Does the cellular antiviral factor RPRD2 inhibit HIV-1 by repressing viral transcription?

Abstract

HIV-1 DNA integrates into the host genome, but despite this, infected cells can recruit the HUSH complex, which recognises viral intronless genes and initiates silencing of transcription through H3K9 histone trimethylation. The antiviral protein RPRD2 was recently found to be a general repressor of transcription, and is known to inhibit HIV-1 infection, although the exact mechanism of viral restriction remains unclear. Here we investigate the role of RPRD2 in repressing transcription of HIV-1 DNA and the interaction between RPRD2 and the HUSH complex. Our data show that knockdown of both RPRD2 and TASOR increased transcription of transfected lentiviral HIV-1 reporters in HEK293T cells and HeLa cells, and that the transcriptional repression is independent of the presence of introns. In contrast, our data indicate that RPRD2 does not suppress transcription of integrated HIV-1 provirus. Knockdown of RPRD2 consistently did not affect the expression of integrated HIV-1 LTR GFP reporter genes in the J-Lat latency model, in transduced HeLa cells, and with the piggyBac-integrated L1-derived reporters in HeLa cells, despite that we detected a physical interaction between RPRD2 and TASOR. Therefore, RPRD2 does not inhibit transcription of integrated HIV-1 DNA, but does restrict transfected plasmid DNA. It remains possible that RPRD2 affects episomal DNA only as is seen for other HUSH-related and HUSH-independent cellular factors. Given that episomal DNA does not contribute to HIV-1 infection, transcriptional inhibition is not the basis of the antiviral effect of RPRD2. However, these data will still aid understanding of the role and mechanism of RPRD2 in cellular transcription. Potentially, the data regarding plasmid DNA could be pertinent for understanding the suppression of viral-derived episomal DNA, including in the context of gene therapy, though this remains to be tested.