CagA structural types of Helicobacter pylori strains isolated from patients with gastric carcinoma and chronic gastritis only

Abstract

Gastric carcinoma (GC) is an important cause of death and is associated with infection by Helicobacter pylori (H. pylori) strains expressing CagA, an oncoprotein encoded by the cagA gene (for a comprehensive discussion of H. pylori infection, see Ref. [1]). Recent studies have shown that CagA can be injected into the colonized mucocytes through a conjugative apparatus encoded by cag genes upstream cagA. Once inside the cell, CagA undergoes phosphorylation by host cell kinases. Phosphorylated CagA is capable of altering the cell morphology and disturbing host-signaling pathways, which ultimately may lead to the development of GC. The fragment of the cagA gene encoding the carboxylterminal end of CagA is polymorphic, as it presents numerous genomic repetitions that contain the tyrosine EPIYA motif, a 5-amino acid sequence (Glu–Pro–Ile–Tyr– Ala), which is the site where CagA undergoes phosphorylation. In 1998, Yamaoka et al. [2] observed that strains with a high number of genomic repetitions in the cagA variable region were isolated more frequently from patients with GC. They classified the cagA structural types in A, B, C and D types, on the basis of the amplicon sizes obtained with primers spanning the entire cagA variable region. Types B and D have similar sizes and can be differentiated by sequencing the amplicons. Later on, the dissection of the cagA 30 repeat region of numerous H. pylori strains indicated that the occurrence of gastric mucosa atrophy, a lesion considered a pre-cancerous condition, was more likely when patients were infected by strains possessing a high number of repeats, i.e. strains with type C cagA gene [3]. In the scientific literature, there are only few reports about the possible association between clinical features and the CagA structural variability. In the present study, we investigated on the possible relationship existing between the polymorphism of the cagA 30 variable region and the occurrence of GC. We also determined the CagA mass expressed by different strains to ascertain whether the CagA size corresponded to the length of the amplicons. Forty H. pylori strains were isolated from resected gastric mucosa of patients with GC and 46 strains from gastric biopsies of patients with chronic gastritis only (CGO). Strains were identified by the Gram stain and oxidase, catalase and urease tests and stored at -80 C until the characterisation of the cagA polymorphism was performed. The cagA structural types were determined by polymerase chain reaction (PCR) using the following primers spanning the cagA variable region [2]; the different sizes of the amplicons obtained range from 642 to 834 bp: