title: Vaccinia virus F1L protein promotes virulence by inhibiting inflammasome activation.
abstract: Host innate immune responses to DNA viruses involve members of the nucleotide-binding domain, leucine-rich repeat and pyrin domain containing protein (NLRP) family, which form "inflammasomes" that activate caspase-1, resulting in proteolytic activation of cytokines interleukin (IL)-1β and IL-18. We hypothesized that DNA viruses would target inflammasomes to overcome host defense. A Vaccinia virus (VACV) B-cell CLL/lymphoma 2 (Bcl-2) homolog, F1L, was demonstrated to bind and inhibit the NLR family member NLRP1 in vitro. Moreover, infection of macrophages in culture with virus lacking F1L (ΔF1L) caused increased caspase-1 activation and IL-1β secretion compared with wild-type virus. Virulence of ΔF1L virus was attenuated in vivo, causing altered febrile responses, increased proteolytic processing of caspase-1, and more rapid inflammation in lungs of infected mice without affecting cell death or virus replication. Furthermore, we found that a hexapeptide from F1L is necessary and sufficient for inhibiting the NLRP1 inflammasome in vitro, thus identifying a peptidyl motif required for binding and inhibiting NLRP1. The functional importance of this NLRP1-binding motif was further confirmed by studies of recombinant ΔF1L viruses reconstituted either with the wild-type F1L or a F1L mutant that fails to bind NLRP1. Cellular infection with wild-type F1L reconstituted virus-suppressed IL-1β production, whereas mutant F1L did not. In contrast, both wild-type and mutant versions of F1L equally suppressed apoptosis. In vivo, the NLR nonbinding F1L mutant virus exhibited an attenuated phenotype similar to ΔF1L virus, thus confirming the importance of F1L interactions with NLRP1 for viral pathogenicity in mice. Altogether, these findings reveal a unique viral mechanism for evading host innate immune responses.
authors.affiliation: Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Motti
authors.initials: M
authors.lastname: Gerlic
authors.forename: Benjamin
authors.initials: B
authors.lastname: Faustin
authors.forename: Antonio
authors.initials: A
authors.lastname: Postigo
authors.forename: Eric Chi-Wang
authors.initials: EC
authors.lastname: Yu
authors.forename: Martina
authors.initials: M
authors.lastname: Proell
authors.forename: Naran
authors.initials: N
authors.lastname: Gombosuren
authors.forename: Maryla
authors.initials: M
authors.lastname: Krajewska
authors.forename: Rachel
authors.initials: R
authors.lastname: Flynn
authors.forename: Michael
authors.initials: M
authors.lastname: Croft
authors.forename: Michael
authors.initials: M
authors.lastname: Way
authors.forename: Arnold
authors.initials: A
authors.lastname: Satterthwait
authors.forename: Robert C
authors.initials: RC
authors.lastname: Liddington
authors.forename: Shahram
authors.initials: S
authors.lastname: Salek-Ardakani
authors.forename: Shu-ichi
authors.initials: S
authors.lastname: Matsuzawa
authors.forename: John C
authors.initials: JC
authors.lastname: Reed
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D020169:Caspases / Q000378:metabolism; D002522:Chlorocebus aethiops; D016207:Cytokines / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007113:Immunity, Innate; D058847:Inflammasomes / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D010641:Phenotype; D011994:Recombinant Proteins / Q000378:metabolism; D014616:Vaccinia virus / Q000378:metabolism*; D014709:Vero Cells; D014764:Viral Proteins / Q000378:metabolism*; D014774:Virulence
chemical_list: D016207:Cytokines; C507356:F1L protein, vaccinia virus; D058847:Inflammasomes; D053583:Interleukin-1beta; D011994:Recombinant Proteins; D014764:Viral Proteins; D020169:Caspases
keywords: innate immunity; poxviruses; virology; virus infection