Phorbol ester-mediated induction of HIV-1 from a chronically infected promonocyte clone: blockade by protein kinase inhibitors and relationship to tat-directed trans-activation

Defining the Effects of PKC Modulator HIV Latency-Reversing Agents on Natural Killer Cells

Background

Latency reversing agents (LRAs) such as protein kinase C (PKC) modulators can reduce rebound-competent HIV reservoirs in small animal models. Furthermore, administration of natural killer (NK) cells following LRA treatment improves this reservoir reduction. It is currently unknown why the combination of a PKC modulator and NK cells is so potent and whether exposure to PKC modulators may augment NK cell function in some way.

Methods

Primary human NK cells were treated with PKC modulators (bryostatin-1, prostratin, or the designed, synthetic bryostatin-1 analog SUW133), and evaluated by examining expression of activation markers by flow cytometry, analyzing transcriptomic profiles by RNA sequencing, measuring cytotoxicity by co-culturing with K562 cells, assessing cytokine production by Luminex assay, and examining the ability of cytokines and secreted factors to independently reverse HIV latency by co-culturing with Jurkat-Latency (J-Lat) cells.

Results

PKC modulators increased expression of proteins involved in NK cell activation. Transcriptomic profiles from PKC-treated NK cells displayed signatures of cellular activation and enrichment of genes associated with the NFκB pathway. NK cell cytotoxicity was unaffected by prostratin but significantly decreased by bryostatin-1 and SUW133. Cytokines from PKC-stimulated NK cells did not induce latency reversal in J-Lat cell lines.

Conclusions

Although PKC modulators have some significant effects on NK cells, their contribution in "kick and kill" strategies is likely due to upregulating HIV expression in CD4+ T cells, not directly enhancing the effector functions of NK cells. This suggests that PKC modulators are primarily augmenting the "kick" rather than the "kill" arm of this HIV cure approach.

Targeting NF-κB signaling with protein kinase C agonists as an emerging strategy for combating HIV latency

Highly active antiretroviral therapy (HAART) is very effective in suppressing HIV-1 replication and restoring immune functions in HIV-infected individuals. However, it fails to eradicate the latent viral reservoirs and fully resolve chronic inflammation in HIV infection. The "shock-and-kill" strategy was recently proposed to induce latent HIV expression in the presence of HAART. Recent studies have shown that the protein kinase C (PKC) agonists are highly potent in inducing latent HIV expression from the viral reservoirs in vitro and ex vivo and in protecting primary CD4(+) T cells from HIV infection through down-modulation of their HIV coreceptor expression. The PKC agonists are excellent candidates for advancing to clinical HIV eradication strategies. This article will present a critical review of the structure and function of known PKC agonists, their mechanisms for the reactivation of latent HIV expression, and the potential of these compounds for advancing clinical HIV eradication strategies.

Urokinase plasminogen activator inhibits HIV virion release from macrophage-differentiated chronically infected cells via activation of RhoA and PKCε

BACKGROUND

HIV replication in mononuclear phagocytes is a multi-step process regulated by viral and cellular proteins with the peculiar feature of virion budding and accumulation in intra-cytoplasmic vesicles. Interaction of urokinase-type plasminogen activator (uPA) with its cell surface receptor (uPAR) has been shown to favor virion accumulation in such sub-cellular compartment in primary monocyte-derived macrophages and chronically infected promonocytic U1 cells differentiated into macrophage-like cells by stimulation with phorbol myristate acetate (PMA). By adopting this latter model system, we have here investigated which intracellular signaling pathways were triggered by uPA/uPAR interaction leading the redirection of virion accumulation in intra-cytoplasmic vesicles.

RESULTS

uPA induced activation of RhoA, PKCδ and PKCε in PMA-differentiated U1 cells. In the same conditions, RhoA, PKCδ and PKCε modulated uPA-induced cell adhesion and polarization, whereas only RhoA and PKCε were also responsible for the redirection of virions in intracellular vesicles. Distribution of G and F actin revealed that uPA reorganized the cytoskeleton in both adherent and polarized cells. The role of G and F actin isoforms was unveiled by the use of cytochalasin D, a cell-permeable fungal toxin that prevents F actin polymerization. Receptor-independent cytoskeleton remodeling by Cytochalasin D resulted in cell adhesion, polarization and intracellular accumulation of HIV virions similar to the effects gained with uPA.

