- The MKN-28 cell line, derived from moderately differentiated human gastric carcinoma, serves as a valuable model for studying Helicobacter pylori–host interactions, particularly those involving the CagA oncoprotein.
- Upon infection with H. pylori strains capable of delivering CagA through the type IV secretion system (T4SS), MKN-28 cells exhibit a range of molecular and functional alterations, although they typically do not display the classic “hummingbird phenotype” observed in AGS cells.
- In MKN-28 cells, CagA is successfully translocated and tyrosine-phosphorylated, particularly on its EPIYA motifs, leading to downstream interactions with host signaling molecules.
- A key consequence of CagA activity in these cells is the disruption of epithelial junctional architecture, especially at adherens and tight junctions. CagA interferes with the localization and stability of junctional proteins such as E-cadherin, β-catenin, and ZO-1, weakening cell-cell adhesion and compromising barrier function.
- Unlike AGS cells, MKN-28 cells maintain more defined epithelial characteristics, including well-developed junctional complexes, making them a suitable model for studying subtle but significant junctional perturbations. CagA’s interaction with PAR1b/MARK2, a polarity-regulating kinase, further disrupts apical-basolateral polarity, contributing to the loss of epithelial integrity.
- CagA also activates key host cell signaling pathways in MKN-28 cells, including the MAPK/ERK and Wnt/β-catenin pathways. For example, by destabilizing the E-cadherin/β-catenin complex, CagA promotes nuclear translocation of β-catenin and the transcription of genes involved in proliferation and survival, which may contribute to precancerous cellular changes.
- Although morphological elongation (hummingbird phenotype) is not a dominant feature in MKN-28 cells, the molecular effects of CagA are robust and highly informative. These include alterations in junctional protein distribution, inflammatory signaling, and disruption of cellular polarity, all of which mirror important aspects of H. pylori-associated gastric pathology.
- When CagA is introduced via transfection, MKN-28 cells exhibit:
- Disruption of cell-cell junctions, including altered localization of E-cadherin, β-catenin, and ZO-1.
- Inhibition of cell polarity via PAR1b/MARK2 binding.
- Activation of host signaling pathways, such as:
- MAPK/ERK
- Wnt/β-catenin
- NF-κB, under some contexts
- Transcriptional changes consistent with pro-oncogenic and inflammatory signaling.
- No pronounced hummingbird phenotype, but modest cytoskeletal remodeling may occur.
- These effects mirror what is seen in infection-based models and confirm that CagA alone—independent of other H. pylori factors—can mediate key aspects of the cellular response.
