Alteration of p53 gene structure and function in laryngeal squamous cell cancer

Abstract

The p53 gene is known as an anti-oncogene that manifests its function by controlling the cell cycle and is responsible for apoptosis of cells with unrepaired DNA. An accelerated p53 protein synthesis is the first response of a cell following DNA damage. However, mutations of the p53 gene can disturb protein synthesis or may be responsible for synthesis of a changed protein unable to control the cell cycle. Laryngeal tissue specimens from 120 patients were tested by immunohistopathological staining to detect mutated wild-type p53 protein. It was found that p53-positive specimens correlated with TNM staging and histopathological grading. Another indication of entering the cell cycle and undertaking an active proliferation by laryngeal cells was shown by detection of proliferating cell nuclear antigen (PCNA) and Ki67 nuclear antigen, which appeared in proliferating cells (late G1, S-G2 and M phase), but was absent in resting cells. Scoring of the staining for p53 protein, PCNA and Ki67 correlated with each other. DNA from 40 specimens was then isolated, amplified by polymerase chain reaction and analysed by single-strand conformation polymorphism and DNA sequencing for mutation in the p53 gene. Fifteen DNA samples were found to be positive, while mutations were detected in exons 5–8 in 13 samples. The majority of mutations were found in tissue specimens from T3 and T4 tumors. A possible explanation is almost half was attributable to genotoxic effects of tobacco smoking. Changes in the p53 gene and its products may also reflect early changes in laryngeal carcinogenesis and be of prognostic value.