Roberta S. Gardella

The microbicide cyanovirin-N expressed on the surface of commensal bacterium Streptococcus gordonii captures HIV-1

ObjectiveTo explore the feasibility of expressing the potent HIV-inactivating protein, cyanovirin-N (CV-N), in the human commensal bacterium Streptococcus gordonii, as a possible approach for local delivery of CV-N to prevent sexual transmission of HIV-1. Design and methodsTo express CV-N in S. gordonii, we used the host-vector system we had previously developed. CV-N was expressed as a fusion protein both attached to the bacterial surface and secreted in soluble form in the supernatant of liquid cultures. The soluble form of recombinant CV-N was tested for gp120-binding activity in an enzyme-linked immunosorbent assay, whereas S. gordonii strain expressing CV-N on the surface was analyzed in an in vitro HIV capturing assay. ResultsTwo recombinant S. gordonii strains secreting or displaying CV-N on the bacterial surface were constructed and the expression of CV-N was confirmed by immunoblot and flow-cytometric analysis. The secreted form of recombinant CV-N exhibited a concentration-dependent binding to the envelope glycoprotein gp120 of HIV-1, whereas CV-N displayed on the bacterial surface was able to capture HIV virions efficiently. ConclusionThe anti-HIV protein CV-N in S. gordonii was expressed in a biologically active form. This represents a first step in the development of a system to deliver and maintain an effective concentration of a microbicide in the vaginal mucosa.

Cultivation of formerly noncultivable strains ofMycoplasma hyorhinis

Growth on axenic agar medium is one of several characters by which mycoplasmas are defined. In apparent contradiction of the definition, DBS 1050 and other noncultivable strains ofMycoplasma hyorhinis do not grow on axenic medium but grow in cell culture. Our results show that BHK-21 cell extracts support DBS 1050 growth in appropriate medium. An inhibition assay, based on a virus neutralization format, shows that a variety of common medium ingredients inhibit DBS 1050 growth. The most potent activity was found in yeast extract. All other noncultivable strains ofM. hyorhinis tested have a yeast extract sensitivity, while cultivable strains do not. The apparent cell dependence of DBS 1050 can be attributed to growth inhibition due to factors present in a wide variety of peptones and extracts commonly used in medium; preferential growth in cell cultures is due to the absence of effective levels of these factors. Data are not available to determine if cell cultures provide growth factors not found in standard medium. The infraspecific taxon,M. hyorhinis cultivar α, is proposed for formerly noncultivable strains ofM. hyorhinis.

Development of a Cell-Based Reporter Assay for Screening of Inhibitors of Hypoxia-Inducible Factor 2-Induced Gene Expression

Reporter cell lines have been developed for the identification of inhibitors of gene expression enhanced by hypoxia-inducible factor 2, which has been implicated as a transcription factor involved in the tumorigenesis of clear cell renal carcinoma. Stably transformed reporter clones of the human renal clear cell carcinoma cell line 786-O were generated by transfection or retroviral infection. Luciferase reporter expression in the vectors used was driven by either the natural human vascular endothelial growth factor (VEGF) promoter-enhancer or by the VEGF and the human endothelial nitric oxide synthase enhancers modulating minimal human cytomegalovirus promoter. Utility of the generated reporter cell lines was validated by introducing the von Hippel-Lindau protein complex and testing for reporter inducibility by hypoxia. The dynamic range in reporter activity under hypoxic stress was found to be at least 30- to 40-fold, with a signal-to-noise ratio of 60:1. Properties of the cell lines such as tolerance to up to 3% DMSO, signal stability with multiple in vitro passages, and utility in both 96- and 384-well plate formats indicated their suitability for use in a high-throughput screen. In addition, the potential use of these reporter lines in the evaluation of high-throughput screening hits in vivo in various mice models has been demonstrated.

Design and initial characterization of a circular permuted variant of the potent HIV-inactivating protein cyanovirin-N.

