Rapid and direct microRNA quantification by an enzymatic luminescence assay.

A quantitative bioluminescence assay for rapid and sensitive microRNA (miRNA) expression analysis was developed. The assay uses miRNA directly as a primer for binding to a circular single-stranded DNA template, followed by rolling circle amplification. The detection of inorganic pyrophosphate (PPi) molecules released during the DNA polymerization and amplification process is performed by a multi-enzyme system. PPi is converted to ATP by ATP-sulfurylase, which provides energy for luciferase to oxidize luciferin and produce light. Experimental results show that the assay has a dynamic range exceeding three orders of magnitude and the ability to discriminate miRNAs with high-homology sequences. Quantification of nine miRNAs in human heart tissues demonstrated high cross-platform consistency between this assay and the TaqMan real-time polymerase chain reaction (PCR) assay with R(2)=0.941. The assay requires fewer reagents, can be performed at an isothermal condition without thermal cycling, and is capable of detecting miRNAs in less than 1h. Compared with the real-time PCR and microarray-based detection methods, this assay provides a simpler, faster, and less expensive platform for miRNA quantification in life science research, drug discovery, and clinical diagnosis.

Real-time bioluminescent assay for inhibitors of RNA and DNA polymerases and other ATP-dependent enzymes.

Viral polymerases are important targets for drug development. However, current methods used to identify and characterize inhibitors of polymerases are time-consuming, use radiolabeled reagents, and are cost-inefficient. Here we present a bioluminescent assay for the identification and characterization of inhibitors of polymerases, as well as other ATP-dependent enzymes, that monitors the decrease of ATP or dATP in real time, allowing detection of enzyme inhibition based on differences in ATP/dATP consumption. The assay works with a variety of RNA and DNA polymerases, using both RNA and DNA templates. The assay measures changes in substrate concentration in real time and provides a faster alternative for kinetic studies of inhibition. Michaelis-Menten plots were obtained from a single reaction, yielding K(m) values that compared well with literature values. The assay could identify the mechanism of inhibition and determine inhibition constants (K(i)) for a weak competitive inhibitor of Klenow fragment and two strong noncompetitive inhibitors of HIV-1 reverse transcriptase with one series of inhibitor concentrations, reducing the total number of experiments that would normally be needed. The assay is also sensitive enough to detect a weak inhibitor with K(i)>100 µM, making it a viable technique for fragment-based drug discovery.

Vitamin D binding protein-macrophage activating factor directly inhibits proliferation, migration, and uPAR expression of prostate cancer cells.

BACKGROUND: Vitamin D binding protein-macrophage activating factor (DBP-maf) is a potent inhibitor of tumor growth. Its activity, however, has been attributed to indirect mechanisms such as boosting the immune response by activating macrophages and inhibiting the blood vessel growth necessary for the growth of tumors. METHODS AND FINDINGS: In this study we show for the first time that DBP-maf exhibits a direct and potent effect on prostate tumor cells in the absence of macrophages. DBP-maf demonstrated inhibitory activity in proliferation studies of both LNCaP and PC3 prostate cancer cell lines as well as metastatic clones of these cells. Flow cytometry studies with annexin V and propidium iodide showed that this inhibitory activity is not due to apoptosis or cell death. DBP-maf also had the ability to inhibit migration of prostate cancer cells in vitro. Finally, DBP-maf was shown to cause a reduction in urokinase plasminogen activator receptor (uPAR) expression in prostate tumor cells. There is evidence that activation of this receptor correlates with tumor metastasis. CONCLUSIONS: These studies show strong inhibitory activity of DBP-maf on prostate tumor cells independent of its macrophage activation.

Efficiency and specificity of microRNA-primed nucleotide analog incorporation by various DNA polymerases.

MicroRNAs (miRNAs) as endogenous regulators of gene expression have spurred a surge of interest for their quantification and expression analysis. High-sensitivity and high-specificity miRNA detection techniques, such as real-time polymerase chain reaction and recently introduced bioluminescent miRNA detection, require systematic study of DNA polymerases for use with miRNAs. In this study, a variety of DNA polymerases were studied to assess their capabilities of using miRNA as a primer and incorporating 2'-deoxyadenosine-5'-O-(1-thiotriphosphate) as a dATP alternative during DNA strand extension. Five DNA polymerases were investigated: mesophilic DNA polymerase I large (Klenow) fragment, 3'-->5' exo(-) Klenow DNA polymerase, thermophilic Bst DNA polymerase large fragment, Therminator DNA polymerase, and Taq DNA polymerase. The experimental results show that, except for Taq DNA polymerase, the polymerases can use miRNA as a primer and have both common and divergent properties of the nucleotide analog incorporation and miRNA discrimination. DNA polymerase I large (Klenow) fragment showed no detectable polymerization product with the thio-modified dATP as a substrate. Thermophilic Bst DNA polymerase had the highest specificity for miRNA recognition on a DNA template. The study provides a novel method for miRNA detection without reverse transcription to complementary DNA that is faster, simpler, and less prone to biases and errors.

Reduction of sample evaporation in small volume microplate luminescence assays.

Luminescence detection has great potential for use in small volume assays for high-throughput applications. However, the need for automated injection of detection reagents dictates an open well format, making small volume luminescence assays very susceptible to sample evaporation effects. Here we describe a technique for reducing evaporation of small sample volumes that uses layering of silicone oil on solution surfaces but still allows the use of automated injection.

Sucrose octasulfate regulates fibroblast growth factor-2 binding, transport, and activity: potential for regulation of tumor growth.

