1E7-03, a low MW compound targeting host protein phosphatase-1, inhibits HIV-1 transcription

CK1 and PP1 regulate Rift Valley fever virus genome replication through L protein phosphorylation

Rift Valley fever virus (RVFV) is an arbovirus in the Phenuiviridae family identified initially by the large 'abortion storms' observed among ruminants; RVFV can also infect humans. In humans, there is a wide variation of clinical symptoms ranging from subclinical to mild febrile illness to hepatitis, retinitis, delayed-onset encephalitis, or even hemorrhagic fever. The RVFV is a tri-segmented negative-sense RNA virus consisting of S, M, and L segments. The L segment encodes the RNA-dependent RNA polymerase (RdRp), termed the L protein, which is responsible for both viral mRNA synthesis and genome replication. Phosphorylation of viral RdRps is known to regulate viral replication. This study shows that RVFV L protein is serine phosphorylated and identified Casein Kinase 1 alpha (CK1α) and protein phosphatase 1 alpha (PP1α) as L protein binding partners. Inhibition of CK1 and PP1 through small molecule inhibitor treatment, D4476 and 1E7-03, respectively, caused a change in the phosphorylated status of the L protein. Inhibition of PP1α resulted in increased L protein phosphorylation whereas inhibition of CK1α decreased L protein phosphorylation. It was also found that in RVFV infected cells, PP1α localized to the cytoplasmic compartment. Treatment of RVFV infected cells with CK1 inhibitors reduced virus production in both mammalian and mosquito cells. Lastly, inhibition of either CK1 or PP1 reduced viral genomic RNA levels. These data indicate that L protein is phosphorylated and that CK1 and PP1 play a crucial role in regulating the L protein phosphorylation cycle, which is critical to viral RNA production and viral replication.

Emerging roles of the Protein Phosphatase 1 (PP1) in the context of viral infections

Protein Phosphatase 1 (PP1) is a major serine/threonine phosphatase in eukaryotes, participating in several cellular processes and metabolic pathways. Due to their low substrate specificity, PP1's catalytic subunits do not exist as free entities but instead bind to Regulatory Interactors of Protein Phosphatase One (RIPPO), which regulate PP1's substrate specificity and subcellular localization. Most RIPPOs bind to PP1 through combinations of short linear motifs (4-12 residues), forming highly specific PP1 holoenzymes. These PP1-binding motifs may, hence, represent attractive targets for the development of specific drugs that interfere with a subset of PP1 holoenzymes. Several viruses exploit the host cell protein (de)phosphorylation machinery to ensure efficient virus particle formation and propagation. While the role of many host cell kinases in viral life cycles has been extensively studied, the targeting of phosphatases by viral proteins has been studied in less detail. Here, we compile and review what is known concerning the role of PP1 in the context of viral infections and discuss how it may constitute a putative host-based target for the development of novel antiviral strategies.

PP1, PP2A and PP2B Interplay in the Regulation of Sperm Motility: Lessons from Protein Phosphatase Inhibitors

Male fertility relies on the ability of spermatozoa to fertilize the egg in the female reproductive tract (FRT). Spermatozoa acquire activated motility during epididymal maturation; however, to be capable of fertilization, they must achieve hyperactivated motility in the FRT. Extensive research found that three protein phosphatases (PPs) are crucial to sperm motility regulation, the sperm-specific protein phosphatase type 1 (PP1) isoform gamma 2 (PP1γ2), protein phosphatase type 2A (PP2A) and protein phosphatase type 2B (PP2B). Studies have reported that PP activity decreases during epididymal maturation, whereas protein kinase activity increases, which appears to be a requirement for motility acquisition. An interplay between these PPs has been extensively investigated; however, many specific interactions and some inconsistencies remain to be elucidated. The study of PPs significantly advanced following the identification of naturally occurring toxins, including calyculin A, okadaic acid, cyclosporin, endothall and deltamethrin, which are powerful and specific PP inhibitors. This review aims to overview the protein phosphorylation-dependent biochemical pathways underlying sperm motility acquisition and hyperactivation, followed by a discussion of the PP inhibitors that allowed advances in the current knowledge of these pathways. Since male infertility cases still attain alarming numbers, additional research on the topic is required, particularly using other PP inhibitors.

