An investigation of the contribution of cigarette smoking and human papillomavirus infection to the epigenetic modulation of cellular genes in cervical epithelium

Abstract

In this thesis, I examine the contribution of cigarette smoking and human papillomavirus infection, two independent risk factors for cervical neoplasia, to the epigenetic modulation of cellular genes in cervical epithelium. To determine the temporal relationship between cigarette smoking and the detection of CDKN2A methylation in cervical cytological samples, I used a unique cohort of 2011 women aged 15-19 who were recruited soon after they first had sexual intercourse. I have shown that compared with never-smokers, women who first started to smoke during follow-up had an increased risk of acquiring methylation of the tumour suppressor gene (TSG), CDKN2A (odds ratio=3.67; 95% confidence interval: 1.09 to 12.33; p=0.04). I was also able to show that this epigenetic change was often reversible following smoking cessation. To determine the spectrum of epigenetic changes associated with HPV infection I performed CpG island and gene expression arrays on two in vitro models, a HPV replication model and a cervical disease progression model. I went on to show that HPV infection is followed by the up-regulation of the DNA methyltransferase DNMT1 which binds to the TSG, RARB, resulting in its de novo methylation. Specific CpG loci in the RARB promoter appeared to be targeted for de novo methylation, rather than methylation of all the CpGs, and may represent the methylation pattern seen at the earliest stages of HPV-induced carcinogenesis.