Pathogenesis of Human Papillomaviruses in Differentiating Epithelia

Abstract

HUMAN PAPILLOMAVIRUSES AND CERVICAL CANCERHuman papillomaviruses (HPVs) are small, double-stranded DNA viruses that infect cutaneous and mucosal epithelial tissues of the anogenital tract, the hands, or the feet. A subset of HPV types are the causative agents of cervical cancer, since 99% of tumors are positive for HPV DNA (150). To date, over 100 different viral types have been identified, and about onethird of these infect epithelial cells in the genital tract. The viral types that infect the genital tract fall into two categories: high risk and low risk. The high-risk types are associated with the development of anogenital cancers including those of the cervix, while infections by the low-risk HPVs induce only benign genital warts. The high-risk types include HPV-16, HPV-18, HPV-31, HPV-33, and HPV-45, while the low-risk types are HPV-6 and HPV-11. HPVs that infect the genital tract are sexually transmitted, and it is estimated that about two-thirds of individuals who have sexual relations with an infected partner will themselves become infected. However, the majority of infections are subclinical (137). Infection by high-risk HPVs is not limited to the genital tract, since approximately 20% of cancers of the oropharynx contain DNA from these HPV types (61).Infection of the genital tract by HPVs can initially result in low-grade lesions termed dysplasias or cervical intraepithelial neoplasia grade I. These lesions exhibit only mildly altered patterns of differentiation, and many of them are cleared by the immune system in less than a year (62, 71). The mechanisms by which the cellular immune response clears HPV infections are still not clearly understood. Some of these lesions, however, are not cleared by the immune system and can persist for periods as long as several decades. Persistence of infection by high-risk HPV types is the greatest risk factor for development of genital malignancies such as squamous cell carcinoma or, less commonly, adenocarcinoma of the cervix (161). Cervical cancer is the second most prevalent cancer worldwide and is the fifth leading cause of cancer deaths in women (120,124). Approximately 470,000 new cases of cervical cancer are diagnosed yearly, with the mean age for the development of malignancy being 52 years (8, 124). Risk factors for tumor development include persistent infection with high-risk viral types, a large number of lifetime sexual partners, coinfection with human immunodeficiency virus, immunosuppression, and cigarette smoking (81). Most cases of cervical cancer are found outside of the United States and Western Europe. In the United States, the number of cases of cervical cancer has declined by over 80% in the last 50 years due to the implementation of the Pap smear as a diagnostic (137). While the number of cases has significantly decreased, approximately 10,000 women are diagnosed with cervical cancer and 5,000 die of this disease annually (120). HUMAN PAPILLOMAVIRUS LIFE CYCLEHPVs are nonenveloped viruses with icosahedral capsids that replicate their genomes wi...

Accelerated degradation of FADD and procaspase 8 in cells expressing human papilloma virus 16 E6 impairs TRAIL-mediated apoptosis

“…20,21 This study further elucidates the mechanisms employed by E6 to modulate cellular responses to death stimuli. Cell death induced by TNF, Fas and TRAIL is transmitted through FADD and caspase 8 from cell surface receptors, to executioner caspases.…”

“…The E6 oncoprotein of high-risk HPVs, such as HPV 16, plays a pivotal role in the pathophysiology of cervical cancer (reviewed in Mantovani and Banks 20 and Longworth and Laimins 21 ), which accounts for a large number of deaths among women worldwide. 22,23 One of the primary targets of E6 is the tumor suppressor p53.…”

E6AP is required for replicative and oncogene-induced senescence in mouse embryo fibroblasts

“…As E6AP has been shown to act as a regulator of p53 in HPV-infected cells (for review see Huibregtse et al, 1991;Scheffner et al, 1990Scheffner et al, , 1993Longworth and Laimins, 2004;andBeaudenon and Huibregtse, 2008) and in certain cells, such as prostate MEFs (p6). Photographs are at the same magnification ( Â 400).…”

Transcriptomic analyses of genes differentially expressed by high-risk and low-risk human papilloma virus E6 oncoproteins

“…They are non-enveloped viruses with icosahedral capsids [21]. In a normal viral life cycle, virions are shed from the infected cell, in case of non-productive life cycle HPV DNA gets integrated into the host genome which results in unregulated expression of viral oncoproteins E6 and E7.…”