Latent HIV-1 TAR Regulates 7SK-responsive P-TEFb Target Genes and Targets Cellular Immune Responses in the Absence of Tat

Sebastian Eilebrecht,Bernd-Joachim Benecke,Arndt G Benecke

doi:10.1016/j.gpb.2017.05.003

Abstract

The transactivating response element (TAR) structure of the nascent HIV-1 transcript is critically involved in the recruitment of inactive positive transcription elongation factor b (P-TEFb) to the promoter proximal paused RNA polymerase II. The viral transactivator Tat is responsible for subsequent P-TEFb activation in order to start efficient viral transcription elongation. In the absence of the viral transactivator of transcription (Tat), e.g., during latency or in early stages of HIV transcription, TAR mediates an interaction of P-TEFb with its inhibitor hexamethylene bis-acetamide-inducible protein 1 (HEXIM1), keeping P-TEFb in its inactive form. In this study, we address the function of HIV-1 TAR in the absence of Tat by analyzing consequences of HIV-1 TAR overexpression on host cellular gene expression. An RNA chimera consisting of Epstein-Barr virus-expressed RNA 2 (EBER2) and HIV-1 TAR was developed to assure robust overexpression of TAR in HEK293 cells. The overexpression results in differential expression of more than 800 human genes. A significant proportion of these genes is involved in the suppression of cellular immune responses, including a significant set of 7SK-responsive P-TEFb target genes. Our findings identify a novel role for HIV-1 TAR in the absence of Tat, involving the interference with host cellular immune responses by targeting 7SK RNA-mediated gene expression and P-TEFb inactivation.

Highlights

HIV-1 latency is established by an interplay of different mechanisms, which render the HIV provirus transcriptionally silent
HIV-1 transactivating response element (TAR) can be efficiently expressed as Epstein-Barr virus-expressed RNA 2 (EBER2) RNA chimera EBER2 is a non-coding nuclear RNA transcribed by RNAPIII
We found that 109 of the EBER2 HIV-1 TAR-regulated genes are responsive to 7SK RNA (Figure 6A), while 251 of the dnCdk9 target genes are regulated by 7SK RNA

Summary

Introduction

HIV-1 latency is established by an interplay of different mechanisms, which render the HIV provirus transcriptionally silent. As soon as sufficient amounts of the viral transactivator of transcription (Tat) are expressed, the protein is able to release 7SK and HEXIM1/2 from the inactive complex, resulting in P-TEFb activation [23,24]. The resulting active Tat/P-TEFb complex is recruited to the promoter proximal paused RNAPII by specific interactions with TAR [13,25], initiating the efficient viral transcription elongation reaction. Sedore and co-workers have previously shown that P-TEFb and HEXIM1 bind to TAR in the absence of Tat [26] In this case, PTEFb is inactive due to the inhibitory function of the HEXMI1 protein present

Methods

Results

Conclusion