cis-acting sequences located downstream of the human immunodeficiency virus type 1 promoter affect its chromatin structure and transcriptional activity.

We have examined the roles of AP-1, AP-3-like, DBF1, and Sp1 binding sites, which are located downstream of the human immunodeficiency virus type 1 (HIV-1) promoter, in regulating basal transcriptional activity directed by the integrated viral long terminal repeat (LTR). Point mutations affecting all four of these elements functionally inactivated the HIV-1 LTR when it was constrained in a chromatin configuration. Analyses of the chromatin structures of the transcriptionally active wild-type and inactive mutated HIV-1 promoters revealed several differences. In the active promoter, the 3' half of the U3 region, including the basal promoter, the enhancer, and the putative upstream regulatory sequences are situated within a nuclease-hypersensitive region. However, the far upstream U3 region appears to be packaged into a nuclease-resistant nucleosomal structure, whereas the R, U5, and gag leader sequences are associated with a region of altered chromatin that is sensitive to restriction endonucleases. In the inactive template, only the basal promoter and enhancer element remain sensitive to nucleases, and the adjacent upstream and downstream regions are incorporated into nuclease-resistant nucleosomal structures. Taken together, these results indicate that the chromatin structure of the integrated HIV-1 LTR plays a critical role in modulating basal transcriptional activity.

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Transcriptional activity of blood-and cerebrospinal fluid–derivednef/long-terminal repeat sequences isolated from a slow progressor infected withnef-deleted human immunodeficiency virus type 1 (HIV-1) who developed HIV-associated dementia

Journal of NeuroVirology ◽

10.1080/13550280600827369 ◽

2006 ◽

Vol 12 (3) ◽

pp. 219-228 ◽

Cited By ~ 4

Author(s):

Melissa J Churchill ◽

Anna Figueiredo ◽

Daniel Cowley ◽

Lachlan Gray ◽

Damian FJ Purcell ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

Cerebrospinal Fluid ◽

Long Terminal Repeat ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Transcriptional Activity ◽

Repeat Sequences ◽

Immunodeficiency Virus ◽

Hiv 1

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Transcriptional Activation of the Integrated Chromatin-Associated Human Immunodeficiency Virus Type 1 Promoter

Molecular and Cellular Biology ◽

10.1128/mcb.18.5.2535 ◽

1998 ◽

Vol 18 (5) ◽

pp. 2535-2544 ◽

Cited By ~ 98

Author(s):

Aboubaker El Kharroubi ◽

Graziella Piras ◽

Ralf Zensen ◽

Malcolm A. Martin

Keyword(s):

Human Immunodeficiency Virus ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Chromatin Structure ◽

Transcriptional Activation ◽

Transcription Initiation ◽

Core Promoter ◽

Immunodeficiency Virus ◽

Hiv 1

ABSTRACT The regulation of human immunodeficiency virus type 1 (HIV-1) gene expression involves a complex interplay between cellular transcription factors, chromatin-associated proviral DNA, and the virus-encoded transactivator protein, Tat. Here we show that Tat transactivates the integrated HIV-1 long terminal repeat (LTR), even in the absence of detectable basal promoter activity, and this transcriptional activation is accompanied by chromatin remodeling downstream of the transcription initiation site, as monitored by increased accessibility to restriction endonucleases. However, with an integrated promoter lacking both Sp1 and NF-κB sites, Tat was unable to either activate transcription or induce changes in chromatin structure even when it was tethered to the HIV-1 core promoter upstream of the TATA box. Tat responsiveness was observed only when Sp1 or NF-κB was bound to the promoter, implying that Tat functions subsequent to the formation of a specific transcription initiation complex. Unlike Tat, NF-κB failed to stimulate the integrated transcriptionally silent HIV-1 promoter. Histone acetylation renders the inactive HIV-1 LTR responsive to NF-κB, indicating that a suppressive chromatin structure must be remodeled prior to transcriptional activation by NF-κB. Taken together, these results suggest that Sp1 and NF-κB are required for the assembly of transcriptional complexes on the integrated viral promoter exhibiting a continuum of basal activities, all of which are fully responsive to Tat.

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IRF-1 Is Required for Full NF-κB Transcriptional Activity at the Human Immunodeficiency Virus Type 1 Long Terminal Repeat Enhancer

Journal of Virology ◽

10.1128/jvi.00599-07 ◽

2008 ◽

Vol 82 (7) ◽

pp. 3632-3641 ◽

Cited By ~ 62

Author(s):

Marco Sgarbanti ◽

Anna L. Remoli ◽

Giulia Marsili ◽

Barbara Ridolfi ◽

Alessandra Borsetti ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

Long Terminal Repeat ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Transcriptional Activity ◽

Terminal Repeat ◽

Viral Transactivator ◽

Immunodeficiency Virus ◽

Hiv 1

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) gene expression is controlled by a complex interplay between viral and host factors. We have previously shown that interferon-regulatory factor 1 (IRF-1) is stimulated early after HIV-1 infection and regulates promoter transcriptional activity even in the absence of the viral transactivator Tat. In this work we demonstrate that IRF-1 is also required for full NF-κB transcriptional activity. We provide evidence that IRF-1 and NF-κB form a functional complex at the long terminal repeat (LTR) κB sites, which is abolished by specific mutations in the two adjacent κB sites in the enhancer region. Silencing IRF-1 with small interfering RNA resulted in impaired NF-κB-mediated transcriptional activity and in repressed HIV-1 transcription early in de novo-infected T cells. These data indicate that in early phases of HIV-1 infection or during virus reactivation from latency, when the viral transactivator is absent or present at very low levels, IRF-1 is an additional component of the p50/p65 heterodimer binding the LTR enhancer, absolutely required for efficient HIV-1 replication.

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