Tumor necrosis factor receptor (TNFR)-associated factor 2 (
TRAF2) is a pivotal intracellular mediator of signaling pathways downstream of
TNFR1 and -2 with known pro- and
antiviral effects. We investigated its role in the replication of the prototype poxvirus vaccinia virus (VACV). Loss of
TRAF2 expression, either through
small interfering RNA treatment of HeLa cells or through genetic knockout in murine embryonic fibroblasts (MEFs), led to significant reductions in VACV growth following low-multiplicity
infection. In single-cycle
infections, there was delayed production of both early and late VACV
proteins as well as accelerated virus-induced alterations to cell morphology, indicating that
TRAF2 influences early stages of virus replication. Consistent with an early role, uncoating assays showed normal virus attachment but delayed virus entry in the absence of
TRAF2. Although alterations to
c-Jun N-terminal kinase (JNK) signaling were apparent in VACV-infected
TRAF2(-/-) MEFs, treatment of wild-type cells with a JNK inhibitor did not affect virus entry. Instead, treatment with an inhibitor of endosomal acidification greatly reduced virus entry into
TRAF2(-/-) MEFs, suggesting that VACV is reliant on the endosomal route of entry in the absence of
TRAF2. Thus,
TRAF2 is a proviral factor for VACV that plays a role in promoting efficient viral entry, most likely via the plasma membrane.
IMPORTANCE:
Tumor necrosis factor receptor-associated factors (TRAFs) are key facilitators of intracellular signaling with roles in innate and adaptive immunity and stress responses. We have discovered that
TRAF2 is a proviral factor in vaccinia virus replication in both HeLa cells and mouse embryonic fibroblasts and that its influence is exercised through promotion of efficient virus entry.