Characterization of P53 gene mutations among patients with colorectal cancer in a tertiary hospital in Metro Manila

• Main Author: Pilante, Jocelyn P.
• Format: text
• Language: English
• Published: Animo Repository 2010
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/3858
• Institution: De La Salle University

P53 is a tumor suppressor gene consisting of 11 exons that code for a protein composed of 393 amino acids long. Mutations in p53 gene are frequently associated with the initiation and progression of colorectal cancer (CRC). The study aims to characterize mutations in the so called hotspot codons within exons 5-8 of p53 gene. These mutations were studied in correlation with clinico-pathological characteristics of the CRC patients. Paired normal and tumor tissues from 39 previously identified CRC patients who underwent surgical resection were included in the study. Genomic DNA was isolated from these frozen colon tissues and was amplified by PCR using 4 sets of primers. Direct sequencing analysis was done to characterize these mutations. Eighteen of the 39 CRC patients carried no mutations in the hotspot codons. On the other hand, tumor samples from 21 (53.8%) of these patients were found to carry mutations with one patient (CCA 321) having mutations in two exons: codon 175 in exon 5 and codon 223 in exon 6. Of the total 22 mutations, twenty were single base insertion occurring at codon 223 in exon 6 resulting to a stop codon. These insertions leading to frameshift mutations were probably pathogenic because they occur within the conserved region of the p53 gene and produced a truncated protein leading to gene inactivation. The remaining two mutations were located in the hotspot codons: codon 175 in exon 5 and codon 248 in exon 7 and these are both missense mutations. Four of the normal tissue samples were found to carry frameshift mutations at codon 223 in exon 6. These mutations are possibly germline in origin. Using chi-square test (p < 0.05), there was no significant association found between p53 mutations and clinic opathological characteristics: age, gender, cancer stage, tumor grade and tumor location of CRC patients and this could be attributed to the small sample size. However, most of the mutations were found in stage III and moderately differentiated tumor samples. In conclusion, the high frequency of frameshift mutations occurring outside the hotspot codons of p53 may suggest a different clinical profile for the Filipinos with CRC. Based on the data obtained from this study, p53 may play a role in the development of colorectal cancer in this sample population.