Published online Dec 7, 2020. doi: 10.3748/wjg.v26.i45.7118
Peer-review started: August 1, 2020
First decision: September 30, 2020
Revised: October 10, 2020
Accepted: November 12, 2020
Article in press: November 12, 2020
Published online: December 7, 2020
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.
To better understand the EPIYA patterns and CM motifs of the cagA gene.
Gastric 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.
All 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.
We 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.
Core Tip: We found the unique African (hpAfrica1-type) CagA-multimerization (CM) motif in Western-type CagA in the Dominican Republic and termed it Africa1-CM (Af1-CM). In addition, a few hpEurope strains carrying the Af1-CM motif had a significantly higher ancestral Africa1 component than those without the Af1-CM motif. This result suggests that the ancestors of these hpEurope strains having the Af1-CM motif underwent genetic recombination with the hpAfrica1 strains in the past. In contrast, there was no significant association between the CM motif patterns and histological scores and clinical outcomes.