Gastric epithelial cells (GES-1) stimulated by Helicobacter pylori (H. pylori) would affect the expression of related genes and induce the immune response of the cells. Abnormal methylation of DNA was one of the main causes. The aim of this study was to investigate phosphoinositol-3-kinase adaptor protein 1(PIK3AP1), which was screened from the chip data as an immune gene candidate to against the inflammatory response of cells caused by H. pylori infection. PIK3AP1 plays a key role in PI3K/AKT signaling pathway. The gene chip analysis and experimental results confirmed that PIK3AP1 expression was downregulated and PIK3AP1 promoter was hypermethylated after H. pylori stimulation in GES-1 cells. Meanwhile, the expression level of PIK3AP1 was significantly upregulated after 5-aza-dc treatment, and its expression was higher after 5-aza-dc and H. pylori co-treatment than that of H. pylori treatment but lower than that of 5-aza-dc treatment. Therefore, hypermethylation was the main reason for the downregulation of PIK3AP1 after H. pylori stimulation. In addition, the intervention of PIK3AP1 inhibited the expression of downstream gene AKT, and suppressing the expression of the immunoinflammatory gene IL-6 in GES-1 cells. Furthermore, the intervention of PIK3AP1 would promote cell proliferation. In summary, hypermethylation of the PIK3AP1 promoter was accompanied by reduction of the expression level of PIK3AP1 in GES-1 cells by H. pylori stimulation. The expression of PIK3AP1, AKT, and IL-6 genes was positively correlated, Meanwhile, the PIK3AP1 can affect the proliferation of GES-1 cells. These results would be helpful to understand the innate immune response function of PIK3AP1 to pathogenic bacterial infection in the stomach. (C) 2020 Elsevier Inc. All rights reserved.