Sodium Tanshinone IIA Sulfonate Inhibits the MEQ, Ul49 and VP22 Expression of Marek's Disease Virus

Our previous studies have demonstrated that sodium tanshinone IIA sulfonate (STS), a natural compound derived from Salviae Miltiorrhizae Radix et Rhizoma (Danshen), could effectively inhibit Marek's disease virus (MDV) infection both in vitro and in vivo, but the underlying mechanisms remain unclear. The main objective of the study was to explore the effect of STS on the meq, ul49 and VP22 expression of MDV in vitro.Quantitative real-time PCR (qRT-PCR) was used to analyse the effect of STS on meq and ul49 expression at both the DNA and messenger RNA (mRNA) level, and the effect of STS on VP22 was assessed by immunofluorescence assay and western blotting.The DNA and mRNA copy numbers of meq and ul49 significantly decreased in the groups treated with STS compared with MDV control (P<0.05), which indicated that STS could inhibit the expression of meq and ul49 at both the DNA and mRNA level. Moreover, the expression of VP22 encoded by ul49 was also significantly inhibited (P<0.05).STS possessed anti-MDV activity in chicken embryo fibroblasts. Its antiviral mechanisms may be ascribed to inactivating MDV directly, disturbing meq and ul49 replication and inhibiting the expression of VP22 encoded by ul49. These results suggested that STS is a promising natural compound to be further developed as an antiviral agent against MDV infection.