Isolation and functional analysis of five HPVE6 variants with respect to p53 degradation

Abstract

Persistent infection with high risk human papillomavirus is a necessary risk factor in the etiology of invasive cervical carcinoma. With regard to molecular details, the best studied types are HPV16 and HPV18 which are found in 70% of cervical cancer worldwide, however factors associated with the progression of individual cervical intraepithelial neoplasias into cancer are still poorly understood. Intratype amino acid variations in the immortalizing and transforming early proteins E6 and E7 were described to be associated with progressive disease and linked to increased viral persistence or progression. One of the key actions of high risk HPVE6 proteins is the inhibition of the function of p53, a tumor suppressor protein, by enhancing its degradation through the ubiquitin pathway. In this study, variants of five HPV type E6 proteins (HPV35, 53, 56, 66, and 70) isolated from patient materials are described and functional analysis of them were done with respect to p53 degradation. Interestingly the E6 protein of HPV type 53, which has no consistent risk classification in the literature showed the highest variability in our study. The analysis of all variants revealed no differences with regard to the degradation ability for p53 compared to the prototype E6 proteins, suggesting that the variants tested revealed no altered functions related to the carcinogenicity of the respective HPV types. It therefore seems more likely that variations in the E6 gene sequence may allow evasion from the hosts immune system, supporting increased viral persistence.

Integrated analysis of chromosome copy number variation and gene expression in cervical carcinoma

“…p53 is a well-known tumor suppressor gene, and an increase in p53 levels plays a critical role in the induction of genes that results in cell cycle arrest [ 7 ], allowing repair of damaged DNA or activation of apoptotic pathways [ 8 ]. In cervical cancer with high risk of HPV-infection, the E6 protein from high-risk HPV can bind to tumor suppressor protein p53 for rapid degradation via a cellular ubiquitin ligase [ 9 ]. Other studies have indicated that p53 protein over-expression is not common or associated with survival in cervical carcinoma [ 10 , 11 ].…”

Evolution of Human Papillomavirus Carcinogenicity

“…Figure 7 shows a summary of recent data on how the E6 proteins of different types affect the steady-state levels of p53 and Magi1c and hDLG (PDZ-containing proteins; Hiller et al , 2006; Hiller et al , 2008; Muench et al , 2009). This tree, based on the nucleotide sequence of the E6 proteins, clusters all the oncogenic types (Bouvard et al , 2010) in a single (red) HR-clade; however, not all members of this clade actually cause disease.…”

“…column shows the epidemiological classification (oncogenic, OT; nonOT, NOT, insufficient data, N/A) according to Bouvard et al (2010). The following columns summarize the data presented in p53 (1) (Hiller et al , 2006), p53 (2) (Hiller et al , 2008), p53 (3) (Fu et al , manuscript submitted), Magi1c (4), and hDLG (4) (Muench et al , 2009). In these columns, “yes” indicates degradation of the target, “no” means no degrading potential, and “~” signifies intermediate potential.…”

Current Understanding and Potential Immunotherapy for HIV‐Associated Squamous Cell Carcinoma of the Anus (SCCA)

“…In addition, Hiller et al . [29] recently stated that several variants of HPV E6 protein may play a role in supporting increased viral persistence by avoiding immune responses.…”

“…It is therefore likely that E6‐mediated abrogation of p53 protein‐dependent apoptosis has the equivalent effect to inactivating mutations of the p53 gene [26]. In addition, Hiller et al [29] recently stated that several variants of HPV E6 protein may play a role in supporting increased viral persistence by avoiding immune responses.…”