STABLE REINTRODUCTION OF WILD-TYPE P53 (MTMP53TS) CAUSES THE INDUCTION OF APOPTOSIS AND NEUROENDOCRINE-LIKE DIFFERENTIATION IN HUMAN DUCTALPANCREATIC-CARCINOMA CELLS

Pancreatic ductal adenocarcinoma is one of the major causes of cancer mortality in the industrialized world, having among the poorest progno sis of any malignancy, Mutations or alterations in the p53 tumor suppr essor gene/protein are observed in 50-70% of these cancers, yet little information is available regarding the phenotypic effects of restorat ion of wild-type (wt) p53 function in pancreatic ductal carcinoma cell s, The consequences of stable reintroduction of wt p53 on apoptosis an d differentiation was examined in a poorly differentiated pancreatic c arcinoma cell line (Panc-1), possessing only mutant (mt) p53 (codon 27 3 mutation), Cells were transfected with a temperature-sensitive mouse p53(val135) (tsp53) vector under additional control of a genetically- modified metallothionein promoter, This tsp53 has a 'mt' phenotype at 37.5 degrees C, and a 'wt' phenotype at 32.5 degrees C and the presenc e of 100 mu M ZnCl2. Stable expression of wt p53 caused upregulation o f the p21/WAF1 gene, and G(1) growth arrest as shown by flow cytometry and BrdU labeling. Additionally, apoptosis was induced 8-12 postinduc tion in the majority of the cells (60-70%), as demonstrated by morphol ogical changes, ill situ TdT labeling and internucleosomal laddering. However, a subpopulation (30%) of the transfectants survived this apop totic fate, Unlike the epithelial parental Pane-1 cells, these cells e xhibited the appearance of a neuroendocrine-like phenotype with extens ive branch-like processes, and marked cytoplasmic and cytoskeletal imm unostaining for tau-2, synaptophysin, and chromogranin A. These studie s suggest that stable and regulated expression of wt p53 can have mult iple phenotypic consequences (apoptosis and altered differentiation to a neuroendocrine-like phenotype) in poorly-differentiate pancreatic c arcinoma cells.