Bovine Delta papillomavirus E5 oncoprotein interacts with TRIM25
and hampers antiviral innate immune response mediated by RIG-I-like
receptors
Running title: E5 oncoprotein impairs RLR-mediated host antiviral
defence
Francesca De Falco1, Anna
Cutarelli2, Ivan Gentile3,
Pellegrino Cerino2, Valeria Uleri1,
Adriana Florinela Catoi4, Sante
Roperto1
1Dipartimento di Medicina Veterinaria e Produzioni
Animali, Università degli Studi di Napoli Federico II, Napoli, Italia
2 Istituto Zooprofilattico Sperimentale del
Mezzogiorno, Portici, Napoli, Italia
3 Dipartimento di Medicina Clinica e Chirurgia,
Università degli Studi di Napoli Federico II, Napoli, Italia
4 Physiopathology Department, Faculty of Medicine
“Iuliu Hatieganu”, University of Medicine and Pharmacy, Cluj-Napoca,
Romania.
Correspondence: Sante Roperto, Dipartimento di Medicina Veterinaria e
Produzioni Animali, Università degli Studi di Napoli Federico II,
Napoli, Italia. E-mail: sante.roperto@unina.it
Abstract – Persistent
infection and tumourigenesis by papillomaviruses (PVs) require viral
manipulation of various of cellular processes, including those involved
in innate immune responses. Herein, we showed that bovine PV (BPV) E5
oncoprotein interacts with a tripartite motif-containing 25 (TRIM25) but
not with Riplet in spontaneous BPV infection of urothelial cells of
cattle. Statistically significant reduced protein levels of TRIM25,
retinoic acid-inducible gene I (RIG-I), and melanoma
differentiation-associated gene 5 (MDA5) were detected by Western blot
analysis. Real-time quantitative PCR revealed marked transcriptional
downregulation of RIG-I and MDA5 in E5-expressing cells compared with
healthy urothelial cells. Mitochondrial antiviral signalling (MAVS)
protein expression did not vary significantly between diseased and
healthy cells. Co-immunoprecipitation studies showed that MAVS
interacted with a protein network composed of Sec13, which is a positive
regulator of MAVS-mediated RLR antiviral signalling, phosphorylated TANK
binding kinase 1 (TBK1), and phosphorylated interferon regulatory factor
3 (IRF3). Immunoblotting revealed significantly low expression levels of
Sec13 in BPV-infected cells. Low levels of Sec13 resulted in a weaker
host antiviral immune response, as it attenuates MAVS-mediated IRF3
activation. Furthermore, western blot analysis revealed significantly
reduced expression levels of pTBK1, which plays an essential role in the
activation and phosphorylation of IRF3, a prerequisite for the latter to
enter the nucleus to activate type 1 IFN genes. Our results suggested
that the innate immune signalling pathway mediated by RIG-I-like
receptors (RLRs) was impaired in cells infected with BPVs. Therefore, an
effective immune response is not elicited against these viruses, which
facilitates persistent viral infection.
Keywords: bovine papillomavirus E5 oncoprotein; melanoma
differentiation-associated gene 5 (MDA5); mitochondrial
antiviral-signalling (MAVS) protein; retinoic acid-inducible gene I
(RIG-I), Tripartite motif containing 25 (TRIM25).