Mudit Tyagi

Human immunodeficiency virus (HIV) latency: the major hurdle in HIV eradication.

Failure of highly active antiretroviral therapy to eradicate the human immunodeficiency virus (HIV), even in patients who suppress the virus to undetectable levels for many years, underscores the problems associated with fighting this infection. The existence of persistent infection in certain cellular and anatomical reservoirs appears to be the major hurdle in HIV eradication. The development of therapeutic interventions that eliminate or limit the latent viral pools or prevent the reemergence of the viruses from producing cells will therefore be required to enhance the effectiveness of current antiretroviral strategies. To achieve this goal, there is a pressing need to understand HIV latency at the molecular level to design novel and improved therapies to either eradicate HIV or find a functional cure in which patients could maintain a manageable viral pool without AIDS in the absence of antiretroviral therapy. The integrated proviral genome remains transcriptionally silent for a long period in certain subsets of T cells. This ability to infect cells latently helps HIV to establish a persistent infection despite strong humoral and cellular immune responses against the viral proteins. The main purpose of this report is to provide a general overview of the HIV latency. We will describe the hurdles being faced in eradicating latent HIV proviruses. We will also briefly discuss the ongoing strategies aimed toward curing HIV infection.

DNA-dependent protein kinase interacts functionally with the RNA polymerase II complex recruited at the human immunodeficiency virus (HIV) long terminal repeat and plays an important role in HIV gene expression

DNA-dependent protein kinase (DNA-PK), a nuclear protein kinase that specifically requires association with DNA for its kinase activity, plays important roles in the regulation of different DNA transactions, including transcription, replication and DNA repair, as well as in the maintenance of telomeres. Due to its large size, DNA-PK is also known to facilitate the activities of other factors by providing the docking platform at their site of action. In this study, by running several chromatin immunoprecipitation assays, we demonstrate the parallel distribution of DNA-PK with RNA polymerase II (RNAP II) along the human immunodeficiency virus (HIV) provirus before and after activation with tumour necrosis factor alpha. The association between DNA-PK and RNAP II is also long-lasting, at least for up to 4 h (the duration analysed in this study). Knockdown of endogenous DNA-PK using specific small hairpin RNAs expressed from lentiviral vectors resulted in significant reduction in HIV gene expression and replication, demonstrating the importance of DNA-PK for HIV gene expression. Sequence analysis of the HIV-1 Tat protein revealed three potential target sites for phosphorylation by DNA-PK and, by using kinase assays, we confirmed that Tat is an effective substrate of DNA-PK. Through peptide mapping, we found that two of these three potential phosphorylation sites are recognized and phosphorylated by DNA-PK. Mutational studies on the DNA-PK target sites of Tat further demonstrated the functional significance of the Tat-DNA-PK interaction. Thus, overall our results clearly demonstrate the functional interaction between DNA-PK and RNAP II during HIV transcription.

Reactivation of latent HIV-1 provirus via targeting protein phosphatase-1.

BackgroundHIV-1 escapes antiretroviral drugs by integrating into the host DNA and forming a latent transcriptionally silent HIV-1 provirus. This provirus presents the major hurdle in HIV-1 eradication and cure. Transcriptional activation, which is prerequisite for reactivation and the eradication of latent proviruses, is impaired in latently infected T cells due to the lack of host transcription factors, primarily NF-κB and P-TEFb (CDK9/cyclin T1). We and others previously showed that protein phosphatase-1 (PP1) regulates HIV-1 transcription by modulating CDK9 phosphorylation. Recently we have developed a panel of small molecular compounds targeting a non-catalytic site of PP1.ResultsHere we generated a new class of sulfonamide-containing compounds that activated HIV-1 in acute and latently infected cells. Among the tested molecules, a small molecule activator of PP1 (SMAPP1) induced both HIV-1 replication and reactivation of latent HIV-1 in chronically infected cultured and primary cells. In vitro, SMAPP1 interacted with PP1 and increased PP1 activity toward a recombinant substrate. Treatment with SMAPP1 increased phosphorylation of CDK9’s Ser90 and Thr186 residues, but not Ser175. Proteomic analysis showed upregulation of P-TEFb and PP1 related proteins, including PP1 regulatory subunit Sds22 in SMAPP1-treated T cells. Docking analysis identified a PP1 binding site for SMAPP1 located within the C-terminal binding pocket of PP1.ConclusionWe identified a novel class of PP1-targeting compounds that reactivate latent HIV-1 provirus by targeting PP1, increasing CDK9 phosphorylation and enhancing HIV transcription. This compound represents a novel candidate for anti-HIV-1 therapeutics aiming at eradication of latent HIV-1 reservoirs.

