs hrgAf and hpMr, hrgAf and locr, and locf and hrgAr (Fig. 1) , we confirmed that in all hrgA-positive strains, hrgA was located upstream of hpyIIIM. Strains were classified as type I when they contained hpyIIIR and type II when they contained hrgA; they were then subclassified based on the MboI susceptibility phenotype. Thus, four subtypes can be recognized (Table 3) . The prevalences of these types were compared with the strain’s geographic origin, cagA status, and clinical manifestations. Among 65 isolates from Western countries, hrgA⁺ strains were more prevalent (52%) than among 143 Asian isolates (25%; P < 0.001; Table 4 ). Among the Western patients studied, none had gastric cancers, and hrgA⁺ strains were more prevalent in cagA⁺ backgrounds (26 of 42; 62%) than in cagA^- backgrounds (9 of 23; 39%; P = 0.04). Among the 138 Asian patients studied (all cagA⁺), hrgA⁺ strains were more prevalent (42%) in gastric cancer patients than in patients without gastric cancer (17%; P < 0.001). These results indicate that hrgA may be a marker for strains associated with gastric cancer in Asia. There was no significant difference in hrgA prevalence in relation to disease outcomes (duodenal ulcer, gastric ulcer, or nonulcer dyspepsia) among nongastric cancer strains from either Asian or Western countries.

View larger version (72K): [in this window] [in a new window] [Download PPT slide]   Fig. 2. ClustalW alignment of translated sequence of putative products of Cj1602 (from C. jejuni strain NCTC11168), hrgA (from strain JP26), and HP0852 (from strain 26695). Black background indicates conserved amino acid in all three strains; gray indicates conserved amino acid in two of the three strains.

	DISCUSSION

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Our findings suggest that hrgA, a strain-specific gene, is associated with gastric cancer among H. pylori isolates from Asian patients. Differing recovery rates of hrgA⁺ versus hrgA^- strains attributable to differential growth may introduce bias, but because we have not observed differences in growth rates between hrgA⁺ and hrgA^- strains in vitro (data not shown), this seems less likely. In previous reports, the vacA s1 genotype and cagA or iceA1 positivity have been identified as markers of strains associated with ulcer disease or gastric cancer among Western populations (21, 22, 23 , 31) . Such a pattern is not immediately evident in East Asia, where regardless of the clinical status of the patient, nearly all isolates are vacA s1 and cagA positive (9 , 32) and iceA1 status does not have predictive value (9) . We could not determine the correlation between hrgA and gastric cancer among Western strains because, at present, our strain collection does not contain a sufficient number of cancer strains from Western countries for adequate comparisons to be made. However, we have initiated collaborations to obtain such strains to address this question in future studies. The lack of differential induction of IL-8 release or apoptosis in gastric epithelial cells by hrgA⁺ strains compared with hpyIIIR strains does not support a direct role in virulence. It cannot be excluded that acquisition of hrgA is selected by gastric cancer development, rather than being a causative factor. Whatever the case, the important clinical point is that hrgA may represent a novel marker for individuals with gastric cancer in Asia, where no such discriminatory H. pylori markers exist at present. The mere presence of hrgA may not be the only relevant factor for gastric cancer. Disease risk also could depend on transcription and/or translation of the hrgA gene product or on indirect effects thereof on expression of other genes. However, these findings provide a framework for future studies that can more mechanistically delineate the role of this locus in gastric carcinogenesis. Further studies are necessary to examine the function of hrgA and to ascertain its correlation with clinical outcome. If this observation is confirmed, hrgA may be used in the future to identify individuals of higher gastric cancer risk.

	ACKNOWLEDGMENTS

 
We thank Dr. Sung-Kook Kim for providing bacterial strains.

	FOOTNOTES

 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by Grants R01DK53707, R01GM63270, R29CA77955, and R0158587 from the NIH and by the Medical Research Service of the Department of Veterans Affairs.

² To whom requests for reprints should be addressed, at First Department of Internal Medicine, Nagoya University School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan. Phone: 81-52-744-2144; Fax: 81-52-744-2157; E-mail: takafumia-gi{at}umin.ac.jp

³ The abbreviations used are: R-M, restriction-modification; IL, interleukin; FBS, fetal bovine serum.

