HMGCR inhibits the early stage of PCV2 infection, while PKC enhances the infection at the late stage*

Porcine IGFBP3 promotes porcine circovirus type 2 replication via PERK/eIF2α mediated DNA damage

The infection of porcine circovirus type 2 (PCV2) triggers activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway and leads to DNA damage. Insulin-like growth factor-binding protein 3 (IGFBP3) may interact with the endoplasmic reticulum (ER). It remains unclear whether IGFBP3 regulates DNA damage via ER stress to mediate PCV2 replication. In this study, we observed an upregulation of porcine IGFBP3 expression during PCV2 infection, and overexpression of IGFBP3 enhanced the expression of PCV2 Cap protein, PCV2 DNA copy number, and viral titers in PK-15 B6 cells and 3D4/21 cells. Additionally, overexpression of IGFBP3 induced an increase in the DNA damage marker γH2AX by activating the PERK/eIF2α pathway without concomitant activation of ATF4, IRE1α, and ATF6α/GRP78 pathways in PK-15 B6 cells and 3D4/21 cells. Knockdown of IGFBP3 had a reverse effect on PCV2 replication in PK-15 B6 cells and 3D4/21 cells. Furthermore, treatment with etoposide enhanced PCV2 replication while KU57788 decreased it. GSK2606414 and salubrinal limited both DNA damage and viral replication. Therefore, our findings suggest that porcine IGFBP3 promotes PCV2 replication through the PERK/eIF2α pathway-mediated induction of DNA damage in PK-15 B6 cells and 3D4/21 cells. Our study provides a basis for exploring novel antiviral strategies via the extensive understanding of the relationships between host cellular proteins and viral replication.

Advances in Crosstalk between Porcine Circoviruses and Host

Porcine circoviruses (PCVs), including PCV1 to PCV4, are non-enveloped DNA viruses with a diameter of about 20 nm, belonging to the genus Circovirus in the family Circoviridae. PCV2 is an important causative agent of porcine circovirus disease or porcine circovirus-associated disease (PCVD/PCVAD), which is highly prevalent in pigs and seriously affects the swine industry globally. Furthermore, PCV2 mainly causes subclinical symptoms and immunosuppression, and PCV3 and PCV4 were detected in healthy pigs, sick pigs, and other animals. Although the pathogenicity of PCV3 and PCV4 in the field is still controversial, the infection rates of PCV3 and PCV4 in pigs are increasing. Moreover, PCV3 and PCV4 rescued from infected clones were pathogenic in vivo. It is worth noting that the interaction between virus and host is crucial to the infection and pathogenicity of the virus. This review discusses the latest research progress on the molecular mechanism of PCVs–host interaction, which may provide a scientific basis for disease prevention and control.

Porcine TRIM21 Enhances Porcine Circovirus 2 Infection and Host Immune Responses, But Inhibits Apoptosis of PCV2-Infected Cells

Tripartite motif protein 21 (TRIM21) is an interferon-inducible E3 ligase, containing one RING finger domain, one B-box motif, one coiled-coil domain at the N-terminal, as well as one PRY domain and one SPRY domain at the C-terminal. TRIM21 is expressed in many tissues and plays an important role in systemic autoimmunity. However, TRIM21 plays different roles in different virus infections. In this study, we evaluate the relationship between porcine TRIM21 and PCV2 infection as well as host immune responses. We found that PCV2 infection modulated the expression of porcine TRIM21. TRIM21 can enhance interferons and proinflammatory factors and decrease cellular apoptosis in PCV2-infected cells. These results indicate that porcine TRIM21 plays a critical role in enhancing PCV2 infection, which is a promising target for controlling and developing the treatment of PCV2 infection.

Basigin-CyP elevated porcine circovirus type2 replication

Porcine circovirus type2 (PCV2) is a member of the circoviridae family. PCV2 was identified as the main pathogen of postweaning multisystemic wasting syndrome (PMWS) in weaned piglets and causes massive economic loss. Basigin, is a transmembrane glycoprotein belonging to the immunoglobulin superfamily; which is also a receptor for cyclophilins. CyP belongs to the immunophilin family that has peptidyl-prolyl cis-trans isomerase activity. Basigin-CyP interaction affects the replication stages of several viruses. In this study, we found that Basigin could elevate the replication of PCV2, and the Basigin only affected the replication stage rather than adsorption or endocytosis stages. In addition, the ligands of Basigin, CyPA and CyPB also elevated the replication of PCV2. Basigin-CyP interation was necessary for elevating PCV2 replication; At last, CyPs were proved to promote the replication of PCV2 by activating ERK signaling.

Porcine HMGCR Inhibits Porcine Circovirus Type 2 Infection by Directly Interacting with the Viral Proteins

Porcine circovirus type 2 (PCV2) is the etiological agent of porcine circovirus diseases and porcine circovirus-associated diseases (PCVDs/PCVADs). However, the pathogenesis of PCV2 is not fully understood. We previously found that 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is negatively associated with PCV2 infection in vitro and in vivo. HMGCR inhibits the early stages of PCV2 infection, while PCV2 infection induces the phosphorylation of HMGCR to inactivate the protein. In this study, we investigated the possibility that adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK), and protein phosphatase 2 (PP2A) participate in HMGCR-mediated inhibition of PCV2 infection and the interaction of porcine HMGCR with PCV2 proteins. The results showed that AMPK activity fluctuated in cells during the early stage of PCV2 infection, while PP2A had little effect on PCV2 infection and HMGCR activity. Furthermore, PCV2 infection may enhance or maintain the level of phosphorylated HMGCR by directly interacting with the protein in PK-15 cells. These findings may provide a better understanding of PCV2 pathogenesis, and HMGCR may be a novel PCV2 antiviral target.