Deciphering the Role of Protein Phosphatases in Apicomplexa: The Future of Innovative Therapeutics?

Parasites belonging to the Apicomplexa phylum still represent a major public health and world-wide socioeconomic burden that is greatly amplified by the spread of resistances against known therapeutic drugs. Therefore, it is essential to provide the scientific and medical communities with innovative strategies specifically targeting these organisms. In this review, we present an overview of the diversity of the phosphatome as well as the variety of functions that phosphatases display throughout the Apicomplexan parasites’ life cycles. We also discuss how this diversity could be used for the design of innovative and specific new drugs/therapeutic strategies.

Targeting Tat-TAR RNA Interaction for HIV-1 Inhibition

The HIV-1 Tat protein interacts with TAR RNA and recruits CDK9/cyclin T1 and other host factors to induce HIV-1 transcription. Thus, Tat–TAR RNA interaction, which is unique for HIV-1, represents an attractive target for anti-HIV-1 therapeutics. To target Tat–TAR RNA interaction, we used a crystal structure of acetylpromazine bound to the bulge of TAR RNA, to dock compounds from the Enamine database containing over two million individual compounds. The docking procedure identified 173 compounds that were further analyzed for the inhibition of HIV-1 infection. The top ten inhibitory compounds with IC₅₀ ≤ 6 µM were selected and the three least toxic compounds, T6780107 (IC₅₀ = 2.97 μM), T0516-4834 (IC₅₀ = 0.2 μM) and T5628834 (IC₅₀ = 3.46 μM), were further tested for HIV-1 transcription inhibition. Only the T0516-4834 compound showed selective inhibition of Tat-induced HIV-1 transcription, whereas the T6780107 compound inhibited equally basal and Tat-induced transcription and the T5628834 compound only inhibited basal HIV-1 transcription. The compounds were tested for the inhibition of translation and showed minimal (<25%) effect. The T0516-4834 compound also showed the strongest inhibition of HIV-1 RNA expression and p24 production in CEM T cells and peripheral blood mononuclear cells infected with HIV-1 IIIB. Of the three compounds, only the T0516-4834 compound significantly disrupted Tat–TAR RNA interaction. Additionally, of the three tested compounds, T5628834 and, to a lesser extent, T0516-4834 disrupted Tat–CDK9/cyclin T1 interaction. None of the three compounds showed significant inhibition of the cellular CDK9 and cyclin T1 levels. In silico modelling showed that the T0516-4834 compound interacted with TAR RNA by binding to the bulge formed by U23, U25, C39, G26,C39 and U40 residues. Taken together, our study identified a novel benzoxazole compound that disrupted Tat–TAR RNA interaction and inhibited Tat-induced transcription and HIV-1 infection, suggesting that this compound might serve as a new lead for anti-HIV-1 therapeutics.

Protein Phosphatase 1 Regulates Human Cytomegalovirus Protein Translation by Restraining AMPK Signaling

Human cytomegalovirus (HCMV) carries the human protein phosphatase 1 (PP1) and other human proteins important for protein translation in its tegument layer for a rapid supply upon infection. However, the biological relevance behind PP1 incorporation and its role during infection is unclear. Additionally, PP1 is a difficult molecular target due to its promiscuity and similarities between the catalytic domain of multiple phosphatases. In this study, we circumvented these shortcomings by using 1E7-03, a small molecule protein–protein interaction inhibitor, as a molecular tool of noncatalytic PP1 inhibition. 1E7-03 treatment of human fibroblasts severely impaired HCMV replication and viral protein translation. More specifically, PP1 inhibition led to the deregulation of metabolic signaling pathways starting at very early time points post-infection. This effect was at least partly mediated by the prevention of AMP-activated protein kinase dephosphorylation, leading to elongation factor 2 hyperphosphorylation and reduced translation rates. These findings reveal an important mechanism of PP1 for lytic HCMV infection.