CONCLUSIONS

These findings illustrate the potential contribution of the uPA/uPAR system in the generation and/or maintenance of intra-cytoplasmic vesicles that actively accumulate virions, thus sustaining the presence of HIV reservoirs of macrophage origin. In addition, our observations also provide evidences that pathways controlling cytoskeleton remodeling and activation of PKCε bear relevance for the design of new antiviral strategies aimed at interfering with the partitioning of virion budding between intra-cytoplasmic vesicles and plasma membrane in infected human macrophages.

Practical synthesis of prostratin, DPP, and their analogs, adjuvant leads against latent HIV

Although antiretroviral therapies have been effective in decreasing active viral loads in AIDS patients, the persistence of latent viral reservoirs prevents eradication of the virus. Prostratin and DPP (12-deoxyphorbol-13-phenylacetate) activate the latent virus and thus represent promising adjuvants for antiviral therapy. Their limited supply and the challenges of accessing related structures have, however, impeded therapeutic development and the search for clinically superior analogs. Here we report a practical synthesis of prostratin and DPP starting from phorbol or crotophorbolone, agents readily available from renewable sources, including a biodiesel candidate. This synthesis reliably supplies gram quantities of the therapeutically promising natural products, hitherto available only in low and variable amounts from natural sources, and opens access to a variety of new analogs.

Recent status of HIV-1 gene expression inhibitors

Human immunodeficiency virus type 1 (HIV-1) gene expression and transcription is a crucial step in the viral replication cycle, which is considered to be a potential target for inhibition of HIV-1. Among the factors involved in this step, the cellular protein nuclear factor (NF)-kappaB is the most powerful inducer of HIV-1 gene expression. On the other hand, the viral protein Tat plays a central role in sustaining a high level of HIV-1 replication. Several compounds have been reported to selectively inhibit the functions of Tat and NF-kappaB. Tat inhibitors target either the Tat/TAR RNA interaction or the Tat cofactor cyclin-dependent kinase 9/cyclin T1. Antioxidants, protein kinase C inhibitors, and IkappaB kinase inhibitors are known to suppress the activation of NF-kappaB. Although some of the compounds inhibit HIV-1 replication in cell cultures at low concentrations, they also have considerable toxicity to the host cells. Considering the increase of treatment failure cases in highly active antiretroviral therapy due to the emergence of multidrug resistance, HIV-1 gene expression inhibitors should be extensively studied as alternative approach to effective anti-HIV-1 chemotherapy.

Mechanisms of HIV receptor and co-receptor down-regulation by prostratin: role of conventional and novel PKC isoforms

Prostratin is an unusual non-tumour promoting phorbol ester with potential as an inductive adjuvant therapy for highly active antiretroviral therapy (HAART) due to its ability to up-regulate viral expression from latent provirus. In addition, prostratin is also able to inhibit de novo HIV infection most probably because it induces down-regulation of HIV receptors from the surface of target cells. In this study, we investigate the mechanisms by which prostratin down-regulates HIV receptor and co-receptor surface expression in lymphocytic and monocytic cell lines. Our results indicate that prostratin induces down-regulation of surface expression of CD4 and CXCR4, but not CCR5, in various cell lines. Down-regulation of CD4 and CXCR4 by prostratin is achieved by internalization through receptor-mediated endocytosis and/or macropinocytosis, which is then followed by degradation of these molecules. Because prostratin is a protein kinase C (PKC) activator, we next examined the potential contribution of distinct PKC isoforms to down-regulate CD4 and CXCR4 in response to prostratin stimulation. Although exposure of cells to prostratin or phorbol-myristate-acetate (PMA) induces the translocation of several PKC isoforms to the plasma membrane, the use of specific PKC inhibitors revealed that novel PKCs are the main mediators of the prostratin-induced CD4 down-regulation, whereas both conventional and novel PKCs contribute to CXCR4 down-regulation. Altogether these results showed that prostratin, through the activation of conventional and/or novel PKC isoforms, rapidly reduces cell surface expression of CD4 and CXCR4, but not CCR5, by inducing their internalization and degradation.