The effects of cocaine on HIV transcription

Illicit drug users are a high-risk population for infection with the human immunodeficiency virus (HIV). A strong correlation exists between prohibited drug use and an increased rate of HIV transmission. Cocaine stands out as one of the most frequently abused illicit drugs, and its use is correlated with HIV infection and disease progression. The central nervous system (CNS) is a common target for both drugs of abuse and HIV, and cocaine intake further accelerates neuronal injury in HIV patients. Although the high incidence of HIV infection in illicit drug abusers is primarily due to high-risk activities such as needle sharing and unprotected sex, several studies have demonstrated that cocaine enhances the rate of HIV gene expression and replication by activating various signal transduction pathways and downstream transcription factors. In order to generate mature HIV genomic transcript, HIV gene expression has to pass through both the initiation and elongation phases of transcription, which requires discrete transcription factors. In this review, we will provide a detailed analysis of the molecular mechanisms that regulate HIV transcription and discuss how cocaine modulates those mechanisms to upregulate HIV transcription and eventually HIV replication.

Models of HIV-1 persistence in the CD4+ T cell compartment: past, present and future.

The limitations of current anti-retroviral therapies (ART) and the lack of a valid anti-HIV-1 vaccine candidate underscore the need for new therapeutic concepts aiming at the eradication of HIV-1, which represents at the same time an ideal goal and a major challenge for AIDS research. At present, this aim is unattainable due to the existence of cellular and anatomical reservoirs of persistent infection. Memory CD4(+) T cells comprise the largest pool of cells harboring silent, stably integrated HIV-1, which remains undetected by the immune system and refractory to conventional anti-retroviral drugs. The eradication of latent HIV-1 reservoirs will require new, potent and specific therapeutic strategies, which in turn must rely upon a deeper understanding of HIV-1 latency. To facilitate the advancement of our knowledge in this new area of research, several in vitro models of HIV-1 latency in CD4(+) T cells have been established. Here, we dissect and critically compare the rationale behind each experimental approach. Furthermore, we outline new avenues of research that will benefit from these models, including the push toward the development of new classes of viral eradication drugs.

New and novel intrinsic host repressive factors against HIV-1: PAF1 complex, HERC5 and others

During the early stages of HIV-1 infection several host restriction factors provide important contributions to the innate immune responses ultimately leading to protection of the host. However, HIV-1 (and possibly other evolutionary conserved retroviruses) has evolved its own set of genes and proteins that counter the intracellular innate responses. In recent years there has been a clear shift in HIV-1 research where host innate molecules have become the new paradigm of attention leading to novel discoveries from both in vitro infections and long-term non-progressor and elite controller AIDS patients. Consequently, various host factors have been identified as restriction factors against HIV-1. Recently, a new strategy of screening using siRNA libraries has been employed to score for suppression of host restriction factors, ultimately leading to activation of the virus. This novel approach has now identified a few additional specific critical factors that may be part of the intracellular innate response to HIV-1 infection.

Localization and sub-cellular shuttling of HTLV-1 Tax with the RNAi machinery component Drosha.