Structural Optimization of 2,3-Dihydro-1H-cyclopenta[b]quinolines Targeting the Noncatalytic RVxF Site of Protein Phosphatase 1 for HIV-1 Inhibition

Combination antiretroviral therapy (cART) suppresses human immunodeficiency virus-1 (HIV-1) replication but is unable to permanently eradicate HIV-1. Importantly, cART does not target HIV-1 transcription, which is reactivated in latently infected reservoirs, leading to HIV-1 pathogenesis including non-infectious lung, cardiovascular, kidney, and neurodegenerative diseases. To address the limitations of cART and to prevent HIV-1-related pathogenesis, we developed small molecules to target the noncatalytic RVxF-accommodating site of protein phosphatase-1 (PP1) to prevent HIV-1 transcription activation. The PP1 RVxF-accommodating site is critical for the recruitment of regulatory and substrate proteins to PP1. Here, we confirm that our previously developed 1E7-03 compound binds to the PP1 RVxF-accommodating site. Iterative chemical alterations to 1E7-03 furnished a new analogue, HU-1a, with enhanced HIV-1 inhibitory activity and improved metabolic stability compared to 1E7-03. In a Split NanoBit competition assay, HU-1a primarily bound to the PP1 RVxF-accommodating site. In conclusion, our study identified HU-1a as a promising HIV-1 transcription inhibitor and showed that the PP1 RVxF-accommodating site is a potential drug target for the development of novel HIV-1 transcription inhibitors.

Diversity of small molecule HIV-1 latency reversing agents identified in low- and high-throughput small molecule screens

The latency phenomenon produced by human immunodeficiency virus (HIV-1) prevents viral clearance by current therapies, and consequently development of a cure for HIV-1 disease represents a formidable challenge. Research over the past decade has resulted in identification of small molecules that are capable of exposing HIV-1 latent reservoirs, by reactivation of viral transcription, which is intended to render these infected cells sensitive to elimination by immune defense recognition or apoptosis. Molecules with this capability, known as latency-reversing agents (LRAs) could lead to realization of proposed HIV-1 cure strategies collectively termed "shock and kill," which are intended to eliminate the latently infected population by forced reactivation of virus replication in combination with additional interventions that enhance killing by the immune system or virus-mediated apoptosis. Here, we review efforts to discover novel LRAs via low- and high-throughput small molecule screens, and summarize characteristics and biochemical properties of chemical structures with this activity. We expect this analysis will provide insight toward further research into optimized designs for new classes of more potent LRAs.

Macrophage HIV-1 Gene Expression and Delay Resolution of Inflammation in HIV-Tg Mice

While antiretroviral therapy increases the longevity of people living with HIV (PLWH), about 30% of this population suffers from three or more concurrent comorbidities, whose mechanisms are not well understood. Chronic activation and dysfunction of the immune system could be one potential cause of these comorbidities. We recently demonstrated reduced macrophage infiltration and delayed resolution of inflammation in the lungs of HIV-transgenic mice. Additionally, trans-endothelial migration of HIV-positive macrophages was reduced in vitro. Here, we analyze macrophages’ response to LPS challenge in the kidney and peritoneum of HIV-Tg mice. In contrast to the lung infiltration, renal and peritoneal macrophage infiltrations were similar in WT and HIV-Tg mice. Higher levels of HIV-1 gene expression were detected in lung macrophages compared to peritoneal macrophages. In peritoneal macrophages, HIV-1 gene expression was increased when they were cultured at 21% O₂ compared to 5% O₂, inversely correlating with reduced trans-endothelial migration at higher oxygen levels in vitro. The resolution of macrophage infiltration was reduced in both the lung and the peritoneal cavity of HIV-Tg mice. Taken together, our study described the organ-specific alteration of macrophage dynamics in HIV-Tg mice. The delayed resolution of macrophage infiltration might constitute a risk factor for the development of multiple comorbidities in PLWH.

