Swine Promyelocytic Leukemia Isoform II Inhibits Pseudorabies Virus Infection by Suppressing Viral Gene Transcription in PML-NBs

Abstract

22Promyelocytic leukaemia nuclear bodies (PML-NBs) possess an important intrinsic 23 antiviral activity against a-herpesvirus infection. PML is the structural backbone of 24 NBs, comprising different isoforms. However, the contribution of each isoform to 25 a-herpesvirus restriction is not well understood. Here, we report the role of PML-26NBs and swine PML (sPML) isoforms in pseudorabies virus (PRV) infection in its 27 natural host swine cells. We found that sPML-NBs exhibit an anti-PRV activity in 28 the context of increasing the expression level of endogenous sPML. Of four sPML 29 isoforms cloned and examined, only isoform sPML-II/IIa, not sPML-I and IVa, 30 expressed in a sPML knockout cells inhibits PRV infection. Both the unique 7b 31 region of sPML-II and sumoylation-dependent normal formation of PML-NBs are 32 required. 7b possesses a transcriptional repression activity and suppresses viral 33 gene transcription during PRV infection with the cysteine residue 589 and 599 34 being critically involved. We conclude that sPML-NBs inhibit PRV infection by 35 repressing viral gene transcription through the 7b region of sPML-II. 36 IMPORTANCE 37PML-NBs are nuclear sites that mediate the antiviral restriction of a-herpesvirus 38 gene expression and replication. However, the contrition of each PML isoform to 39 this activity of PML-NBs is not well characterized. Using PRV and its natural host 40 swine cells as a system, we have discovered that the unique C-terminus of sPML 41 isoform II is required for PML-NBs to inhibit PRV infection by directly engaging in 42 repression of viral gene transcription. Our study not only confirms in swine cells 43 that PML-NBs have an anti-viral function, but also presents a mechanism to 44 suggest that PML-NBs inhibit viral infection in an isoform specific manner. 45 MATERIALS AND METHODS 108Cell culture and viruses 109