A Unique Thyroid Hormone Response Element in the Human Immunodeficiency Virus Type 1 Long Terminal Repeat That Overlaps the Sp1 Binding Sites

We report that thyroid hormone (T3) receptor (T3R) can activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). Purified chick T3R-alpha 1 (cT3R-alpha 1) binds as monomers and homodimers to a region in the LTR (nucleotides -104 to -75 [-104/-75]) which contains two tandem NF-kappa B binding sites and to a region (-80/-45) which contains three Sp1 binding sites. In contrast, human retinoic acid receptor alpha (RAR-alpha) and mouse retinoid X receptor beta (RXR-beta) do not bind to these elements. However, RXR-beta binds to these elements as heterodimers with cT3R-alpha 1 and to a lesser extent with RAR-alpha. Gel mobility shift assays also revealed that purified NF-kappa B p50/65 or p50/50 can bind to one but not both NF-kappa B sites simultaneously. Although the binding sites for p50/65, p50/50, and T3R, or Sp1 and T3R, overlap, their binding is mutually exclusive, and with the inclusion of RXR-beta, the major complex is the RXR-beta-cT3R-alpha 1 heterodimer. The NF-kappa B region of the LTR and the NF-kappa B elements from the kappa light chain enhancer both function as T3 response elements (TREs) when linked to a heterologous promoter. The TREs in the HIV-1 NF-kappa B sites appear to be organized as a direct repeat with an 8- or 10-bp gap between the half-sites. Mutations within the NF-kappa B motifs which eliminate binding of cT3R-alpha 1 also abolish stimulation by T3, indicating that cT3R-alpha 1 binding to the Sp1 region does not independently mediate activation by T3. The Sp1 region, however, is converted to a functionally strong TRE by the viral tat factor. These studies indicate that the HIV-1 LTR contains both tat-dependent and tat-independent TREs and reveal the potential for T3R to modulate other genes containing NF-kappa B- and Sp1-like elements. Furthermore, they indicate the importance of other transcription factors in determining whether certain T3R DNA binding sequences can function as an active TRE.

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The NF-kappa B and Sp1 motifs of the human immunodeficiency virus type 1 long terminal repeat function as novel thyroid hormone response elements.

Molecular and Cellular Biology ◽

10.1128/mcb.13.8.5057 ◽

1993 ◽

Vol 13 (8) ◽

pp. 5057-5069 ◽

Cited By ~ 38

Author(s):

V Desai-Yajnik ◽

H H Samuels

Keyword(s):

Human Immunodeficiency Virus ◽

Thyroid Hormone ◽

Long Terminal Repeat ◽

Human Immunodeficiency Virus Type ◽

Binding Sites ◽

Nf Kappa B ◽

Response Elements ◽

Immunodeficiency Virus ◽

Hiv 1

We report that thyroid hormone (T3) receptor (T3R) can activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). Purified chick T3R-alpha 1 (cT3R-alpha 1) binds as monomers and homodimers to a region in the LTR (nucleotides -104 to -75 [-104/-75]) which contains two tandem NF-kappa B binding sites and to a region (-80/-45) which contains three Sp1 binding sites. In contrast, human retinoic acid receptor alpha (RAR-alpha) and mouse retinoid X receptor beta (RXR-beta) do not bind to these elements. However, RXR-beta binds to these elements as heterodimers with cT3R-alpha 1 and to a lesser extent with RAR-alpha. Gel mobility shift assays also revealed that purified NF-kappa B p50/65 or p50/50 can bind to one but not both NF-kappa B sites simultaneously. Although the binding sites for p50/65, p50/50, and T3R, or Sp1 and T3R, overlap, their binding is mutually exclusive, and with the inclusion of RXR-beta, the major complex is the RXR-beta-cT3R-alpha 1 heterodimer. The NF-kappa B region of the LTR and the NF-kappa B elements from the kappa light chain enhancer both function as T3 response elements (TREs) when linked to a heterologous promoter. The TREs in the HIV-1 NF-kappa B sites appear to be organized as a direct repeat with an 8- or 10-bp gap between the half-sites. Mutations within the NF-kappa B motifs which eliminate binding of cT3R-alpha 1 also abolish stimulation by T3, indicating that cT3R-alpha 1 binding to the Sp1 region does not independently mediate activation by T3. The Sp1 region, however, is converted to a functionally strong TRE by the viral tat factor. These studies indicate that the HIV-1 LTR contains both tat-dependent and tat-independent TREs and reveal the potential for T3R to modulate other genes containing NF-kappa B- and Sp1-like elements. Furthermore, they indicate the importance of other transcription factors in determining whether certain T3R DNA binding sequences can function as an active TRE.

