Abstract 1175: The tumor-associated p53 R172H mutation does not display gain-of-function properties in hepatocellular carcinoma

Abstract

Abstract Hepatocellular carcinoma is a highly deadly malignancy, accounting for approximately 600,000 deaths worldwide every year. A common genetic change in HCC, present in 30% of cases, is mutation of the p53 tumor suppressor gene. p53R175H (corresponding to R172H in mice) is a hotspot for mutation that demonstrates “prometastatic” gain-of-function in pancreatic cancer. Since the frequency of p53 mutation increases with tumor grade in HCC, we hypothesized that p53R172H is a gain-of-function mutation in HCC that contributes to an increase in metastasis and a decrease in tumor-free survival. To study the role of p53 mutation in HCC, we used the RCAS-TVA mouse model. Albumin-TVA, p53LSL-R172H/fl, Albumin-cre mice were crossed to Albumin-TVA, p53fl/fl, Albumin-cre mice to generate litters in which half of the progeny are p53fl/fl and half are p53R172H/fl. Injection of these litters with DF1 chicken fibroblasts producing RCAS viruses encoding the mouse polyoma virus middle T antigen (PyMT), resulted in specific infection and expression of PyMT in the liver. We found that p53R172H/fl mice did not have increased tumor incidence, nor did they display increased rates of metastasis, relative to p53fl/fl mice, suggesting that mutant p53 does not display gain-of-function properties during HCC development in vivo. Interestingly, while shRNA-mediated knockdown of p53 in R172H expressing HCC cell lines resulted in decreased cell migration, suggestive of gain-of-function properties, analysis of a panel of HCC cell lines from p53 null and R172H expressing tumors found no differences in anchorage-independent growth and cell migration between the two groups. Thus, although p53R172H expressing HCC cells depend on this mutant for their transformation, p53 mutant cells and tumors do not have enhanced properties relative to p53 null HCC cells and tumors. These data suggest that important pathway(s) impacted by mutant p53 are inhibited by alternate mechanisms in p53 null cells resulting in equivalent phenotypes. Interestingly, cell lines derived from HCCs with conditional p53 deletion exhibit decreased levels of a p63 isoform compared to cells from p53R172H mice. Since p53 mutants have been previously shown to bind and inhibit p63, reduced p63 expression in p53 deficient HCC cells may explain this observation. Elucidation of the role of p63 in regulating HCC migration and metastasis is currently underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1175. doi:1538-7445.AM2012-1175