The antithrombotic activity of heparin has largely been credited with the success found in some cancer treatment by heparin. There are, however, many potent growth factors involved in tumor and blood vessel growth that bind to heparin with high affinity and their regulation by heparin may play a role in heparin's efficacy. We therefore chose to study the activity of a heparin analog, sucrose octasulfate (SOS), which has been similarly shown to interact with heparin-binding growth factors. Using mouse melanoma and lung carcinoma models, we demonstrate in vivo inhibition of tumor growth by SOS. SOS, however, showed little effect in coagulation assays indicating that this activity was not a primary mechanism of action for this molecule. Studies were then performed to assess the effect of SOS on basic fibroblast growth factor (FGF-2) activity, a growth factor which promotes tumor and blood vessel growth and is produced by B16 melanoma cells. SOS potently inhibited FGF-2 binding to endothelial cells and stripped pre-bound FGF-2 from cells. SOS also regulated FGF-2 stimulated proliferation. Further, SOS facilitated FGF-2 diffusion through Descemet's membrane, a heparan sulfate-rich basement membrane from the cornea, suggesting a possible role in FGF-2 clearance. Our results suggest that molecules such as SOS have the potential to remove growth factors from tumor microenvironments and the approach offers an attractive area for further study.

Calmodulin-mediated reversible immobilization of enzymes.

This work demonstrates the use of the protein calmodulin, CaM, as an affinity tag for the reversible immobilization of enzymes on surfaces. Our strategy takes advantage of the of the reversible, calcium-mediated binding of CaM to its ligand phenothiazine and of the ability to produce fusion proteins between CaM and a variety of enzymes to reversibly immobilize enzymes in an oriented fashion to different surfaces. Specifically, we employed two different enzymes, organophosphorus hydrolase (OPH) and beta-lactamase and two different solid supports, a silica surface and cellulose membrane modified by covalently attaching a phenothiazine ligand, to demonstrate the versatility of our immobilization method. Fusion proteins between CaM-OPH and CaM-beta-lactamase were prepared by using genetic engineering strategies to introduce the calmodulin tail at the N-terminus of each of the two enzymes. In the presence of Ca(2+), CaM adopts a conformation that favors interaction between hydrophobic pockets in CaM and phenothiazine, while in the presence of a Ca(2+)-chelating agent such as EGTA, the interaction between CaM and phenothiazine is disrupted, thus allowing for removal of the CaM-fusion protein from the surface under mild conditions. CaM also acts as a spacer molecule, orienting the enzyme away from the surface and toward the solution, which minimizes enzyme interactions with the immobilization surface. Since the method is based on the highly selective binding of CaM to its phenothiazine ligand, and this is covalently immobilized on the surface, the method does not suffer from ligand leaching nor from interference from other proteins present in the cell extract. An additional advantage lies in that the support can be regenerated by passing through EGTA, and then reused for the immobilization of the same or, if desired, a different enzyme. Using a fusion protein approach for immobilization purposes avoids the use of harsh conditions in the immobilization and/or regeneration steps, which could cause inactivation of the immobilized enzyme. Moreover, we have demonstrated that the CaM affinity tag allows immobilization of enzymes on a variety of surfaces without compromising their enzymatic activity substantially; for example, the immobilized OPH retained more than 80% of the activity of the free enzyme. Our results with beta-lactamase showed the feasibility of using a phenothiazine surface in several consecutive loading and regeneration cycles. This can be advantageous when expensive and/or difficult to obtain immobilization surfaces have to be employed; the immobilization surface could be reused to immobilize the same or a different enzyme using the CaM affinity tail. We also determined that the phenothiazine-modified silica particles are stable for long periods of time, i.e., up to 2 years when stored at 4 degrees C. It is envisioned that this type of reversible immobilization may find applications in the development of reversible, reusable biosensors and bioreactors endowed with the additional advantage that the biological element at the surface of the sensor or bioreactor could be replaced under mild conditions when needed to sense or process a different target molecule.

Gastroduodenal Crohn's disease is associated with NOD2/CARD15 gene polymorphisms, particularly L1007P homozygosity.

Limited data exist on the specific association between gastroduodenal Crohn's disease (GDCD) and NOD2/CARD15 gene polymorphisms. The aim of this study was to assess the association between NOD2 polymorphisms and GDCD, and to assess the specific association between each of the 3 major allelic variants G908R, L1007P, and R702W and the clinical features of Crohn's disease. We retrospectively reviewed the records of 202 patients with confirmed Crohn's disease and complete data was performed. Seventy-one patients (35%) had at least 1 allelic variant: 55 had 1 variant, 4 were homozygous for L1007fs, 2 homozygous for R702W, and 10 were compound heterozygous. Eighteen patients with confirmed GDCD were identified; 10 (56%) had wild type, 4 (22%) had 1 variant, and 4 (22%) had 2 allelic variants (2 were L1007P homozygous and 2 compound heterozygous). Compared to patients without gastroduodenal involvement, those with GDCD were more likely to have 2 allelic variants (22% vs. 6%; odds ratio [OR] 2.7; 95% confidence interval [CI] 1.6-7.3) and to be homozygous for L1007P (11% vs. 1%; OR 5.2; 95% CI 2.5-9.4). G908R heterozygosity was associated with ileal involvement (OR 1.4; 95% CI 1.1-2.9) and smoking habits (OR 2.4; 95% CI 1.2-3.8), whereas L1007P homozygosity was associated with GDCD (OR 5.8; 95% CI 2.6-10.8). L1007P variation was associated with younger age at diagnosis as well. There was no specific association between R702W homo- or heterozygosity and any of the characteristics examined. In conclusion, GDCD is associated with double dose of the NOD2/CARD15 gene variants, particularly L1007P homozygosity. There is evidence of specific variant-phenotype associations. G908R heterozygosity is associated with ileal involvement and smoking, whereas L1007P homozygosity is strongly associated with GDCD and younger age at diagnosis.