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A Point Mutation in the HIV-1 Tat Responsive Element Is Associated

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A Point Mutation in the HIV-1 Tat Responsive Element Is Associated Proc. Natl. Acad. Sci. USA Vol. 93, pp. 6377-6381, June 1996 Medical Sciences A point mutation in the HIV-1 Tat responsive element is associated with postintegration latency STEPHANE EMILIANI*, CARINE VAN LINT*, WOLFGANG FISCHLE*, PETER PARAS, JR.t, MELANIE Orr*, JOHN BRADYt, AND ERIC VERDIN*§ *The Picower Institute for Medical Research, Manhasset, NY 11030; tLaboratory of Viral and Molecular Pathogenesis, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892; and tLaboratory of Molecular Virology, National Cancer Institute, Bethesda, MD 20892 Communicated by Anthony Cerami, the Picower Institute for Medical Research, Manhasset, NY February 27, 1996 (received for review October 25, 1995) ABSTRACT Study of the mechanism of HIV-1 postint- environment might play a role in causing latency (14, 15). In egration latency in the ACH2 cell line demonstrates that these agreement with this model, we have demonstrated that a cells failed to increase HIV-1 production following treatment chromatin disruption.occurs in the promoter of HIV-1 during with exogenous Tat. Reasoning that the defect in ACH2 cells transcriptional activation in ACH2 cells (16, 17). However, this involves the Tat response, we analyzed the sequence of tat chromatin disruption is not specific for the ACH2 cells and has cDNA and Tat responsive element (TAR) from the virus been observed in all cell lines examined, independent of the integrated in ACH2. Tat cDNA sequence is closely related to site of integration of the virus (16, 17). On the other hand, the that of HIVLAI, and the encoded protein is fully functional in virus integrated in the ACH2 cells is uniquely unresponsive to terms of long terminal repeat (LTR) transactivation. Cloning exogenous Tat (18, 19), suggesting that the Tat-Tat responsive of a region corresponding to the 5'-LTR from ACH2, however, element (TAR) axis might be altered in HIV-lACH2. Here, we identified a point mutation (C37 -> T) in TAR. This mutation report that a single point mutation located in the TAR impaired Tat responsiveness of the LTR in transient trans- accounts for postintegration latency in the ACH2 cell line. fection assays, and the measured defect was complemented in cells that had been treated with tetradecanoyl phorbol acetate MATERIALS AND METHODS or tumor necrosis factor type a (TNF-a). A compensatory mutation in TAR (G28 -> A), designed to reestablish base Cell Culture. All cell lines were obtained from the AIDS pairing in the TAR hairpin, restored wild-type Tat respon- Research and Reference Reagent Program (National Institute siveness. When the (C37 -> T) mutation was introduced in an of Allergy and Infectious Diseases, National Institutes of infectious clone of HIV-1, no viral production was measured Health, Bethesda, MD) and grown as reported (16, 17). in the absence of TNF-a, whereas full complementation was Cloning of ACH2 tat cDNA. RNA was purified from tetra- observed when the infection was conducted in the presence of decanoyl phorbol acetate (TPA)-treated ACH2 cells (10 nM TNF-a or when a compensatory mutation (G28 -> A) was for 16 hr) using Trizol (GIBCO/BRL). Oligo(dT)-primed introduced into TAR. These experiments identify a novel cDNA synthesis was performed using the lst-Strand cDNA mutation associated with HIV-1 latency and suggest that synthesis kit (CLONTECH). This cDNA was used as a sub- alterations in the Tat-TAR axis can be a crucial determinant strate in PCRs using oligonucleotide primers with the follow- of the latent phenotype in infected individuals. ing sequence: sense, 5'-ACGTGGATCCTTACTCAACAGA- GGAGAGCAAGAA=nt5409-3'andantisense,5A'-A=nt8O80GAT- Although active viral replication occurs during all phases of CGTCCCAGATAAGTGCTAAGGATCCGTTCA-3' (a new HIV-1 infection in patients (1, 2), evidence has been presented BamHI site, introduced to facilitate cloning, is indicated in that a large proportion of HIV-1-infected cells carry the virus boldface type). The PCR fragment was gel-purified, digested in an latent state (3-7). This state is characterized by the with BamHI, and ligated into the unique BamHI site ofpREP9 presence of integrated viral DNA and low levels of viral RNA (Invitrogen). The sequences of 10 independent transformants or protein and has been coined postintegration latency (8, 9). were determined using an automated sequencer and the Prism The mechanism of postintegration latency and its relevance to kit (Applied Biosystems). The nucleotide sequence all 10 HIV pathogenesis are subjects of intense study; however, no clones were identical, in agreement with the fact that the description at the molecular level has emerged. ACH2 cell line contains a single