Received 11/19/01. Accepted 2/14/02.

	REFERENCES

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Blaser M. J. Hypothesis: the changing relationships of Helicobacter pylori and humans: implications for health and disease. J. Infect. Dis., 179: 1523-1530, 1999.[Medline]
2. Goossens H., Glupczynski Y., Burette A., Lambert J. P., Vlaes L., Butzler J. P. Role of the vacuolating toxin from Helicobacter pylori in the pathogenesis of duodenal and gastric ulcer. Med. Microbiol. Lett., 1: 153-159, 1992.
3. Covacci A., Censini S., Bugnoli M., Petracca R., Burroni D., Macchia G., Massone A., Papini E., Xiang Z., Figura N., Rappuoli R. Molecular characterization of the 128-kDa immunodominant antigen of Helicobacter pylori associated with cytotoxicity and duodenal ulcer. Proc. Natl. Acad. Sci. USA, 90: 5791-5795, 1993.[Abstract/Free Full Text]
4. Crabtree J. E., Farmery S. M. Helicobacter pylori and gastric mucosal cytokines: evidence that CagA-positive strains are more virulent. Lab. Investig., 73: 742-745, 1995.[Medline]
5. Blaser M. J., Perez-Perez G. I., Kleanthous H., Cover T. L., Peek R. M., Chyou P. H., Stemmermann G. N., Nomura A. Infection with Helicobacter pylori strains possessing cagA is associated with an increased risk of developing adenocarcinoma of the stomach. Cancer Res., 55: 2111-2115, 1995.[Abstract/Free Full Text]
6. Cover T. L., Glupczynski Y., Lage A. P., Burette A., Tummuru M. K., Perez-Perez G. I., Blaser M. J. Serologic detection of infection with cagA⁺ Helicobacter pylori strains. J. Clin. Microbiol., 33: 1496-1500, 1995.[Abstract]
7. Maeda S., Ogura K., Yoshida H., Kanai F., Ikenoue T., Kato N., Shiratori Y., Omata M. Major virulence factors, VacA and CagA, are commonly positive in Helicobacter pylori isolates in Japan. Gut, 42: 338-343, 1998.[Abstract/Free Full Text]
8. Sadakane Y., Kusaba K., Nagasawa Z., Tanabe I., Kuroki S., Tadano J. Prevalence and genetic diversity of cagD, cagE, and vacA in Helicobacter pylori strains isolated from Japanese patients. Scand. J. Gastroenterol., 34: 981-986, 1999.[Medline]
9. Zheng P. Y., Hua J., Yeoh K. G., Ho B. Association of peptic ulcer with increased expression of Lewis antigens but not cagA, iceA, and vacA in Helicobacter pylori isolates in an Asian population. Gut, 47: 18-22, 2000.[Abstract/Free Full Text]
10. Xu Q., Morgan R. D., Roberts R. J., Blaser M. J. Identification of type II restriction and modification systems in Helicobacter pylori reveals their substantial diversity among strains. Proc. Natl. Acad. Sci. USA, 97: 9671-9676, 2000.[Abstract/Free Full Text]
11. Tomb J. F., White O., Kerlavage A., Clayton R. A., Sutton G. G., Fleischmann R. D., Ketchum K. A., Klenk H. P., Gill S., Dougherty B. A., Nelson K., Quackenbush J., Zhou L., Kirkness E. F., Peterson S., Loftus B., Richardson D., Dodson R., Khalak H. G., Glodek A., McKenney K., Fitzegerald L. M., Lee N., Adams M. D., Hickey E. K., Berg D. E., Gocayne J. D., Fujii C., Bowman C., Watthey L., Walin E., Hayes W. S., Borodorsky M., Karp P. D., Smith H. O., Fraser C. M., Venter J. C. The complete genome sequence of the gastric pathogen Helicobacter pylori. Nature (Lond.), 388: 539-547, 1997.[Medline]
12. Alm R. A., Trust T. J. Analysis of the genetic diversity of Helicobacter pylori: the role of two genomes. J. Mol. Med., 77: 834-846, 1999.[Medline]
13. Kong H., Lin L. F., Porter N., Stickel S., Byrd D., Posfai J., Roberts R. J. Functional analysis of putative restriction-modification system genes in the Helicobacter pylori J99 genome. Nucleic Acids Res., 28: 3216-3223, 2000.[Abstract/Free Full Text]
14. Lin L. F., Posfai J., Roberts R. J., Kong H. Comparative genomics of the restriction-modification systems in Helicobacter pylori. Proc. Natl. Acad. Sci. USA, 98: 2740-2745, 2001.[Abstract/Free Full Text]