Interactions among human immunodeficiency virus (HIV)-1, interferon-gamma and receptor of activated NF-kappa B ligand (RANKL): implications for HIV pathogenesis

We reported recently that exposure of human T cells to soluble HIV-1 envelope glycoprotein gp120 induced biologically active tumour necrosis factor (TNF)-alpha-related cytokine receptor of activated NF-kappaB ligand (RANKL), the primary drive to osteoclast differentiation and bone resorption. Furthermore, certain anti-HIV protease inhibitors linked clinically to accelerated bone loss in HIV disease blocked the physiological control of RANKL activity by interferon (IFN)-gamma through inhibition of degradation of the RANKL nuclear adapter signalling protein, TNF receptor associated protein 6 (TRAF6). We now report a series of reciprocal interactions among HIV-1, RANKL and IFN-gamma. RANKL augmented HIV replication in acutely and chronically infected cells of T lymphocyte and monocyte lineage, effects which occurred at a transcriptional level in conjunction with activation of NF-kappaB. TNF-alpha and RANKL were markedly synergistic in induction of HIV. Low pharmacological levels of IFN-gamma (0.75-3 ng/ml) suppressed RANKL-driven enhancement of HIV replication, as did L-T6DP-1, a cell-permeable peptide inhibitor of TRAF6. In contrast, HIV replication induced by TNF-alpha and phorbol ester were not inhibited, and in some cases augmented, by IFN-gamma. We conclude that a positive feedback loop exists between RANKL production and HIV replication, which may be relevant to both the pathophysiology of HIV-linked osteopenia and control of HIV growth. This pathway appears distinct from those of other cytokine activators of HIV, with respect to its utilization of TRAF6 and its suppression by IFN-gamma. These data raise the possibility that TRAF-specific inhibitory peptides, alone or in conjunction with IFN-gamma, could be used to regulate HIV activation in vivo.

Vanicosides C-F, new phenylpropanoid glycosides from Polygonum pensylvanicum

The isolation of the protein kinase C inhibitors, vanicoside A (1) and vanicoside B (2), from Polygonum pensylvanicum prompted continued interest in the active principles of this plant. A new, more efficient isolation procedure has been developed to facilitate separation of homologues of vanicosides A and B from the complex extract. Several new phenylpropanoid glycosides have since been isolated. The structures of these principles were determined to be 2'-O-acetylhydropiperoside (4), 6'-O-p-coumarylhydropiperoside (5), 4'-O-acetylvanicoside A (6), and 3'-O-acetylvanicoside B (7) using negative ion FABMS, 1H NMR, and 2D NMR techniques.

The cAMP-dependent protein kinase A and protein kinase C-beta pathways synergistically interact to activate HIV-1 transcription in latently infected cells of monocyte/macrophage lineage

The HIV-1 long terminal repeat (LTR) responds to a variety of cellular signal transduction pathways. We demonstrate that the cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) signaling pathways synergize to increase HIV-1 LTR-mediated transcription and viral replication in a latently infected promonocytic cell line (U1). The LTR-mediated synergy induced by cholera toxin (Ctx), a potent activator of the cAMP-dependent PKA pathway, and the PKC activator phorbol 12-myristate 13-acetate (PMA) was abrogated by a PKC-beta-specific inhibitor (LY333531). In contrast, the LTR-mediated synergy induced by Ctx and TNF alpha was not affected by LY333531. The synergy induced by Ctx and TNF alpha was also abrogated by mutation of the cAMP-responsive downstream sequence elements (DSE) in the 5' untranslated leader region, whereas the DSE mutations did not affect the synergy induced by Ctx and PMA. These distinctions indicate that Ctx cooperates differently with TNF alpha and PMA to activate the HIV-1 LTR. Ctx and PMA synergistically activated AP-1- and NF-kappa B-dependent transcription, even though no cooperative binding of AP-1 or NF-kappa B was observed in gel shift assays. An extensive mutational analysis of the HIV-1 LTR that included the NF-kappa B and AP-1 binding sites revealed no distinct cis-acting element or region within the HIV-1 LTR that was required for the transcriptional synergy. Ctx and PMA also synergistically interact to activate the HTLV-1 LTR. These results indicate that the transcriptional synergy elicited by Ctx and PMA targets multiple functional elements and promoters, requires a cooperative interaction between the PKA and PKC-beta pathways, and differs mechanistically from the transcriptional synergy induced by Ctx and TNF alpha.

