p53 codon 72 polymorphism and its association with bladder cancer

Abstract

p53 codon 72 Arg homozygosity has been associated with increased risk of developing cervical cancer. This association has been tested in various human cancers with controversial results. In the present study we investigated the impact of this polymorphism in a population-based case-control study of bladder cancer. Using allele-specific polymerase chain reaction to detect the p53 codon 72 polymorphism, we tested peripheral blood samples from 50 patients with bladder cancer and 99 healthy individuals of similar age and from the same geographical region. Tumor specimens from all bladder cancer patients were examined for the presence of human papilloma virus (HPV). The distribution of p53 alleles in bladder cancer patients and in controls was statistically significant (P<0.002; odds ratio, 2.67; 95% confidence interval, 1.38–5.20), and homozygosity for arginine at residue 72 was associated with an increased risk for bladder cancer (P<0.00002; odds ratio, 4.69; 95% confidence interval, 2.13–10.41). The presence of HPV was found in six of the 50 patients (12%). This is the first study correlating p53 codon 72 polymorphism with bladder cancer. Our results provide evidence that this p53 polymorphism is implicated in bladder carcinogenesis and that individuals harboring the Arg/Arg genotype have an increased risk of developing bladder cancer.

Introduction

Bladder cancer is the sixth most common cancer in the USA with an estimated 54,300 new diagnoses and 12,400 tumor-associated deaths for the year 2001 [1]. Factors reported to be causally related to the disease include occupational exposure to chemicals, cigarette smoking, coffee drinking, artificial sweeteners and bacterial, parasitic or viral infections [2]. Several oncogenes and tumor suppressor genes, such as p16, p21^WAF1/CIP1, Rb1, ras, c-erbB-1 and p53 are involved in the development and progression of bladder cancer [3].

The human papilloma virus (HPV) family has been implicated in the development of bladder cancer. HPV genome consists of 7200–8000 bp and encodes six early (E1–E7) and two late proteins (L1 and L2) [4]. The early proteins E6 and E7, especially of high-risk HPVs, are capable of interacting with cellular proteins involved in the control of cell proliferation and in the prevention of cell immortalization [5]. E6, in particular, binds the cellular tumor-suppressor protein p53 and promotes its degradation with the E6-AP protein through the ubiquitin-dependent proteolytic pathway [6], [7]. The presence of HPV DNA in squamous and transitional cell carcinoma of the bladder has been detected in 0–80% of tumors examined [8]. Nevertheless, most studies report low HPV numbers (<10%) [9], [10], [11], suggesting that HPV plays an important role in a small portion of bladder cancer cases.

The human p53 tumor suppressor gene encodes a 393 amino acid, 53-kDa nuclear phosphoprotein [12], which is a central element in fundamental cellular processes, including induction of cell cycle arrest, gene transcription, DNA repair and apoptosis [13]. The p53 gene is mutated in 20–60% of bladder tumors [14], with codons 280 and 285 being mutational hotspots [15]. These alterations seem to be more frequent in invasive than in superficial tumors [16], and are usually correlated with worse clinical outcome [17].

p53 codon 72 polymorphism, encoding either arginine or proline [18], has been proposed to affect the susceptibility of p53 protein to HPV E6-mediated degradation in vitro. Moreover, the frequency of the Arg/Arg genotype was found to be significantly higher in cervical cancer patients compared to the general population, indicating that individuals homozygous for Arg are seven times more susceptible to HPV-associated tumorigenesis than heterozygotes [19]. Similar studies have been conducted in several human tumors, such as cervical [20], [21], [22], head and neck [23], esophageal [24], lung [25], breast [26], skin [27] or laryngeal cancer [28], but the results were controversial. Despite the great variety of human tumors that have been already examined for p53 codon 72 polymorphism, no study on bladder cancer has been carried out yet.

In the present study, we conducted a case-control study in a geographically homogeneous Greek population, to examine the genotypic frequency of the p53 codon 72 polymorphism and the presence of HPV in 50 bladder cancer patients compared to matched healthy controls, in order to determine any association to bladder carcinogenesis.