Developments in antivirals against influenza, smallpox and hemorrhagic fever viruses

INTRODUCTION

the search for effective inhibitors to multiple infectious agents including influenza, smallpox and hemorrhagic fever viruses is an area of active research as many of these agents pose dramatic health and economic challenges to the human population. Many of these infectious agents are not only endemic threats in different parts of the globe, but are also considered to have the potential of being used as bioterrorism agents.

AREAS COVERED

this review focuses on inhibitors that are currently in use in the research community against specific emerging infectious agents and those that have bioterrorism potential. The paper provides information about the availability of FDA approved drugs, whenever applicable, and insights into the specific aspect of the agent life cycle that is affected by drug treatment, when known.

EXPERT OPINION

the key message that is conveyed in this review is that a combination of pathogen and host-based inhibitors may have to be used for successful control of viral replication to limit the development of drug resistance.

Varying modulation of HIV-1 LTR activity by Baf complexes

The human immunodeficiency virus type 1 (HIV-1) long terminal repeat is present on both ends of the integrated viral genome and contains regulatory elements needed for transcriptional initiation and elongation. Post-integration, a highly ordered chromatin structure consisting of at least five nucleosomes, is found at the 5' long terminal repeat, the location and modification state of which control the state of active viral replication as well as silencing of the latent HIV-1 provirus. In this context, the chromatin remodeling field rapidly emerges as having a critical role in the control of viral gene expression. In the current study, we focused on unique Baf subunits that are common to the most highly recognized of chromatin remodeling proteins, the SWI/SNF (switching-defective-sucrose non-fermenting) complexes. We find that at least two Baf proteins, Baf53 and Baf170, are highly regulated in HIV-1-infected cells. Previously, studies have shown that the depletion of Baf53 in uninfected cells leads to the expansion of chromosomal territories and the decompaction of the chromatin. Baf53, in the presence of HIV-1 infection, co-elutes off of a chromatographic column as a different-sized complex when compared to uninfected cells and appears to be predominantly phosphorylated. The innate function of Baf53-containing complexes appears to be transcriptionally suppressive, in that knocking down Baf53 increases viral gene expression from cells both transiently and chronically infected with HIV-1. Additionally, cdk9/cyclin T in the presence of Tat is able to phosphorylate Baf53 in vitro, implying that this posttranslationally modified form relieves the suppressive effect and allows for viral transcription to proceed.

Alteration in superoxide dismutase 1 causes oxidative stress and p38 MAPK activation following RVFV infection

Rift Valley fever (RVF) is a zoonotic disease caused by Rift Valley fever virus (RVFV). RVFV is a category A pathogen that belongs to the genus Phlebovirus, family Bunyaviridae. Understanding early host events to an infectious exposure to RVFV will be of significant use in the development of effective therapeutics that not only control pathogen multiplication, but also contribute to cell survival. In this study, we have carried out infections of human cells with a vaccine strain (MP12) and virulent strain (ZH501) of RVFV and determined host responses to viral infection. We demonstrate that the cellular antioxidant enzyme superoxide dismutase 1 (SOD1) displays altered abundances at early time points following exposure to the virus. We show that the enzyme is down regulated in cases of both a virulent (ZH501) and a vaccine strain (MP12) exposure. Our data demonstrates that the down regulation of SOD1 is likely to be due to post transcriptional processes and may be related to up regulation of TNFα following infection. We also provide evidence for extensive oxidative stress in the MP12 infected cells. Concomitantly, there is an increase in the activation of the p38 MAPK stress response, which our earlier published study demonstrated to be an essential cell survival strategy. Our data suggests that the viral anti-apoptotic protein NSm may play a role in the regulation of the cellular p38 MAPK response. Alterations in the host protein SOD1 following RVFV infection appears to be an early event that occurs in multiple cell types. Activation of the cellular stress response p38 MAPK pathway can be observed in all cell types tested. Our data implies that maintaining oxidative homeostasis in the infected cells may play an important role in improving survival of infected cells.

Targeting the inflammasome and adenosine type-3 receptors improves outcome of antibiotic therapy in murine anthrax

AIM: To establish whether activation of adenosine type-3 receptors (A3Rs) and inhibition of interleukin-1β-induced inflammation is beneficial in combination with antibiotic therapy to increase survival of mice challenged with anthrax spores.