HIV-1 Transcription Inhibitor 1E7-03 Restores LPS-Induced Alteration of Lung Leukocytes' Infiltration Dynamics and Resolves Inflammation in HIV Transgenic Mice

Human immunodeficiency virus (HIV)-infected individuals treated with anti-retroviral therapy often develop chronic non-infectious lung disease. To determine the mechanism of HIV-1-associated lung disease we evaluated the dynamics of lung leukocytes in HIV-1 transgenic (Tg) mice with integrated HIV-1 provirus. In HIV-Tg mice, lipopolysacharide (LPS) induced significantly higher levels of neutrophil infiltration in the lungs compared to wild-type (WT) mice. In WT mice, the initial neutrophil infiltration was followed by macrophage infiltration and fast resolution of leukocytes infiltration. In HIV-Tg mice, resolution of lung infiltration by both neutrophils and macrophages was significantly delayed, with macrophages accumulating in the lumen of lung capillaries resulting in a 45% higher rate of mortality. Trans-endothelial migration of HIV-Tg macrophages was significantly reduced in vitro and this reduction correlated with lower HIV-1 gene expression. HIV-1 transcription inhibitor, 1E7-03, enhanced trans-endothelial migration of HIV-Tg macrophages in vitro, decreased lung neutrophil infiltration in vivo, and increased lung macrophage levels in HIV-Tg mice. Moreover, 1E7-03 reduced levels of inflammatory IL-6 cytokine, improved bleeding score and decreased lung injury. Together this indicates that inhibitors of HIV-1 transcription can correct abnormal dynamics of leukocyte infiltration in HIV-Tg, pointing to the utility of transcription inhibition in the treatment of HIV-1 associated chronic lung disease.

Protein Phosphatase 1-Targeting Small-Molecule C31 Inhibits Ebola Virus Replication

Background

Ebola virus (EBOV) infection causes severe hemorrhagic fever. EBOV transcription is controlled by host protein phosphatase 1 (PP1), which dephosphorylates VP30 protein. We previously developed 1E7-03, a compound targeting a noncatalytic site of PP1 that induced VP30 phosphorylation and inhibited EBOV transcription. Here, we attempted to further improve 1E7-03, which was not stable in murine serum.

Results

High-throughput screening with EBOV-green fluorescent protein was conducted on 72 1E7-03 analogs and identified 6 best inhibitory and the least toxic compounds. A parallel in silico screening of compounds from the ZINC database by docking to PP1 identified the best-binding compound C31, which was also present among the top 6 compounds found in the viral screen. C31 showed the best EBOV inhibitory activity among the top 6 compounds and also inhibited EBOV minigenome. C31 bound to the PP1 C-terminal groove in vitro and increased VP30 phosphorylation in cultured cells. C31 demonstrated improved stability in mouse plasma and cell permeability, compared with 1E7-03. It was also detected for 24 hours after injection in mice.

Conclusion

C31 represents a novel PP1-targeting EBOV inhibitor with improved pharmacological properties that can be further evaluated for future antifiloviral therapy.

Targeting the Non-catalytic RVxF Site of Protein Phosphatase-1 With Small Molecules for Ebola Virus Inhibition

