Robust p53 phenotypes and prospective downstream targets in telomerase-immortalized human cells

Cancers that retain wild type <i>TP53</i> presumably harbor other clonal alterations that permitted their precursors to bypass p53-mediated growth suppression. Consequently, studies that employ <i>TP53</i>-wild type cancer cells and their isogenic derivatives may systematically fail to appreciate the full scope of p53 functionality. Several <i>TP53</i> phenotypes are known to be absent in the widely used isogenic HCT116 colorectal cancer (CRC) model, which originated from a tumor that had retained wild type <i>TP53</i>. In contrast, we show that restoration of p53 in the <i>TP53</i>-mutant CRC cell line DLD-1 impeded cell proliferation, increased levels of senescence and sensitized cells to ionizing radiation (IR). To study p53 in a non-cancer context, we disrupted <i>TP53</i> in hTERT-RPE1 cells. Derived from primary cells that were immortalized <i>in vitro</i>, hTERT-RPE1 expressed striking p53-dependent phenotypes and appeared to select for p53 loss during routine culture. hTERT-RPE1 expressed a p53-responsive transcriptome that was highly representative of diverse experimental systems. We discovered several novel downstream p53 targets of potential clinical relevance including <i>ALDH3A1</i>, which is involved in the detoxification of aldehydes and the metabolism of reactive oxygen species, and <i>nectin cell adhesion molecule 4</i> (<i>NECTIN4</i>) which encodes a secreted surface protein that is overexpressed in many tumors.