Phosphorylation of Akt/PKB is required for suppression of cancer cell apoptosis and tumor progression in human colorectal carcinoma.

BACKGROUND

Akt/protein kinase B (PKB), which is included in phosphatidyl inositol-3-OH kinase (PI3K) signaling, controls many intracellular processes, such as the suppression of apoptosis and the promotion of the cell cycle. Therefore, the authors investigated phosphorylated Akt (Ser473) in colorectal carcinomas to reveal the role of PI3K signaling during the development of colorectal carcinoma.

METHODS

Expression of phosphorylated Akt (Ser473) in two colon carcinoma cell lines (DLD-1 and Colo205) and 65 human colorectal carcinomas was analyzed using western blotting and immunohistochemistry, respectively. Growth inhibition and induction of apoptosis caused by LY294002, a specific inhibitor of PI3K, were also examined in these cell lines. In tumor samples, the level of cell proliferation activity (Ki-67) and number of apoptotic bodies (single stranded DNA) were determined by counting positive cells.

RESULTS

LY294002 significantly affected the proliferation and apoptosis of Colo205 cells, suggesting an association with the low phosphorylation level of Akt protein. Immunohistochemic analysis showed that 46% of the tumors had a high level of expression of phosphorylated Akt with a close association with Ki-67 proliferative activity (P < 0.001) and the number of apoptotic bodies (P < 0.001). Akt phosphorylation was also correlated with some clinicopathologic parameters of the malignancies, including depth of invasion, infiltration to venous vessels, lymph node metastasis, and clinicopathologic stage.

CONCLUSIONS

The phosphorylated Akt level can monitor cell growth and resistance to apoptosis, indicating that activation of Akt plays an important role during the progression of colorectal carcinomas by helping promote cell growth and rescue cells from apoptosis. These findings also suggest the possibility of using LY294002 for treatment of colorectal carcinoma.