White Spot Syndrome Virus IE1 and WSV056 Modulate the G ₁ /S Transition by Binding to the Host Retinoblastoma Protein

Abstract

c DNA viruses often target cellular proteins to modulate host cell cycles and facilitate viral genome replication. However, whether proliferation of white spot syndrome virus (WSSV) requires regulation of the host cell cycle remains unclear. In the present study, we show that two WSSV paralogs, IE1 and WSV056, can interact with Litopenaeus vannamei retinoblastoma (Rb)-like protein (lv-RBL) through the conserved LxCxE motif. Further investigation revealed that IE1 and WSV056 could also bind to Drosophila retinoblastoma family protein 1 (RBF1) in a manner similar to how they bind to lv-RBL. Using the Drosophila RBF-E2F pathway as a model system, we demonstrated that both IE1 and WSV056 could sequester RBF1 from Drosophila E2F transcription factor 1 (E2F1) and subsequently activate E2F1 to stimulate the G 1 /S transition. Our findings provide the first evidence that WSSV may regulate cell cycle progression by targeting the Rb-E2F pathway. White spot syndrome virus (WSSV), the only species of the genus Whispovirus, family Nimaviridae, is a major pathogen of shrimp. It is a large double-stranded DNA virus with a broad host range among crustaceans (1). Although WSSV was first discovered 20 years ago, the mechanism by which this virus modulates cellular pathways during infection remains to be explored.The immediate early (IE) genes of DNA viruses encode regulatory proteins critical for the initiation of primary infection and the switch from latent to lytic infection (2). Twenty-one IE genes have been identified from WSSV so far (3-5). IE1 is the most studied WSSV IE protein. It has been found to exhibit transactivation and DNA-binding activities (6), suggesting that it has a role as a transcription factor. Based on detailed mapping of IE1 promoters, progress has been made in understanding the cellular regulation of IE1 expression. Several transcription factors have been found to affect IE transcription, including shrimp homologs of STAT (7, 8), NF-B (9, 10), and a TATA box binding protein (11). JAK-STAT and NF-B pathways are believed to be critical for antiviral defense (12, 13); therefore, the findings for WSSV indicate that this virus takes advantage of the host immune system to assist its own proliferation. The biological significance of IE1 during WSSV infection was demonstrated by RNA interference experiments which revealed that depletion of IE1 strongly inhibits the replication of WSSV (11). A recent report showed that the shrimp thioredoxin PmTrx can bind to IE1 and restore its DNAbinding activity under oxidizing conditions, indicating a role for IE1 in WSSV pathogenicity (14). However, since little is known about the targets (proteins or genes) of IE1, how this viral protein functions during infection remains unknown.Interestingly, a new member of the WSSV IE proteins, WSV056 (5), is highly homologous to IE1 in its amino acid sequence, implying a potential similarity in function. Further analysis showed that both of the proteins contain a conserved LxCxE motif at the C terminus, which is characteristic of prote...

The interaction of nonstructural protein 9 with retinoblastoma protein benefits the replication of genotype 2 porcine reproductive and respiratory syndrome virus in vitro

“…A conserved motifll-cycle regulating proteins. lar proteins to modulate in the Nsp9-overexpressing cells byRNAdependent RNA polymerases (Bhardwaj et al, 2012;Corbeil and Branton, 1994;Munakata et al, 2005Munakata et al, , 2007; Ran et al, 2013). We found the presence of a conserved motif-LACAE in the Nsp9 of genotype 2 PRRSV by aligning the amino acid sequences of the Nsp9 among 17 representative strains of genotype 2 PRRSV.…”

Molecular Mechanisms of White Spot Syndrome Virus Infection and Perspectives on Treatments

“…Different viruses exploit different phases of the host cell cycle for viral genome replication. Some arrest cells in G0, G1, or at the G1/S boundary so host DNA replication is prevented, whereas others tend to favor the S-phase where host DNA replication machinery is widely available [ 117 ]. Those that arrest host cells in G0/G1/G1/S, which include the herpes simplex virus and Epstein–Barr virus, often carry DNA replication machinery in their genomes instead of relying on the host [ 117 , 154 , 155 ].…”

Spring Viremia of Carp Virus N Protein Suppresses Fish IFNφ1 Production by Targeting the Mitochondrial Antiviral Signaling Protein

“…In aquaculture, a number of viruses have been identified as the etiological agents of aquatic animal diseases (16), however, the mechanism(s) used by aquatic viruses to escape the host IFN system are still unclear. Spring viremia of carp virus (SVCV) is the causative agent of SVC and causes significant mortality in common carp (Cyprinus carpio).…”