Previous studies have shown that regeneration gene 3 () is significantly expressed in gastric mucosa tissues with (HP) cytotoxin-associated gene A (CagA)-positive (HP-CagA+). CagA-positive HP increases the risk of gastric cancer. The purpose of this study was to investigate the correlation between and HP-CagA+ and explore the effects of on the proliferation of gastric cancer cells and the development of tissues and organs. We analyzed the expression of reg3 in human tissues and organs. The results showed that expression in gastric tissues was significantly higher than that in other tissues and organs. In addition, influenced the prognosis of gastric, lung, and ovarian cancers. Immunohistochemical analysis indicated that the expression of and CagA in cancerous tissues was higher than that in adjacent tissues. HP-CagA infection of gastric cancer cells promotes reg3 expression, suggesting that may be a target gene of CagA in gastric cancer, which together affects the formation and development of gastric cancer. and CagA promote cell proliferation, and then affect the development of mouse tissues and organs by regulating G1/S phase transition of the cell cycle via the formation of the cell cycle-dependent complex CDK4/CyclinD1. This is the first study that shows the influence of CagA on the cell cycle and induction of cell proliferation by promoting expression.