PI3K/AKT pathway activation in bladder carcinogenesis.

The PI3K/AKT pathway is considered to play a major role in bladder carcinogenesis, but its relationships with other molecular alterations observed in bladder cancer remain unknown. We investigated PI3K/AKT pathway activation in a series of human bladder urothelial carcinomas (UC) according to PTEN expression, PTEN deletions and FGFR3, PIK3CA, KRAS, HRAS, NRAS and TP53 gene mutations. The series included 6 normal bladder urothelial samples and 129 UC (Ta n = 25, T1 n = 34, T2-T3-T4 n = 70). Expression of phospho-AKT (pAKT), phospho-S6-Ribosomal Protein (pS6) (one downstream effector of PI3K/AKT pathway) and PTEN was evaluated by reverse phase protein Array. Expression of miR-21, miR-19a and miR-222, known to regulate PTEN expression, was also evaluated. pAKT expression levels were higher in tumors than in normal urothelium (p < 0.01), regardless of stage and showed a weak and positive correlation with pS6 (Spearman coefficient RS = 0.26; p = 0.002). No association was observed between pAKT or pS6 expression and the gene mutations studied. PTEN expression was decreased in PTEN-deleted tumors, and in T1 (p = 0.0089) and T2-T3-T4 (p < 0.001) tumors compared to Ta tumors; it was also negatively correlated with miR-19a (RS = -0.50; p = 0.0088) and miR-222 (RS = -0.48; p = 0.0132), but not miR-21 (RS = -0.27; p = 0.18) expression. pAKT and PTEN expressions were not negatively correlated, and, on the opposite, a positive and moderate correlation was observed in Ta (RS = 0.54; p = 0.0056) and T1 (RS = 0.56; p = 0.0006) tumors. Our study suggests that PI3K/AKT pathway activation occurs in the entire spectrum of bladder UC regardless of stage or known most frequent molecular alterations, and independently of low PTEN expression.

Inactivation of RASSF1A, RARbeta2 and DAP-kinase by promoter methylation correlates with lymph node metastasis in nasopharyngeal carcinoma.

Epigenetic modification is one of the mechanisms leading to gene silencing in neoplastic cells. By methylation-specific PCR, we analyzed the promoter methylation of three cancer-related genes: Ras Association domain Family 1A (RASSF1A), Death Associated Protein kinase (DAP-kinase) and Retinoic Acid Receptor beta2 (RARbeta2) in two NPC xenografts (C15 and C17), 68 primary NPC tumors, and nine normal nasopharyngeal epithelia. We showed that C15 and C17 displayed a complete promoter methylation of RASSF1A, RARbeta2 and DAP-kinase genes. In primary NPC tumors, the incidence of promoter methylation was very high for all three tested genes: 91% for RASSF1A, 88% for both RARbeta2 and DAP-kinase whereas all normal nasopharyngeal epithelia were unmethylated. Interestingly, our study revealed that aberrant promoter methylation of the three genes were statistically associated with the lymph node involvement (p < 0.0001). In addition, hypermethylation of RASSF1A was correlated with age at diagnosis (p = 0.047) and T stage (p = 0.037) while the RARbeta2 hypermethylation was associated with histological type (p = 0.011). Taken together, our results demonstrate that silencing of RASSF1A and RARbeta2 expression by promoter hypermethylation is associated with highly differentiated tumors, advanced tumor stage and the presence of lymph node metastasis. To assess the functional significance of the epigenetic silencing of RARbeta2 and DAP-kinase in NPC, we analysed the expression of two downstream target genes COX-2 and p53 by reverse PCR (RT-PCR) and immunohistochemistry (IHC). We revealed a significant association between expression of COX-2 and loss of RARbeta2 through aberrant methylation (p = 0.003) in NPC biopsies. We concluded that the inactivation of RASSF1A, RARbeta2 and DAP-Kinase by hypermethylation is a key step in NPC tumorigenesis and progression.