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Human papillomavirus (HPV) exhibits epithelial and mucosal tropism. HPV type 17 belongs to the Betapapillomavirus genus and molecular cloning experiments have identified two subtypes (17a and 17b) isolated from epidermodysplasia verruciformis (EV). HPV subtypes are characterized by dissimilarities from 2 to 10% at the nucleotide level from their referenced HPV. The aim of this study was to characterize the L1, E6, E7 and LCR sequences from an isolate, which was recovered from the oral mucosa of an asymptomatic 63 year-old woman. The whole late gene 1 (L1) was amplified using several sets of primers. The complete early genes 6 and 7 (E6, E7) and the long control region (LCR) were amplified using specific primers. Potential binding sites for transcriptional factors within the LCR were also investigated. Within these sets, the DNA sequence was altered at 91 positions (68 in L1, 13 in E6, 8 in E7, and 2 in LCR sequences). L1 analysis showed high dissimilarity compared with the HPV 17 prototype, reaching 4% of nucleotide substitutions and leading to a probable third 17 subtype. The E6 oncoprotein presented the highest modification among the sequences studied, with four amino acid changes in comparison with the prototype isolate. One amino acid was modified at a position 62 (S-T), a zinc-binding domain (CxxC(C)29 CxxC). Our findings provide data on genetic variations seen in this genotype, reaching to dichotomic branching and pointing to an evolutionary process.

The aim of this study was to determine whether detection of β-HPV gene products, as defined in epidermodysplasia verruciformis skin cancer, could also be observed in lesions from kidney transplant recipients alongside the viral DNA. A total of 111 samples, corresponding to 79 skin lesions abscised from 17 kidney transplant recipients, have been analyzed. The initial PCR analysis demonstrated that β-HPV-DNA was highly present in our tumor series (85%). Using a combination of antibodies raised against the E4 and L1 proteins of the β-genotypes, we were able to visualize productive infection in 4 out of 19 actinic keratoses, and in the pathological borders of 1 out of 14 squamous cell carcinomas and 1 out of 31 basal cell carcinomas. Increased expression of the cellular proliferation marker minichromosome maintenance protein 7 (MCM7), that extended into the upper epithelial layers, was a common feature of all the E4-positive areas, indicating that cells were driven into the cell cycle in areas of productive viral infections. Although the present study does not directly demonstrate a causal role of these viruses, the detection of E4 and L1 positivity in actinic keratosis and the adjacent pathological epithelium of skin cancer, clearly shows that β-HPV are actively replicating in the intraepidermal precursor lesions of kidney transplant recipients and can therefore cooperate with other carcinogenic agents, such as UVB, favoring skin cancer promotion.

Beta-human papillomaviruses (β-HPV) infect cutaneous epithelia, and accumulating evidence suggests that the virus may act as a co-factor with UV-induced DNA damage in the development and progression of non-melanoma skin cancer, although the molecular mechanisms involved are poorly understood. The E6 protein of cutaneous β-HPV types encodes functions consistent with a role in tumorigenesis, and E6 expression can result in papilloma formation in transgenic animals. The E6 proteins of high-risk α-HPV types, which are associated with the development of anogenital cancers, have a conserved 4 aa motif at their extreme C terminus that binds to specific PDZ domain-containing proteins to promote cell invasion. Likewise, the high-risk β-HPVs HPV5 and HPV8 E6 proteins also share a conserved C-terminal motif, but this is markedly different from that of α-HPV types, implying functional differences. Using binding and functional studies, we have shown that β-HPV E6 proteins target β1-integrin using this C-terminal motif. E6 expression reduced membrane localization of β1-integrin, but increased overall levels of β1-integrin protein and its downstream effector focal adhesion kinase in human keratinocytes. Altered β1-integrin localization due to E6 expression was associated with actin cytoskeleton rearrangement and increased cell migration that was abolished by point mutations in the C-terminal motif of E6. We concluded that modulation of β1-integrin signalling by E6 proteins may contribute towards the pathogenicity of these β-HPV types.