METHODS: DBA/2 mice were challenged with Bacillus anthracis spores of the toxigenic Sterne strain 43F2. Survival of animals was monitored for 15 d. Ciprofloxacin treatment (50 mg/kg, once daily, intraperitoneally) was initiated at day +1 simultaneously with the administration of inhibitors, and continued for 10 d. Two doses (2.5 mg/kg and 12.5 mg/kg) of acetyl-tyrosyl-valyl-alanyl-aspartyl-chloromethylketone (YVAD) and three doses (0.05, 0.15 and 0.3 mg/kg) of 1-[2-Chloro-6-[[(3-iodophenyl) methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-β-D- ribofuranuronamide (Cl-IB-MECA) were tested. Animals received YVAD on days 1-4, and Cl-IB-MECA on days 1-10 once daily, subcutaneously. Human lung epithelial cells in culture were challenged with spores or edema toxin and the effects of IB-MECA on phosphorylation of AKT and generation of cAMP were tested.

RESULTS: We showed that the outcome of antibiotic treatment in a murine anthrax model could be substantially improved by co-administration of the caspase-1/4 inhibitor YVAD and the A3R agonist Cl-IB-MECA. Combination treatment with these substances and ciprofloxacin resulted in up to 90% synergistic protection. All untreated mice died, and antibiotic alone protected only 30% of animals. We conclude that both substances target the aberrant host signaling that underpins anthrax mortality.

CONCLUSION: Our findings suggest new possibilities for combination therapy of anthrax with antibiotics, A3R agonists and caspase-1 inhibitors.

Inhibition of Tat-mediated HIV-1 replication and neurotoxicity by novel GSK3-beta inhibitors

The HIV-1 protein Tat is a critical regulator of viral transcription and has also been implicated as a mediator of HIV-1 induced neurotoxicity. Here using a high throughput screening assay, we identified the GSK-3 inhibitor 6BIO, as a Tat-dependent HIV-1 transcriptional inhibitor. Its ability to inhibit HIV-1 transcription was confirmed in TZM-bl cells, with an IC(50) of 40nM. Through screening 6BIO derivatives, we identified 6BIOder, which has a lower IC(50) of 4nM in primary macrophages and 0.5nM in astrocytes infected with HIV-1. 6BIOder displayed an IC(50) value of 0.03nM through in vitro GSK-3β kinase inhibition assays. Finally, we demonstrated 6BIO and 6BIOder have neuroprotective effects on Tat induced cell death in rat mixed hippocampal cultures. Therefore 6BIO and its derivatives are unique compounds which, due to their complex mechanisms of action, are able to inhibit HIV-1 transcription as well as to protect against Tat induced neurotoxicity.

Analysis of the roles of HIV-derived microRNAs

IMPORTANCE OF THE FIELD

HIV-1 is a retrovirus that has infected millions in recent decades. The level of life cycle complexity and host control exerted by this small virus with only nine proteins is astonishing. An interesting direction that has emerged in recent years is the role of small non-coding RNAs in viral gene expression.

AREAS COVERED IN THIS REVIEW

We focus on HIV-1 produced microRNAs (miRNAs), namely, TAR, Nef and miR-H1, and their roles in HIV-1 biogenesis. The article provides insights into TAR miRNA-mediated downregulation of viral and host gene expression by recruitment of chromatin remodeling components (HDAC1).

WHAT THE READER WILL GAIN

We address the influence of TAR miRNA on host cell cycle progression and apoptosis, and the role of Nef miRNA in the regulation of viral and host gene expression. The review also highlights an intriguing connection between miR-H1 and HIV-1-associated neurological pathogenesis, and the influence of the miRNA machinery in the establishment of latency. In the Expert Opinion section, we analyze the issue of host-based therapeutics against HIV-1 and how transcription inhibitors are influenced by viral miRNA production.

TAKE HOME MESSAGE

HIV-derived miRNAs are of significance not only to understand host-virus interactions, but also for the design of effective therapeutics.