Ebola virus (EBOV) is a non-segmented negative-sense RNA virus that causes a severe human disease. The ongoing EBOV outbreak in the Eastern part of Democratic Republic of the Congo has resulted to date in over 2500 confirmed cases including over 1500 deaths. Difficulties with vaccine administration indicate the necessity for development of new general drugs and therapeutic strategies against EBOV. Host Ser/Thr protein phosphatases, particularly PP1 and PP2A, facilitate EBOV transcription by dephosphorylating the EBOV VP30 protein and switching activity of the polymerase complex toward replication. Previously, we developed small molecule 1E7-03 that targeted host protein phosphatase-1 (PP1) and induces phosphorylation of EBOV VP30 protein thus shifting transcription-replication balance and inhibiting EBOV replication. Here, we developed a new EBOV inhibitor, 1E7-07, that potently inhibits EBOV replication and displays significantly improved metabolic stability when compared to previously described 1E7-03. Proteome analysis of VP30 shows that 1E7-07 increases its phosphorylation on Thr-119 and Ser-124 over 3-fold with p < 0.001, which likely contributes to EBOV inhibition. We analyzed 1E7-07 binding to PP1 using a mass spectrometry-based protein painting approach. Combined with computational docking, protein painting shows that 1E7-07 binds to several PP1 sites including the RVxF site, C-terminal groove and NIPP1-helix binding pocket. Further analysis using surface plasmon resonance and a split NanoBiT system demonstrates that 1E7-07 binds primarily to the RVxF site. Together, detailed analysis of 1E7-07 binding to PP1 and identification of the RVxF site as the main binding site opens up an opportunity for future development of PP1-targeting EBOV inhibitors.

Functions and therapeutic potential of protein phosphatase 1: Insights from mouse genetics

Protein phosphatase 1 (PP1) catalyzes more than half of all phosphoserine/threonine dephosphorylation reactions in mammalian cells. In vivo PP1 does not exist as a free catalytic subunit but is always associated with at least one regulatory PP1-interacting protein (PIP) to generate a large set of distinct holoenzymes. Each PP1 complex controls the dephosphorylation of only a small subset of PP1 substrates. We screened the literature for genetically engineered mouse models and identified models for all PP1 isoforms and 104 PIPs. PP1 itself and at least 49 PIPs were connected to human disease-associated phenotypes. Additionally, phenotypes related to 17 PIPs were clearly linked to altered PP1 function, while such information was lacking for 32 other PIPs. We propose structural reverse genetics, which combines structural characterization of proteins with mouse genetics, to identify new PP1-related therapeutic targets. The available mouse models confirm the pleiotropic action of PP1 in health and diseases.

Protein Phosphatase 1α Interacts with Venezuelan Equine Encephalitis Virus Capsid Protein and Regulates Viral Replication through Modulation of Capsid Phosphorylation

Protein phosphatase 1 (PP1) is a serine/threonine phosphatase which has been implicated in the regulation of a number of viruses, including HIV-1, Ebolavirus, and Rift Valley fever virus. Catalytic subunits of PP1 (PP1α, PP1β, and PP1γ) interact with a host of regulatory subunits and target a wide variety of cellular substrates through a combination of short binding motifs, including an RVxF motif present in the majority of PP1 regulatory subunits. Targeting the RVxF-interacting site on PP1 with the small molecule 1E7-03 inhibits HIV-1, Ebolavirus, and Rift Valley fever virus replication. In this study, we determined the effect of PP1 on Venezuelan equine encephalitis virus (VEEV) replication. Treatment of VEEV-infected cells with 1E7-03 decreased viral replication by more than 2 logs (50% effective concentration [EC₅₀] = 0.6 μM). 1E7-03 treatment reduced viral titers starting at 8 h postinfection. Viral replication was also decreased after treatment with PP1α-targeting small interfering RNA (siRNA). Confocal microscopy demonstrated that PP1α shuttles toward the cytosol during infection with VEEV and that PP1α colocalizes with VEEV capsid. Coimmunoprecipitation experiments confirmed VEEV capsid interaction with PP1α. Furthermore, immunoprecipitation and mass spectrometry data showed that VEEV capsid is phosphorylated and that phosphorylation is moderated by PP1α. Finally, less viral RNA is associated with capsid after treatment with 1E7-03. Coupled with data showing that 1E7-03 inhibits several alphaviruses, this study indicates that inhibition of the PP1α RVxF binding pocket is a promising therapeutic target and provides novel evidence that PP1α modulation of VEEV capsid phosphorylation influences viral replication.IMPORTANCE Venezuelan equine encephalitis virus (VEEV) causes moderate flu-like symptoms and can lead to severe encephalitic disease and potentially death. There are currently no FDA-approved therapeutics or vaccines for human use, and understanding the molecular underpinning of host-virus interactions can aid in the rational design of intervention strategies. The significance of our research is in identifying the interaction between protein phosphatase 1 (PP1) and the viral capsid protein. This interaction is important for viral replication, as inhibition of PP1 results in decrease viral replication. Inhibition of PP1 also inhibited multiple biomedically important alphaviruses, indicating that PP1 may be a potential therapeutic target for alphavirus-induced disease.

