Porcine Circovirus Type 3 Cap Inhibits Type I Interferon Induction Through Interaction With G3BP1.

Pengfei Zhang,Xianhui Liu,Hanqin Shen,Zheng Xu,Yanling Liu,Changxu Song,Shuangyun Wang

doi:10.3389/fvets.2020.594438

Pengfei Zhang, Xianhui Liu + Show 5 more

Open Access

https://doi.org/10.3389/fvets.2020.594438

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Abstract

Porcine circovirus 3 (PCV3) infections cause clinical diseases similar to those seen in porcine circovirus 2 (PCV2) infections. It is unclear whether PCV3 infections can also cause immunosuppression like that seen with PCV2. Here, we report that Cap inhibits DNA-induced IFN-β mRNA transcription and IFN promoter activation. Cap was also found to inhibit cyclic GMP-AMP (cGAMP) synthase (cGAS) binding to interferon-stimulating DNA (ISD). Immunoprecipitation and mass spectrometry were used to identify cellular interaction partners of Cap. Cap interacted with G3BP1 and inhibited the interaction between GTPase-activating protein-(SH3 domain)-binding protein 1 (G3BP1) and cGAS. Furthermore, the destruction of endogenously expressed G3BP1 by siRNA significantly reduced IFN promoter activation, and phosphorylation of tank-binding kinase 1 (TBK1) was induced by ISD. Overexpression of G3BP1 attenuated the inhibition of ISD binding of cGAS by Cap and promoted phosphorylation of TBK1 and IRF3 induced by ISD. Collectively, our results show that the interaction between Cap and G3BP1 prevents cGAS from recognizing DNA, thereby inhibiting the IFN production.

Highlights

Porcine circovirus 3 (PCV3), a DNA virus, has a genome of only 2 kb in size with two main open reading frames (ORFs) encoding the replicase protein and capsid (Cap) protein [1]
At 24 hpt, cells were transfected with 2 μg/ml of interferon-stimulating DNA (ISD) for another 6 h, total cellular RNA was extracted, and IFN-β mRNA levels were quantified by realtime PCR
The results showed that ISD and Poly significantly enhanced the activity of the IFN promoter, but overexpression of Cap significantly suppressed the IFN promoter activity induced by DNA [ISD and Poly], and the effect was dose dependent (Figures 1B–D)

Summary

Introduction

Porcine circovirus 3 (PCV3), a DNA virus, has a genome of only 2 kb in size with two main open reading frames (ORFs) encoding the replicase protein and capsid (Cap) protein [1]. In 2015, a third disease, PCV3, was first identified in the USA from a case of PDNS [7]. PCV3 has been reported in multiple countries, where it is often associated with PDNS, multisystemic inflammation, congenital tremors, and respiratory disease [8,9,10,11,12]. In 2019, porcine circovirus 4 (PCV4) was detected in diseased pigs with PDNS, respiratory, and enteric signs [13]. PCV3 was detected in a coinfection with PCV2 and porcine epidemic diarrhea virus from a severe case of diarrheal disease in China, and the authors reported a triple infection rate of 48.68% [14]. Recent reports suggest that more attention should be given to PCV3-associated disease

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