title: Protein Kinase R Degradation Is Essential for Rift Valley Fever Virus Infection and Is Regulated by SKP1-CUL1-F-box (SCF)FBXW11-NSs E3 Ligase.
abstract: Activated protein kinase R (PKR) plays a vital role in antiviral defense primarily by inhibiting protein synthesis and augmenting interferon responses. Many viral proteins have adopted unique strategies to counteract the deleterious effects of PKR. The NSs (Non-structural s) protein which is encoded by Rift Valley fever virus (RVFV) promotes early PKR proteasomal degradation through a previously undefined mechanism. In this study, we demonstrate that NSs carries out this activity by assembling the SCF (SKP1-CUL1-F-box)(FBXW11) E3 ligase. NSs binds to the F-box protein, FBXW11, via the six amino acid sequence DDGFVE called the degron sequence and recruits PKR through an alternate binding site to the SCF(FBXW11) E3 ligase. We further show that disrupting the assembly of the SCF(FBXW11-NSs) E3 ligase with MLN4924 (a small molecule inhibitor of SCF E3 ligase activity) or NSs degron viral mutants or siRNA knockdown of FBXW11 can block PKR degradation. Surprisingly, under these conditions when PKR degradation was blocked, NSs was essential and sufficient to activate PKR causing potent inhibition of RVFV infection by suppressing viral protein synthesis. These antiviral effects were antagonized by the loss of PKR expression or with a NSs deleted mutant virus. Therefore, early PKR activation by disassembly of SCF(FBXW11-NSs) E3 ligase is sufficient to inhibit RVFV infection. Furthermore, FBXW11 and BTRC are the two homologues of the βTrCP (Beta-transducin repeat containing protein) gene that were previously described to be functionally redundant. However, in RVFV infection, among the two homologues of βTrCP, FBXW11 plays a dominant role in PKR degradation and is the limiting factor in the assembly of the SCF(FBXW11) complex. Thus, FBXW11 serves as a master regulator of RVFV infection by promoting PKR degradation. Overall these findings provide new insights into NSs regulation of PKR activity and offer potential opportunities for therapeutic intervention of RVFV infection.
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.
authors.forename: Rajini
authors.initials: R
authors.lastname: Mudhasani
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.
authors.forename: Julie P
authors.initials: JP
authors.lastname: Tran
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.
authors.forename: Cary
authors.initials: C
authors.lastname: Retterer
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.|Perkin Elmer, Waltham, Massachusetts, United States of America.
authors.forename: Krishna P
authors.initials: KP
authors.lastname: Kota
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.
authors.forename: Chris A
authors.initials: CA
authors.lastname: Whitehouse
authors.affiliation: Molecular and Translational Sciences Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, United States of America.
authors.forename: Sina
authors.initials: S
authors.lastname: Bavari
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002460:Cell Line; D044842:Cullin Proteins / Q000378:metabolism; D044783:F-Box Proteins / Q000378:metabolism*; D005809:Genes, Regulator / Q000235:genetics; D006801:Humans; D010766:Phosphorylation / Q000235:genetics; D012296:Rift Valley fever virus; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D014779:Virus Replication / Q000235:genetics*
chemical_list: D000998:Antiviral Agents; C100318:Cullin 1; D044842:Cullin Proteins; D044783:F-Box Proteins; D017361:Viral Nonstructural Proteins; D044767:Ubiquitin-Protein Ligases
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