The mechanism of the inhibition of the replication of carcinogenic human papillomaviruses by the NCOR/SMRT-repressor complex

• Applicant: Professor Dr. Frank Stubenrauch
• Subject Area: Virology
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 232531764

Persistent infections with high-risk (HR) human papillomaviruses (HPV) 16, 18, 31 etc. cause ano-genital and oro-pharyngeal cancers in humans. Furthermore, infections with HPV from the genus beta have been implicated in the development of non-melanoma skin cancer. The viral E2 protein family controls transcription of the viral oncogenes and the replication of the genomes. Sequence analyses indicate that all HPV can express an E8^E2C protein in addition to the E2 replication activator protein. The HPV16 and 31 E8^E2C proteins have been shown to be crucial, negative regulators of the viral replication in the persistent phase. Results of the first funding period show for the first time that E8^E2C´s function is highly conserved among HPV as E8^E2C knock-out genomes of HPV1, a mu-PV and HPV8, a beta-PV over replicate in human keratinocytes. Published results from the first funding period demonstrate that E8^E2C surprisingly also limits the productive replication of HPV16. In addition, we also found that HPV16 E8^E2C is transcribed from a novel promoter within the E1 gene that is positively and negatively regulated by host cell and viral proteins. E8^E2C proteins have two conserved domains: the E8 domain is responsible for the inhibition of viral transcription and genome replication whereas the E2C part mediates specific DNA-binding and dimerization. Results from the first funding period indicate that the inhibition of transcription and DNA replication is the consequence of a conserved interaction between the HPV E8 repressor domain and the cellular NCoR/SMRT co-repressor complex, which consists of the GPS2, HDAC3, NCoR, SMRT, TBL1 and TBLR1 proteins. This suggests for the first time that the NCoR/SMRT complex not only controls cellular gene expression but also inhibits HPV replication. Results from the first funding period show that the recruitment of the NCoR/SMRT complex by E8^E2C to the viral replication origin interferes with the binding of cellular replication proteins to the viral E1 helicase which most likely contributes to the inhibition of replication. Aims of the project are to investigate in detail the interactions of viral replication activator proteins with cellular replication proteins in vitro and in vivo in the absence and presence of E8^E2C in order to elucidate the molecular mechanism of the NCoR/SMRT-mediated inhibition of viral replication. Furthermore, the influence of the E8^E2C-NCoR/SMRT interaction on host cell gene expression and the DNA damage pathway during the HPV life cycle will be investigated. The long-term goal of the study is the identification of novel targets for anti-HPV therapy.

• DFG Programme: Research Grants