Protein Phosphatase-1 -targeted Small Molecules, Iron Chelators and Curcumin Analogs as HIV-1 Antivirals

BACKGROUND

Despite efficient suppression of HIV-1 replication, current antiviral drugs are not able to eradicate HIV-1 infection. Permanent HIV-1 suppression or complete eradication requires novel biological approaches and therapeutic strategies. Our previous studies showed that HIV-1 transcription is regulated by host cell protein phosphatase-1. We also showed that HIV-1 transcription is sensitive to the reduction of intracellular iron that affects cell cycle-dependent kinase 2. We developed protein phosphatase 1-targeting small molecules that inhibited HIV-1 transcription. We also found an additional class of protein phosphatase-1-targeting molecules that activated HIV-1 transcription and reported HIV-1 inhibitory iron chelators and novel curcumin analogs that inhibit HIV-1. Here, we review HIV-1 transcription and replication with focus on its regulation by protein phosphatase 1 and cell cycle dependent kinase 2 and describe novel small molecules that can serve as future leads for anti-HIV drug development.

RESULTS

Our review describes in a non-exhaustive manner studies in which HIV-1 transcription and replication are targeted with small molecules. Previously, published studies show that HIV-1 can be inhibited with protein phosphatase-1-targeting and iron chelating compounds and curcumin analogs. These results are significant in light of the current efforts to eradicate HIV-1 through permanent inhibition. Also, HIV-1 activating compounds can be useful for "kick and kill" therapy in which the virus is reactivated prior to its inhibition by the combination antiretroviral therapy.

CONCLUSION

The studies described in our review point to protein phosphatase-1 as a new drug target, intracellular iron as subject for iron chelation and novel curcumin analogs that can be developed for novel HIV-1 transcription- targeting therapeutics.

Inhibition of HIV-1 infection in humanized mice and metabolic stability of protein phosphatase-1-targeting small molecule 1E7-03

We recently identified the protein phosphatase-1 - targeting compound, 1E7-03 which inhibited HIV-1 in vitro. Here, we investigated the effect of 1E7-03 on HIV-1 infection in vivo by analyzing its metabolic stability and antiviral activity of 1E7-03 and its metabolites in HIV-1 infected NSG-humanized mice. 1E7-03 was degraded in serum and formed two major degradation products, DP1 and DP3, which bound protein phosphatase-1 in vitro. However, their anti-viral activities were significantly reduced due to inefficient cell permeability. In cultured cells, 1E7-03 reduced expression of several protein phosphatase-1 regulatory subunits including Sds22 as determined by a label free quantitative proteomics analysis. In HIV-1-infected humanized mice, 1E7-03 significantly reduced plasma HIV-1 RNA levels, similar to the previously described HIV-1 transcription inhibitor F07#13. We synthesized a DP1 analog, DP1-07 with a truncated side chain, which showed improved cell permeability and longer pharmacokinetic retention in mice. But DP1-07 was less efficient than 1E7-03 as a HIV-1 inhibitor both in vitro and in vivo, indicating that the full side chain of 1E7-03 was essential for its anti-HIV activity. Analysis of 1E7-03 stability in plasma and liver microsomes showed that the compound was stable in human, primate and ferret plasma but not in rodent plasma. However, 1E7-03 was not stable in human liver microsomes. Our findings suggest that 1E7-03 is a good candidate for future development of HIV-1 transcription inhibitors. Further structural modification and advanced formulations are needed to improve its metabolic stability and enhance its antiviral activity in non-human primate animals and humans.

