Kaposi's sarcoma-associated herpesvirus ORF57 protein interacts with PYM to enhance translation of viral intronless mRNAs.

Kaposi's sarcoma-associated herpesvirus (KSHV) expresses numerous intronless mRNAs that are unable to access splicing-dependent cellular mRNA nuclear export pathways. To circumvent this problem, KSHV encodes the open reading frame 57 (ORF57) protein, which orchestrates the formation of an export-competent virus ribonucleoprotein particle comprising the nuclear export complex hTREX, but not the exon-junction complex (EJC). Interestingly, EJCs stimulate mRNA translation, which raises the intriguing question of how intronless KSHV transcripts are efficiently translated. Herein, we show that ORF57 associates with components of the 48S pre-initiation complex and co-sediments with the 40S ribosomal subunits. Strikingly, we observed a direct interaction between ORF57 and PYM, a cellular protein that enhances translation by recruiting the 48S pre-initiation complex to newly exported mRNAs, through an interaction with the EJC. Moreover, detailed biochemical analysis suggests that ORF57 recruits PYM to intronless KSHV mRNA and PYM then facilitates the association of ORF57 and the cellular translation machinery. We, therefore, propose a model whereby ORF57 interacts directly with PYM to enhance translation of intronless KSHV transcripts.

The use of high-frequency ultrasound imaging and biofluorescence for in vivo evaluation of gene therapy vectors.

BACKGROUND: Non-invasive imaging of the biodistribution of novel therapeutics including gene therapy vectors in animal models is essential. METHODS: This study assessed the utility of high-frequency ultrasound (HF-US) combined with biofluoresence imaging (BFI) to determine the longitudinal impact of a Herpesvirus saimiri amplicon on human colorectal cancer xenograft growth. RESULTS: HF-US imaging of xenografts resulted in an accurate and informative xenograft volume in a longitudinal study. The volumes correlated better with final ex vivo volume than mechanical callipers (R2 = 0.7993, p = 0.0002 vs. R2 = 0.7867, p = 0.0014). HF-US showed that the amplicon caused lobe formation. BFI demonstrated retention and expression of the amplicon in the xenografts and quantitation of the fluorescence levels also correlated with tumour volumes. CONCLUSIONS: The use of multi-modal imaging provided useful and enhanced insights into the behaviour of gene therapy vectors in vivo in real-time. These relatively inexpensive technologies are easy to incorporate into pre-clinical studies.

A Herpesvirus saimiri-based vector expressing TRAIL induces cell death in human carcinoma cell lines and multicellular spheroid cultures.

Herpesvirus saimiri (HVS) is capable of infecting a range of human carcinoma cell types with high efficiency and the viral genome persists as high copy number, circular, non-integrated episomes which segregate to progeny upon cell division. This allows HVS-based vectors to stably transduce a dividing cell population and provide sustained transgene expression for an extended period of time both in vitro and in vivo. Moreover, the insertion of a bacterial artificial chromosome cassette into the HVS genome simplifies the incorporation of large amounts of heterologous DNA for gene delivery. Herein we have produced a recombinant HVS-based vector containing full-length human TRAIL under the control of the α-survivin promoter, and subsequently challenged a variety of cancer cell lines with this vector. The TRAIL transgene was expressed in infected colorectal SW480 cells, causing considerable apoptosis induction. Apoptosis was also observed when several other cancer cell lines derived from different tissues were infected. Moreover, co-treatment with Jak inhibitor AG490 led to the disruption of spheroid cultures grown from the melanoma Mel888 line. These data suggest that an HVS gene therapy vector expressing TRAIL could be an effective treatment against cancer.

Herpesvirus saimiri-mediated delivery of the adenomatous polyposis coli tumour suppressor gene reduces proliferation of colorectal cancer cells.

Colorectal cancer (CRC) is a major cause of cancer-related mortality. A contributing factor to the progression of this disease is sporadic or hereditary mutation of the adenomatous polyposis coli (APC) gene, a negative regulator of the Wnt signalling pathway. Inherited mutations in APC cause the disorder familial adenomatous polyposis (FAP), which leads to CRC development in early adulthood. However, the gene is also disrupted in some 60% of sporadic cancers. Restoration of functional APC may slow the growth of CRC by negatively regulating proliferation-associated genes such as c-myc. Therefore, we have cloned the cDNA of the APC tumour suppressor gene into a replication competent Herpesvirus saimiri (HVS)-based vector to assess APC gene delivery in SW480 and SW620 CRC cell lines. Our results demonstrate that full length APC protein was efficiently expressed from the HVS vector and that transgene expression inhibited proliferation of both the SW480 and the metastatic SW620 cancer cell lines. Moreover, a sustained effect could be observed for at least 8 weeks after initial infection in SW480 cells. In addition, monolayer wounding assays showed a marked reduction in proliferation and migration in HVS-GFP-APC infected cells. We believe that this is the first instance of infectious delivery and APC cDNA expression from a virus-based vector.