Porcine reproductive and respiratory syndrome virus (PRRSV)
infection eliminates production of
type I interferons (IFNs) in host cells, which triggers an
antiviral immune response through the induction of downstream IFN-stimulated genes (ISGs), thus escaping the fate of host-mediated clearance. The IFN-induced transmembrane 3 (IFITM3) has recently been identified as an ISG and plays a pivotal role against enveloped RNA viruses by restricting cell entry. However, the role of IFITM3 in PRRSV replication is unknown. The present study demonstrated that overexpression of IFITM3 suppresses PRRSV replication, while silencing of endogenous IFITM3 prominently promoted PRRSV replication. Additionally, it was shown that IFITM3 undergoes S-palmitoylation and ubiquitination modification, and both posttranslational modifications contribute to the anti-PRRSV activity of IFITM3. Further study showed that PRRSV particles are transported into endosomes and then into lysosomes during the early stages of
infection, and confocal microscopy results revealed that PRRSV particles are transported to IFITM3-positive cellular vesicles. By using a single virus particle fluorescent labeling technique, we confirmed that IFITM3 can restrict PRRSV membrane fusion by inducing accumulation of
cholesterol in cellular vesicles. Additionally, we found that both endogenous and exogenous IFITM3 are incorporated into newly producing
PRRS virions and diminish viral intrinsic infectivity. By using cell coculture systems, we found that IFITM3 effectively restricted PRRSV intercellular transmission, which may have been caused by disrupted membrane fusion and reduced viral infectivity. In conclusion, our results demonstrate, for the first time, that swine IFITM3 interferes with the life cycle of PRRSV, and possibly other enveloped
arteritis viruses, at multiple steps.IMPORTANCE
Porcine reproductive and respiratory syndrome (
PRRS), which is caused by
PRRS virus (PRRSV), is of great economic significance to the swine industry. Due to the complicated immune escape mechanisms of PRRSV, there are no effective
vaccines or therapeutic drugs currently available against
PRRS. Identification of cellular factors and underlying mechanisms that establish an effective
antiviral state against PRRSV can provide unique strategies for developing
antiviral vaccines or drugs. As an
interferon (IFN)-stimulated gene, the role of IFN-induced transmembrane 3 (IFITM3) in PRRSV
infection has not been reported as of yet. In the present study, it was shown that IFITM3 can exert a potent anti-PRRSV effect, and
PRRS virions are trafficked to IFITM3-containing cell vesicles, where viral membrane fusion is impaired by
cholesterol accumulation that is induced by IFITM3. Additionally, both endogenous and exogenous IFITM3 are incorporated into newly assembled progeny virions, and this decreased their intrinsic infectivity.