Abstract 583: Differential expression of codon 72 of TP53 in colorectal tumors
Authors: Oliveira Ligia P. , Lisboa Bianca G. , Lopez Ignácio , Santos Erika M. , Carraro Dirce M. , Soares Fernando A. , Rossi Benedito M. , Coudry Renata A. 
Published: May 2015

Background & Aim: Correlations between DNA variation and human phenotypic differences, such as susceptibility to certain diseases, are not well understood. Polymorphisms can contribute to the observed variation in complex human traits, but their relative contributions remain to be determined. Expression differences between alleles of the same gene have been observed, contributing to phenotypic variation between individuals. Studies showed that variations exist in the relative allelic expression levels in certain genes of heterozygote individuals. Polymorphism at codon 72 of TP53 results in either Arginine or Proline, whose functional significance in carcinogenesis is controversial. Studies showed that the Pro72 is less efficient than Arg72 allele in suppressing cell transformation and inducing apoptosis. We have investigated if the expression of these p53 polymorphs is selectively regulated, using mRNA and DNA from colorectal cancer tissues (CRC). Methods: 28 non-related patients treated at ACCamargo Cancer Center in Brazil were evaluated. DNA and RNA were isolated from frozen tumor tissue using Trizol and phenol/chloroform based protocol. TP53 sequences from DNA and RNA were evaluated by Sanger sequencing and quantified using Pyrosequencing. The assay for allele quantification was designed with the software PyroMark Assay Design Software 2.0, featuring algorithms for full quality control. Results: We found 28 p53 codon 72 SNP heterozygotes tumors and 11 (39.3%) of these showed differential expressions, and most of them preferentially expressed the Pro allele. Pyrogram peak heights are proportional to the frequency of an allele in the sample, providing accurate measures of the proportion of the alleles. Previous results revealed that these SNP expression was significantly associated with gender (P= 0.037), recurrence (P= .005), dirty tumor necrosis (P= 0.025), border pattern of tumor growth (P= 0.05), post chemoradiotherapy use (P= 0.002), p53 immunohistochemistry expression (P= 0.041) and TP53 mutation (P= 0.004), suggesting that the expression of the Pro72 allele is associated with worse tumor features. The expression of Arg72 (OR 3.83; CI 1.02-14.35; P= 0.046) and the TNM grouping stage (OR 7.15; CI 1.45-35.29; P= 0.016) were independent predictors for recurrence. This is the first report describing the differential expression of the p53 codon 72 SNP in CRC and revealed that heterozygotes preferentially express the Pro allele, suggesting that the Pro allele is selectively activated in CRC. Conclusions: The expression of the different p53 polymorphs is selectively regulated in Pro72Arg heterozygotes individuals. Thus, the expression status of the p53 polymorphs, rather than the genotypic status, might be an useful indicator tumor aggressiveness.

Citation Format: Ligia P. Oliveira, Bianca G. Lisboa, Ignácio Lopez, Erika MM Santos, Dirce M. Carraro, Fernando A. Soares, Benedito M. Rossi, Renata A. Coudry. Differential expression of codon 72 of TP53 in colorectal tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 583. doi:10.1158/1538-7445.AM2014-583