Nucleosome assembly on pre-integrated DNA of HIV-1-based vectors: Histone composition and post-translational modifications
Virology
Final Report Abstract
Retroviruses are characterized by the reverse transcription of the viral RNA genome into DNA and the integration of that DNA to form the provirus. However, little is known about the nature of unintegrated HIV-1 DNAs early upon delivery into the nucleus. Using ChIP assays, I found that both core and H1 linker histones are deposited onto unintegrated HIV-1 DNAs. I also confirmed transcriptional silencing of unintegrated HIV- 1 DNAs and determined the presence of post-translational histone modifications characteristic of inactive chromatin. Invading viral DNAs constitute a high risk for the infected cell and are high profile targets of antiviral host factors. Nevertheless, not much is known about silencing machineries in the nucleus that act to prevent transcription or retroviral integration of extrachromosomal DNA. I identified CHAF1A and CHAF1B as two novel players that mediate silencing of unintegrated HIV-1 DNAs. My findings provide evidence that these factors act independently of their canonical nucleosome assembly complex to induce silencing early in infection. My results will help to increase the efficiency of expression from non-integrating HIV-1-based vectors (e.g. gene therapy applications). My originally scientific questions of my submitted proposal read as the following: “This will address the question as to whether there is a potential common extrachromosomal defense mechanism. In conclusion, the findings of this fellowship proposal will reveal the principles of nucleosome formation onto preintegrated retroviral DNA and will have also implications for integration-deficient retroviral vectors and non-viral transfected DNA. Furthermore, it may define new, broadly utilized anti-viral defense mechanisms.” I am proud to reveal that I have successfully addressed most of the scientific goals of my submitted proposal. My data show evidence that there is no common extrachromosomal defense mechanism that the silencing of invading viral DNAs differ substantially between virus (HIV-1 vs. MLV) and cell types (HeLa vs. lymphoid cells) and is much more complex that one might have expected (manuscript in preparation). My project revealed the histone profile of unintegrated HIV-1 DNAs in detail. Furthermore, I identified novel silencing factors of HIV-1.
Publications
- “Unintegrated HIV-1 DNAs are loaded with core and linker histones and transcriptionally silenced”, PNAS November 19, 2019 116 (47) 23735-23742
Franziska K. Geis, Stephen P. Goff
(See online at https://doi.org/10.1073/pnas.1912638116) - “Silencing and Transcriptional Regulation of Endogenous Retroviruses: An Overview”, Viruses 2020 Aug 13;12(8):884
Franziska K. Geis, Stephen P. Goff
(See online at https://doi.org/10.3390/v12080884)