Bacillus anthracis interacts with plasmin(ogen) to evade C3b-dependent innate immunity

The causative agent of anthrax, Bacillus anthracis, is capable of circumventing the humoral and innate immune defense of the host and modulating the blood chemistry in circulation to initiate a productive infection. It has been shown that the pathogen employs a number of strategies against immune cells using secreted pathogenic factors such as toxins. However, interference of B. anthracis with the innate immune system through specific interaction of the spore surface with host proteins such as the complement system has heretofore attracted little attention. In order to assess the mechanisms by which B. anthracis evades the defense system, we employed a proteomic analysis to identify human serum proteins interacting with B. anthracis spores, and found that plasminogen (PLG) is a major surface-bound protein. PLG efficiently bound to spores in a lysine- and exosporium-dependent manner. We identified α-enolase and elongation factor tu as PLG receptors. PLG-bound spores were capable of exhibiting anti-opsonic properties by cleaving C3b molecules in vitro and in rabbit bronchoalveolar lavage fluid, resulting in a decrease in macrophage phagocytosis. Our findings represent a step forward in understanding the mechanisms involved in the evasion of innate immunity by B. anthracis through recruitment of PLG resulting in the enhancement of anti-complement and anti-opsonization properties of the pathogen.

Hepcidin induces HIV-1 transcription inhibited by ferroportin

BACKGROUND

Physiological regulation of cellular iron involves iron export by the membrane protein, ferroportin, the expression of which is induced by iron and negatively modulated by hepcidin. We previously showed that iron chelation is associated with decreased HIV-1 transcription. We hypothesized that increased iron export by ferroportin might be associated with decreased HIV-1 transcription, and degradation of ferroportin by hepcidin might in turn induce HIV-1 transcription and replication. Here, we analyzed the effect of ferroportin and hepcidin on HIV-1 transcription.

RESULTS

Expression of ferroportin was associated with reduced HIV-1 transcription in 293T cells and addition of hepcidin to ferroportin-expressing cells counteracted this effect. Furthermore, exposure of promonocytic THP-1 cells to hepcidin was associated with decreased ferroportin expression, increased intracellular iron and induction of reporter luciferase gene expression. Finally, exposure of human primary macrophages and CD4+ T cells to hepcidin and iron was also associated with induction of viral production.

CONCLUSION

Our results suggest that the interplay between ferroportin-mediated iron export and hepcidin-mediated degradation of ferroportin might play a role in the regulation of HIV-1 transcription and may be important for understanding of HIV-1 pathogenesis.

Reverse-phase phosphoproteome analysis of signaling pathways induced by Rift valley fever virus in human small airway epithelial cells

Rift valley fever virus (RVFV) infection is an emerging zoonotic disease endemic in many countries of sub-Saharan Africa and in Egypt. In this study we show that human small airway epithelial cells are highly susceptible to RVFV virulent strain ZH-501 and the attenuated strain MP-12. We used the reverse-phase protein arrays technology to identify phosphoprotein signaling pathways modulated during infection of cultured airway epithelium. ZH-501 infection induced activation of MAP kinases (p38, JNK and ERK) and downstream transcriptional factors [STAT1 (Y701), ATF2 (T69/71), MSK1 (S360) and CREB (S133)]. NF-κB phosphorylation was also increased. Activation of p53 (S15, S46) correlated with the increased levels of cleaved effector caspase-3, -6 and -7, indicating activation of the extrinsic apoptotic pathway. RVFV infection downregulated phosphorylation of a major anti-apoptotic regulator of survival pathways, AKT (S473), along with phosphorylation of FOX 01/03 (T24/31) which controls cell cycle arrest downstream from AKT. Consistent with this, the level of apoptosis inhibitor XIAP was decreased. However, the intrinsic apoptotic pathway marker, caspase-9, demonstrated only a marginal activation accompanied by an increased level of the inhibitor of apoptosome formation, HSP27. Concentration of the autophagy marker, LC3B, which often accompanies the pro-survival signaling, was decreased. Cumulatively, our analysis of RVFV infection in lung epithelium indicated a viral strategy directed toward the control of cell apoptosis through a number of transcriptional factors. Analyses of MP-12 titers in challenged cells in the presence of MAPK inhibitors indicated that activation of p38 represents a protective cell response while ERK activation controls viral replication.