Protein Phosphatase-1 Regulates Expression of Neuregulin-1

Protein phosphatase 1 (PP1), a cellular serine/threonine phosphatase, is targeted to cellular promoters by its major regulatory subunits, PP1 nuclear targeting subunit, nuclear inhibitor of PP1 (NIPP1) and RepoMan. PP1 is also targeted to RNA polymerase II (RNAPII) by NIPP1 where it can dephosphorylate RNAPII and cycle-dependent kinase 9 (CDK9). Here, we show that treatment of cells with a small molecule activator of PP1 increases the abundance of a neuregulin-1 (NRG-1)-derived peptide. NRG-1 mRNA and protein levels were increased in the cells stably or transiently expressing mutant NIPP1 (mNIPP1) that does not bind PP1, but not in the cells expressing NIPP1. Expression of mNIPP1 also activated the NRG-1 promoter in an NF-κB-dependent manner. Analysis of extracts from mNIPP1 expressing cells by glycerol gradient centrifugation showed a redistribution of PP1 and CDK9 between large and small molecular weight complexes, and increased CDK9 Thr-186 phosphorylation. This correlated with the increased CDK9 activity. Further, RNAPII co-precipitated with mNIPP1, and phosphorylation of RNAPII C-terminal domain (CTD) Ser-2 residues was greater in cells expressing mNIPP1. In mNIPP1 expressing cells, okadaic acid, a cell-permeable inhibitor of PP1, did not increase Ser-2 CTD phosphorylation inhibited by flavopiridol, in contrast to the NIPP1 expressing cells, suggesting that PP1 was no longer involved in RNAPII dephosphorylation. Finally, media conditioned with mNIPP1 cells induced the proliferation of wild type 84-31 cells, consistent with a role of neuregulin-1 as a growth promoting factor. Our study indicates that deregulation of PP1/NIPP1 holoenzyme activates NRG-1 expression through RNAPII and CDK9 phosphorylation in a NF-κB dependent manner.

Improving combination antiretroviral therapy by targeting HIV-1 gene transcription

INTRODUCTION

Combination Antiretroviral Therapy (cART) has not allowed the cure of HIV. The main obstacle to HIV eradication is the existence of quiescent reservoirs. Several other limitations of cART have been described, such as strict life-long treatment and high costs, restricting it to Western countries, as well as the development of multidrug resistance. Given these limitations and the impetus to find a cure, the development of new treatments is necessary. Areas covered: In this review, we discuss the current status of several efficient molecules able to suppress HIV gene transcription, including NF-kB and Tat inhibitors. We also assess the potential of new proteins belonging to the intriguing DING family, which have been reported to have potential anti-HIV-1 activity by inhibiting HIV gene transcription. Expert opinion: Targeting HIV-1 gene transcription is an alternative approach, which could overcome cART-related issues, such as the emergence of multidrug resistance. Improving cART will rely on the identification and characterization of new actors inhibiting HIV-1 transcription. Combining such efforts with the use of new technologies, the development of new models for preclinical studies, and improvement in drug delivery will considerably reduce drug toxicity and thus increase patient adherence.

Protein Phosphatase-1 regulates Rift Valley fever virus replication

Rift Valley fever virus (RVFV), genus Phlebovirus family Bunyaviridae, is an arthropod-borne virus endemic throughout sub-Saharan Africa. Recent outbreaks have resulted in cyclic epidemics with an increasing geographic footprint, devastating both livestock and human populations. Despite being recognized as an emerging threat, relatively little is known about the virulence mechanisms and host interactions of RVFV. To date there are no FDA approved therapeutics or vaccines for RVF and there is an urgent need for their development. The Ser/Thr protein phosphatase 1 (PP1) has previously been shown to play a significant role in the replication of several viruses. Here we demonstrate for the first time that PP1 plays a prominent role in RVFV replication early on during the viral life cycle. Both siRNA knockdown of PP1α and a novel PP1-targeting small molecule compound 1E7-03, resulted in decreased viral titers across several cell lines. Deregulation of PP1 was found to inhibit viral RNA production, potentially through the disruption of viral RNA transcript/protein interactions, and indicates a potential link between PP1α and the viral L polymerase and nucleoprotein. These results indicate that PP1 activity is important for RVFV replication early on during the viral life cycle and may prove an attractive therapeutic target.

