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Papillomaviruses (PVs) are established agents of human and animal cancers. They infect cutaneous and mucous epithelia. High Risk (HR) Human PVs (HPVs) are consistently associated with cancer of the uterine cervix, but are also involved in the etiopathogenesis of other cancer types. The early oncoproteins of PVs: E5, E6 and E7 are known to contribute to tumour progression. While the oncogenic activities of E6 and E7 are well characterised, the role of E5 is still rather nebulous. The widespread causal association of PVs with cancer makes their study worthwhile not only in humans but also in animal model systems. The Bovine PV (BPV) system has been the most useful animal model in understanding the oncogenic potential of PVs due to the pivotal role of its E5 oncoprotein in cell transformation. This review will highlight the differences between HPV-16 E5 (16E5) and E5 from other PVs, primarily from BPV. It will discuss the targeting of E5 as a possible therapeutic agent.

Bovine papillomavirus type 2 (BPV-2) infection has been associated with urinary bladder tumours in adult cattle grazing on bracken fern-infested land. In this study, we investigated the simultaneous presence of BPV-2 in whole blood and urinary bladder tumours of adult cattle in an attempt to better understand the biological role of circulating BPV-2. Peripheral blood samples were collected from 78 cattle clinically suffering from a severe chronic enzootic haematuria. Circulating BPV-2 DNA was detected in 61 of them and in two blood samples from healthy cows. Fifty of the affected animals were slaughtered at public slaughterhouses and neoplastic proliferations in the urinary bladder were detected in all of them. BPV-2 DNA was amplified and sequenced in 78 % of urinary bladder tumour samples and in 38.9 % of normal samples as a control. Circulating episomal BPV-2 DNA was detected in 78.2 % of the blood samples. Simultaneous presence of BPV-2 DNA in neoplastic bladder and blood samples was detected in 37 animals. Specific viral E5 mRNA and E5 oncoprotein were also detected in blood by RT-PCR and Western blot/immunocytochemistry, respectively. It is likely that BPV-2 can persist and be maintained in an active status in the bloodstream, in particular in the lymphocytes, as a reservoir of viral infection that, in the presence of co-carcinogens, may cause the development of urinary bladder tumours. INTRODUCTIONBovine papillomaviruses (BPVs) are species-specific, double-stranded DNA viruses responsible for cutaneous and mucosal neoplastic lesions. They are small non-enveloped viruses with an icosahedral capsid. Their open reading frames (ORFs) are divided into early (E) and late (L) regions. The early region encodes non-structural proteins E1 to E7, of which, E5, E6 and E7 are known to be oncoproteins. The late region encodes structural proteins L1 and L2 forming the capsid. Bovine papillomavirus type 2 (BPV-2) is classified in the genus Deltapapillomavirus, species 4, the biological properties of which are characterized by the induction of fibropapillomas in cattle and sarcoids in equids (Brandt et al., 2008;Chambers et al., 2003;de Villiers et al., 2004). BPV-2 infection in the presence of environmental carcinogens, such as ptaquiloside (PT) of bracken fern (Pteridium aquilinum), has been associated with urinary bladder neoplastic lesions in adult cattle, in which chronic enzootic haematuria (CEH) is the most important clinical sign (Campo, 1997; Campo et al., 1992;Hopkins, 1986).The effect of the route of viral infection, and the synergistic relationship between BPV-2 and immunosuppressive and oncogenic compounds present in the bracken fern in the malignant progression of bladder lesions (Campo, 1997; Campo et al., 1992; Jarrett et al., 1978;Reddy & Fialkow, 1983;Stocco dos Santos et al., 1998) are not well-known, thus deserving further investigations.To date, the BPV-2 genome has been detected in lymphocytes during latent papillomavirus infection in cattle (Campo et al., 1994). In addition, the occurrence of horiz...

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A minor groove binder (MGB) probe assay was developed to discriminate between type 2-based vaccines and field strains of canine parvovirus (CPV). Considering that most of the CPV vaccines contain the old type 2, no longer circulating in canine population, two MGB probes specific for CPV-2 and the antigenic variants (types 2a, 2b and 2c), respectively, were labeled with different fluorophores. The MGB probe assay was able to discriminate correctly between the old type and the variants, with a detection limit of 10(1) DNA copies and a good reproducibility. Quantitation of the viral DNA loads was accurate, as demonstrated by comparing the CPV DNA titres to those calculated by means of the TaqMan assay recognising all CPV types. This assay will ensure resolution of most diagnostic problems in dogs showing CPV disease shortly after CPV vaccination, although it does not discriminate between field strains and type 2b-based vaccines, recently licensed to market in some countries.