Iron chelators of the di-2-pyridylketone thiosemicarbazone and 2-benzoylpyridine thiosemicarbazone series inhibit HIV-1 transcription: identification of novel cellular targets--iron, cyclin-dependent kinase (CDK) 2, and CDK9

HIV-1 transcription is activated by HIV-1 Tat protein, which recruits cyclin-dependent kinase 9 (CDK9)/cyclin T1 and other host transcriptional coactivators to the HIV-1 promoter. Tat itself is phosphorylated by CDK2, and inhibition of CDK2 by small interfering RNA, the iron chelator 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), and the iron chelator deferasirox (ICL670) inhibits HIV-1 transcription. Here we have analyzed a group of novel di-2-pyridylketone thiosemicarbazone- and 2-benzoylpyridine thiosemicarbazone-based iron chelators that exhibit marked anticancer activity in vitro and in vivo (Proc Natl Acad Sci USA 103:7670-7675, 2006; J Med Chem 50:3716-3729, 2007). Several of these iron chelators, in particular 2-benzoylpyridine 4-allyl-3-thiosemicarbazone (Bp4aT) and 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), inhibited HIV-1 transcription and replication at much lower concentrations than did 311 and ICL670. Neither Bp4aT nor Bp4eT were toxic after a 24-h incubation. However, longer incubations for 48 h or 72 h resulted in cytotoxicity. Analysis of the molecular mechanism of HIV-1 inhibition showed that the novel iron chelators inhibited basal HIV-1 transcription, but not the nuclear factor-κB-dependent transcription or transcription from an HIV-1 promoter with inactivated SP1 sites. The chelators inhibited the activities of CDK2 and CDK9/cyclin T1, suggesting that inhibition of CDK9 may contribute to the inhibition of HIV-1 transcription. Our study suggests the potential usefulness of Bp4aT or Bp4eT in antiretroviral regimens, particularly where resistance to standard treatment occurs.

Transcription through the HIV-1 nucleosomes: effects of the PBAF complex in Tat activated transcription

The SWI/SNF complex remodels nucleosomes, allowing RNA Polymerase II access to the HIV-1 proviral DNA. It has not been determined which SWI/SNF complex (BAF or PBAF) remodels nucleosomes at the transcription start site. These complexes differ in only three subunits and determining which subunit(s) is required could explain the regulation of Tat activated transcription. We show that PBAF is required for chromatin remodeling at the nuc-1 start site and transcriptional elongation. We find that Baf200 is required to ensure activation at the LTR level and for viral production. Interestingly, the BAF complex was observed on the LTR whereas PBAF was present on both LTR and Env regions. We found that Tat activated transcription facilitates removal of histones H2A and H2B at the LTR, and that the FACT complex may be responsible for their removal. Finally, the BAF complex may play an important role in regulating splicing of the HIV-1 genome.

Erratum to: microRNA machinery is an integral component of drug-induced transcription inhibition in HIV-1 infection

[This corrects the article on p. 386 in vol. 6, PMID: 20628499.].

The identification of unique serum proteins of HIV-1 latently infected long-term non-progressor patients

BACKGROUND

The search for disease biomarkers within human peripheral fluids has become a favorable approach to preventative therapeutics throughout the past few years. The comparison of normal versus disease states can identify an overexpression or a suppression of critical proteins where illness has directly altered a patient's cellular homeostasis. In particular, the analysis of HIV-1 infected serum is an attractive medium with which to identify altered protein expression due to the ease and non-invasive methods of collecting samples as well as the corresponding insight into the in vivo interaction of the virus with infected cells/tissue. The utilization of proteomic techniques to globally identify differentially expressed serum proteins in response to HIV-1 infection is a significant undertaking that is complicated due to the innate protein profile of human serum.

RESULTS

Here, the depletion of 12 of the most abundant serum proteins, followed by two-dimensional gel electrophoresis coupled with identification of these proteins using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, has allowed for the identification of differentially expressed, low abundant serum proteins. We have analyzed and compared serum samples from HIV-1 infected subjects who are being treated using highly active antiretroviral therapy (HAART) to those who are latently infected but have not progressed to AIDS despite the absence of treatment, i.e. long term non-progressors (LTNPs). Here we have identified unique serum proteins that are differentially expressed in LTNP HIV-1 patients and may contribute to the ability of these patients to combat HIV-1 infection in the absence of HAART. We focused on the cdk4/6 cell cycle inhibitor p16INK4A and found that the treatment of HIV-1 latently infected cell lines with p16INK4A decreases viral production despite it not being expressed endogenously in these cells.

CONCLUSIONS

Identification of these unique proteins may serve as an indication of altered viral states in response to infection as well as a natural phenotypic variability in response to HIV-1 infection in a given population.