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Evolution of the Human Immunodeficiency Virus Type 1 Long Terminal Repeat Promoter by Conversion of an NF-κB Enhancer Element into a GABP Binding Site

Journal of Virology ◽

10.1128/jvi.73.2.1331-1340.1999 ◽

1999 ◽

Vol 73 (2) ◽

pp. 1331-1340 ◽

Cited By ~ 51

Author(s):

Koen Verhoef ◽

Rogier W. Sanders ◽

Veronique Fontaine ◽

Shigetaka Kitajima ◽

Ben Berkhout

Keyword(s):

Human Immunodeficiency Virus ◽

Transcription Factor ◽

Long Terminal Repeat ◽

Binding Site ◽

Human Immunodeficiency Virus Type ◽

Binding Sites ◽

Immunodeficiency Virus ◽

Ltr Promoter ◽

Hiv 1

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) transcription is regulated by the viral Tat protein and cellular factors, of which the concentration and activity may depend on the cell type. Viral long terminal repeat (LTR) promoter sequences are therefore optimized to suit the specific nuclear environment of the target host cell. In long-term cultures of a Tat-defective, poorly replicating HIV-1 mutant, we selected for a faster-replicating virus with a 1-nucleotide deletion in the upstream copy of two highly conserved NF-κB binding sites. The variant enhancer sequence demonstrated a severe loss of NF-κB binding in protein binding assays. Interestingly, we observed a new binding activity that is specific for the variant NF-κB sequence and is present in the nuclear extract of unstimulated cells that lack NF-κB. These results suggest that inactivation of the NF-κB site coincides with binding of another transcription factor. Fine mapping of the sequence requirements for binding of this factor revealed a core sequence similar to that of Ets binding sites, and supershift assays with antibodies demonstrated the involvement of the GABP transcription factor. Transient transfection experiments with LTR-chloramphenicol acetyltransferase constructs indicated that the variant LTR promoter is specifically inhibited by GABP in the absence of Tat, but this promoter was dramatically more responsive to Tat than the wild-type LTR. Introduction of this GABP site into the LAI virus yielded a specific gain of fitness in SupT1 cells, which contain little NF-κB protein. These results suggest that GABP potentiates Tat-mediated activation of LTR transcription and viral replication in some cell types. Conversion of an NF-κB into a GABP binding site is likely to have occurred also during the worldwide spread of HIV-1, as we noticed the same LTR modification in subtype E isolates from Thailand. This typical LTR promoter configuration may provide these viruses with unique biological properties.

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Chromatin Disruption and Histone Acetylation in Regulation of the Human Immunodeficiency Virus Type 1 Long Terminal Repeat by Thyroid Hormone Receptor

Molecular and Cellular Biology ◽

10.1128/mcb.22.12.4043-4052.2002 ◽

2002 ◽

Vol 22 (12) ◽

pp. 4043-4052 ◽

Cited By ~ 50

Author(s):

Shao-Chung Victor Hsia ◽

Yun-Bo Shi

Keyword(s):

Human Immunodeficiency Virus ◽

Thyroid Hormone ◽

Long Terminal Repeat ◽

Histone Acetylation ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Immunodeficiency Virus ◽

Hiv 1

ABSTRACT The human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) controls the expression of HIV-1 viral genes and thus viral propagation and pathology. Numerous host factors participate in the regulation of the LTR promoter, including thyroid hormone (T3) receptor (TR). In vitro, TR can bind to the promoter region containing the NF-κB and Sp1 binding sites. Using the frog oocyte as a model system for chromatin assembly mimicking that in somatic cells, we demonstrated that TR alone and TR/RXR (9-cis retinoic acid receptor) can bind to the LTR in vivo independently of T3. Consistent with their ability to bind the LTR, both TR and TR/RXR can regulate LTR activity in vivo. In addition, our analysis of the plasmid minichromosome shows that T3-bound TR disrupts the normal nucleosomal array structure. Chromatin immunoprecipitation assays with anti-acetylated-histone antibodies revealed that unliganded TR and TR/RXR reduce the local histone acetylation levels at the HIV-1 LTR while T3 treatment reverses this reduction. We further demonstrated that unliganded TR recruits corepressors and at least one histone deacetylase. These results suggest that chromatin remodeling, including histone acetylation and chromatin disruption, is important for T3 regulation of the HIV-1 LTR in vivo.

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