Bovine papillomavirus load and mRNA expression, cell proliferation and p53 expression in four clinical types of equine sarcoid

Abstract

Equine sarcoids, the most common skin tumours in horses, are induced by bovine papillomavirus (BPV). Their clinical appearance varies from small stable patches to aggressively growing masses. Differences in BPV load and mRNA expression and Ki67 and p53 immunostaining among four clinical types (fibroblastic, occult, nodular and verrucous sarcoids) were evaluated to test the hypothesis that the clinical behaviour of equine sarcoids correlates with BPV activity. Viral load and expression of the BPV E2, E5, E6 and E7 genes were determined using quantitative real-time PCR. The proliferative fraction (PF) of the tumours was determined by Ki67 immunostaining and expression of p53 was analysed by immunohistochemistry. Nodular sarcoids showed a significantly higher viral load than the other types. A significant overall difference among the four types was observed for E2, E5, E6 and E7 mRNA expression. Nodular sarcoids showed the highest expression level for each BPV gene examined, followed by verrucous, fibroblastic and occult tumours. Viral DNA and mRNA outcomes correlated with each other, indicating a similar transcription pattern in each type of sarcoid. The PF was significantly higher in the superficial layers of verrucous and fibroblastic sarcoids compared with occult and nodular types. No significant difference was observed for the PF in the deep layers and for p53 expression. These results clearly demonstrate the omnipresence and active transcription of BPV in equine sarcoids. However, the hypothesis that the clinical behaviour of an equine sarcoid can be explained on the basis of differences in BPV activity could not be demonstrated. INTRODUCTIONEquine sarcoid is the most common skin tumour in horses. The clinical aspect can vary remarkably, ranging from small, stable patches to aggressively growing tumours up to more than 10 cm in diameter. A sarcoid can appear as a single tumour, but horses often show multiple lesions. Although equine sarcoids do not metastasize, they recur frequently if not treated properly. Different clinical types have been described (Pascoe & Knottenbelt, 1999). The fibroblastic type, with a typically ulcerated epidermis, usually presents an aggressive clinical behaviour (Fig. 1a). Occult types are flat, alopecic patches, sometimes with hyperkeratosis or small nodules on their surface (Fig. 1b). These tumours will often not evolve, even over several years. Nodular sarcoids are round masses with an intact epithelium (Fig. 1c). The overlying skin can be loose from the stromal tissue or (partially) attached to the fibroblastic portion of the tumour. Verrucous sarcoids have a typically warty appearance (Fig. 1d). Nodular and verrucous sarcoids display a clinical behaviour in between the fibroblastic and the occult sarcoid, mostly with moderate growth. Mixed sarcoids, composed of two or more of the described types, are also commonly observed. Occult sarcoids, and even nodular and verrucous sarcoids, can remain stable for many years and then suddenly, without any apparent reason, change dramatica...

Loss of Retinoblastoma Protein, But Not p53, Is Associated With the Presence of Papillomaviral DNA in Feline Viral Plaques, Bowenoid In Situ Carcinomas, and Squamous Cell Carcinomas

“…This is consistent with bovine PV-induced equine sarcoids that also demonstrate p53 immunostaining in a proportion of tumors. 4 Likewise, no interaction between cottontail rabbit papillomavirus proteins and p53 could be detected. 15 In the present study, immunostaining against p53 was visible in 5 of 10 BISCs.…”

Transcriptional Changes Induced by Bovine Papillomavirus Type 1 in Equine Fibroblasts

“…Up-regulation of c-IAP-1 would abrogate apoptotic responses in sarcoids. Interestingly, p53 is disabled in sarcoids and sarcoid cells (10,49,69).…”

“…BPV DNA has not been detected in other equine tumors, including melanomas, papillomas, and squamous cell carcinomas (15), although we and others have shown that BPV-1/BPV-2 DNA can be detected in some cases of equine inflammatory skin disease (3,15,68). BPV DNA is localized to the fibroblast nuclei (37,60) and is maintained as a high-copynumber episome, and infection results in the expression of viral genes (2,10,15,49,67). We have recently shown that BPV-1 transforms primary equine fibroblasts (69).…”

Localization of Bovine Papillomavirus Nucleic Acid in Equine Sarcoids

“…These studies have identified early and late gene transcripts in at least a subset of naturally occurring sarcoids indicating the initiation of viral transcription and replication. 9,25,36 Further evidence indicates that viral proteins, including E2, 36 E5, 11,36 E7, 11 and L1, 10,11 are also produced in naturally occurring equine sarcoids. While examination of sarcoids for BPV has identified viral DNA, viral transcripts, and even viral proteins, to date there has been no visualization of viral particles in sarcoids, and infection is thus generally considered nonproductive.…”