Helicobacter pylori (H. pylori) is a Gram-negative bacterium and causative agent of gastric cancer. H. pylori induce defective autophagy or inhibit it by means of CagA and vacuolating cytotoxin A (VacA) toxins leading to the gastric cancer induction. Impaired or defective autophagy leads to the accumulation of cytotoxic materials, such as ROS and P62 that lead to increased mutations in the DNA, genome instability, and risk of cancer formation. H. pylori CagA may inhibit autophagy through the c-Met-PI3k/Akt-mTOR signaling pathway. However, VacA induces autophagy by some signaling pathways. In the gastric epithelial cells, VacA is a necessary and sufficient factor for the creation of autophagy. While CagA is a negative regulator of this phenomenon, the elimination of this gene from H. pylori has increased autophagy and the production of inflammatory cytokines is reduced. In gastrointestinal cancers, some of the microRNAs (miRNAs) act as tumor suppressors and some other are oncogenes by regulating various genes expression. H. pylori can also modify autophagy through a mechanism that includes the function of miRNAs. In autophagy, oncogenic miRNAs inhibit activation of some tumor suppressor signaling pathways (e.g., ULK1 complex, Beclin-1 function, and Atg4 messaging), whereas tumor suppressor miRNAs can block the activation of oncogenic signaling pathways. For instance, Beclin-1 is negatively regulated by miRNA-376b (oncogenic miRNA) and miRNA-30a (tumor suppressor miRNA). Similarly, Atg4 by miRNA-376b (oncogenic miRNA) and miRNA-101 (tumor suppressor miRNA). So, this apparent paradox can be explained as that both Beclin-1 and Atg4 play different roles in a particular cell or tissue.
Keywords: Helicobacter pylori; autophagy; gastric cancer; miRNAs.
© 2019 Wiley Periodicals, Inc.