Abstract
Integration of HIV-1 linear DNA into host chromatin is required for high levels of viral expression, and constitutes a key therapeutic target. Unintegrated viral DNA (uDNA) can support only limited transcription but may contribute to viral propagation, persistence and/or treatment escape under specific situations. The molecular mechanisms involved in the differential expression of HIV uDNA vs integrated genome (iDNA) remain to be elucidated. Here, we demonstrate, for the first time, that the expression of HIV uDNA is mainly supported by 1-LTR circles, and regulated in the opposite way, relatively to iDNA, following NF-κB pathway modulation. Upon treatment activating the NF-κB pathway, NF-κB p65 and AP-1 (cFos/cJun) binding to HIV LTR iDNA correlates with increased iDNA expression, while uDNA expression decreases. On the contrary, inhibition of the NF-κB pathway promotes the expression of circular uDNA, and correlates with Bcl-3 and AP-1 binding to its LTR region. Finally, this study identifies NF-κB subunits and Bcl-3 as transcription factors binding the HIV promoter differently depending on viral genome topology, and opens new insights on the potential roles of episomal genomes during the HIV-1 latency and persistence.
Highlights
Integration of the HIV genome is an essential step of the retroviral cycle, supporting massive production of viral particles
3 days post-infection by the HIV-1 NL4-3 strain, the expression of the reporter gene decreased while the dose of integrase strand transfer inhibitors (INSTIs) increased, until it reached a minimal threshold
Only efavirenz (EFA) fully inhibits HIV expression, confirming that reverse-transcription and expression from neosynthetized genomes are required for lacZ transcription in HelaP4 cells (Fig. 1A). Since this reporter gene expression is dependent upon the activation of the integrated HIV-1 LTR present in HelaP4 cell genome, these observations indicate that Tat is expressed from unintegrated neosynthetized viral genomes at levels sufficient to transactivate integrated HIV-1 LTR
Summary
Integration of the HIV genome is an essential step of the retroviral cycle, supporting massive production of viral particles. Expression of uDNAs can be several orders of magnitude lower than that of an integrated provirus[13,15], it can lead to the expression of accessory proteins such as Nef and Tat[14,15] This low level of Nef expression is sufficient to down-regulate CD4 expression on host cell surfaces and to induce T cell activation[7], highlighting the importance of uDNA expression on HIV-host interaction. Interaction of the NF-κB p50-p50 homodimer with the IκB-like protein, Bcl-3, can switch the balance from inhibition to activation of HIV transcription[25,26,27] This interaction may be important to modulate HIV expression in differentiated macrophages that express a constitutive nuclear pool of NF-κB, mainly constituted of p5028. These observations emphasize the dual role of NF-κB and AP-1 activations during HIV-1 cycle
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