A transcription inhibitor, actinomycin D, enhances HIV-1 replication through an interleukin-6-dependent pathway

Quantitative nascent proteome profiling by dual-pulse labelling with O-propargyl-puromycin and stable isotope-labelled amino acids

Monitoring translational regulation in response to environmental signals is crucial for understanding cellular proteostasis. However, only limited approaches are currently available for quantifying acute changes in protein synthesis induced by stimuli. Recently, a clickable puromycin analogue, O-propargyl-puromycin (OPP), was developed and applied to label the C-termini of nascent polypeptide chains (NPCs). Following affinity purification via a click reaction, OPP allows for a proteomic analysis of NPCs. Despite its advantage, the affinity purification of NPCs using magnetic beads or resins inherently suffers from significant non-specific protein binding, which hinders accurate quantification of the nascent proteins. To address this issue, we employed dual-pulse labelling of NPCs with both OPP and stable isotope-labelled amino acids to distinguish bona fide NPCs from non-specific proteins, thereby enabling the accurate quantitative profiling of NPCs. We applied this method to dissecting translation responses upon transcriptional inhibition and quantified ∼3,000 nascent proteins. We found that the translation of a subset of ribosomal proteins (e.g. RPSA, RPLP0) as well as signalling proteins (e.g. BCAR3, EFNA1, DUSP1) was significantly repressed by transcription inhibition. Together, the present method provides an accurate and broadly applicable nascent proteome profiling for many biological applications at the level of translation.

Actinobacteria from Antarctica as a source for anticancer discovery

Although many advances have been achieved to treat aggressive tumours, cancer remains a leading cause of death and a public health problem worldwide. Among the main approaches for the discovery of new bioactive agents, the prospect of microbial secondary metabolites represents an effective source for the development of drug leads. In this study, we investigated the actinobacterial diversity associated with an endemic Antarctic species, Deschampsia antarctica, by integrated culture-dependent and culture-independent methods and acknowledged this niche as a reservoir of bioactive strains for the production of antitumour compounds. The 16S rRNA-based analysis showed the predominance of the Actinomycetales order, a well-known group of bioactive metabolite producers belonging to the Actinobacteria phylum. Cultivation techniques were applied, and 72 psychrotolerant Actinobacteria strains belonging to the genera Actinoplanes, Arthrobacter, Kribbella, Mycobacterium, Nocardia, Pilimelia, Pseudarthrobacter, Rhodococcus, Streptacidiphilus, Streptomyces and Tsukamurella were identified. The secondary metabolites were screened, and 17 isolates were identified as promising antitumour compound producers. However, the bio-guided assay showed a pronounced antiproliferative activity for the crude extracts of Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653. The TGI and LC50 values revealed the potential of these natural products to control the proliferation of breast (MCF-7), glioblastoma (U251), lung/non-small (NCI-H460) and kidney (786-0) human cancer cell lines. Cinerubin B and actinomycin V were the predominant compounds identified in Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653, respectively. Our results suggest that the rhizosphere of D. antarctica represents a prominent reservoir of bioactive actinobacteria strains and reveals it as an important environment for potential antitumour agents.

New Metabolites and Bioactive Actinomycins from Marine-Derived Streptomyces sp. ZZ338

An extract prepared from the culture of a marine-derived actinomycete Streptomyces sp. ZZ338 was found to have significant antimicrobial and antiproliferative activities. A chemical investigation of this active extract resulted in the isolation of three known bioactive actinomycins (1–3) and two new metabolites (4 and 5). The structures of the isolated compounds were identified as actinomycins D (1), V (2), X_0β (3), 2-acetylamino-3-hydroxyl-4-methyl-benzoic acid methyl ester (4), and N-1S-(4-methylaminophenylmethyl)-2-oxo-propyl acetamide (5) based on their nuclear magnetic resonance (NMR) and high resolution electrospray ionization mass spectroscopy (HRESIMS) data as well as their optical rotation. This class of new compound 5 had never before been found from a natural resource. Three known actinomycins showed activities in inhibiting the proliferation of glioma cells and the growth of methicillin-resistant Staphylococcus aureus, Escherichia coli, and Candida albicans and are responsible for the activity of the crude extract. Actinomycin D (1) was also found to downregulate several glioma metabolic enzymes of glycolysis, glutaminolysis, and lipogenesis, suggesting that targeting multiple tumor metabolic regulators might be a new anti-glioma mechanism of actinomycin D. This is the first report of such a possible mechanism for the class of actinomycins.

In vitro reactivation of latent HIV-1 by cytostatic bis(thiosemicarbazonate) gold(III) complexes

Background

A number of cytostatic agents have been investigated for the ability to reactivate latent viral reservoirs, which is a major prerequisite for the eradication of HIV-1 infection. Two cytostatic bis(thiosemicarbazonate) gold(III) complexes (designated 1 and 2) were tested for this potential in the U1 latency model of HIV-1 infection.

Methods

Cell viability in the presence or absence of 1 and 2 was determined using a tetrazolium dye and evidence of reactivation was assessed by p24 antigen capture following exposure to a latency stimulant, phorbol myristate acetate (PMA) and or test compounds. The latency reactivation mechanism was explored by determining the effect of the complexes on protein kinase C (PKC), histone deacetylases (HDAC) and proinflammatory cytokine production.

