Correlation between p53 gene mutations and circulating antibodies in betel- and tobacco-consuming North Indian population
Introduction
Carcinoma of the oral cavity is one of the most frequent malignant tumours worldwide [1] with major predominance in south east Asia and India [2]. The development of oral cancer is a multistep process, arising from pre-existing red or white patches termed erythroplakia or leukoplakia (potentially malignant lesions); 5–10% of these potentially malignant lesions undergo transition to frank malignancy. The incidence and mortality from oral cancer are reportedly increasing [2]. Epidemiological studies indicate that intervention studies at an early stage may reduce oral cancer-related deaths. Concerted efforts are therefore required to define multiple markers for early detection of the disease as well as for management and monitoring the efficacy of the treatment. These efforts may also be of value for proactive intervention of high risk groups (potentially malignant lesions).
Several genetic events initiate the progression of normal oral mucosa to squamous cell carcinomas (SCCs); mutations of the p53 tumour suppressor gene play an important role in this process [3]. Numerous studies report specific mutations of the p53 gene in oral SCCs among diverse population groups from several parts of the world (reviewed in [3] and references therein). The importance of alterations of p53 tumour suppressor as a molecular marker in the clinical diagnosis of oral cancer is being extensively investigated [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. The profile of p53 gene mutations has been associated with several factors, such as prolonged exposure of the oral cavity to various external carcinogens and co-carcinogens that are components of chewable tobacco, and/or betel quid (processed/unprocessed areca nut) [16], [17], [18], [19], [20], [21], [22].
The alternative approach of assessing p53 alteration by detection of p53 protein in tumour cells by immunohistochemistry (IHC) indicates discordancy rates of 30–35% when compared with techniques that determine the gene status [11]. Circulating p53 antibodies in the sera of cancer patients have been reported to be yet another alternative strategy for assessing p53 aberrations in several cancers [23], [24], [25], [26], [27], [28]. Our group and others reported the presence of circulating p53 antibodies in patients with oral leukoplakia and oral SCCs [29], [30]. However, a composite study of the relationship between p53 gene mutations, p53 protein accumulation in the same tumours and circulating anti-p53 antibodies in the tobacco-induced oral cancer patients in the Indian population have not been carried out so far.
We further wanted to assess the ability of p53 antibodies as a surrogate marker for identifying p53 alterations which may be helpful in assessing the ability of p53 to identify the high risk group patients that potentially can benefit from adjutant therapy. Therefore, the aim of the present study was to analyse p53 gene mutations and correlate the specific mutations with intratumoural protein accumulation as well as serum p53-Abs in matched patient samples.
Section snippets
Tissue specimens
Surgical tissue specimens from 30 untreated primary SCCs of the oral cavity and 30 potentially malignant lesions (leukoplakia) were obtained from the Department of Surgical Disciplines, All India Institute of Medical Sciences, New Delhi, India. A pre-tested semi-structured questionaire was used to collect information on the consumption of alcohol, tobacco (chewing or smoking) and use of areca nut in betel quid; betel and areca nut use: moderate=5–10 betel per day for 2–10 years; heavy=over 10
Genetic analysis of p53 in human oral potentially malignant and malignant lesions
The relationships between p53 mutational profile and p53 protein status, circulating p53-Abs as well as clinicopathological parameters of the patients with oral potentially malignant and malignant lesions are shown in Table 1, Table 2, respectively. Genetic analysis of p53 was carried out in 30 potentially malignant lesions and 30 oral SCCs by PCR followed by direct sequencing. Representative DNA sequence scans showing p53 mutations in oral potentially malignant lesions and SCC are shown in
Discussion
p53 gene mutation is one of the most common events in human carcinogenesis and approximately 90% of its mutations are of the missense type [9]. Knowledge of p53 mutations in oral potentially malignant lesions is meagre and their relevance in identifying lesions at high risk of transition to malignancy is not available [15]. The most striking feature of the present study was the correlation observed between p53 missense mutations, p53 antibodies and p53 protein accumulation in matched
Acknowledgements
The authors wish to thank: (1) IGBMC core and oligonucleotide synthesis and DNA sequencing facilities for tremendous help and support; (2) the members of Boh WasylykÆs lab for help and constructive discussion; and (3) members of CEFIPRA for their scientific support. The financial assistance from Indo-French Centre For Promotion of Advanced Research is gratefully acknowledged. S.A. was supported by Senior Research Fellowship from University Grant Commission, India.
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R.R. and S.A. contributed equally to this study.