Abstract B4: Expression evaluation of TP53 in colorectal cancer
Authors: Oliveira Ligia Petrolini , López Ignacio , Tucci Paula , Marín Mónica , Coudry Renata de Almeida 
Published: June 2012

Background and Aim: Colorectal cancer (CRC) is the third most common type of cancer in men and women worldwide. CRC is thought to result from an interaction between environmental and genetic factors. Variation in the function of genes responsible for DNA repair mechanisms and cell cycle control in the presence of carcinogen-mediated cell damage is an attractive mechanism for explaining any inter-individual variation in CRC susceptibility. The TP53 tumor suppressor gene is one of the most commonly mutated genes in all types of cancer, playing a key role in the development and progression of disease. In addition to gene mutation, multiple single nucleotide polymorphisms (SNPs) have been identified in this gene, however the relevance of most of them is unclear. The p53 codon 72 SNP leads to a Proline to Arginine substitution, with different capacities for inducing gene transcription, interacting with other proteins or modulating apoptosis. Studies evaluating the association between this SNP and CRC showed inconsistent results, none evaluating the expression status. The aim of this study was to evaluate the expression status of TP53 expressed by tumor samples and their association with clinicopathological variables.

Methods: 101 non-related patients with CRC were evaluated (52 women and 49 men) treated at ACCamargo Hospital in Brazil. Immunohistochemistry (IHC) was performed with monoclonal antibody and polymer-based detection system. RNA was isolated from frozen tumor tissue using phenol/chloroform protocol. The TP53 expression status was evaluated by RT-PCR followed by DNA Sanger sequencing. Associations were analyzed by Pearson Chi-Square or Fisher Exact tests and Multiple Logistic Regression.

Results: TP53 mutation was found as a common event in this study. There were found different types of mutations among CRC patients. As expected, mutations were found more frequent in the positive than in negative IHC groups (P &lt; .0001). Mutation profiles (missense, nonsense, silent and rearrangements types) were also different between p53 IHC positive and negative groups (P &lt; .0001). The majority of mutations were concentrated in the TP53 DNA binding domain, mainly in codons considered as mutation hotspots. There were found changes in three samples that could be explained as putative splicing variants or splicing errors. The p53 codon 72 SNP was significantly associated with gender (P = .037), recurrence (P = .005), dirty tumor necrosis (P = .025), pattern border of tumor growth (P = .05), post chemoradiotherapy use (P = .002), p53 IHC expression (P = .041) and TP53 mutation (P = .004), suggesting that the expression of at least one Arg72 allele is associated with better prognosis. According to multiple logistic regression the only variable that remained independently associated with the presence of the Arginine allele is the absence of tumor necrosis factor (OD = 8.64-P = .047). Allele frequency of p53 Pro72 was 0.26. This is the first report describing the expression status of the p53 codon 72 alleles in CRC and indicates that this SNP is associated with CRC.

Conclusions: The analysis of the whole transcript sequence of TP53 mRNA is important to determine its mutation pattern and the specific contribution of the p53 expressing allele. This approach is congruent with the tightly association of TP53 mutation presence with its protein accumulation pattern in cancer, permitting the appropriate identification of protein stabilization, which leads to the nuclear accumulation of p53. This strategy also facilitated the detection of possible splicing variants, which might have been underestimated in previous analyses. In relation of SNP analysis, the results suggest that p53 codon 72 SNP may play a role in CRC developing and progression, thus representing a possible genetic risk factor.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B4.