An epidermotropic canine papillomavirus with malignant potential contains an E5 gene and establishes a unique genus.

A novel canine papillomavirus, CfPV-2, was cloned from a footpad lesion of a golden retriever. Unlike the known canine oral papillomavirus (COPV), which has a double-stranded DNA genome size of 8607 bps, the genome of CfPV-2 is 8101 bps. Some of this size difference is due to an abbreviated early-late region (ELR), which is 1200 bps shorter than that of COPV. However, CfPV-2 has other differences from COPV, including the presence of an E5 ORF between the E2 gene and the ELR and an enlarged E4 ORF (one of the largest PV E4 open reading frames). The genome of CfPV-2 shares low homology with all the other papillomaviruses and, even in the most highly conserved ORF of L1, the nucleotide sequence shares only 57% homology with COPV. Due to this highly divergent DNA sequence, CfPV-2 establishes a new PV genus, with its closest phylogenetic relatives being amongst the Xi and Gamma genuses. CfPV-2 also has unique biological features; it induces papillomas on footpads and interdigital regions which, if infection is persistent, can progress to highly metastatic squamous cell carcinoma. CfPV-2 does not induce oral papillomas in immunocompetent animals and antibodies generated against COPV and CfPV-2 are type-specific. The availability of a new canine papillomavirus with differing genetic and biological properties now makes it possible to study type-specific host immune responses, tissue tropism and the comparative analysis of viral gene functions in the dog.

The E6AP ubiquitin ligase is required for transactivation of the hTERT promoter by the human papillomavirus E6 oncoprotein.

Most human cancer cells display increased telomerase activity that appears to be critical for continued cell proliferation and tumor formation. The E6 protein of malignancy-associated human papillomaviruses increases cellular telomerase in primary human keratinocytes at least partly via transcriptional activation of the telomerase catalytic subunit, hTERT. In the present study, we investigated whether E6AP, a ubiquitin ligase well known for binding and mediating some of the activities of the E6 oncoprotein, participated in the transactivation of the hTERT promoter. Our results demonstrate that E6 mutants that fail to bind E6AP are also defective for increasing telomerase activity and transactivating the hTERT promoter. More importantly, E6AP knock-out mouse cells and small interfering RNA techniques demonstrated that E6AP was required for hTERT promoter transactivation in both mouse and human cells. Neither E6 nor E6AP bound to the hTERT promoter or activated the promoter in the absence of the partner protein. With all transactivation-competent E6 proteins, induction of the hTERT promoter was dependent upon E box elements in the core promoter. It appears, therefore, that E6-mediated activation of the hTERT promoter requires a complex of E6-E6AP to engage the hTERT promoter and that activation is dependent upon Myc binding sites in the promoter. The recruitment of a cellular ubiquitin ligase to the hTERT promoter during E6-mediated transcriptional activation suggests a role for the local ubiquitination (and potential degradation) of promoter-associated regulatory proteins, including the Myc protein.