Recombinant Myxoma Virus Expressing Walleye Dermal Sarcoma Virus orfC Is Attenuated in Rabbits

The poxvirus, myxoma virus (MYXV) has shown efficacy as an oncolytic virus (OV) in some cancer models. However, MYXV replication within murine cancer models and spontaneous canine sarcomas is short-lived. In mice, successful treatment of tumors requires frequent injections with MYXV. We hypothesize that treatment of cancer with a recombinant MYXV that promotes apoptosis could improve the efficacy of MYXV. The orfC gene of walleye dermal sarcoma virus (WDSV), which induces apoptosis, was recombined into the MYXV genome (MYXVorfC). A marked increase in apoptosis was observed in cells infected with MYXVorfC. To ensure that expression of WDSV orfC by MYXV does not potentiate the pathogenesis of MYXV, we evaluated the effects of MYXVorfC inoculation in the only known host of MYXV, New Zealand white rabbits. Virus dissemination in rabbit tissues was similar for MYXVorfC and MYXV. Virus titers recovered from tissues were lower in MYXVorfC-infected rabbits as compared to MYXV-infected rabbits. Importantly, rabbits infected with MYXVorfC had a delayed onset of clinical signs and a longer median survival time than rabbits infected with MYXV. This study indicates that MYXVorfC is attenuated and suggests that MYXVorfC will be safe to use as an OV therapy in future studies.

Walleye Dermal Sarcoma Virus Retroviral Cyclin Directly Contacts TAF9

ABSTRACT Walleye dermal sarcoma virus (WDSV) is a complex retrovirus associated with dermal sarcomas in walleye fish. A WDSV accessory gene encodes a cyclin homolog or retroviral cyclin (rv-cyclin). WDSV rv-cyclin was found to be associated with transcription complexes and to affect transcription in a cell-type and promoter-dependent manner. It inhibited the WDSV promoter in walleye fibroblasts and activated transcription from GAL4 promoters when fused to the GAL4 DNA binding domain, and an activation domain (AD) has been localized to 30 amino acids in the carboxyl region. rv-cyclin can block the pulldown of transcription coactivators by the AD of VP16, and the isolated rv-cyclin AD interferes specifically with the interaction between the carboxyl halves of the VP16 AD, VP16C, and TATA-binding protein-associated factor 9 (TAF9). The carboxyl region and isolated AD can bind TAF9 directly in assays of protein-protein interaction in vitro. Furthermore, rv-cyclin and the isolated rv-cyclin AD interfere specifically with the function of VP16C in transcription assays. A previously identified motif within the VP16C sequence mediates TAF9 binding, and this motif is present in the activation domains of a variety of TAF9-binding transcriptional activators. A similar motif is present in the rv-cyclin AD, and point mutations within this motif affect rv-cyclin function and protein-protein interactions. The results support a model of transcription regulation by direct interaction with TAF9.