15. Vitkute J., Stankevicius K., Tamulaitiene G., Maneliene Z., Timinskas A., Berg D. E., Janulaitis A. Specificities of eleven different DNA methyltransferases of Helicobacter pylori strain 26695. J. Bacteriol., 183: 443-450, 2001.[Abstract/Free Full Text]
16. Bennett S. P., Halford S. E. Recognition of DNA by type II restriction enzymes. Curr. Top. Cell. Regul., 30: 57-104, 1989.[Medline]
17. Bickle T. A., Kruger D. H. Biology of DNA restriction. Microb. Rev., 57: 434-450, 1993.[Abstract/Free Full Text]
18. Pingoud A., Jeltsch A. Recognition and cleavage of DNA by type-II restriction endonucleases. Eur. J. Biochem., 246: 1-22, 1997.[Medline]
19. Ueno T., Ito H., Kimizuka F., Kotani H., Nakajima K. Gene structure and expression of the MboI restriction-modification system. Nucleic Acids Res., 21: 2309-2313, 1993.[Abstract/Free Full Text]
20. Ando T., Xu Q., Torres M., Kusugami K., Israel D. A., Blaser M. J. Restriction-modification system differences in Helicobacter pylori are a barrier to interstrain plasmid transfer. Mol. Microbiol., 37: 1052-1065, 2000.[Medline]
21. Peek R. M., Thompson S. A., Donahue J. P., Tham K. T., Atherton J. C., Blaser M. J., Miller G. G. Adherence to gastric epithelial cells induces expression of a Helicobacter pylori gene, iceA, that is associated with clinical outcome. Proc. Assoc. Am. Physicians, 110: 531-544, 1998.[Medline]
22. van Doorn L. J., Figueiredo C., Sanna R., Plaisier A., Schneeberger P., de Boer W., Quint W. Clinical relevance of the cagA, vacA, and iceA status of Helicobacter pylori. Gastroenterology, 115: 58-66, 1998.[Medline]
23. Kidd M., Peek R. M., Lastovica A. J., Israel D. A., Kummer A. F., Louw J. A. Analysis of iceA genotypes in South African Helicobacter pylori strains and relationship to clinically significant disease. Gut, 49: 629-635, 2001.[Abstract/Free Full Text]
24. Sambrook J., Fritsch E. F., Maniatis T. . Molecular Cloning: A Laboratory Manual, 2nd Ed. Cold Spring Harbor Laboratory Cold Spring Harbor, NY 1989.
25. Wilson K. Preparation of genomic DNA from bacteria Ausubel F. M. Brent R. Kingston R. E. Moore D. D. Seidman J. G. Smith J. A. Struhl K. eds. . Current Protocols in Molecular Biology, Vol. 1: 2.4.1-2.4.5, John Wiley & Sons New York 1995.
26. Wang Y., Taylor D. E. Chloramphenicol resistance in Campylobacter coli. Gene, 94: 23-28, 1990.[Medline]
27. Ando T., Kusugami K., Ohsuga M., Shinoda M., Sakakibara M., Saito H., Fukatsu A., Ichiyama S., Ohta M. Interleukin-8 activity correlates with histological severity in Helicobacter pylori-associated antral gastritis. Am. J. Gastroenterol., 91: 1150-1156, 1996.[Medline]
28. Figueiredo C., Quint W. G., Sanna R., Sablon E., Donahue J. P., Xu Q., Miller G. G., Peek R. M., Blaser M. J., van Doorn L. J. Genetic organization and heterogeneity of the iceA locus of Helicobacter pylori. Gene, 246: 59-68, 2000.[Medline]
29. Xu Q., Blaser M. J. Promoters of the CATG-specific methyltransferase gene hpyIM differ between iceA1 and iceA2 Helicobacter pylori strains. J. Bacteriol., 183: 3875-3884, 2001.[Abstract/Free Full Text]
30. Xu Q., Peek R. M., Miller G. G., Blaser M. J. The Helicobacter pylori genome is modified at CATG by the product of hpyIM. J. Bacteriol., 179: 6807-6815, 1997.[Abstract/Free Full Text]
31. Miehlke S., Kirsch C., Agha-Amiri K., Gunther T., Lehn N., Malfertheiner P., Stolte M., Ehninger G., Bayerdorffer E. The Helicobacter pylori vacA s1, m1 genotype and cagA is associated with gastric carcinoma in Germany. Int. J. Cancer, 87: 322-327, 2000.[Medline]
32. Van Doorn L. J., Figueiredo C., Megraud F., Pena S., Midolo P., Queiroz D. M., Carneiro F., Vanderborght B., Pegado M. D., Sanna R., De Boer W., Schneeberger P. M., Correa P., Ng E. K., Atherton J., Blaser M. J., Quint W. G. Geographic distribution of vacA allelic types of Helicobacter pylori. Gastroenterology, 116: 823-830, 1999.[Medline]

