Correlation Between The Expression Of Pten And B7-h1 In Gastric Carcinoma And Its Mechanism

PTEN,also known as MMAC1 or TEP1,is a new tumor suppressor gene confirmed in recent years and has dual specific phosphatase activity.And it is the most important tumor suppressor gene after P53.PTEN protein possesses activity of lipid phosphatase and protein phosphatase and can down-regulate PI3K/AKT pathway through dephosphorylating its substrate PIP3.It has been confirmed that PTEN exerts its tumor suppression effect mainly through suppressing PI3K/AKT pathway.It has been discovered that loss or mutation of PTEN gene and abnormal expression of PTEN protein occur in many human malignancies.B7-H1,also known as PD-L1,is a new co-stimulatory molecule identified in recent years.Although expression of B7-H1 mRNA is found in a broad range of human normal tissues,expression of human B7-H1 protein is limited to the macrophage-derived cells.Recently it has been indicated that many tumor tissues and tumor cell lines also express B7-H1 protein and B7-H1 protein plays an important role in apoptosis induction of specific T cells and tumor immune escape.There are few studies on the regulation of the expression of B7-H1 protein in malignancies.Not long ago a report in Nature Medicine indicates that loss of PTEN increases B7-H1 expression and immunoresistance in glioma.The report also has identified regulation of translation through PI3K-AKT-mTOR-S6K cascade as a candidate mechanism by which the loss of PTEN increases B7-H1 protein in glioma. Gastric carcinoma occurs with a high incidence in the world.The regulation of the expression of B7-H1 protein in gastric carcinoma has not been studied so far.So,in this study,we adopted immunohistochemistry and Western Blot techniques to investigate the expression of PTEN,B7-H1,S6K and P-S6K in gastric carcinoma tissue,and analyzed the correlation between the expression of PTEN and B7-H1 in gastric carcinoma tissue and explored the mechanism in which.Methods1.ImrnunohistochemistryImmunohistochemistry technique was used to detect the in situ expression of PTEN,B7-H1,S6K and P-S6K protein in 48 cases of gastric carcinoma tissue and 11 cases of adjacent normal gastric mucosal tissue.Then,we analyzed the expression of PTEN and B7-H1 in gastric carcinoma tissue and analyzed their relationship to the patients' clinicopathological variables,respectively.Furthermore we analyzed the relation of PTEN,B7-H1,S6K and P-S6K protein in gastric carcinoma tissue.2.Western BlotWestern Blot technique was used to observe the expression of PTEN,B7-H1, S6K and P-S6K in gastric carcinoma tissue.Semi-quantitative results of the expression of each index were analyzed by Fluorchem software.We further analyzed the relation of PTEN,B7-H1,S6K and P-S6K protein in gastric carcinoma tissue.3.Statistical analysisSPSS13.0 statistical software was used to analyze experimental data.The comparison of positive rates used theχ~2 test;The relation of two variables was analyzed by the correlation analysis of enumeration data or the Spearman's rank correlation.The significance level was set at 0.05.Results1.Immunohistochemistry1.1 PTEN in situ expression in gastric carcinoma tissueThe positive incidence of PTEN expression in gastric carcinoma tissue was 43.75%(21/48).PTEN protein was located in the cell cytoplasm and/or nucleus. However,the positive incidence of PTEN expression in adjacent normal gastric mucosal tissue was 100%(11/11).The difference between them was statistically significant(P＜0.05).No correlation was observed between PTEN expression and sex, age,tumor size(P＞0.05).Conversely,the expression of PTEN was significantly correlated with depth of invasion,lymph node metastasis,differentiation degree and TNM stage of gastric carcinoma(P＜0.05).1.2 B7-H1 in situ expression in gastric carcinoma tissueThe positive incidence of B7-H1 expression in gastric carcinoma tissue was 62.50%(30/48).B7-H1 protein was located in the cell member and/or cytoplasm. However,there was no B7-H1 protein expression in adjacent normal gastric mucosal tissue.The difference between them was statistically significant(P＜0.05).No correlation was observed between PTEN expression and sex,age,tumor size,or differentiation degree(P＞0.05).Conversely,the expression of PTEN was significantly correlated with depth of invasion,lymph node metastasis and TNM stage of gastric carcinoma(P＜0.05).1.3 The relation of the in situ expression of PTEN,B7-H1,S6K and P-S6K protein in gastric carcinoma tissueStatistical analysis showed that there was an obvious negative correlation between the in situ expression of PTEN and B7-H1 protein(P＜0.05),there was an obvious negative correlation between the in situ expression of PTEN and P-S6K protein(P＜0.05),there was an obvious positive correlation between the in situ expression of B7-H1 and P-S6K protein(P＜0.05),there was no correlation between the in situ expression of PTEN and S6K protein(P=0.383),there was no correlation between the in situ expression of B7-H1 and S6K protein(P=0.551).2.Western BlotIn gastric carcinoma tissue,there was a strong negative correlation between the expression of PTEN and B7-H1 protein(P＜0.05,r=-0.667),there was a strong negative correlation between the expression of PTEN and P-S6K protein(P＜0.05, r=-0.610),there was a strong positive correlation between the expression of B7-H1 and P-S6K protein(P＜0.05,r=0.724),there was no correlation between the expression of PTEN and S6K protein(P=0.601),there was no correlation between the expression of B7-H1 and S6K protein(P=0.495).Conclusions1.Both loss of PTEN protein expression and abnormal high expression of B7-H1 protein are present in gastric carcinoma tissue,which participate in the occurrence and development of gastric carcinoma.2.During the occurrence of gastric carcinoma,loss of PTEN protein expression may upregulate the expression of B7-H1 protein through activating S6K,the downstream molecule of PI3K/Akt cell signaling pathway,thus promoting gastric carcinoma cells immune escape.