The innate ability of the human cell to silence endogenous retroviruses through RNA sequences encoding microRNAs, suggests that the cellular RNAi machinery is a major mean by which the host mounts a response against contemporary retroviruses, such as HIV-1 and HTLV-1. Several recent publications have identified cellular miRNAs that target and hybridize to specific sequences of both the HIV-1 and HTLV-1 transcripts. However, much like the variety of host immune responses to retroviral infection, the virus itself contains mechanisms that assist in the evasion of viral inhibition through manipulation of the cellular RNAi pathway. Retroviruses can hijack both the enzymatic and catalytic components of the RNAi pathway, in some cases to produce novel viral miRNAs that can either assist in active viral infection or promote a latent state of infection. Here, we propose that HTLV-1 viral proteins contribute to the dysregulation of the RNAi pathway by altering expression of key components of the pathway. A survey of uninfected and infected cell lines revealed that Drosha was present at lower levels in all HTLV infected lines. Additionally, transfection of HeLa cells with Tax shows colocalization of Tax and Drosha in the nucleus (speckles), suggesting that the HTLV-1 viral transactivator physically interacts with Drosha and targets it to specific areas of the cell. This data suggests the direct interaction of HTLV-1 viral components with RNAi machinery proteins which may lead to their dysregulation in infected cells.

Cocaine promotes both initiation and elongation phase of HIV-1 transcription by activating NF-κB and MSK1 and inducing selective epigenetic modifications at HIV-1 LTR.

Cocaine accelerates human immunodeficiency virus (HIV-1) replication by altering specific cell-signaling and epigenetic pathways. We have elucidated the underlying molecular mechanisms through which cocaine exerts its effect in myeloid cells, a major target of HIV-1 in central nervous system (CNS). We demonstrate that cocaine treatment promotes HIV-1 gene expression by activating both nuclear factor-kappa B (NF-ĸB) and mitogen- and stress-activated kinase 1 (MSK1). MSK1 subsequently catalyzes the phosphorylation of histone H3 at serine 10, and p65 subunit of NF-ĸB at 276th serine residue. These modifications enhance the interaction of NF-ĸB with P300 and promote the recruitment of the positive transcription elongation factor b (P-TEFb) to the HIV-1 LTR, supporting the development of an open/relaxed chromatin configuration, and facilitating the initiation and elongation phases of HIV-1 transcription. Results are also confirmed in primary monocyte derived macrophages (MDM). Overall, our study provides detailed insights into cocaine-driven HIV-1 transcription and replication.

Tat controls transcriptional persistence of unintegrated HIV genome in primary human macrophages

In HIV infected macrophages, a large population of viral genomes persists as the unintegrated form (uDNA) that is transcriptionally active. However, how this transcriptional activity is controlled remains unclear. In this report, we investigated whether Tat, the viral transactivator of transcription, is involved in uDNA transcription. We demonstrate that de novo Tat activity is generated from uDNA, and this uDNA-derived Tat (uTat) transactivates the uDNA LTR. In addition, uTat is required for the transcriptional persistence of uDNA that is assembled into repressive episomal minichromatin. In the absence of uTat, uDNA minichromatin is gradually silenced, but remains highly inducible by HDAC inhibitors (HDACi). Therefore, functionally, uTat antagonizes uDNA minichromatin repression to maintain persistent viral transcription in macrophages. uTat-mediated viral persistence may establish a viral reservoir in macrophages where uDNA were found to persist.

Mechanisms of HIV Transcriptional Regulation by Drugs of Abuse.

BACKGROUND There is a strong correlation between the use and abuse of illicit drugs and the spread of Human Immunodeficiency Virus (HIV). It is well established that illicit drugs users are a high risk population for infection with HIV with an increased rate of HIV transmission and replication. Cocaine, amphetamine, methamphetamine, heroin and morphine stand out as the most frequently abused illicit drugs and their use correlates well with HIV infection and AIDS progression. Notably, the high incidence of HIV infection in illicit drug abusers is primarily due to high risk activities such as needle sharing and unprotected sex. Several studies have also demonstrated that drugs of abuse increase viral RNA concentrations by enhancing HIV replication, in particular in the central nervous system (CNS). The CNS is a common target for both drugs of abuse and HIV, and their synergistic action accelerates neuronal injury and cognitive impairment. In order to generate complete genomic transcripts, HIV gene expression has to progress through both the initiation and elongation phases of transcription, which requires coordinated action of different transcription factors. CONCLUSION In this review, we will provide the latest updates of the molecular mechanisms that regulate HIV transcription and discuss how drugs of abuse, such as cocaine, amphetamine, methamphetamine, heroin and morphine, modulate those mechanisms to upregulate HIV transcription and eventually HIV replication.