Abstract
Previously, we reported that cellular transcription factor ZASC1 facilitates DNA-dependent/RNA-independent recruitment of HIV-1 TAT and the cellular elongation factor P-TEFb to the HIV-1 promoter and is a critical factor in regulating HIV-1 transcriptional elongation (PLoS Path e1003712). Here we report that cellular transcription factor ZBTB2 is a novel repressor of HIV-1 gene expression. ZBTB2 strongly co-immunoprecipitated with ZASC1 and was dramatically relocalized by ZASC1 from the cytoplasm to the nucleus. Mutations abolishing ZASC1/ZBTB2 interaction prevented ZBTB2 nuclear relocalization. We show that ZBTB2-induced repression depends on interaction of cellular histone deacetylases (HDACs) with the ZBTB2 POZ domain. Further, ZASC1 interaction specifically recruited ZBTB2 to the HIV-1 promoter, resulting in histone deacetylation and transcription repression. Depleting ZBTB2 by siRNA knockdown or CRISPR/CAS9 knockout in T cell lines enhanced transcription from HIV-1 vectors lacking Vpr, but not from these vectors expressing Vpr. Since HIV-1 Vpr activates the viral LTR by inducing the ATR kinase/DNA damage response pathway, we investigated ZBTB2 response to Vpr and DNA damaging agents. Expressing Vpr or stimulating the ATR pathway with DNA damaging agents impaired ZASC1’s ability to localize ZBTB2 to the nucleus. Moreover, the effects of DNA damaging agents and Vpr on ZBTB2 localization could be blocked by ATR kinase inhibitors. Critically, Vpr and DNA damaging agents decreased ZBTB2 binding to the HIV-1 promoter and increased promoter histone acetylation. Thus, ZBTB2 is recruited to the HIV-1 promoter by ZASC1 and represses transcription, but ATR pathway activation leads to ZBTB2 removal from the promoter, cytoplasmic sequestration and activation of viral transcription. Together, our data show that ZASC1/ZBTB2 integrate the functions of TAT and Vpr to maximize HIV-1 gene expression.
Highlights
Human immunodeficiency viruses type-1 and 2 (HIV-1 and HIV-2) are the causative agents of acquired immune deficiency syndrome (AIDS)
We reported that ZASC1, a cellular transcription factor linked to multiple squamous cell carcinomas and inherited ataxias, contributes to an RNA-independent, DNA-dependent step in recruiting the TAT/P-TEFb complex that is critical for Human immunodeficiency virus 1 (HIV-1) transcription elongation to the HIV-1 promoter
ZASC1 interaction relocalizes ZBTB2 from the cytoplasm to the HIV-1 promoter in the nucleus where ZBTB2 interacts with cellular histone deacetylases (HDACs), increases HIV-1 promoter histone deacetylation and represses viral transcription
Summary
Human immunodeficiency viruses type-1 and 2 (HIV-1 and HIV-2) are the causative agents of acquired immune deficiency syndrome (AIDS). The resulting provirus is transcribed by host RNA polymerase II (pol II) from the unique 3’ (U3) element in the viral long terminal repeat (LTR). The HIV-1 promoter efficiently initiates transcription but pol II stalls after extending approximately 100 nucleotides [3]. This block in elongation is overcome by the viral TAT protein and a structured RNA element in the nascent mRNA known as the transactivation response region (TAR). TAT recruits the cellular transcriptional elongation factor P-TEFb to TAR, resulting in phosphorylation of the negative elongation factor (NELF), DRB sensitivity inducing factor (DSIF) and the C-terminal domain (CTD) of pol II by P-TEFb, releasing the stalled polymerase and dramatically increasing transcription elongation [4,5]
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