Secretion of extracellular factor(s) induced by X-irradiation activates the HIV type 1 long terminal repeat through its kappaB motif

X-irradiation has been used in the treatment of several human diseases, including AIDS-related-malignancies. X-irradiation might induce the transcription and the replication of human immunodeficiency virus type 1 (HIV-1) and enhance nuclear factor kappa B (NF-kappaB). In the present article we show that the activation of the HIV-1 long terminal repeat (LTR) by direct X-irradiation can be mimicked by coculture of transfected cells with X-irradiated nontransfected (HIV-1-negative) cells. In the human colonic carcinoma cell line HT29, the activation seems to depend on an extracellular factor(s) released by a cell line treated with X-rays. The HIV-1 LTR cis-acting element conferring X-indirect responsiveness was identified as the kappaB tandem motif. The two main nuclear HIV-1 kappaB-binding complexes activated by X-direct and -indirect irradiation were the NF-kappaB p50/p65 and c-Rel/p65 heterodimers. Nuclear NF-kappaB activation was dependent on protein neosynthesis. It was partially inhibited by 100 microM pyrrolidine dithiocarbamate, a potent antioxidant drug, but was not correlated with a significant decrease in cellular IkappaBalpha. Furthermore, X-irradiation induces the expression of several cytokine genes generally associated with stress response and antibodies against interleukin 6 and TNF-alpha partially inhibited the X-indirect activation of the HIV-1 LTR. The use of protein kinase C (PKC)-specific inhibitor and of forskolin, an adenylate cyclase activator, suggests that a PKC-dependent pathway and the cAMP intracellular concentration could play a role in the X-indirect enhancement of HIV-1 LTR transcription in the HT29 cell line. In addition, supernatants of an X-irradiated HT29 cell culture activated the HIV-1 stimulation in infected peripheral blood monocytes.

Role of protein kinase C-beta isozyme in activation of latent human immunodeficiency virus type 1 in promonocytic U1 cells by phorbol-12-myristate acetate

Protein kinase C (PKC) appears to play a role in replication of human immunodeficiency virus type 1 (HIV-1). PKC is a family of at least 12 isozymes. In this study, we investigated a role of Ca(2+)-dependent PKC isozymes (alpha, beta, and gamma) in activation of latent HIV-1 in U1, a chronically infected promonocytic cell line, using polyclonal rabbit anti-PKC isozyme antibodies as specific inhibitors. Antibodies were introduced intracellularly by electroporation and then cells were stimulated with PMA. HIV-1 production was measured as p24 antigen using ELISA and reverse transcriptase activity. Anti-PKC beta antibody significantly inhibited PMA-induced HIV-1 production, whereas antibodies against PKC alpha and gamma had no significant effect. Furthermore, anti-PKC beta antibody inhibited PMA-induced activation of NF-kappa B and HIV-1 LTR. Preincubation of anti-PKC beta antibody with its antigenic peptide reversed the inhibitory effect of anti-PKC beta antibody. This study suggest that PKC beta plays a role in PMA-induced activation of latent HIV-1.

Photoactivated inhibition of superoxide generation and protein kinase C activity in neutrophils by blepharismin, a protozoan photodynamically active pigment

Blepharismin is an endogenous photosensitizing pigment found in the protozoan Blepharisma. This pigment inhibited the generation of superoxide anion (O2-.) in neutrophils not only via a diacylglycerol-induced protein kinase C (PKC)-dependent reaction but also by an arachidonate-induced PKC-independent reaction. The inhibition was light and concentration dependent for both reactions. Light-activated inhibition was strong at wavelengths between 520 and 570 nm but not above 610 nm. PKC activity in neutrophils and from rat brain was inhibited by blepharismin in a light- and concentration-dependent manner. Moreover, arachidonate-activated NADPH oxidase activity in a cell-free system was also inhibited by the pigment in a light- and concentration-dependent manner. These results suggest that blepharismin inhibits NADPH oxidase activation through the non-specific inhibition of various membrane-bound enzymes and that this inhibition may also be correlated with that of PKC.