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

Background

HIV-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.

Results

Here 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.

Conclusion

We 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.

Activation of HIV-1 with Nanoparticle-Packaged Small-Molecule Protein Phosphatase-1-Targeting Compound

Complete eradication of HIV-1 infection is impeded by the existence of latent HIV-1 reservoirs in which the integrated HIV-1 provirus is transcriptionally inactive. Activation of HIV-1 transcription requires the viral Tat protein and host cell factors, including protein phosphatase-1 (PP1). We previously developed a library of small compounds that targeted PP1 and identified a compound, SMAPP1, which induced HIV-1 transcription. However, this compound has a limited bioavailability in vivo and may not be able to reach HIV-1-infected cells and induce HIV-1 transcription in patients. We packaged SMAPP1 in polymeric polyethylene glycol polymethyl methacrylate nanoparticles and analyzed its release and the effect on HIV-1 transcription in a cell culture. SMAPP1 was efficiently packaged in the nanoparticles and released during a 120-hr period. Treatment of the HIV-1-infected cells with the SMAPP1-loaded nanoparticles induced HIV-1 transcription. Thus, nanoparticles loaded with HIV-1-targeting compounds might be useful for future anti-HIV-1 therapeutics.

Therapeutics for postexposure treatment of Ebola virus infection

The current Ebola virus disease (EVD) outbreak in West Africa is the largest with over 5100 deaths in four West African countries as of 14 November 2014. EVD has high case-fatality rates but no licensed treatment or vaccine is yet available. Several vaccine candidates that protected nonhuman primates are not yet available for clinical use. Slow development of vaccine-stimulated immunity, sporadic nature and fast progression of EVD underlines the need for the development of effective postexposure therapeutic drugs. WHO encouraged the use of untested drugs for EVD to curb the fast-spreading outbreak. Here, we summarize therapeutics for EVD including monoclonal antibody-based therapy and inhibitors of viral replication including our recently developed small-molecule inhibitors of VP30 dephosphorylation.

Role of protein phosphatase 1 in dephosphorylation of Ebola virus VP30 protein and its targeting for the inhibition of viral transcription

The filovirus Ebola (EBOV) causes the most severe hemorrhagic fever known. The EBOV RNA-dependent polymerase complex includes a filovirus-specific VP30, which is critical for the transcriptional but not replication activity of EBOV polymerase; to support transcription, VP30 must be in a dephosphorylated form. Here we show that EBOV VP30 is phosphorylated not only at the N-terminal serine clusters identified previously but also at the threonine residues at positions 143 and 146. We also show that host cell protein phosphatase 1 (PP1) controls VP30 dephosphorylation because expression of a PP1-binding peptide cdNIPP1 increased VP30 phosphorylation. Moreover, targeting PP1 mRNA by shRNA resulted in the overexpression of SIPP1, a cytoplasm-shuttling regulatory subunit of PP1, and increased EBOV transcription, suggesting that cytoplasmic accumulation of PP1 induces EBOV transcription. Furthermore, we developed a small molecule compound, 1E7-03, that targeted a non-catalytic site of PP1 and increased VP30 dephosphorylation. The compound inhibited the transcription but increased replication of the viral genome and completely suppressed replication of EBOV in cultured cells. Finally, mutations of Thr(143) and Thr(146) of VP30 significantly inhibited EBOV transcription and strongly induced VP30 phosphorylation in the N-terminal Ser residues 29-46, suggesting a novel mechanism of regulation of VP30 phosphorylation. Our findings suggest that targeting PP1 with small molecules is a feasible approach to achieve dysregulation of the EBOV polymerase activity. This novel approach may be used for the development of antivirals against EBOV and other filovirus species.