Abstract 781: Functional consequence of the p53 codon 72 polymorphism in colorectal cancer

Abstract

Background: The codon 72 polymorphism in p53 has been implicated in colorectal cancer (CRC) and CRC health disparities. In this study, we determine the functional consequence of this polymorphism in CRC following both in-vitro cell based and in-vivo mouse model studies.

Experimental Design: Plasmids (pCMV6) that express different phenotypes of p53 [p53 wild type (wt) at codon 72 (R72^wt), R72^wt with mutation at codon 273 cysteine (R72^273Cys), p53 mutation at codon 72 (P72^wt) and P72^wt with mutation at codon 273 (P72^273Cys)] were constructed. We selected a CRC cell line Caco2, which does not express p53 for in vitro studies. Severe combined immunodeficient mice were inoculated with CRC cells (HT29, SW480, and LS174) to establish tumor xenografts (tumors). Tumor angiogenesis was assessed in tumors by immunostaing for CD31. Sequencing analysis for codon 72 polymorphism of p53 was performed using genomic DNA purified from tumors. Western blot (WB) or immunostaining analyses for proteins of signaling mechanisms were performed to assess the functional consequence of P72 phenotype of p53.

Results: Our study demonstrated that P72 tumors had well established vascularity, while R72 tumors had very poor vascularization. Indeed, the mean micro vessel density was higher in P72 tumors than in R72 tumors. WB analyses revealed that P72^wt or mutant phenotypes effectively induced the activation of p38 and RAF/MEK/ extracellular signal-regulated kinase (ERK) MAP kinases. Up-regulation of phosphorylated SEK1/MKK4, an upstream kinase of p38 MAPK was associated with P72^wt or mutant phenotypes. This activation was accompanied by up-regulation of phosphorylated-MAPKAPK-2, -Hsp27, and -CREB, downstream targets of p38 MAPK. Increased activation of CREB was found to be higher in tumors that exhibit P72 phenotype. Metastatic lesions of CRC expressed more phospho-CREB than non-metastatic lesions. Furthermore, suppression of RAF/MEK/ERK activation was significantly higher in cells that express R72^wt phenotype compared to cells that express P72^wt or mutant phenotypes. The expression of P72^wt or mutant phenotypes displayed decreased expression of E cadherin and/or an increased expression of vimentin, fibrinectin, CD44, thereby promoting CRC metastasis.

Conclusions: These findings offer significant novel insights into the mechanism by which P72 contributes to the aggressiveness of CRC. Because P72 is over-expressed in CRC, specifically in African-American patients, these studies suggest a role for P72 in cancer health disparities. This work was supported by NIH/NCI Workforce Diversity Grant R21-CA171251.

Citation Format: Venkat R. Katkoori, Upender Manne, Harvey Bumpers. Functional consequence of the p53 codon 72 polymorphism in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 781. doi:10.1158/1538-7445.AM2017-781