CagL Protein Polymorphism Fine-Tunes Helicobacter pylori Cancer Signaling

The gastric pathogen Helicobacter pylori carries a syringe-like molecular machine known as the cag type IV secretion system, a structure long recognized as a key determinant in the development of gastric cancer. At the surface of this machine’s pilus sits a protein called CagL, a VirB5 ortholog that helps the bacterium bind host target cells so it can inject cargo such as the CagA oncoprotein and the metabolite ADP-heptose. A new study published in Cell Communication and Signaling examined a hypervariable region of CagL at amino acid positions 58 and 59, previously proposed to influence gastric cancer progression, and found that the identity of just two amino acids at these positions can dramatically change the cancer-driving behavior of the bacterium.

Previous work had flagged positions 58 and 59 as a hypervariable spot in CagL, but the authors of the new study noted that earlier analyses lacked both a large number of H. pylori strains and detailed functional experiments. To close that gap, the team surveyed the CagL status in 2,267 worldwide H. pylori genomes, analyzed the variation from an evolutionary perspective and in relation to gastric disease status, and then directly compared the two major variants in controlled infection experiments.

The two variants differ in a specific way: one carries tyrosine at position 58 and glutamate at position 59, abbreviated Y58/E59, while the other carries asparagine and lysine at the same positions, abbreviated N58/K59. The researchers compared these forms in the gastric cancer-associated H. pylori strain 7.13, testing their effects on T4SS pilus formation and cancer signaling during infection of gastric epithelial cells in vitro and during infection of Mongolian gerbils in vivo.

Structural analysis showed that the polymorphism sits in an amino acid loop flanked by two alpha-helices, and that the identity of the residues in this loop affects CagL conformation and functional activity. Remarkably, when the researchers examined pilus assembly, both variants produced similar robust T4SS pilus formation. The physical apparatus, in other words, was built equally well by either version of the protein. The functional consequences, however, diverged sharply.

In infection experiments, wild-type H. pylori 7.13 encoding the N58/K59 form of CagL triggered gastric cancer development in Mongolian gerbils. In gastric epithelial cells, this variant drove a characteristic set of gastric cancer signaling events: phosphorylation of the CagA oncoprotein after its delivery into host cells, activation of the MAP kinases p38, ERK1/2 and JNK, activation of beta-catenin, increased cell motility, pronounced induction of interleukin-8 production through the pro-inflammatory transcription factor NF-kappaB, and the formation of DNA double-strand breaks. Each of these responses is a recognized feature of the cancer-promoting program that the cag secretion system activates in infected stomach tissue.

The Y58/E59 variant told a different story. H. pylori carrying this form of CagL elicited markedly attenuated responses across the same battery of readouts. The attenuated signaling points to a specific defect: according to the study’s conclusions, the Y58/E59 mutation impairs translocation of CagA into host cells.

Importantly, the mutation did not disable the secretion system entirely. The Y58/E59 variant retained both T4SS pilus formation and ADP-heptose-dependent NF-kappaB activation.

Taken together, these data suggest that CagL mutation may act as a molecular regulator of the type IV secretion system, fine-tuning CagA delivery, host inflammation and other oncogenic responses. The authors draw a parallel with CagY, another T4SS pilus protein previously reported to cause the gain or loss of interleukin-8 production through genetic polymorphisms arising from recombination events.

The study’s scope reflects both its strengths and its limits. The evolutionary survey covered 2,267 genomes, giving a broad picture of how widespread the two CagL variants are among worldwide strains and how they relate to gastric disease status. The functional comparisons were performed in a single gastric cancer-associated strain background, strain 7.13, using gastric epithelial cells in culture and Mongolian gerbils as the in vivo model.

Subject of Research: A genetic polymorphism in the Helicobacter pylori CagL type IV secretion pilus protein that modulates gastric cancer signaling

Article Title: Evolution and function of genetic polymorphisms in the Helicobacter pylori type IV secretion pilus protein CagL in gastric carcinogenesis

Article References: Tegtmeyer, N., Romero-Gallo, J., Linz, B., Piazuelo, M. B., Noman, O., Rohde, M., Sticht, H., Peek, R. M., Jr., & Backert, S. (2026). Evolution and function of genetic polymorphisms in the Helicobacter pylori type IV secretion pilus protein CagL in gastric carcinogenesis. Cell Communication and Signaling. https://doi.org/10.1186/s12964-026-03334-9

Image Credits: AI Generated

DOI: 10.1186/s12964-026-03334-9

Keywords: Helicobacter pylori, CagL, type IV secretion system, gastric cancer, CagA, NF-κB, Mongolian gerbils, genetic polymorphism, T4SS pilus, ADP-heptose, interleukin-8, DNA double-strand breaks