title: Role of the actin-associated protein cortactin in infections with the gastrointestinal pathogen Helicobacter pylori
title: Rolle des Aktin-Bindeproteins Cortactin während der Infektion mit dem gastrointestinalen Pathogen Helicobacter pylori
Creators: name: Knorr, Jakob
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2025

description: The Gram-negative pathogen Helicobacter pylori is the causative agent of gastric diseases, including gastritis, ulcers, MALT lymphoma, and stomach cancer. Clinical problems are usually caused by H. pylori strains possessing the cag pathogenicity island (cagPAI) that encodes a type IV secretion system (T4SS). H. pylori employs the T4SS to translocate virulence factors, including the effector protein CagA, into host cells. Translocated CagA interacts with a multitude of host cell proteins, both dependent and independent of CagA phosphorylation, to manipulate host cell signaling. Among the proteins manipulated by CagA is the actin-associated protein cortactin. Cortactin plays a central role in the regulation of the actin cytoskeleton, which is exploited by a variety of pathogens (Sharafutdinov et al., 2022). H. pylori CagA triggers cortactin tyrosine dephosphorylation by activation of a yet unknown phosphatase. By creating an AGSΔshp2 knockout cell-line we showed that cortactin dephosphorylation is not facilitated by the previously suggested phosphatase SHP2 (Knorr et al., 2020). However, the precise mechanisms by which H. pylori employs cortactin to manipulate host cell functions are not entirely understood. To further study the role of cortactin during H. pylori infection we also generated a cortactin knockout AGS cell-line (AGSΔcttn). AGSΔcttn cells showed morphological differences compared to AGS wild-type cells, as they exhibited an enlarged cell surface area and accumulation of actin stress fibers. Furthermore, AGSΔcttn cells infected with H. pylori showed a significantly diminished proportion of tyrosine phosphorylated CagA compared to AGS wild-type cells. Likewise, host cell tyrosine kinases Src, Abl, and FAK were markedly less activated in AGSΔcttn cells. Interestingly, transfection with constitutively active mutants of either of these kinases recovered CagA phosphorylation. These results led to the discovery of a novel cortactin-dependent pathway employed by CagA to induce its own tyrosine phosphorylation. A signaling pathway was proposed, in which CagA induces serine phosphorylation and tyrosine dephosphorylation of cortactin. The changed phosphorylation status of cortactin then allows FAK binding and autophosphorylation at Y-397. Phosphorylated FAK binds and activates Src, which in turn phosphorylates the remaining FAK tyrosine phosphorylation sites, increasing its activity. Following full activation of FAK, Src phosphorylates and activates Abl. Finally, the activated kinases Src and Abl both target and phosphorylate CagA, which subsequently allows phosphorylation-dependent interaction with host cell proteins (Knorr et al., 2021). When infected with cagPAI positive H. pylori strains, AGS cells exhibit a distinct phenotype that is characterized by loss of cell-cell-connection and an elongated cell shape. This phenotype is dependent on phosphorylation of CagA. AGSΔcttn cells exhibited diminished expression of this elongation phenotype compared to AGS wild-type cells, demonstrating that cortactin plays an important part in the CagA dependent manipulation of the actin cytoskeleton (Sharafutdinov et al., 2021b). Further hallmarks of H. pylori infection are transcription factor NF-κB activation and subsequent upregulation and secretion of the pro-inflammatory cytokine IL-8. However, H. pylori infected AGSΔcttn cells showed markedly lowered amounts of both NF-κB and IL-8 compared to the parental AGS wild-type. These results indicate cortactin´s essential role in the NF-κB and IL-8 triggering signaling pathway. Interestingly, transfection of AGSΔcttn cells with a constitutively active Src kinase construct recovered NF-κB and IL-8 production. These results suggest both cortactin and Src as members of the H. pylori triggered NF-κB and IL-8 activation pathway (Tegtmeyer et al., 2022). In contrast to its essential role in CagA-dependent manipulation of host cell pathways, cortactin does not appear to be involved in pathogenicity -mediated by the H. pylori cytotoxin VacA (Sharafutdinov et al., 2021b).