Host factors regulating HIV latency and reactivation - Our central premise is that HIV transcriptional inhibitors can be used as latency promoting agents (LPAs) in
block-and-lock functional cure approaches, aimed at reducing residual viremia during antiretroviral therapy (ART)
and limiting viral rebound upon treatment interruption (TI). This hypothesis came about with the discovery of the
Tat inhibitor, didehydro-Cortistatin A (dCA)2,3. In in vitro and in vivo models of HIV latency combining ART with
dCA accelerated HIV-1 suppression to below the limit of detection and blocked viral rebound upon TI or
stimulation with latency reversing agents (LRAs)4. The transcriptional shutdown by dCA resulted in the
heterochromatinization and loss of RNAPII at the HIV promoter5. We recently reported on another LPA, the
generic drug, Spironolactone (SP). Interestingly this drug degrades the host XPB subunit of the general
transcription factor TFIIH6 inhibiting HIV transcription in primary cells from infected individuals and blocking viral
reactivation from latency without affecting cellular transcriptomics7. This study is important because it highlights
that a host factor can be targeted to silence HIV without affecting cellular viability. In sum, the more knowledge
we gain on the interconnectivity between Tat, transcription factors regulatory mechanisms and how these affect
nucleosomes positioning around the HIV promoter, the more we can leverage transcriptional regulators as
antiviral targets.
To identify novel host factors regulating HIV transcription we used a chromatin affinity purification assay
together with mass spectrometry (ChAP-MS)8. We identified p32 (ASF/SF2 splicing factor-associated protein)
and FUBP3 (Far upstream element binding protein 3) in productively infected ART treated promoters but not in
dCA-treated where HIV was silenced; and PHB2 (prohibitin-2) was enriched in dCA treated promoters but
reduced in ART only treated ones. These results suggest that p32 and FUBP3 are HIV transcriptional
activators while PHB2 is a HIV silencing factor. Preliminary studies confirmed their transcriptional activity on
HIV. Here we propose a detailed molecular mechanistic study on how p32 and FUBP3 enhance and how PHB2
inhibits HIV transcription. Understanding their role in pre-initiation complex (PIC) formation, initiation, elongation
and nucleosome organization at the latent HIV promoter will be key for developing successful strategies for
durable HIV silencing. Strong effects of one or more of these factors will prompt the search for small-molecule
modulators. Our overarching goal is to durably silence latent HIV proviruses by driving each into stable
heterochromatin where they will remain “locked.”
We propose the following aims:
1) Define the roles of p32, FUBP3 and PHB2 in HIV transcription and chromatin structure.
2) Identify protein complexes associated with p32, FUBP3 and PHB2.
3) Investigate p32, FUBP3 and PHB2 dependence on the Tat/TAR circuitry.