This article has been cited by other articles:

				O. Humbert and N. R. Salama The Helicobacter pylori HpyAXII restriction-modification system limits exogenous DNA uptake by targeting GTAC sites but shows asymmetric conservation of the DNA methyltransferase and restriction endonuclease components Nucleic Acids Res., December 1, 2008; 36(21): 6893 - 6906. [Abstract] [Full Text] [PDF]

				S K Tiwari, G Manoj, G V. Kumar, G Sivaram, S I Hassan, B Prabhakar, U Devi, S Jalaluddin, K Kumar, S Ahmed, et al. Prognostic significance of genotyping Helicobacter pylori infection in patients in younger age groups with gastric cancer Postgrad. Med. J., April 1, 2008; 84(990): 193 - 197. [Abstract] [Full Text] [PDF]

				C. Ghose, G. I. Perez-Perez, L. J. van Doorn, M. G. Dominguez-Bello, and M. J. Blaser High Frequency of Gastric Colonization with Multiple Helicobacter pylori Strains in Venezuelan Subjects J. Clin. Microbiol., June 1, 2005; 43(6): 2635 - 2641. [Abstract] [Full Text] [PDF]

				Y. J. Chang, M. S. Wu, J. T. Lin, B. S. Sheu, T. Muta, H. Inoue, and C.-C. Chen Induction of Cyclooxygenase-2 Overexpression in Human Gastric Epithelial Cells by Helicobacter pylori Involves TLR2/TLR9 and c-Src-Dependent Nuclear Factor-{kappa}B Activation Mol. Pharmacol., December 1, 2004; 66(6): 1465 - 1477. [Abstract] [Full Text] [PDF]

				T. Nagasako, T. Sugiyama, T. Mizushima, Y. Miura, M. Kato, and M. Asaka Up-regulated Smad5 Mediates Apoptosis of Gastric Epithelial Cells Induced by Helicobacter pylori Infection J. Biol. Chem., February 7, 2003; 278(7): 4821 - 4825. [Abstract] [Full Text] [PDF]

				T. Ando, R. A. Aras, K. Kusugami, M. J. Blaser, and T. M. Wassenaar Evolutionary History of hrgA, Which Replaces the Restriction Gene hpyIIIR in the hpyIII Locus of Helicobacter pylori J. Bacteriol., January 1, 2003; 185(1): 295 - 301. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ando, T. Articles by Blaser, M. J. Search for Related Content PubMed PubMed Citation Articles by Ando, T. Articles by Blaser, M. J.