Curcumin is a non-competitive and selective inhibitor of phosphorylase kinase

Recently, we reported that curcumin (diferuloylmethane) inhibits the growth of several different kinds of tumor cells. In order to investigate the mechanism of this inhibition, we examined the effects of curcumin on different protein kinases: highly purified protein kinase A (PkA), protein kinase C (PkC), protamine kinase (cPK), phosphorylase kinase (PhK), autophosphorylation-activated protein kinase (AK) and pp60c-src tyrosine kinase. While all kinases tested were inhibited by curcumin, only PhK was completely inhibited at relatively lower concentrations. At around 0.1 mM curcumin, PhK, pp60c-src, PkC, PkA, AK, and cPK were inhibited by 98%, 40%, 15%, 10%, 1%, and 0.5%, respectively. Lineweaver-Burk plot analysis indicated that curcumin is a non-competitive inhibitor of PhK with a Ki of 0.075 mM. Overall, our results indicate that curcumin is a potent and selective inhibitor of phosphorylase kinase, a key regulatory enzyme involved in the metabolism of glycogen. This has important implications for the anti-proliferative effects of curcumin.

Novel indolocarbazole protein kinase C inhibitors prevent reactivation of HIV-1 in latently infected cells

Suppression of human immunodeficiency virus-1 (HIV-1) reactivation in latently infected cells by protein kinase C (PKC) inhibitors has been described. Based on an initial finding with the indolocarbazole inhibitor Gö 6976 we have examined several members of this new class of potent and specific PKC inhibitors with respect to their ability to prevent the PKC-mediated induction of HIV-1 replication in the latently infected U1 cell line. Two of these compounds strongly inhibited not only PMA-induced release of p24-antigen and infectious virus particles into the supernatant (50% inhibition at 0.04-0.35 microM) but also TNF-alpha-mediated HIV-1 reactivation in the same concentration range. Significant lower toxicities compared to Gö 6976 were observed for the new compounds, with 50% cytotoxic concentrations at 5.2 microM for Gö 7775 and 3.4 microM for Gö 7716. This resulted in selectivity indices which were 10-20-times higher compared to the reference compound Gö 6976 and were comparable to those of registered anti-AIDS drugs. No anti-HIV-1 activity was observed for a closely related indolocarbazole analogue with no inhibitory activity in the PKC in vitro enzyme assay. This study demonstrates the important role of PKC in reactivation of HIV-1 in latently infected cells and points to the potential of indolocarbazoles to preserve the latent state of HIV-1 infection.

Inducible transcriptional activation of the human immunodeficiency virus long terminal repeat by protein kinase inhibitors

The protein kinase inhibitor 2-aminopurine (2-AP) greatly stimulated expression in human promonocytes-macrophages of plasmid constructs carrying various reporter genes (chloramphenicol acetyltransferase, lacZ, firefly luciferase [luc], and Salmonella typhimurium histidinol dehydrogenase [his]) driven by the human immunodeficiency virus type 1 (HIV-1) long terminal repeat. Adenine, adenosine, and caffeine were also effective inducers, but other purine or pyrimidine derivatives were ineffective. Experiments with mutant derivatives of the HIV-1 long terminal repeat revealed no specific eukaryotic promoter elements necessary for 2-AP induction but indicated the need for some minimum combination of such elements. Induction of HIV-1-directed gene expression appeared not to require action of the transcription factor NF-kappa B. The mechanism of induction was investigated by using the luc and his genes linked to the HIV-1 long terminal repeat. 2-AP induced marked, steady rises in mRNA accumulation from both transfected and chromosomally integrated HIV-1 constructs but no increases from an endogenous gene encoding gamma-actin or glucose 6-phosphate dehydrogenase. Thus, induction is selective and not an artifact induced by transfecting DNA into cells. In run-on transcription experiments, the rates of transcription initiation of both transfected and integrated copies of the his gene increased about sixfold in cells treated with 2-AP. Thus, while increased initiation accounted for a portion of 2-AP induction, it could not cause the far greater increase in steady-state mRNA levels. 2-AP induction did not change mRNA decay rates and differed from the phorbol ester (phorbol myristate acetate)-induced activation of the protein kinase C-NF-kappa B pathway in its time course and in its requirement for new protein synthesis. Gel retardation assays showed that unlike phorbol myristate acetate induction, 2-AP induction is enhancer independent. Whereas many previous studies have implicated the activation of various protein kinases in gene induction, we here describe a mechanism of gene activation that appears to involve protein kinase inhibition as a component of the induction response.

