OVEREXPRESSION OF 14-3-3?? CONFERS A GROWTH AND SURVIVAL ADVANTAGE IN PANCREATIC CANCER

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that is characterized at the molecular level by a high frequency of K-ras, p53, p16, and Smad4 mutations, in conjunction with overexpression of tyrosine kinase receptors and their ligands and excessive activation of mitogenic signaling pathways. 14-3-3σ is a member of the 14-3-3 family of genes, which has been most directly implicated in human cancers. In contrast to several other human cancers where the 14-3-3σ gene is down-regulated as a result of epigenetic silencing, expression of this gene is increased in pancreatic PDAC. To date, the exact role of 14-3-3σ in PDAC has not been elucidated. In this study, we assessed the expression levels of all seven members of the 14-3-3 gene family in human pancreatic cancer cell lines, and sought to determine the potential role of 14-3-3σ in PDAC. All seven isoforms of 14-3-3 were expressed in pancreatic cancer cell lines as determined by quantitative PCR (Q-PCR) analysis and immunoblotting. 14-3-3σ mRNA and protein levels were relatively high in BxPC3, COLO-357, and T3M4, and relatively low in PANC-1 and ASPC-1 cells. To further assess the role of 14-3-3σ in pancreatic cancer cells, we next prepared clones of PANC-1 cells transfected with the full-length cDNA encoding human 14-3-3σ. Engineered overexpression of 14-3-3σ in these cells led to increased anchorage independent growth as determined in soft agar assays, and enhanced resistance to cisplatinum-induced apoptosis as determined by monitoring PARP cleavage, caspase-3 cleavage, and annexin V staining. Taken together, these findings indicate that 14-3-3σ may enhance the growth of pancreatic cancer cells, and may contribute to their chemoresistance. It is possible, therefore, that 14-3-3σ may be a novel therapeutic target in PDAC.