Phosphorylation status of Akt and caspase-9 in gastric and colorectal carcinomas

The serine/threonine protein kinase B/Akt plays a central role in the coordination of multiple signal transduction processes involved in transcriptional regulation, cell survival, and apoptosis. Activation of Akt kinase is a prognostic factor in several types of cancers; however, its role in gastrointestinal cancers is not fully understood. Caspase-9 is an Akt substrate that belongs to the caspase family of proteases, which function as initiators of the mitochondrial apoptotic pathway. Little is known about the role of caspase-9 phosphorylation, which downregulates the apoptotic activity of the enzyme. In this study, we investigated the expression of phosphorylated (p)-Akt and phosphorylated (p)-caspase-9 in gastric and colorectal carcinoma and the relationship between p-Akt and p-caspase-9 expression and clinicopathological parameters of gastric and colorectal cancer patients. In total, 75 samples of advanced gastric adenocarcinoma (37 well-to-moderately differentiated and 38 poorly differentiated) and 76 samples of advanced colorectal adenocarcinoma (69 well-to-moderately differentiated and 7 poorly differentiated) were analyzed for p-Akt and p-caspase-9 expression by immunohistochemistry. Our results reveal a correlation between p-Akt and p-caspase-9 expression in gastric and colorectal cancers. Levels of p-caspase-9 were significantly higher in colorectal cancer than in gastric cancer, indicating tumor-specific regulation. Although the biological role of p-Akt/p-caspase-9 signaling remains unclear, we suggest that phosphorylation of caspase-9 may be a useful tool to assess the state of gastrointestinal cancer and the effects of anti-cancer therapy.