Molecular Biology of Human Papillomavirus Infection

There are many different types of human papillomavirus (HPV). They all infect epithelial tissue such as the skin, but some cause common warts while others cause genital warts. Certain HPV types are classified as high-risk, because they cause cervical lesions (flat warts) that can in some women progress to cervical cancer. These high-risk HPV types are responsible for virtually all cases of cervical cancer worldwide. Cervical cancer is the second most common cancer amongst women with about half a million cases occurring each year.||Our aim is to understand the molecular basis of disease, and to identify the events that deregulate the normal virus life cycle. This work follows a number of different paths. One aspect establishes the function of the viral proteins and aims to understand how they work together to produce disease. As part of this work we are using model systems of the skin to culture the virus in the laboratory. Another aspect of the work is looking at how the virus changes cellular gene expression, and what causes a wart like infection of the cervix to progress to neoplasia. This work has potential for improved cervical screening and better strategies for vaccination and therapy.

Human papillomaviruses cause a range of epithelial lesions including benign genital warts and cervical intraepithelial neoplasia (CIN). Both are of significant medical importance, with certain HPV types (known as high-risk types) being responsible for the development of cervical cancer in women who cannot resolve their infection. Our focus is on the Alpha papillomaviruses that cause genital warts and cervical disease, but we are also interested in the four other evolutionary groups of papillomavirus including the Beta HPV types that may be involved in the development of skin cancers and which can be a problem in immunosuppressed individuals. The work of the lab falls into three broad areas, which are described below. 1. Molecular Analysis of Human Papillomavirus Protein Function. This has concentrated on the E4 protein, which we have shown previously to bind keratin and certain cyclin dependent kinases to induce G2 arrest. Our current studies centre around the finding that E4 can assemble into amyloid fibrils, and that its function is modulated by phosphorylation and proteolytic cleavage. The finding that high-risk E4 contributes to viral genome amplification in model systems has prompted us to study the importance of the association between the HPV16 E4 protein and the viral replication factor E2. 2. Role of Viral Gene Products During Infection using Model Systems. To understand how viral protein function is modulated during infection, we have used raft culture and gene knock-outs. This system is also allowing us to examine the mechanisms that regulate normal HPV gene expression and to establish what factors are involved in the progression to high-grade neoplasia and cancer. Raft culture provides an important system for the validation of the results generated from the molecular studies described above. Where involvement of the immune system needs to be considered, we are using the rabbit oral papillomavirus model. This is particularly valuable in understanding the basis of viral latency. 3. Natural History of Infection in Humans. The third part of the work examines gene expression patterns in clinical tissue, as this is the gold standard that the molecular studies and the use of model systems must explain. Our goal is to understand the intermediate states that connect productive infection to cervical cancer, and to establish what factors may contribute to life cycle de-regulation in infected cervix. An important off-shoot of this work is the development of biomarker approaches for the evaluation of cervical neoplasia. The biomarker work is of relevance to industry, and we have close contacts with a number of diagnostic and vaccine companies and are currently involved in collaborative studies aimed at improving cervical diagnosis. In addition to the above, we have recently used intrabodies to inhibit HPV protein function in cells. This has contributed to our knowledge of which viral proteins are important for maintenance of the disease state.