integrated copy of HIV-1. The The ACH2 cell line was established by rescuing and cloning same strategy was used to clone the two-exon form of tat from A3.01 cells surviving an acute infection with HIVLA1 and the vector pCV1 (20) with the following oligonucleotides: contains a single integrated copy of HIV-1 (10, 11). Under sense,5'-ACGTGGATCCTTACTCAACAGAGGAGAGCA- basal conditions, the virus integrated in ACH2 cells (called AGAA-3' and antisense, 5'-CGCGGATCCGATGGAG CCA- HIVACH2 hereafter) shows very low basal transcription and a GTAGATCCTAGACTAGAGC-3' (boldface type indicates predominance of multiply spliced transcripts encoding HIV-1 BamHI sequence). This vector is designated pREP9/tat2exon. regulatory proteins (12). Upon stimulation with tumor necro- Cloning of ACH2 Provirus Long Terminal Repeat (LTR). sis factor type a (TNF-a) or phorbol esters, an increase in DNA purified- from exponentially growing ACH2 cells, as transcription is noted, followed by the appearance of unspliced described (17), was used in PCR with the following primers: transcripts encoding viral structural proteins and viral produc- sense, 5'-GCCTGCAGTGGAAGGGCTAATTCACTCCCA- tion (11-13). The molecular mechanism underlying the sup- ACG (nt 1-25, HIVLAI) and antisense, 5'-GCTCTAGACTC- pression of transcription under basal conditions in ACH2 cells is unclear. It has been suggested that the site of integration of Abbreviations: TNF-a, tumor necrosis factor type a; TAR, Tat the virus in the cellular genome and its local chromatin responsive element; TPA, tetradecanoyl phorbol acetate; LTR, long terminal repeat; CAT, chloramphenicol acetyltransferase; TCID5o, tissue culture 50% infective dose. The publication costs of this article were defrayed in part by page charge §To whom reprint requests should be addressed at: The Picower payment. This article must therefore be hereby marked "advertisement" in Institute for Medical Research, 350 Community Drive, Manhasset, accordance with 18 U.S.C. §1734 solely to indicate this fact. NY 11030. e-mail: [email protected]. 6377 Downloaded by guest on October 2, 2021 6378 Medical Sciences: Emiliani et al. Proc. Natl. Acad. Sci. USA 93 (1996) TCTCCTTCTAGCCTCCGC (nt 791-769, HIVLAI). These 400 primers contain added restriction sites for PstI (sense) and XbaI (antisense) restriction enzymes (highlighted in boldface type above) to allow directional cloning of the PCR product. 300 The PCR fragment cloned into pCAT-BASIC (Promega) was S1 digested with PstI and XbaI. Several clones were selected, sequenced on both strands, and found to have identical 0 200 sequences. This plasmid is designated pLTRACH2-CAT. The same strategy was used to clone the LTR of HIVLA, using .4 pLAI2 as a substrate in the PCR. This plasmid is designated pLTRLAI-CAT. a.i 100 DEAE-Dextran Transient Transfections. Transient trans- fection assays were carried as described (21). Transfection experiments were repeated three or more times in duplicate or triplicate. Transfection efficiency varied by <20% from ex- 1 10 100 1000 10000 periment to experiment. Tat (ng) Site-Directed Mutagenesis. Mutagenesis was performed using double-stranded plasmids and a selection oligonucleo- FIG. 1. Effect of exogenous Tat on HIV-1 production in ACH2 and tide with the Transformer kit (CLONTECH). Two different Ul cells. Each cell line (106 cells) was incubated with purified Tat for mutations, corresponding to the changes (C37 -> T) and (G28 24 hr (28), and viral production was estimated by measuring secreted -- A + C37 -> T) were introduced into pLTR1AI-CAT using p24 antigen in supernatants. ACH2, *; and Ul,E. the following oligonucleotides: 5'-GAGCCTGGGAGT- TCTCTGGCTAAC-3',5'-CCAGATTTGAACCTGGGAGT- components necessary for Tat activity. These include: (i) the TCTCTGGCTAAC-3' (mutations in boldface type), and a gene for Tat itself, as some tat mutations exhibit a dominant selection oligonucleotide changing a unique BamHI site in negative phenotype (30, 31); (ii) cellular cofactors necessary pLTRLAI-CAT into an SphI site, 5'-CATGTCTGCATGCCCC- for Tat activity; and (iii) the TAR, where Tat and one or GGAATTC-3'. One mutation was introduced in pLTRACH2- several cofactors bind. CAT (T37 -> C) with the oligonucleotide 5'-GAGCCTGGG- Sequence and Function Analysis of tat Gene from HIVACH2- AGCTCTCTGGCTAAC-3' and the same selection oligonu- First, we examined the sequence of the tat gene from ACH2 cleotide as above. provirus and the function of the Tat protein that it encodes. A Generation of Infectious Provirus. A NarI-SphI fragment fragment corresponding to the two-exon form of the tat gene containing the complete HIV-1 LTR was obtained after was amplified by PCR using cDNA obtained from the ACH2 partial digestion with Narl and complete digestion with SphI cells and cloned downstream of the RSV promoter. Analysis of of pNL4-3 (22). This fragment
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