Our previous studies have demonstrated that the expression and activity of protein kinase G (PKG) II are significantly lower in human gastric cancer cell lines than in normal cells. This study was designed to investigate the effect of PKG II activation on the proliferation of human cultured BGC-823 gastric cancer cells. An adenoviral construct encoding the PKG II gene (Ad-PKG II) was used to infect BGC-823 cells, and the activity of the enzyme was induced by cGMP analogue 8-pCPT-cGMP. The proliferation-inhibitory effect of PKG II was analyzed by the MTT assay, BrdU incorporation assay and detection of proliferating cell nuclear antigen (PCNA) expression. Colony formation in soft agarose was performed to analyze the effect of PKG II on the anchorage-independent growth of the cells. The effect of PKG II in vivo was investigated in an immunocompromised nude mice model, and its effect on the cell cycle was analyzed by flow cytometry. The results showed that Ad-PKG II infection increased the expression of PKG II in BGC-823 cells. The activation of PKG II by 8-pCPT-cGMP caused a significant decrease in the number of live cells and inhibited DNA synthesis in individual cells. PKG II activation inhibited the EGF-induced increase in PCNA expression. The activation of PKG II also caused a significant inhibition of colony formation in soft agarose and significantly suppressed the in vivo growth of BGC-823 cells in immunocompromised nude mice. There was substantial cell arrest at the G1 phase and a decrease in the number of S phase cells in the Ad-PKG II/8-pCPT-cGMP-treated cells. These data indicate that the activation of PKG II by 8-pCPT-cGMP inhibits the proliferation of human gastric cancer cells.

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