Methylation of the tumor suppressor protein, BRCA1, influences its transcriptional cofactor function

BACKGROUND

Approximately half of hereditary breast cancers have mutations in either BRCA1 or BRCA2. BRCA1 is a multifaceted tumor suppressor protein that has implications in processes such as cell cycle, transcription, DNA damage response and chromatin remodeling. This multifunctional nature of BRCA1 is achieved by exerting its many effects through modulation of transcription. Many cellular events are dictated by covalent modification of proteins, an important mechanism in regulating protein and genome function; of which protein methylation is an important posttranslational modification with activating or repressive effects.

METHODS/PRINCIPAL FINDINGS

Here we demonstrate for the first time that BRCA1 is methylated both in breast cancer cell lines and breast cancer tumor samples at arginine and lysine residues through immunoprecipitation and western blot analysis. Arginine methylation by PRMT1 was observed in vitro and the region of BRCA1 504-802 shown to be highly methylated. PRMT1 was detected in complex with BRCA1 504-802 through in vitro binding assays and co-immunoprecipitated with BRCA1. Inhibition of methylation resulted in decreased BRCA1 methylation and alteration of BRCA1 binding to promoters in vivo as shown through chromatin immunoprecipitation assays. Knockdown of PRMT1 also resulted in increased BRCA1 binding to particular promoters in vivo. Finally, following methylation inhibition, Sp1 was found to preferentially associate with hypo-methylated BRCA1 and STAT1 was found to preferentially associate with hyper-methylated BRCA1.

CONCLUSIONS/SIGNIFICANCE

These results suggest that methylation may influence either the ability of BRCA1 to bind to specific promoters or protein-protein interactions which alters the recruitment of BRCA1 to these promoters. Thus, given the importance of BRCA1 to genomic stability, methylation of BRCA1 may ultimately affect the tumor suppressor ability of BRCA1.

Absence of DICER in monocytes and its regulation by HIV-1

MicroRNAs (miRNAs) are a class of small RNA molecules that function to control gene expression and restrict viral replication in host cells. The production of miRNAs is believed to be dependent upon the DICER enzyme. Available evidence suggests that in T lymphocytes, HIV-1 can both suppress and co-opt the host's miRNA pathway for its own benefit. In this study, we examined the state of miRNA production in monocytes and macrophages as well as the consequences of viral infection upon the production of miRNA. Monocytes in general express low amounts of miRNA-related proteins, and DICER in particular could not be detected until after monocytes were differentiated into macrophages. In the case where HIV-1 was present prior to differentiation, the expression of DICER was suppressed. MicroRNA chip results for RNA isolated from transfected and treated cells indicated that a drop in miRNA production coincided with DICER protein suppression in macrophages. We found that the expression of DICER in monocytes is restricted by miR-106a, but HIV-1 suppressed DICER expression via the viral gene Vpr. Additionally, analysis of miRNA expression in monocytes and macrophages revealed evidence that some miRNAs can be processed by both DICER and PIWIL4. Results presented here have implications for both the pathology of viral infections in macrophages and the biogenesis of miRNAs. First, HIV-1 suppresses the expression and function of DICER in macrophages via a previously unknown mechanism. Second, the presence of miRNAs in monocytes lacking DICER indicates that some miRNAs can be generated by proteins other than DICER.

microRNA machinery is an integral component of drug-induced transcription inhibition in HIV-1 infection

RNA interference plays a significant role in manipulating cellular and viral mechanisms to maintain latency during HIV-1 infection. HIV-1 produces several microRNAs including one from the TAR element which alter the host's response to infection. Since cyclin/cdk complexes are important for viral transcription, these studies focus on the possible cdk inhibitors that inhibit viral transcription, without affecting normal cellular mechanisms. Roscovitine and Flavopiridol are well-studied cdk inhibitors that are effective at suppressing their target cdks at a low IC50. These cdk inhibitors and possibly future generations of drugs are affected by microRNA mechanisms. From our studies, we developed a third generation derivative called CR8#13. In cells that lack Dicer there was a higher level of basal viral LTR-reporter transcription. When drugs, specifically Flavopiridol and CR8#13 were added, the transcriptional inhibition of the LTR was less potent in cells that lacked Dicer. Also, after transfection with HIV-1 clone (pNL4.3), CR8 and CR8#13 derivatives were shown to be more effective viral transcription inhibitors in cell lines that contained Dicer (T-cells) as compared to Dicer deficient lines (monocytes). We next asked whether the addition of CR8 or CR8#13 could possibly increase levels of TAR microRNA in HIV-1 LTR containing cells. We demonstrate that the 3'TAR microRNA is produced in higher amounts after drug treatment, resulting in microRNA recruitment to the LTR. MicroRNA recruitment results in chromatin alteration, changes in Pol II phosphorylation and viral transcription inhibition. In conclusion, our results indicate that viral microRNA, specifically the TAR microRNA produced from the HIV-1 LTR is responsible for maintaining latent infections by manipulating host cell mechanisms to limit transcription from the viral LTR promoter. With the microRNA machinery present, cdk inhibitors are able to significantly increase the amount of TAR microRNA, leading to downregulation of viral LTR transcription.

