Mutation analysis of tumor suppressor gene PTEN in patients with gastric carcinomas and its impact on PI3K/AKT pathway.

The aim of this study was to clarify the participation of PTEN mutation in gastric carcinogenesis and its impact on PI3K/AKT pathway. All nine exons of PTEN were screened for mutations by direct sequencing in 144 patients with pathologically proven gastric carcinoma and their corresponding normal mucosae, followed by Western blotting to detect the changes in PI3K/AKT pathway. Direct sequencing indicated there were 27 cases with mutations among 144 patients consisting of 15 cases (55.6%) of missense mutation, nine nonsense mutations (33.3%), two 1-bp deletion (7.4%), and a mutation within intron 6 (3.7%). The mutation hot spots at codons 36, 75, 232 and 393 had not been observed previously, and the mutation sites in exons 3, 5, 6 and 8 were not found, suggesting that there might be some unique characteristic of PTEN inactivation mechanism in the Shanghai population. The PTEN mutation rate was significantly higher at pTMN stages III and IV than that at stages I and II (P<0.005), and it was higher in poorly differentiated gastric cancer than in well or moderately differentiated types (P<0.05). PTEN and E-cadherin protein expression in gastric cancer was significantly down-regulated comparing with that in paracancerous tissues, while the PI3K, AKT, MMP-2, MMP-9 and NF-kappaBp65 protein were overexpressed in cancer tissues. Our results implicated that the mutations of PTEN did not occur at a significant rate in gastric carcinoma in Shanghai, but might play a role in tumorigenesis. The mutation status of PTEN was significantly relevant to pTNM staging and degree of cell differentiation, hinting that PTEN might be a prognostic biomarker of gastric cancer. The decreased expression of PTEN and E-cadherin, together with the overexpression of PI3K, AKT, MMP-2, MMP-9 and NF-kappaBp65, contributed cooperatively to the accelerated progress of gastric cancer.