A natural antisense RNA derived from the HIV-1 env gene encodes a protein which is recognized by circulating antibodies of HIV+ individuals

434

590

The RNA genome of the human T-cell leukemia virus type 1 (HTLV-1) codes for proteins involved in infectivity, replication, and transformation. We report in this study the characterization of a novel viral protein encoded by the complementary strand of the HTLV-1 RNA genome. This protein, designated HBZ (for HTLV-1 bZIP factor), contains a N-terminal transcriptional activation domain and a leucine zipper motif in its C terminus. We show here that HBZ is able to interact with the bZIP transcription factor CREB-2 (also called ATF-4), known to activate the HTLV-1 transcription by recruiting the viral trans-activator Tax on the Taxresponsive elements (TxREs). However, we demonstrate that the HBZ/CREB-2 heterodimers are no more able to bind to the TxRE and cyclic AMP response element sites. Taking these findings together, the functional inactivation of CREB-2 by HBZ is suggested to contribute to regulation of the HTLV-1 transcription. Moreover, the characterization of a minus-strand gene protein encoded by HTLV-1 has never been reported until now.Human T-cell leukemia virus type 1 (HTLV-1), the etiologic agent of adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis, is a T-cell-tropic virus that belongs to the HTLV-bovine leukemia virus (HTLV-BLV) group of the retrovirus family. Other group members include HTLV-2, BLV, and the simian T-cell leukemia viruses. All retroviruses share similarity in their genome organization, with four genes encoding proteins necessary for the production of infectious virions, the order of these genes being invariably gag, pro, pol, env (from 5Ј to 3Ј) (Fig. 1A). gag codes for internal structural proteins of the virion, pro codes for the viral protease, pol codes for reverse transcriptase, and env codes for envelope glycoproteins of the virion. The expression of the HTLV-1 genome is controlled by two regulatory genes, the rex and tax genes, located in the 3Ј region of the viral genome. Tax is a potent transactivator of viral transcription (5, 30), and Rex acts at the posttranscriptional level by modulating the transport of the viral RNAs (14). Moreover, the HTLV-1 genome carries between the env gene and the 3Ј long terminal repeat (LTR) other open reading frames encoding proteins with unknown functions. All these viral proteins are encoded by the viral plus-strand RNA.The trans-activation of the viral transcription by Tax operates through three 21-bp repeats (6, 28) located in the U3 region of the LTR. These conserved repeats, called Tax-responsive elements (TxREs), contain an imperfect cyclic AMP response element (CRE) (17) that is recognized by CREB (4, 37, 38) and CREM (29), two members of the activating transcription factor/CRE-binding protein (ATF/CREB) family. These factors are characterized by basic leucine zipper (bZIP) C-terminal structures required for DNA binding and protein dimerization. To activate transcription of the HTLV-1 genome, Tax interacts with CREB or CREM bound to the TxREs (4, 38) and then can recruit the transcriptional coactivator CR...

Section: Discussionmentioning

confidence: 99%

The Complementary Strand of the Human T-Cell Leukemia Virus Type 1 RNA Genome Encodes a bZIP Transcription Factor That Down-Regulates Viral Transcription

Gaudray

Gachon

Basbous

et al. 2002

434

590

“…Importantly, these CTL responses are not limited to ARFs in the sense direction, but may also target antisense-encoded ARFs (5,6). Antisense transcription of known host genes in human and rodent cells has been extensively described (7)(8)(9)(10), and the existence of an antisense protein (ASP) in HIV was first proposed more than 20 years ago (10)(11)(12). The extent to which such viral antisense transcripts encode functional proteins remains largely unknown.…”

Section: Irus-specific Cd8mentioning

confidence: 99%

Immune Screening Identifies Novel T Cell Targets Encoded by Antisense Reading Frames of HIV-1

Berger

Llano

Carlson

et al. 2015

k Cytotoxic-T lymphocyte (CTL) responses to epitopes in alternative HIV reading frames have been reported. However, the extent of CTL responses to putative proteins encoded in antisense reading frames is unknown. Using sequence alignments and computational approaches, we here predict five potential antisense HIV proteins and characterize common CTL responses against them. Results suggest that antisense-derived sequences are commonly transcribed and translated and could encode functional proteins that contain important targets of anti-HIV cellular immunity. V irus-specific CD8ϩ cytotoxic-T lymphocyte (CTL) responses are important in the control of HIV infection (1-3). Accumulating evidence indicates that in addition to CTL responses targeting known structural and nonstructural HIV proteins, CTL responses to epitopes in alternative reading frames (ARFs) of HIV can contribute to in vivo immune selection pressure (4-6). Importantly, these CTL responses are not limited to ARFs in the sense direction, but may also target antisense-encoded ARFs (5, 6). Antisense transcription of known host genes in human and rodent cells has been extensively described (7-10), and the existence of an antisense protein (ASP) in HIV was first proposed more than 20 years ago (10-12). The extent to which such viral antisense transcripts encode functional proteins remains largely unknown.Here, we sought to provide further evidence supporting the existence of fully translated ASPs in HIV by assessing the presence of ASP-specific cellular host immune responses. In a first step, 355 unique full-length HIV-1 clade B sequences were retrieved from the Los Alamos database (13) to generate a consensus sequence for all three antisense reading frames. Five sequences starting with a classical methionine translation start codon followed by Ͼ150 nucleotides without stop codons and with conservation of Ͼ50% (range, 56 to 78%) at all amino acid positions were identified (Fig. 1). The highest conservation scores were obtained for the MAN sequence (entropy score, 0.04; i.e., 99.4% conservation), followed by those for MLK (0.11, 98.2%), MGS (0.18, 97.9%), MPQ (0.16, 97.4%), and the putative MAL protein (0.31, 92.5%). This analysis placed the five ASPs in the range of conservation between the highly conserved HIV p24 (0.21, 99.7%) and the variable Vpu (0.34, 92%) proteins, overall being comparable to other regular reading frame-encoded HIV proteins (14). The ASP sequences ranged from 50 to 179 amino acids in length and included a previously predicted ASP (11). To find immunological evidence that proteins were indeed produced from these antisense open reading frames (ORFs), HIV-infected individuals were tested for T cell responses against corresponding consensus overlapping peptide (OLP) sets by gamma interferon (IFN-␥)-enzyme-linked immunosorbent spot (ELISpot) assay (4) (see Table 1 in the supplemental material). A total of 60 HLA-typed individuals, including 40 chronically HIV-infected subjects and 20 HIV-uninfected controls, were tested. Responses to the A...

“…Antisense transcription has also been suggested in other retroviruses like HIV-1 (2,8,9,27,33,36,44,48). We have recently demonstrated that antisense transcription could be detected in HTLV-2 and that the encoded antisense protein of HTLV-2 (APH-2) shares a Tax-inhibiting activity like HBZ (21).…”

mentioning

confidence: 93%

Human T-Cell Lymphotropic Virus Type 3 (HTLV-3)- and HTLV-4-Derived Antisense Transcripts Encode Proteins with Similar Tax-Inhibiting Functions but Distinct Subcellular Localization

Larocque

Halin

Marriott

et al. 2011