Results

The CC₅₀ of the complexes in U1 cells were 0.53 ± 0.12 μM for 1 and 1.0 ± 0.4 μM for 2. In the absence of PMA and at non toxic concentrations of 0.2 and 0.5 μM, 1 and 2 significantly (p ≤ 0.02) reactivated virus in U1 cells by 2.7 and 2.3 fold respectively. In comparison, a 2.6 fold increase (p = 0.03) in viral reactivation was observed for hydroxyurea (HU), which was used as a cytostatic and latent HIV reactivation control. Viral reactivation was absent for the complexes during co-stimulation with PMA indicating the lack of an additive effect between the chemicals as well as an absence of inhibition of PMA induced HIV reactivation but for HU inhibition of the stimulant’s activity was observed (p = 0.01). Complex 1 and 2 activated PKC activity by up to 32% (p < 0.05) but no significant inhibition of HDAC was observed. Increases in TNF-α levels suggested that the reactivation of virus by the complexes may have been due to contributions from the latter and the activation of PKC.

Conclusion

The ethyl group structural difference between 1 and 2 seems to influence bioactivity with lower active concentrations of 1, suggesting that further structural modifications should improve specificity. The cytostatic effect of 1 and 2 and now HIV reactivation from a U1 latency model is consistent with that of the cytostatic agent, HU. These findings suggest that the complexes have a potential dual (cytostatic and reactivation) role in viral “activation/elimination”.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0680-3) contains supplementary material, which is available to authorized users.

Inhibiting eukaryotic transcription: Which compound to choose? How to evaluate its activity?

This review first discusses ways in which we can evaluate transcription inhibition, describe changes in nuclear structure due to transcription inhibition, and report on genes that are paradoxically stimulated by transcription inhibition. Next, it summarizes the characteristics and mechanisms of commonly used inhibitors: α-amanitin is highly selective for RNAP II and RNAP III but its action is slow, actinomycin D is fast but its selectivity is poor, CDK9 inhibitors such as DRB and flavopiridol are fast and reversible but many genes escape transcription inhibition. New compounds, such as triptolide, are fast and selective and able to completely arrest transcription by triggering rapid degradation of RNAP II.

Non-coding RNAs regulating the transcriptional machinery

During the past decade, numerous ncRNAs (non-coding RNAs) have been identified as regulators of transcription. This review focuses on a few examples of ncRNAs that directly interact with and regulate components of the transcription machinery. Artificial RNA aptamers have been selected against components of the transcriptional machinery. The bacterial 6S RNA and the eukaryotic B2 RNA directly target RNA polymerases. The 7SK RNA, U1 snRNA (small nuclear RNA) and SRA (steroid receptor RNA activator) RNA bind to and regulate the activity of transcription factors. Xist (X-inactive-specific transcript) and roX (RNA on the X) RNAs are involved in epigenetic regulation of transcription through the recruitment of histone-modifying enzymes.

Hydroxyurea and interleukin-6 synergistically reactivate HIV-1 replication in a latently infected promonocytic cell line via SP1/SP3 transcription factors

The existence of viral latency limits the success of highly active antiretroviral therapy. With the therapeutic intention of reactivating latent virus to induce a cure, in this study we assessed the impact of cell synchronizers on HIV gene activation in latently infected U1 cells and investigated the molecular mechanisms responsible for such effect. Latently infected U1 cells were treated with 10 drugs including hydroxyurea (HU) and HIV-1 replication monitored using a p24 antigen capture assay. We found that HU was able to induce HIV-1 replication by 5-fold. HU has been used in the clinical treatment of HIV-1-infected patients in combination with didanosine; therefore, we investigated the impact of HU on HIV-1 activation in the presence of the proinflammatory cytokines, interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha). IL-6 or TNF-alpha alone induced HIV replication by 18- and approximately 500-fold, respectively. Of interest, in the presence of HU, IL-6-mediated HIV-1 activation was enhanced by >90-fold, whereas TNF-alpha-mediated activation was inhibited by >30%. A reporter gene assay showed that HU and IL-6 synergized to activate HIV promoter activity via the Sp1 binding site. Electrophoretic mobility shift and supershift assays revealed increased binding of the Sp1 and Sp3 transcription factors to this region. Western blot analysis showed that HU and IL-6 co-stimulation resulted in increased levels of Sp1 and Sp3 proteins. In contrast, treatment with HU plus TNF-alpha down-regulated the expression of NF-kappaB. These findings suggest that Sp1/Sp3 is involved in controlling the HU/IL-6-induced reactivation of HIV-1 in latently infected cells.

Noninfectious papilloma virus-like particles inhibit HIV-1 replication: implications for immune control of HIV-1 infection by IL-27

Human papilloma virus (HPV)-like particles (VLPs) have been used as a vaccine to prevent HPV infection. Recent studies demonstrate that VLPs bind to dendritic cells and induce the expression of antiviral cytokines such as interferon-alpha (IFN-alpha), interleukin-10 (IL-10) and IFN-gamma. In the present study, we evaluated the effect of VLPs on HIV-1 replication in peripheral blood mononuclear cells (PBMCs), CD4+ T cells, and macrophages. Here, we show that VLPs suppress the replication of both X4 and R5 HIV-1 without affecting the expression of CD4, CXCR4, and CCR5. Soluble factor(s) released by PBMCs and macrophages on VLPs treatment inhibited HIV-1 replication. To determine the inhibitory factors, DNA microarray analysis was performed using VLP-treated PBMCs and macrophages. VLPs induced the genes associated with IFN induction, immune responses, and antiviral responses, among with the recently described cytokine IL-27. Subsequently, IL-27 was found to be a potent inhibitor of HIV-1 replication in PBMCs, CD4+ T cells, and macrophages. Taken together, our studies identify a novel role of IL-27 in restricting HIV-1 replication and suggest that further examination of the inhibitory property of IL-27 may pave the way for a novel therapy for HIV-1 infection.