Stimulation of the liver X receptor pathway inhibits HIV-1 replication via induction of ATP-binding cassette transporter A1

Cholesterol plays an important role in the HIV life cycle, and infectivity of cholesterol-depleted HIV virions is significantly impaired. Recently, we demonstrated that HIV-1, via its protein Nef, inhibits the activity of the major cellular cholesterol transporter ATP binding cassette transporter A1 (ABCA1), suggesting that the virus may use this mechanism to get access to cellular cholesterol. In this study, we investigated the effect on HIV infection of a synthetic liver X receptor (LXR) ligand, N-(2,2,2-trifluoro-ethyl)-N-[4-(2,2,2-trifluoro-1-hydroxy-1-trifluoromethyl-ethyl)-phenyl]-benzenesulfonamide (TO-901317), which is a potent stimulator of ABCA1 expression. We demonstrate that TO-901317 restores cholesterol efflux from HIV-infected T lymphocytes and macrophages. TO-901317 potently suppressed HIV-1 replication in both cell types and inhibited HIV-1 replication in ex vivo cultured lymphoid tissue and in RAG-hu mice infected in vivo. This anti-HIV activity was dependent on ABCA1, because the effect of the drug was significantly reduced in ABCA1-defective T cells from a patient with Tangier disease, and RNA interference-mediated inhibition of ABCA1 expression eliminated the effect of TO-901317 on HIV-1 replication. TO-901317-mediated inhibition of HIV replication was due to reduced virus production and reduced infectivity of produced virions. The infectivity defect was in part due to reduced fusion activity of the virions, which was directly linked to reduced viral cholesterol. These results describe a novel approach to inhibiting HIV infection by stimulating ABCA1 expression.

Inhibition of human immunodeficiency virus type-1 by cdk inhibitors

Current therapy for human immunodeficiency virus (HIV-1) infection relies primarily on the administration of anti-retroviral nucleoside analogues, either alone or in combination with HIV-protease inhibitors. Although these drugs have a clinical benefit, continuous therapy with the drugs leads to drug-resistant strains of the virus. Recently, significant progress has been made towards the development of natural and synthetic agents that can directly inhibit HIV-1 replication or its essential enzymes. We previously reported on the pharmacological cyclin-dependent kinase inhibitor (PCI) r-roscovitine as a potential inhibitor of HIV-1 replication. PCIs are among the most promising novel antiviral agents to emerge over the past few years. Potent activity on viral replication combined with proliferation inhibition without the emergence of resistant viruses, which are normally observed in HAART patients; make PCIs ideal candidates for HIV-1 inhibition. To this end we evaluated twenty four cdk inhibitors for their effect on HIV-1 replication in vitro. Screening of these compounds identified alsterpaullone as the most potent inhibitor of HIV-1 with activity at 150 nM. We found that alsterpaullone effectively inhibits cdk2 activity in HIV-1 infected cells with a low IC₅₀ compared to control uninfected cells. The effects of alsterpaullone were associated with suppression of cdk2 and cyclin expression. Combining both alsterpaullone and r-roscovitine (cyc202) in treatment exhibited even stronger inhibitory activities in HIV-1 infected PBMCs.

Cell-type-specific proteome and interactome: using HIV-1 Tat as a test case

HIV-1 is a small retrovirus that wreaks havoc on the human immune system. It is a puzzle to the scientific community how a virus that encodes only nine proteins can take complete control of its host and redirect the cell to complete replication or maintain latency when necessary. One way to explain the control elicited by HIV-1 is through numerous protein partners that exist between viral and host proteins, allowing HIV-1 to be intimately involved in virtually every aspect of cellular biology. In addition, we postulate that the complexity exerted by HIV-1 can not merely be explained by the large number of protein-protein interactions documented in the literature but, rather, cell-type-specific interactions and post-translational modifications of viral proteins must be taken into account. We use HIV-1 Tat and its influence on viral transcription as an example of cell-type-specific complexity. The influence of post-translational modifications (acetylation and methylation), as well as subcellular localization on Tat binding partners, is also discussed.

