p38 mitogen-activated protein kinase is crucial for bovine papillomavirus type-1 transformation of equine fibroblasts

Abstract

Equine sarcoids represent the most common skin tumours in equids worldwide, characterized by extensive invasion and infiltration of lymphatics, rare regression and high recurrence after surgical intervention. Bovine papillomavirus type-1 (BPV-1) and less commonly BPV-2 are the causative agents of the diseases. It has been demonstrated that BPV-1 viral gene expression is necessary for maintaining the transformation phenotype. However, the underlying mechanism for BPV-1 transformation remains largely unknown, and the cellular factors involved in transformation are not fully understood. Previously mitogen-activated protein kinase (MAPK) signalling pathway has been shown to be important for cellular transformation. This study investigated the role of p38 MAPK (p38) in the transformation of equine fibroblasts by BPV-1. Elevated expression of phosphorylated p38 was observed in BPV-1 expressing fibroblasts due to the expression of BPV-1 E5 and E6. The phosphorylation of the MK2 kinase, a substrate of p38, was also enhanced. Inhibition of p38 activity by its selective inhibitor SB203580 changed cell morphology, reduced the proliferation of sarcoid fibroblasts and inhibited cellular invasiveness, indicating the indispensable role of p38 in BPV-1 transformation of equine fibroblasts. These findings provide new insights into the pathogenesis of equine sarcoids and suggest that p38 could be a potential target for equine sarcoid therapy. INTRODUCTIONEquine sarcoids are the most common fibroblastic skin tumours in equids worldwide (Jackson, 1936;Pascoe & Summers, 1981;Ragland et al., 1970). These tumours can occur as single or multiple lesions in different clinical types including occult, verrucose, nodular, fibroblastic, mixed and malevolent types (Knottenbelt, 2005). Extensive localized infiltration and invasion, rare regression and high recurrence are characteristic of this type of tumour (Knottenbelt, 2005;Martens et al., 2001a;Tarwid et al., 1985). It is now widely accepted that bovine papillomavirus (BPV) types 1 and 2 are the causative agents of sarcoids. Experimental inoculation of equine skin with BPV induces sarcoid-like lesions in horses (Ragland & Spencer, 1969). The viral genome is frequently detected in tumours (Ashrafi et al., 2008; Martens et al., 2001a, b;Nixon et al., 2005;Otten et al., 1993) and its proteins are expressed (Borzacchiello et al., 2008;Carr et al., 2001;Nasir & Reid, 1999;Nixon et al., 2005). It is likely that sarcoidspecific BPV DNA is transmitted between equids by flies (Finlay et al., 2009). The BPV-1 genome isolated from a sarcoid can transform equine fetal fibroblasts and inhibition of viral gene expression by small interfering RNAs (siRNA) reverts the transformed phenotype of sarcoid fibroblasts (Yuan et al., 2008a(Yuan et al., , 2011.While BPV infection plays a major role in the pathogenesis of sarcoid, numerous cellular factors have been shown to be important for initiation and progression of tumours. The downregulation of major histocompatibility complex type I (MHC I) by BPV-1 E5 and...

Bovine papillomavirus: opening new trends for comparative pathology

“…E5 and E6 induce the over-expression of p38 mitogen-activated protein kinase (MAPK) which in turn leads to phosphorylation of an AP-1 component (Fra-1), triggering MMP-1 expression. Both increased proliferation and invasiveness were shown to be mediated by MAPK [40]. The MAPK-AP-1-MMP-1 signalling cascade was thus shown to be involved in the invasiveness of equine sarcoid fibroblasts.…”

Upregulation of equine matrix metalloproteinase 1 by bovine papillomavirus type 1 is through the transcription factor activator protein-1

“…AP-1 is crucial for cellular invasion (Malliri et al, 1998;Ozanne et al, 2007), and inhibition of AP-1 activity can block cell invasion and metastasis (Leaner et al, 2009). In our recent study (Yuan et al, 2011b), we found that p-Fra-1 expression was associated with p38 MAPK activity, and that inhibition of p38 by the inhibitor SB203580 caused abolition of p-Fra-1 expression, a significant decrease in MMP-1 expression and reversion of the transformed phenotype of equine fibroblasts. This finding supports the necessity of AP-1 for the stimulation of MMP-1 and the transformation of equine fibroblasts by BPV-1.…”

The E5 proteins

“…These experiments also demonstrated that transformation required PDGF β receptor kinase activity (Drummond-Barbosa et al, 1995). In addition, transformation of fibroblasts was blocked by pharmacologic inhibition of PDGF receptor enzymatic activity or by genetic manipulations that inhibited expression or activity of the PDGF β receptor or its signaling pathway (Figure 5) (Klein et al, 1998; Lai, Edwards, and DiMaio, 2005; Petti and Ray, 2000; Riese and DiMaio, 1995; Yuan et al, 2011a; Yuan et al, 2011b). …”