Viral factors involved in Marek's disease virus (MDV) genome integration
Final Report Abstract
Some herpesviruses including Marek’s disease virus (MDV), a highly oncogenic alphaherpesvirus, and human herpesvirus 6 (HHV-6) integrate their genetic material into host telomeres during the latent stage of infection, which ensures viral genome maintenance in replicating host cells during the quiescent phase of infection termed latency. MDV, HHV-6 and several other herpesviruses harbor telomeric repeats (TMRs) identical to host telomere sequences (TTAGGG)n at either end of their linear genomes, which suggests a conserved integration mechanism. MDV harbors two sets of such telomeric repeats: a long telomeric repeat region (mTMR) with a variable length of 27 to 100 repeats and a short telomeric repeat region (sTMR) with a fixed number of 6 repeats. We recently demonstrated that the MDV mTMR region is essential for virus genome integration into host telomeres and that this integration process is critical for efficient lymphomagenesis, but also for reactivation from the quiescent state of infection. However, the role of the sTMR region in MDV replication and integration remains unknown. Furthermore, MDV and other herpesviruses encode two proteins termed pUL12 and pICP8 that resemble the Red recombination system encoded by bacteriophages such as λ. The pUL12/ICP8 complex is thought to aid the replication of the herpesvirus genome, a process requiring homologous recombination events. pUL12 and ICP8 of HSV-1 facilitate recombination in vitro, but the role of pUL12 and ICP8 in MDV replication and especially integration of the virus genome into host chromosomes remains elusive. We hypothesize that the sTMR region at the MDV genomic termini as well as the MDV encoded pUL12/ICP8 recombinase complex facilitate integration of the virus genome into host telomeres. We tested our hypothesis by two specific aims: 1) To determine the role of the sTMR region in MDV replication, integration, and disease development. 2) To test if the MDV pUL12/ICP8 recombinase complex facilitates virus genome integration into host telomeres and if this process requires viral and/or cellular DNA replication. With the DFG grant, we successfully investigated the role of the sTMR in MDV replication, tumor formation and genome integration. We demonstrate that deletion of sTMR sequences abrogates MDV replication, but that the exact sTMR sequence is not important for production of progeny virus in vitro. A panel of sTMR truncation mutants confirmed that the exact length of the sTMR is crucial for efficient MDV replication. In addition, mutation of the sTMR reduced integration frequency and impaired MDV pathogenesis and tumor formation. In addition, we laid the groundwork for the analysis of the role of pUL12 and ICP8 in virus genome integration. This part of the project is currently still ongoing. Furthermore, the worked laid the groundwork for my ERC grant application that was recently granted.
Publications
- 2013. Detection of Integrated Herpesvirus Genomes by Fluorescence In Situ Hybridization (FISH). Methods Mol. Biol. 1064:141-152
Kaufer B. B.
- 2014. Herpesvirus Genome Integration into Telomeric Repeats of Host Cell Chromosomes. Annual Review of Virology 1
Osterrieder N., N. Wallaschek, and B. B. Kaufer
(See online at https://doi.org/10.1146/annurev-virology-031413-085422) - 2014. Role of the short telomeric repeat region in Marek's disease virus (MDV) replication, genomic integration and lymphomagenesis. J Virol.
Greco, A., N. Fester, A. T. Engel, and B. B. Kaufer
(See online at https://doi.org/10.1128/JVI.02437-14) - 2016. The telomeric repeats of human herpesvirus 6A (HHV-6A) are required for efficient virus integration, PLoS Pathogens
Wallaschek N., A. Sanyal, F. Pirzer, A. Gravel, Y. Mori, L. Flamand, B. B. Kaufer
(See online at https://doi.org/10.1371/journal.ppat.1005666)
