Modeling wild type and mutant p53 in telomerase-immortalized human cells

Genetic alterations that change the functions of p53 or other proteins in the p53 pathway contribute to a majority of cancers. Accordingly, many technological approaches and model systems have been employed to dissect the complex phenotypes of this critical tumor suppressor and its mutants. Studies of human p53 are commonly conducted in tumor-derived cell lines that retain wild type TP53 alleles and isogenic derivatives with engineered TP53 alterations. While this genetic approach has provided numerous insights, such studies are bound to paint an incomplete picture of p53 and its many effects on the cell. Given the preponderance of p53 pathway defects in cancer, it is reasonable to assume that cancers that arise without mutations in the TP53 coding sequence would very likely harbor other genetic or epigenetic alterations that effect the normal function of this pathway. One possible solution to this conundrum is to study p53 in cells that have been artificially immortalized. Unlike cells derived from tumors ex vivo, cells that have been immortalized in vitro are not shaped by evolutionary selection during tumorigenesis, and presumably retain many of the normal functions of p53 and other tumor suppressors. We report here a functional characterization of p53 in the immortalized human cell line hTERT-RPE1 and describe the dominant-negative effects of a heterozygous missense p53 A276P mutation that apparently arose during serial culture. Detailed studies of this contact mutant, also found in human tumors, demonstrate the practical utility of this model system for studying the complex phenotypes of human p53.