Abstract
The major risk factor for developing OSCC in countries like Pakistan is the excessive chewing habit of paan (betel quid), chhaliya (betel nut), tobacco, niswar (type of dipping tobacco, made from fresh tobacco leaves, calcium oxide, and wood ash), gutka (the preparation of crushed betel nut, tobacco, catechu, lime, saffron, spices, menthol, and sweet or savory flavors), and manpuri (the powder of betel nut, tobacco and slaked lime). It has been reported that exon 4–9 were the hot spots of the mutation in TP53. This study aims to find out the loss of TP53 functions due to mutation/polymorphism caused by genomic alteration and interaction with tobacco and its related ingredients in Pakistan.
A total of 260 OSCC patient’s tissue and blood specimens were collected with informed consent from local hospitals of Karachi and compared with blood samples of 260 age and sex matched controls. Mutations in exons 2–11 of TP53 were examined by polymerase chain reaction and single stranded conformational polymorphisms (PCR-SSCP). The samples showing mobility shift were purified and directly sequenced.
The novel “AGT” to “ACT” missence mutation was identified at position 719 in exon 7 ofTP53. This change substitutes the amino acid serine with threonine at position 240 of p53 protein suggesting that the threonine allele of p53 gene is associated with mutation in conserved region. This mutation was observed in the tumors of the OSCC patients. The blood samples of the patients and the controls have not shown the nucleotide change in this region.
This novel missence mutations in DNA binding domain indicated that the DNA structure may be damaged by the use of exogeneous DNA-damaging agents including tobacco related carcinogens present in gutka, niswar and manpuri, which may result in the loss of cellular processes and p53 protein function.