Swine Promyelocytic Leukemia Isoform II Inhibits Pseudorabies Virus Infection by Suppressing Viral Gene Transcription in Promyelocytic Leukemia Nuclear Bodies

Abstract

<jats:p>Promyelocytic leukaemia nuclear bodies (PML-NBs) possess an important intrinsic antiviral activity against α-herpesvirus infection. PML is the structural backbone of NBs, comprising different isoforms. However, the contribution of each isoform to α-herpesvirus restriction is not well understood. Here, we report the role of PML-NBs and swine PML (sPML) isoforms in pseudorabies virus (PRV) infection in its natural host swine cells. We found that sPML-NBs exhibit an anti-PRV activity in the context of increasing the expression level of endogenous sPML. Of four sPML isoforms cloned and examined, only isoform sPML-II/IIa, not sPML-I and IVa, expressed in a sPML knockout cells inhibits PRV infection. Both the unique 7b region of sPML-II and sumoylation-dependent normal formation of PML-NBs are required. 7b possesses a transcriptional repression activity and suppresses viral gene transcription during PRV infection with the cysteine residue 589 and 599 being critically involved. We conclude that sPML-NBs inhibit PRV infection partly by repressing viral gene transcription through the 7b region of sPML-II.</jats:p> <jats:p><jats:bold>IMPORTANCE</jats:bold> PML-NBs are nuclear sites that mediate the antiviral restriction of α-herpesvirus gene expression and replication. However, the contribution of each PML isoform to this activity of PML-NBs is not well characterized. Using PRV and its natural host swine cells as a system, we have discovered that the unique C-terminus of sPML isoform II is required for PML-NBs to inhibit PRV infection by directly engaging in repression of viral gene transcription. Our study not only confirms in swine cells that PML-NBs have an anti-viral function, but also presents a mechanism to suggest that PML-NBs inhibit viral infection in an isoform specific manner.</jats:p>

Molecular Cloning of Alternative Splicing Variants of the Porcine PML Gene and Its Expression Patterns During Japanese Encephalitis Virus Infection

“…PML-7 contained exons 1–4 and retained a partial sequence of intron 4 (4a: 540–865 bp), and it encoded a product of only 420 amino acids. The PML-1 and PML-3 alternative splicing variants cloned here were the same as sPML-I and sPML-II cloned in a previous study ( 20 ).…”

“…Therefore, the differences in the C-terminal sequences result in different biological functions of each PML isoform ( 19 ). Recently, based on the predicted cDNA sequences through analysis of the human and swine PML gene sequence, four porcine PML isoforms were cloned by PCR using the cDNAs generated from IFNα-stimulated PK15 cells as templates ( 20 ). However, there may be other porcine PML isoforms produced by alternative splicing.…”

A Tug of War: Pseudorabies Virus and Host Antiviral Innate Immunity

“…The nuclear domain 10 (ND10) complex consists of three key components, namely, promyelocytic leukemia antigen (PML), speckled protein of 100 kDa (Sp100), and human death domain-associated protein 6 (hDaxx) [ 98 , 99 ]. Yu et al found that promyelocytic leukemia nuclear bodies (PML-NBs) inhibit PRV infection by directly engaging in the repression of viral gene transcription [ 100 ]. Everett et al found that PRV EP0 induces a reduction in the SUMO-modified forms but not the other isoforms of PML.…”

Evasion of I Interferon-Mediated Innate Immunity by Pseudorabies Virus

“…They can inhibit viral replication through multiple mechanisms such as suppressing viral gene transcription and inducing epigenetic silence of viral genomes ( Everett and Chelbi-Alix, 2007 ; Geoffroy and Chelbi-Alix, 2011 ; Alandijany et al, 2018 ). We have recently reported that swine PML-NBs also inhibit PRV replication ( Yu et al, 2020 ). PML is IFN induced protein.…”

“…Indeed, in PML knockout cells, the difference in the sensitivity to IFN between PRV-EP0 and PRV-WT is reduced. However, PRV-EP0 is still more sensitive to IFN treatment, indicating other mechanisms are also involved ( Yu et al, 2020 ).…”