A circular permuted variant of the potent human immunodeficiency virus (HIV)‐inactivating protein cyanovirin‐N (CV‐N) was constructed. New N‐ and C‐termini were introduced into an exposed helical loop, and the original termini were linked using residues of the original loop. Since the three‐dimensional structure of wild‐type cyanovirin‐N is a pseudodimer, the mutant essentially exhibits a swap between the two pseudo‐symmetrically related halves. The expressed protein, which accumulates in the insoluble fraction, was purified, and conditions for in vitro refolding were established. During refolding, a transient dimeric species is also formed that converts to a monomer. Similar to the wild‐type CV‐N, the monomeric circular permuted protein exhibits reversible thermal unfolding and urea denaturation. The mutant is moderately less stable than the wild‐type protein, but it displays significantly reduced anti‐HIV activity. Using nuclear magnetic resonance spectroscopy, we demonstrate that this circular permuted monomeric molecule adopts the same fold as the wild‐type protein. Characterization of these two architecturally very similar molecules allows us to embark, for the first time, on a structure guided focused mutational study, aimed at delineating crucial features for the extraordinary difference in the activity of these molecules. Proteins 2002;46:153–160.

Identification and evaluation of soft coral diterpenes as inhibitors of HIF-2α induced gene expression

Kidney cancer was the cause of almost 13,000 deaths in the United States in 2009. Loss of function of the VHL tumor suppressor gene (von Hippel-Lindau disease) dramatically increases the risk of developing clear cell kidney cancer. The VHL protein is best understood for its regulation of hypoxia inducible factor (HIF). HIF responds to changes in oxygen levels in the cell and is responsible for mediating the transcriptional response to hypoxia. Of the three known HIFα gene products, HIF-2α appears to play a fundamental role in renal carcinoma. A high throughput screen was developed to identify small molecule inhibitors of HIF-2 gene expression. The screen was performed and yielded 153 confirmed active natural product extracts. Three of the active extracts were from marine soft corals of the order Alcyonacea: Sarcophyton sp., Lobophytum sarcophytoides and Asterospicularia laurae. Bioassay-guided fractionation led to the isolation of two new cembrane diterpenes, (4Z,8S*,9R*,12E,14E)-9-hydroxy-1-(prop-1-en-2-yl)-8,12-dimethyl-oxabicyclo[9.3.2]-hexadeca-4,12,14-trien-18-one (1), and (1E,3E,7R*,8R*,11E)-1-(2-methoxypropan-2-yl)-4,8,12-trimethyloxabicyclo[12.1.0]-pentadeca-1,3,11-triene (7), as well as eight known compounds, 2-6 and 8-10.

Isolation and characterization of anti‐HIV peptides from Dorstenia contrajerva and Treculia obovoidea

Using a high throughput screen based on the interaction of the HIV‐1 gp41 ectodomain with the virucidal protein cyanovirin‐N (CV‐N), we isolated two new peptides which inhibited the binding of CV‐N to gp41 and which subsequently showed anti‐HIV activity in a whole cell assay. A 5‐kDa (contrajervin) and 10 kDa (treculavirin) peptide were isolated from Dorstenia contrajerva and Treculia obovoidea, respectively. Treculavirin was composed of two subunits, each containing 50 amino acid residues, which are covalently linked by at least one disulfide bond between the subunits. Both peptides were shown to bind to gp41 and gp120 and to inhibit the cytopathic effects of HIV‐1RF infection in a human T‐lymphoblastoid cell line (CEM‐SS).

High throughput screening for cyanovirin-N mimetics binding to HIV-1 gp41.

