Novel pathways of
transcriptional and post-transcriptional regulation of post-integrative HIV-1
Presented by Alessandro Marcello (Italy).
A. Marcello, A. Kula, M. Dieudonne, A. Knezevich, P. Maiuri
ICGEB, Trieste, Italy
Background: Therapeutic targeting of HIV latency
requires an understanding of the basic mechanisms regulating viral quiescence
Methods: We identified several
levels of transcriptional and post-transcriptional control of viral genes´
expression. By looking at the organization of chromatin at the site of
integration by chromatin conformation capture and in situ hybridization we found that chromatin imposes
silencing in a highly specific spatial and temporal pattern. We also identified
several cellular factors that interact with viral RNA by a proteomic approach pointing to post-transcriptional processes that have been greatly overlooked as mechanisms
of HIV post-integrative latency.
Results: HIV-1 can integrate
within active genes at the periphery of the nucleus
and silencing may involve repression from a peri-centromeric region in trans. Hence, a mechanism of
active spatial reorganization of chromatin at the site of proviral integration
may be ultimately responsible for virus silencing. Particularly relevant to flushing therapies of the viral
reservoir is the observation that the silent state of an integrated provirus in
a clonal population of activated lymphocytes is not homogeneous, with a small
number of cells carrying a provirus embedded into heterochromatin, compared to
the majority of cells where the provirus is already poised for transcription.
Proteomic analysis revealed
several novel cellular factors including PSF, MATR3 and p54nrb that have been previously recently in nuclear retention of RNA.
We demonstrated that PSF/p54nrb binds
nascent HIV RNA at the transcription site but MATR3 defines a novel sub-nuclear
compartment where this viral RNA is retained. Rev is able to associate with
unspliced HIV RNA co-transcriptionally directing its nuclear export. These
observations lead to a model for a novel cellular pathway of RNA retention that
is hijacked by the virus.
Conclusions: Both the control imposed by the organization of the nucleus and by
post-transcriptional mechanisms are relevant for the
control of HIV-1 post-integrative latency.
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