Novel p53 codon 240 Ser > Thr coding region mutation in the patients of oral squamous cell carcinoma (OSCC)

Chewing habits of tobacco, betel quid (paan), and betel nut (chhaliya) are common traditions in Pakistan. Different other preparations and combination of flavors with tobacco, paan, and chhaliya ingredients are commonly available in the market and have received considerable attention as sources of carcinogens that promote OSCC. Mutagens can damage DNA and generate promutagenic lesions. The germ line mutation/polymorphism of p53 gene has been reported to be involved in multiple steps of carcinogenesis. This study aims to find out the loss of TP53 functions due to mutation/polymorphism caused by genomic alteration and interaction with tobacco-related ingredients.Tissue and blood specimens from 260 OSCC patients were collected and compared with blood samples of 260 age- and sex-matched controls. Mutations in exons 2-11 of p53 gene were examined by PCR-SSCP and directly sequenced.A novel mutation was found in exon 7 of p53 gene. This mutation was observed in the tumors of the OSCC patients. The blood samples of the patients and the controls did not show the nucleotide change in this region. The "AGT" to "ACT" missense mutation was identified at position 719 at TP53. This results in the substitution of amino acid serine with threonine at codon 240 of p53 protein.This novel missence mutation in the DNA-binding domain indicated that the DNA structure may be damaged by the use of exogenous DNA-damaging agents, including tobacco-related carcinogens present in gutka, niswar, and manpuri, which may result in the loss of p53 protein function.