Inducible transcriptional activation of the human immunodeficiency virus long terminal repeat by protein kinase inhibitors

The protein kinase inhibitor 2-aminopurine (2-AP) greatly stimulated expression in human promonocytes-macrophages of plasmid constructs carrying various reporter genes (chloramphenicol acetyltransferase, lacZ, firefly luciferase [luc], and Salmonella typhimurium histidinol dehydrogenase [his]) driven by the human immunodeficiency virus type 1 (HIV-1) long terminal repeat. Adenine, adenosine, and caffeine were also effective inducers, but other purine or pyrimidine derivatives were ineffective. Experiments with mutant derivatives of the HIV-1 long terminal repeat revealed no specific eukaryotic promoter elements necessary for 2-AP induction but indicated the need for some minimum combination of such elements. Induction of HIV-1-directed gene expression appeared not to require action of the transcription factor NF-kappa B. The mechanism of induction was investigated by using the luc and his genes linked to the HIV-1 long terminal repeat. 2-AP induced marked, steady rises in mRNA accumulation from both transfected and chromosomally integrated HIV-1 constructs but no increases from an endogenous gene encoding gamma-actin or glucose 6-phosphate dehydrogenase. Thus, induction is selective and not an artifact induced by transfecting DNA into cells. In run-on transcription experiments, the rates of transcription initiation of both transfected and integrated copies of the his gene increased about sixfold in cells treated with 2-AP. Thus, while increased initiation accounted for a portion of 2-AP induction, it could not cause the far greater increase in steady-state mRNA levels. 2-AP induction did not change mRNA decay rates and differed from the phorbol ester (phorbol myristate acetate)-induced activation of the protein kinase C-NF-kappa B pathway in its time course and in its requirement for new protein synthesis. Gel retardation assays showed that unlike phorbol myristate acetate induction, 2-AP induction is enhancer independent. Whereas many previous studies have implicated the activation of various protein kinases in gene induction, we here describe a mechanism of gene activation that appears to involve protein kinase inhibition as a component of the induction response.

The effect of cytokines and pharmacologic agents on chronic HIV infection

The ability of the human immunodeficiency virus (HIV) to replicate in CD+ T lymphocytes and mononuclear phagocytes(MP) is strongly influenced by immunoregulatory cytokines. In the T cell system, interleukin-2 (IL-2) provides a mitogenic signal leading to both cell proliferation and virus replication. Among other HIV-inductive cytokines, only tumor necrosis factor-alpha or -beta (TNF-alpha/-beta) have been shown thus far to trigger virus expression both in T cells and MP. The mechanism of action of TNF involves the activation of the cellular transcription factor NF-kB which binds to specific consensus sequences present in the enhancer region of the HIV proviral LTR. In addition, several other cytokines (including colony stimulating factors, IL-1, IL-3, and IL-6) have demonstrated upregulatory effects on HIV production in MP, whereas nonimmune interferons (INF-alpha/-beta) have been shown to suppress HIV replication in T cells and MP by acting at different phases in the virus life cycle. Finally, cytokines such as TGF-beta, IFN-gamma, and IL-4 have demonstrated either upregulatory or suppressive effects on virus expression depending on the experimental conditions. This scenario indicates that HIV expression is under the control of a complex network of immunoregulatory cytokines, in addition to its own endogenous regulatory proteins, suggesting that new pharmacologic strategies may be aimed at either mimicking or interrupting cytokine-dependent virus expression. In this regard, a number of different physiologic and pharmacologic agents capable of interfering with cytokine-mediated events, including glucocorticoids, anti-oxidants, such as N-Acetyl-L-Cysteine (NAC), and retinoic acid (RA) have already been shown to profoundly affect HIV replication in vitro.

Induction of chronic human immunodeficiency virus infection is blocked in vitro by a methylphosphonate oligodeoxynucleoside targeted to a U3 enhancer element

Oligodeoxynucleosides with internucleoside methylphosphonate linkages complementary to regions within U3 of human immunodeficiency virus type 1 were evaluated for their ability to block phorbol myristate acetate upregulation of virus in chronically infected promonocytic and T-lymphoblastoid cell lines. One such oligomer, targeted to an NF-kappa B enhancer element, inhibited phorbol myristate acetate induction of viral replication and tat-mediated trans activation of the human immunodeficiency virus long terminal repeat. The effect of this construct is contrasted with classical antisense methylphosphonate-derivatized oligomers complementary to initiation codon and splice acceptor sites of human immunodeficiency virus structural and regulatory genes. Its activity suggests a novel application of the modified oligonucleotide strategy in the blockade of viral induction from latently infected cells.