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Bovine papillomavirus type 2 (BPV-2) is an oncogenic virus infecting both epithelial and mesenchymal cells. Its life cycle, similar to other papillomaviruses (PVs), appears to be linked to epithelial differentiation. Human and bovine PVs have been known to reside in a latent, episomal form in PBMCs; therefore, it is believed that blood cells, like all mesenchymal cells, function as non-permissive carriers. Here, for the first time in veterinary and comparative medicine, the BPV-2 E5 oncoprotein and the major structural L1 capsid protein, known to be expressed only in productive infections, were shown to occur in defined subsets of PBMCs. E5 oncoprotein was detected in sorted T-and B-cells as well as in monocytes by flow cytometry and Western blot analysis. However, CD4 + and CD8 + lymphocytes appeared to be the main circulating targets of the virus, thus possibly representing the most important reservoir of active BPV-2 in blood. L1 protein was identified by flow cytometry in a population of blood cells recognized as lymphocytes by morphological scatter properties. Western blot analysis was performed on lysates obtained from the sorted subpopulations of PBMCs and detected L1 protein in CD4 + and CD8 + cells only. Thus, this study showed that CD4 + and CD8 + lymphocytes are permissive for BPV-2 and are new, hitherto unknown sites of productive PV infection. In light of these observations, the life cycle of PVs needs to be revisited to gain novel insights into the epidemiology of BPV infection and the pathogenesis of related diseases. INTRODUCTIONBovine papillomaviruses (BPVs) are a heterogeneous group of viruses responsible for tumours of the skin, genital and paragenital area, eye, upper gastrointestinal tract and urinary bladder (IARC, 2007). BPVs, like all other papillomaviruses (PVs), are usually strictly species specific. However, cases of cross-species infection are known to occur. BPV type 1 (BPV-1) and BPV-2, belonging to the genus Deltapapillomavirus (de Villiers et al., 2004), are responsible for infections in equids resulting in sarcoids (Chambers et al., 2003;Trenfield et al., 1985), as well as in bison and water buffaloes leading to warts (Literák et al., 2006;Silvestre et al., 2009). In addition, a variant of BPV-8, classified in the genus Epsilonpapillomavirus, also causes papillomas of the skin in bison (Tomita et al., 2007). More recently, it has been suggested that BPVs could be responsible for cutaneous sarcoids in cats and captive African lions (Munday & Knight, 2010;Orbell et al., 2010).BPV-1 and -2 are closely related serotypes (Shafti-Keramat et al., 2009) and can infect both epithelial and mesenchymal cells. Similar to other PVs, BPV-1/-2 replication and virion production are confined to the epithelial region of the lesions, whilst infection of mesenchymal cells appears to be non-productive (Campo, 2006;Shafti-Keramat et al., 2009).BPV-2 is known to play a central role in bladder carcinogenesis of adult cattle reared on pasturelands rich in bracken fern. In these animals, tumours of the u...

Bovine papillomavirus type 2 (BPV-2) has been shown to infect and play a role in urinary bladder carcinogenesis of buffaloes grazed on pastures with ferns from the Marmara and Black Sea Regions of Turkey. BPV-2 DNA has been found in both neoplastic and non-neoplastic lesions of the urinary bladder. Furthermore, this virus may be a normal inhabitant of the urinary bladder since BPV-2 DNA has also been detected in clinically normal buffaloes. The viral activation by fern immunosuppressant or carcinogen may trigger the urothelial cell transformation. The E5 oncoprotein was solely detected in urothelial tumours and appeared to be co-localized with the overexpressed and phosphorylated platelet derived growth factor (PDGF) b receptor in a doublecolour immunofluorescence assay. Our results indicate that the E5-PDGF b receptor interaction also occurs in spontaneous tumours of the bubaline urinary bladder, revealing an additional role of BPV-2 in bladder carcinogenesis of buffaloes.