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| Author(s): |
Tatiana Rabachini
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2002-12-20 |
| Examining board members: |
Luisa Lina Villa;
Emmanuel Dias Neto;
Eugenia Costanzi Strauss
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| Advisor: | Luisa Lina Villa |
| Field of knowledge: | Biological Sciences - Biochemistry |
| Indexed in: | Banco de Dados Bibliográficos da USP-DEDALUS |
| Location: | Universidade de São Paulo. Biblioteca do Conjunto das Químicas; CQ T/574.64; R122p |
| Abstract | |
In recent years, a number of epidemiological studies have pointed toward a strong association between cervical cancer and infection by Human Papillomavirus (HPV). This association derives from the discovery that these viruses code for oncoproteins, among them E6 and E7 that have transforming properties. The E7 gene product associates with the retinoblastoma gene product, causing the latter to lose its function as a negative regulator of the cell cycle. The E6 gene product interacts with the tumor suppressor p53 gene product, resulting in its degradation via ubiquitin dependent proteolysis. The p53 gene is a tumor suppressor that funcions in the regulation of the cell cycle. It presents a number of distinct polymorfisms in diverse ethnic groups, and has been widely studied, both in normal and tumor tissues. The polymorfism of codon 72 is the most studied, and may present three different alleles in the population. One allele codes for arginine (Arg), another codes for proline (Pro), and a third, rarely found, codes for cystein (Cys). In 1993 an epidemilogical study of the natural history of infection by HPV and its possible association with cervical neoplasia was initiated in a population of low income females in São Paulo, Brazil, one of the areas of greatest risk in the world. The study focuses on persistent infection by oncogenic types of HPV as a precursor to carcinogenesis of the cervix, and seeks to understand the attributes of the natural history of viral infection and of illnesses associated with the cervix. One of the objectives of the study is to evaluate if the polymorfisms of codon 72 of p53 can or not be used as a marker of predisposition to cervical cancer, given the finding in the initial study that patients who were homozygous for the p53Arg genotype were 7 times more susceptible to developing cervical neoplasias than those patients who were homozygous for p53Pro, or heterozygous p53 Pro/ Arg. Previous studies have been realized both supporting and disputing these findings. The current study had two main objectives: to verify if the polymorfism of p53 codon 72 could be associated with persistent infections of HPV and the risk of cervical neoplasia, as well as to compare methods of detection used by other studies, in an attempt to clarify if the discording results of past studies could be due to methodological classification errors. Seven detection methods were compared. Only one of these, allele specific PCR, presented discording results from the rest. Coincidentally, this method was widely used in a number of studies which found both positive and negative associations. This might indicate that the method-dependent classification errors could influence the results of correlation between codon 72 polymorphism and the risk of cervical neoplasia. The correlations observed by this study did not demonstrate an association between codon 72 polymorphism and the risk of persistent HPV infection and precursor lesions of cervical cancer. (AU) | |