Classical swine fever virus (CSFV) is the causative agent of classical swine fever (CSF), a highly contagious, economically important viral disease in many countries. The E rns and E2 envelope glycoproteins are responsible for the binding to and entry into the host cell by CSFV. To date, only one cellular receptor, heparan sulfate (HS), has been identified as being involved in CSFV attachment. HS is also present on the surface of various cells that are nonpermissive to CSFV. Hence, there must be another receptor(s) that has been unidentified to date. In this study, we used a set of small interfering RNAs (siRNAs) against a number of porcine cell membrane protein genes to screen cellular proteins involved in CSFV infection. This approach resulted in the identification of several proteins, and of these, the laminin receptor (LamR) has been demonstrated to be a cellular receptor for several viruses. Confocal analysis showed that LamR is colocalized with CSFV virions on the membrane, and a coimmunoprecipitation assay indicated that LamR interacts with the CSFV E rns protein. In inhibition assays, anti-LamR antibodies, soluble laminin, or LamR protein significantly inhibited CSFV infection in a dose-dependent manner. Transduction of PK-15 cells with a recombinant lentivirus expressing LamR yielded higher viral titers. Moreover, an attachment assay demonstrated that LamR functions during virus attachment. We also demonstrate that LamR acts as an alternative attachment receptor, especially in SK6 cells. These results indicate that LamR is a cellular attachment receptor for CSFV. IMPORTANCE Classical swine fever virus (CSFV) is the causative agent of classical swine fever (CSF), an economically important viral disease affecting the pig industry in many countries. To date, only heparan sulfate (HS) has been identified to be an attachment receptor for CSFV. Here, using RNA interference screening with small interfering RNAs (siRNAs) against a number of porcine membrane protein genes, we identified the laminin receptor (LamR) to be another attachment receptor. We demonstrate the involvement of LamR together with HS in virus attachment, and we elucidate the relationship between LamR and HS. LamR also serves as an attachment receptor for many viral pathogens, including dengue virus, a fatal human flavivirus. The study will help to enhance our understanding of the life cycle of flaviviruses and the development of antiviral strategies for flaviviruses. C lassical swine fever virus (CSFV) is the causative agent of classical swine fever (CSF), a highly contagious and often fatal viral disease in pigs. The disease leads to significant economic losses in many countries. CSFV is a member of the Pestivirus genus within the Flaviviridae family (1). The virus possesses a singlestranded, positive-sense RNA genome of approximately 12.3 kb (2, 3). Its genome contains a single, large open reading frame that encodes a precursor polyprotein of 3,898 amino acids (aa). The polyprotein is co-and posttranslationally processed by viral an...

The mechanisms on metabolic regulation of immune responses are still elusive. We show here that viral infection induces immediate-early NF-κB activation independent of viral nucleic acid-triggered signaling, which triggers a rapid transcriptional induction of bile acid (BA) transporter and rate-limiting biosynthesis enzymes as well as accumulation of intracellular BAs in divergent cell types. The accumulated intracellular BAs activate SRC kinase via the TGR5-GRK-β-arrestin axis, which mediates tyrosine phosphorylation of multiple antiviral signaling components including RIG-I, VISA/MAVS, MITA/STING, TBK1 and IRF3. The tyrosine phosphorylation of these components by SRC conditions for efficient innate antiviral immune response. Consistently, TGR5 deficiency impairs innate antiviral immunity, whereas BAs exhibit potent antiviral activity in wild-type but not TGR5-deficient cells and mice. Our findings reveal an intrinsic and universal role of intracellular BA metabolism in innate antiviral immunity.

The E2 protein of classical swine fever virus (CSFV) is an envelope glycoprotein that is involved in virus attachment and entry. To date, the E2-interacting cellular proteins and their involvement in viral replication have been poorly documented. In this study, thioredoxin 2 (Trx2) was identified to be a novel E2-interacting partner using yeast two-hybrid screening from a porcine macrophage cDNA library. Trx2 is a mitochondrion-associated protein that participates in diverse cellular events. The Trx2-E2 interaction was further confirmed by glutathione S-transferase (GST) pulldown, in situ proximity ligation, and laser confocal assays. The thioredoxin domain of Trx2 and the asparagine at position 37 (N37) in the E2 protein were shown to be critical for the interaction. C lassical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly contagious, often fatal porcine disease with significant economic losses. CSFV belongs to the Pestivirus genus within the Flaviviridae family (1). It is an enveloped virus with a single-stranded, positive-sense RNA genome of approximately 12.3 kb in length. The RNA genome contains a single large open reading frame (ORF). This ORF is translated into a polyprotein, which is further processed into 12 mature proteins (N pro -C-E rns -E1-E2-p7-NS2-3-NS4A-NS4B-NS5A-NS5B) by viral and cellular proteases (2). The C, E rns , E1, and E2 proteins represent the structural components of the virion. The E1 and E2 glycoproteins are anchored to the envelope by their carboxyl termini, while E rns is loosely associated with the envelope. E rns presents as homodimers linked by disulfide bridges in virus-infected cells and in virions (3, 4). The C terminus of E2 functions as a membrane-spanning domain anchoring the E2-E1 or E2-E2 dimer to the viral envelope (5). E2 is also involved in virus attachment to and entry into the target cell (6). Furthermore, as a virulence determinant in pigs (7), the E2 protein can efficiently induce protective immune responses (8-13). Additionally, we recently showed that host ␤-actin interacts with E2 and modulates the early life cycle of CSFV (14).Thioredoxins (Trxs) are a class of ubiquitously expressed redox proteins that contain a conserved consensus amino acid sequence (Cys-Gly-Pro-Cys) in the catalytic center. There are two distinct forms of Trxs (Trx1 and Trx2), which act as antioxidants facilitating the reduction of other proteins by cysteine thiol-disulfide exchange. Trx2 consists of 157 amino acid (aa) residues, and its thioredoxin domain is located in the C terminus of the protein.Trxs are involved in diverse biological processes, such as cell growth, proliferation, apoptosis, and gene regulation (15-18). Additionally, they interact with several transcription factors and