Progress 08/15/06 to 08/14/09
Outputs
OUTPUTS: Marek's disease is one of the most important of all infectious diseases affecting poultry production worldwide and is arguably the most costly to control. Currently, all commercial broilers are vaccinated in ovo or at hatch with cell associated vaccines. Despite the great efficacy in the prevention of tumor formation, highly pathogenic strains of MDV persist and sporadic outbreaks often occur, which lead to the evolution of very virulent strains of MDV. One of the strategies to develop improved vaccines against the very virulent strains is to identify the key oncogene of MDV,the herpesvirus which causes MD and generate a recombinant virus that deletes the oncogenecity, without compromising the replicative potential of the virus. As most of the viral genes play multiple roles, it is important to identify the key oncogene involved and to understand the oncogenic pathways, such that proper mutants can be developed. We have identified Meq, a bZIP (basic-leucine zipper) protein as a strong candidate of MDV oncogene Meq is encoded only by the oncogenic serotype of MDV, but not the vaccine strains. Past progress from us showed that Meq exhibits transforming properties and Meq-null mutants completely failed to induce tumors in chickens, yet retain its replicative ability. We report here that Meq is able to activate the jun and ski oncogenic pathways in chicken cells.Meq functions both as a transcriptional activator and as a transcriptional repressor, depending on its dimerization partner. The transcriptional activation is largely due to the Meq/Jun heterodimer, which stabilizes c-jun and activates the oncogenic jun pathway by turning on genes involved in transformation (e.g.,HB-EGF). To demonstrate that heterodimer is crucial, a Meq mutant which can only form homodimer was generated by substituting the leucine-zipper domain of Meq with that of yeast GCN4. After verification of its ability to only form homodimer, its ability to transform cells was tested and was shown to be ineffective. In collaboration with Dr. Sanjay Reddy, the mutant molecule was "knocked in" the viral genome to substitute for the wild type Meq. This MeqG virus fails to induce Marek's disease in vivo. Similarly, if Meq is engineered to only homodimerize, it also fails to transform, suggesting both homo and hetero-dimerization properties are required. Our next question was concerned with the repression function of Meq, and our hypothesis is that ctBP, a strong repressor and a tumor suppressor gene is critical in this process. Interestingly, we found that Meq rapidly degrades ctBP, and this degradation is proteosome mediated and depends on ubiquitination of ctBP. Importantly, Meq is also able to destabilize p53, another tumor suppressor associated with Meq. To look for possible functions of Meq in mediating the degradation, we looked for proteins associated with Meq using tandem mass spectroscopy. If established, this is a novel mechanism how viral oncogene can shut off host tumor suppressor to orchestrate the oncogenic program. Finally, in collaboration with Dr. Lucy Lee, the studies on Meq-null MDV as an effective vaccine were completed. PARTICIPANTS: Dr. Yoshi Izumiya, UC Davis Cancer Center, Dept. Dermatology, UCDMC, Res III, 4645 2nd Ave, Sacramento, CA 95817 Dr. Sanjay Reddy. Texas A&M University. Dept. of Pathobiology, TAMU (MS 4467), 206 VMR Bldg. 1197,College Station, TX 77843-4476,United States TARGET AUDIENCES: Investigators interested in vaccine development for Mareks disease virus PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The most exciting outcome of this project is to conclusively demonstrate that Meq is the oncoprotein of Marek's disease virus. Deletion of this gene leads to the generation of a recombinant virus which replicates well but completely lacks oncogenecity. This virus has been shown to be among the most efficacious vaccine virus toward the highly virulent strain of MDV.
Publications
- Ajithdoss DK, Reddy SM, Suchodolski PF, Lee LF, Kung HJ, Lupiani B. In vitro characterization of the Meq proteins of Mareks disease virus vaccine strain CV1988.Virus Res. 142(1-2):57-67.(2009) Suchodolski P, Izumiya Y, Lupiani B, Ajithdoss D, Gilad O, Lee LF, Kung HJ, and Reddy SJ. Homodimerization of Mareks disease virus encoded Meq protein is not sufficient for transformation of lymphocytes in chicken. J. Virol. 83(2):859-869.(2009)
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