The HIV-1 restriction factor RPRD2 does not inhibit transcription of HIV-1 or endogenous retroelements
A vital question in transcription regulation is how and to what extent transcription of different DNA species, including viral DNA, episomal DNA and endogenous retroelements, is differentially regulated to transcription of host genes. RPRD2 has previously been characterized as an HIV restriction factor that blocks reverse transcription. However, RPRD2 has also been characterized as a regulator of global transcription of host genes. Therefore, we hypothesized that RPRD2 may also regulate nascent transcription from HIV provirus and endogenous retroelements. First, we used a combination of experimental and computational methods to characterize the binding of RPRD2 to RNA and DNA:RNA hybrids. Using immunoprecipitation, we identified that RPRD2 interacts with both the transcription regulator PAF1 and the HUSH complex member TASOR, independently. Immunofluorescence revealed that GFP-RPRD2 localizes to foci in the nucleus, and these foci overlap with nuclear speckles. To measure the effect of RPRD2 on transcription, we used plasmid-borne HIV LTR-driven reporter constructs and observed that RPRD2 depletion increased transcription of constructs both with and without an intron. We next investigated transcription from integrated proviruses and found no effect of RPRD2 depletion using several different systems. Lastly, we measured transcription of endogenous retroelements and found that RPRD2 depletion did not affect transcription of LINE-1 or HERV-K. Finally, we investigated whether RPRD2 regulates production of IFN in response to nucleic acid species or affects transcription of IFN-stimulated genes. We found that depletion of RPRD2 had no effect on IFN production or ISG expression. Together, our findings demonstrate how regulation of transcription is not universal for host genes, integrated provirus, unintegrated plasmid and endogenous retroviruses, and confirmed that although RPRD2 governs cellular transcription, it does not regulate transcription of HIV-1 provirus or of endogenous retroelements.