A Point Mutation, E95D, in the Mumps Virus V Protein Disengages STAT3 Targeting from STAT1 Targeting

Abstract

Mumps virus, like other paramyxoviruses in the Rubulavirus genus, encodes a V protein that can assemble a ubiquitin ligase complex from cellular components, leading to the destruction of cellular signal transducer and activator of transcription (STAT) proteins. While many V proteins target the interferon-activated STAT1 or STAT2 protein, mumps virus V protein is unique in its ability to also target STAT3 for ubiquitin modification and proteasome-mediated degradation. Here we report that a single amino acid substitution in the mumps virus V protein, E95D, results in defective STAT3 targeting while maintaining the ability to target STAT1. Results indicate that the E95D mutation disrupts the ability of the V protein to associate with STAT3. A recombinant mumps virus carrying the E95D mutation in its P and V proteins replicates normally in cultured cells but fails to induce targeting of STAT3. Infection with the recombinant virus results in the differential regulation of a number of cellular genes compared to wild-type mumps virus and increases cell death in infected cells, producing a large-plaque phenotype.

Ubiquitination-mediated regulation of interferon responses

“…For example, accelerated turnover of STAT1 is triggered by infection with Sendai virus (24), paramixoviruses (76, 77), and mumps virus (62, 78, 85). STAT2 appears to be a target of ubiquitin-mediated proteasomal degradation stimulated by human cytomegalovirus (42, 75), respiratory syncytial virus (19, 66, 71), paramyxoviruses (61, 76, 77) and Dengue virus (2) among others.…”

Paramyxovirus evasion of innate immunity: Diverse strategies for common targets

“…The MuV V protein VDC polyubiquitinates and degrades not only STAT1, but also STAT3 [84,99] , such that MuV V protein can inhibit STAT3-dependent transcriptional activation by IL-6 and v-Src [99] . MuV targeting of STAT3 is independent of STAT1 targeting, as a point mutation abrogating targeting of STAT3 did not affect STAT1 [100] , and STAT3 degradation does not require the STAT2 "cofactor" [99] . STAT3 targeting by the V protein of MuV is also highly specific to this species, as the V proteins of the rubulaviruses MPRV, hPIV2 and hPIV4 do not reduce cellular levels of STAT3 [87,101,102] .…”

“…MeV V also interacts with IRF-9, which is likely to affect ISGF3 formation ( Figure 4) [104] , and with STAT3 [104] , a property thus far restricted in the paramyxovirus family to MeV and MuV V proteins [99,100,104,110] . HeV V and PIV5 V have been shown to lack STAT3 binding function, and while SeV infection can inhibit IFNα-dependent STAT3 phosphorylation, this appears to relate to upstream effects on Tyk2 rather than STAT3 directly [111] .…”

The V Protein of Tioman Virus Is Incapable of Blocking Type I Interferon Signaling in Human Cells

“…In contrast, hPIV2 V protein uses STAT1 as an adaptor to target STAT2 for degradation (although in some cases it can directly target STAT1 for degradation) [23], [25], [26], [27]. MuV-V has also evolved a distinct binding interface to recruit directly STAT3 for ubiquitination and degradation [28], [29], resulting in the inhibition of IL-6 signaling, another pathway involved in the host antiviral response. Alike MuV-V, the V protein of TioV (TioV-V) has been shown to bind MDA5 and LGP2, thus inhibiting IFN induction by viral RNA molecules [10], [13].…”