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Project A3: Mona Dachsel, doctoral researcher (MD)

The role of Vpx and the HUSH complex in HTLV reactivation from latency and enhanced transcription of endogenous retroelements

SIV-2 and related SIVs encode the accessory protein Vpx, which is essential for efficient HIV infection of myeloid cells by mediating the proteasomal degradation of the restriction factor SAMHD1. This project will complement the GRK-funded project on Vpx-mediated degradation of SAMHD1 (A3) and analyze the SAMHD1-independent effects of Vpx on retroviral and retroelement replication.

Vpx has been shown to promote HIV reactivation from latency by degrading the host repressor complex HUSH, which recruits methyl-transferases resulting in repressive histone modifications (H3K9me3) (Chougui, Nat. Micro., 2018). Whether the HUSH complex or H3K9me3 methylation play a role in HTLV latency, however, is not known. In collaboration with the project of Andrea Thoma-Kress (A2), this study will ask whether the HUSH complex represses HTLV transcription, and whether it could be counteracted by Vpx-containing VLPs as part of a kick-and-kill strategy to reactivate and eliminate HTLV-1 in infected T cells. In addition, transcription of the endogenous retroelement LINE-1 is controlled by the HUSH complex. Recently, it became clear that the HUSH-mediated repression of LINE-1 transcripts suppresses innate immunity in tumor cells and is therefore essential for tumor growth, e.g. in acute myeloid leukemia (Gu, Nat. Genetics, 2021). Thus, the student will analyze the impact of HUSH proteins on LINE-1 transcription and immune activation using Vpx-expressing VLPs and ask whether HUSH inactivation might be a promising target in AML treatment. 

The medical doctoral student will design HTLV and LINE-1 transcription reporter assays to assess the impact of the HUSH complex on viral transcription. He will treat cells transfected with reporter plasmids and Vpx-containing VLPs or shRNA-encoding vectors targeting different components of the HUSH complex. In addition, the student will assess the role of the HUSH complex in HTLV-1 replication and LINE-1 retrotransposition by analyzing reporter assays via Flow cytometry. Finally, the MD candidate will analyze possible immune responses following reactivation by quantitative PCR, ELISA, or FACS, and determine the consequences for retroviral or retroelement replication.

Together, this project will deepen the interaction between research projects A2 and A3 by analyzing the SAMHD1-independent activities of Vpx and determine the role of the repressor complex HUSH for reactivating HTLV from latency and enhancing endogenous retroelements transcription. Thus, this project might contribute to the identification of potential HTLV-1 treatment options and potential mechanisms to enhance tumor immunogenicity.