Novel HIV-1 therapeutics through targeting altered host cell pathways

The emergence of drug-resistant HIV-1 strains presents a challenge for the design of new drugs. Anti-HIV compounds currently in use are the subject of advanced clinical trials using either HIV-1 reverse transcriptase, viral protease or integrase inhibitors. Recent studies show an increase in the number of HIV-1 variants resistant to anti-retroviral agents in newly infected individuals. Targeting host cell factors involved in the regulation of HIV-1 replication might be one way to combat HIV-1 resistance to the currently available anti-viral agents. A specific inhibition of HIV-1 gene expression could be expected from the development of compounds targeting host cell factors that participate in the activation of the HIV-1 LTR promoter. Here we discuss how targeting the host can be accomplished either by using small molecules to alter the function of the host's proteins such as p53 or cdk9, or by utilizing new advances in siRNA therapies to knock down essential host factors such as CCR5 and CXCR4. Finally, we will discuss how the viral protein interactomes should be used to better design therapeutics against HIV-1.

Cyclin dependent kinases as attractive targets to prevent transcription from viral genomes

Most viral treatments target the virus itself, providing very specific effects and limiting side-effects on uninfected cells. However, this strategy of drug design often results in resistant viruses, especially among RNA viruses. Therefore, the focus has turned to drugs that target cellular proteins that are essential for viral replication, but not for cellular viability. Pharmacological CDK inhibitors are a prime example of this type of approach. Reviewed within are the various functions of CDKs, their role in the life cycle of selected Retroviruses and Herpesviruses, and the pharmacological CDK inhibitors that have been focused on in terms of viral inhibition.

Regulation of HIV-1 transcription at 3% versus 21% oxygen concentration

HIV transcription is induced by the HIV-1 Tat protein, in concert with cellular co-factors including CDK9, CDK2, NF-kappaB, and others. The cells of most of the body's organs are exposed to approximately 3-6% oxygen, but most in vitro studies of HIV replication are conducted at 21% oxygen. We hypothesized that activities of host cell factors involved in HIV-1 replication may differ at 3% versus 21% O(2), and that such differences may affect HIV-1 replication. Here we show that Tat-induced HIV-1 transcription was reduced at 3% O(2) compared to 21% O(2). HIV-1 replication was also reduced in acutely or chronically infected cells cultured at 3% O(2) compared to 21% O(2). This reduction was not due the decreased cell growth or increased cellular toxicity and also not due to the induction of hypoxic response. At 3% O(2), the activity of CDK9/cyclin T1 was inhibited and Sp1 activity was reduced, whereas the activity of other host cell factors such as CDK2 or NF-kappaB was not affected. CDK9-specific inhibitor ARC was much less efficient at 3% compared to 21% O(2) and also expression of CDK9/cyclin T1-dependent IkappaB inhibitor alpha was repressed. Our results suggest that lower HIV-1 transcription at 3% O(2) compared to 21% O(2) may be mediated by lower activity of CDK9/cyclin T1 and Sp1 at 3% O(2) and that additional host cell factors such as CDK2 and NF-kappaB might be major regulators of HIV-1 transcription at low O(2) concentrations.

Chromatin dynamics associated with HIV-1 Tat-activated transcription

Chromatin remodeling is an essential event for HIV-1 transcription. Over the last two decades this field of research has come to the forefront, as silencing of the HIV-1 provirus through chromatin modifications has been linked to latency. Here, we focus on chromatin remodeling, especially in relation to the transactivator Tat, and review the most important and newly emerging studies that investigate remodeling mechanisms. We begin by discussing covalent modifications that can alter chromatin structure including acetylation, deacetylation, and methylation, as well as topics addressing the interplay between chromatin remodeling and splicing. Next, we focus on complexes that use the energy of ATP to remove or secure nucleosomes and can additionally act to control HIV-1 transcription. Finally, we cover recent literature on viral microRNAs which have been shown to alter chromatin structure by inducing methylation or even by remodeling nucleosomes.