TRAF2 facilitates Vaccinia virus replication by promoting rapid virus entry.

Tumour necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) is a pivotal intracellular mediator of signalling 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 siRNA 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 JNK signalling 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.