Stable reintroduction of wild-type P53 (MTmp53ts) causes the induction of apoptosis and neuroendocrine-like differentiation in human ductal pancreatic carcinoma cells

Abstract

Pancreatic ductal adenocarcinoma is one of the major causes of cancer mortality in the industrialized world, having among the poorest prognosis of any malignancy. Mutations or alterations in the p53 tumor suppressor gene/protein are observed in 50–70% of these cancers, yet little information is available regarding the phenotypic effects of restoration of wild-type (wt) p53 function in pancreatic ductal carcinoma cells. The consequences of stable reintroduction of wt p53 on apoptosis and differentiation was examined in a poorly differentiated pancreatic carcinoma cell line (Panc-1), possessing only mutant (mt) p53 (codon 273 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°C, and a `wt' phenotype at 32.5°C and the presence of 100 μM ZnCl₂. Stable expression of wt p53 caused upregulation of the p21/WAF1 gene, and G₁ growth arrest as shown by flow cytometry and BrdU labeling. Additionally, apoptosis was induced 8–12 post-induction in the majority of the cells (60–70%), as demonstrated by morphological changes, in situ TdT labeling and internucleosomal laddering. However, a subpopulation (30%) of the transfectants survived this apoptotic fate. Unlike the epithelial parental Panc-1 cells, these cells exhibited the appearance of a neuroendocrine-like phenotype with extensive branch-like processes, and marked cytoplasmic and cytoskeletal immunostaining for tau-2, synaptophysin, and chromogranin A. These studies suggest that stable and regulated expression of wt p53 can have multiple phenotypic consequences (apoptosis and altered differentiation to a neuroendocrine-like phenotype) in poorly-differentiated pancreatic carcinoma cells.