The human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein gp4l is an important mediator of viral entry into host cells. Previous studies showed that the virucidal protein cyanovirin-N (CV-N) bound to both gpl20 and gp4l, and that this binding was associated with its antiviral activity. We constructed an HTS assay based on the interaction of europium-labeled CV-N with recombinant glycosylated gp4l ectodomain to support identification of small-molecule mimetics of CV-N that might be developed as antiviral drug leads. Primary screening of over 107,000 natural product extracts in the assay yielded 347 confirmed hits. Secondary assays eliminated extracts that bound directly to labeled CV-N or for which the simple sugars mannose and N-acetylglucosamine blocked the interaction with gp4l (lectin activity). Extracts were further prioritized based on anti-HIV activity and other biological, biochemical, and chemical criteria. The distribution of source organism taxonomy of active extracts was analyzed, as was the cross-correlation of activity between the CV-N-gp4l binding competition assay and the previously reported CV-N-gpl20 binding competition assay. A limited set of extracts was selected for bioassay-guided fractionation.

Natural Products Active in Aberrant c‐Kit Signaling

Development of modulators of constitutively active, kinase domain mutants of c‐Kit has proved to be very difficult. Therefore, a high‐throughput differential cytotoxicity assay was developed to screen for compounds that preferentially kill cells expressing constitutively active c‐Kit. The cells used in the assay, murine IC2 mast cells, express either the D814Y activating mutation (functionally equivalent to human D816Y) or wild type protein. This assay is robust and highly reproducible. When applied to libraries of natural product extracts (followed by assay‐guided fractionation), two differentially active compounds were identified. To assess possible mechanisms of action, the active compounds were tested for inhibitory activity against a panel of signaling enzymes (including wild type and mutant c‐Kit). Neither of the compounds significantly affected any of the 73 enzymes tested. The effects of commercially available modulators of known signaling components were also assessed using the screening assay. None of these inhibitors reproduced the differential activity seen with the natural products. Finally, both compounds were found to affect mitochondrial potential in cells expressing c‐KitD814Y. These results suggest that the newly identified natural products may provide new avenues for intervention in aberrant c‐Kit signaling pathways.

Antibiotic treatment of mycoplasma-infected cell cultures

This chapter evaluates some of the earlier approaches to mycoplasma eradication from cells and outlines a technique that has successfully performed under a wide range of circumstances. A variety of novel techniques to cure mycoplasma-infected cell cultures have been used with variable success. Cells have been treated by passage in nude mice; exposed to 5-bromouracil, bisbenzimide H33258 fluorochrome, and light; treated with serum or antiserum; and exposed to heat or detergents. Antibiotic treatment is the most conventional and probably the most common method, but this too has met with variable success. Some procedures in the literature involve the use of antibiotics long available to the cell culturists, whereas others describe the use of a new series of antibiotics either recently evaluated for or specifically designed for the treatment of mycoplasma-infected cell cultures. Some of the newer additions include ciprofloxacin, mycoplasma removal agent (MRA), and enrofloxacin.

Quantitative detection of cell culture Mycoplasmas by a one step polymerase chain reaction method

A rapid, sensitive assay was developed that can detect the six species of Mycoplasmas that account for the vast majority of cell culture infections. This assay, a modification of the method published by Wong-Lee & Lovett [1], allows direct evaluation of culture medium by a single-step PCR method that utilizes primers complementary to conserved 16S rRNA sequences. Extensive testing of medium from uninfected cultures spiked with purified Mycoplasma DNAs showed that the method described in this report can detect the equivalent of one Mycoplasma in 15 μl culture medium; thus, evaluation of a single culture sample allows detection of Mycoplasmas in cultures infected with the equivalent of 10 or more Mycoplasmas per 15 μl (or ≥6.7×102 Mycoplasma equivalents/ml) with greater than 99.99% confidence. Comparison of results obtained with this PCR-based assay and a standard biological colony-forming assay revealed that the PCR assay is capable of detecting 0.0015-0.015 colony forming units, suggesting that the PCR assay may also be detecting nonviable Mycoplasmas. The high level of amplification achieved with this method allows direct detection of amplification products by ethidium bromide staining of agarose gels, and thus allows rapid screening of cell cultures.