Compounds Identified from Marine Mangrove Plant (Avicennia alba) as Potential Antiviral Drug Candidates Against WDSV, an In-Silico Approach.

Walleye dermal sarcoma virus (WDSV) is a type of retrovirus, which affects most of the adult walleye fishes during the spawning time. The virus causes multiple epithelial tumors on the fish's skin and fins that are liable for more than 50% of the mortality rate of fish around the world. Till now, no effective antiviral drug or vaccine candidates have been developed that can block the progression of the disease caused by the pathogen. It was found that the 582-amino-acid (aa) residues long internal structural gag polyprotein of the virus plays an important role in virus budding and virion maturation outside of the cell. Inhibition of the protein can block the budding and virion maturation process and can be developed as an antiviral drug candidate against the virus. Therefore, the study aimed to identify potential natural antiviral drug candidates from the tropical mangrove marine plant Avicennia alba, which will be able to block the budding and virion maturation process by inhibiting the activity of the gag protein of the virus. Initially, a homology modeling approach was applied to identify the 3D structure, followed by refinement and validation of the protein. The refined protein structures were then utilized for molecular docking simulation. Eleven phytochemical compounds have been isolated from the marine plant and docked against the virus gag polyprotein. Three compounds, namely Friedlein (CID244297), Phytosterols (CID12303662), and 1-Triacontanol (CID68972) have been selected based on their docking score -8.5 kcal/mol, -8.0 kcal/mol and -7.9 kcal/mol, respectively, and were evaluated through ADME (Absorption, Distribution, Metabolism and Excretion), and toxicity properties. Finally, molecular dynamics (MD) simulation was applied to confirm the binding stability of the protein-ligands complex structure. The ADME and toxicity analysis reveal the efficacy and non-toxic properties of the compounds, where MD simulation confirmed the binding stability of the selected three compounds with the targeted protein. This computational study revealed the virtuous value of the selected three compounds against the targeted gag polyprotein and will be effective and promising antiviral candidates against the pathogen in a significant and worthwhile manner. Although in vitro and in vivo study is required for further evaluation of the compounds against the targeted protein.

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.

Retroviral cyclin enhances cyclin-dependent kinase-8 activity.

Alterations in the functional levels of cyclin-dependent kinase-8 (CDK8) or its partner, cyclin C, have been clearly associated with cancers, including colon cancer, melanoma, and osteosarcoma. Walleye dermal sarcoma virus encodes a retroviral cyclin (RV-cyclin) that localizes to interchromatin granule clusters and binds CDK8. It also binds to the Aα subunit (PR65) of protein phosphatase 2A (PP2A). Binding to the Aα subunit excludes the regulatory B subunit, but not the catalytic C subunit, in a manner similar to that of T antigens of the small DNA tumor viruses. The expression of the RV-cyclin enhances the activity of immune affinity-purified CDK8 in vitro for RNA polymerase II carboxy-terminal domain (CTD) and histone H3 substrates. PP2A also enhances CDK8 kinase activity in vitro for the CTD but not for histone H3. The PP2A enhancement of CDK8 is independent of RV-cyclin expression and likely plays a role in the normal regulation of CDK8. The manipulation of endogenous PP2A activity by inhibition, amendment, or depletion confirmed its role in CDK8 activation by triggering CDK8 autophosphorylation. Although RV-cyclin and PP2A both enhance CDK8 activity, their actions are uncoupled and additive in kinase reactions. PP2A may be recruited to CDK8 in the Mediator complex by a specific PP2A B subunit or additionally by the RV-cyclin in infected cells, but the RV-cyclin appears to activate CDK8 directly and in a manner independent of its physical association with PP2A.

Walleye dermal sarcoma virus cyclin interacts with components of the mediator complex and the RNA polymerase II holoenzyme.

Walleye dermal sarcoma virus (WDSV) encodes an accessory protein, OrfA, with sequence homology to cyclins (retrovirus cyclin). In cells transfected with an expression construct, OrfA was localized to the nucleus and was concentrated in interchromatin granule clusters (IGCs), sites where splicing factors are concentrated. Other proteins identified in IGCs include transcription factors, the large subunit of RNA polymerase II (Pol II), and cyclin-dependent kinase 8 (cdk8). cdk8 is the kinase partner of cyclin C and a component of the mediator complex, associated with the Pol II holoenzyme. cdk8 and cyclin C can regulate transcription via phosphorylation of cyclin H and the carboxy-terminal domain of Pol II. OrfA in transfected HeLa cells was found to colocalize and copurify with hyperphosphorylated forms of Pol II (Pol IIO) in IGCs, and OrfA was coimmunoprecipitated from lysates of transfected cells with an antibody against Pol IIO. Likewise, Pol IIO could be coprecipitated with an antibody against OrfA. A survey with antibodies against several different cdks resulted in coimmunoprecipitation of OrfA with anti-cdk8, and antiserum against OrfA was able to coprecipitate cdk8 from lysates of cells that express OrfA. Coprecipitation of OrfA with anti-cyclin C demonstrated that it was included in complexes with OrfA and cdk8. OrfA has sequence and structural similarities to cyclin C, and, functionally, OrfA appears to have the capacity to both enhance and inhibit the activity of promoters in a cell-specific manner, similar to functions of the mediator complex. These data suggest that WDSV OrfA functions through its interactions with these large, transcription complexes. Further investigations will clarify the role of the retrovirus cyclin in control of virus expression and transformation.