Glowing jellyfish, luminescence and a molecule called coelenterazine

Skin-Driven Ultrasensitive Mechanoluminescence Sensor Inspired by Spider Leg Joint Slits

Inspired by the spider's slit organ embedded in the leg joint exoskeleton and its ultrasensitive stress perception, we propose to fix the conflict between the stress concentration requirement for bright mechanoluminescence (ML) and the stress dispersion effect of soft material via integrating slit microstructures into flexible films. The designed slits focus weak stresses onto the corner to achieve high sensitivity, leading to 10-30 times ML intensity improvement at weak strain (<10% stretch) application. Slit morphology and various patterns were well investigated to address the stress distribution regularity. The slit-based ML film offers a facile light-luminescent artificial skin for visualizable stress presentations or detections without electricity power source. It is a practical endeavor of photonic skin for visible vocalization and a significant contribution to dysaudia auxiliary or luminescence augmented expressions for human social interactions, similar to jellyfish or squids.

Development of a novel, sensitive cell-based corin assay

Corin (atrial natriuretic peptide-converting enzyme, EC 3.4.21) is a transmembrane serine protease expressed in cardiomyocytes. Corin exerts its cardioprotective effects via the proteolytic cleavage and activation of pro-atrial natriuretic peptide (pro-ANP) to ANP. We recently described an ANP reporter cell line stably expressing the ANP receptor, a cGMP-dependent cation channel used as a real-time cGMP biosensor, and the Ca²⁺-sensitive photoprotein aequorin. Here, we describe the generation of a novel reporter cell line expressing the calcium biosensor GCaMP6 instead of aequorin. In contrast to the luminescence-based assay, ANP stimulation of our novel GCaMP6 reporter cell resulted in stable, long-lasting fluorescence signals. Using this novel reporter system, we were able to detect pro-ANP to ANP conversion by purified, soluble wildtype corin (solCorin), but not the active site mutant solCorin(S985A), resulting in left-shifted concentration-response curves. Furthermore, cellular pro-ANPase activity could be detected on HEK 293 cells after transient expression of wildtype corin. In contrast, corin activity was not detected after transfection with the inactive corin(S985A) variant. In supernatants from cardiomyocyte-derived HL-1 cells pro-ANP to ANP conversion could also be detected, while in HL-1 corin knockout cells no conversion was observed. These findings underline the role of corin as the pro-ANP convertase. Our novel fluorescence-based ANP reporter cell line is well-suited for the sensitive detection of corin activity, and may be used for the identification and characterization of novel corin modulators.

Chromophores in photoproteins of a glowing squid and mollusk

Bioluminescence is a chemical reaction process for light emission in vivo. An organic substance is normally oxidized in the protein to obtain the energy required for the light emission. Determination of the structure of the substance is one of the most important parts of bioluminescent research. Photoproteins of a flying squid and a mollusk contain chromophores that are formed by connecting an apo-protein and dehydrocoelenterazine. The chromophore has a chemical structure that can emit light in a photoprotein. The structural analysis of the chromophores in the photoproteins is described.

A yeast expression system for functional and pharmacological studies of the malaria parasite Ca²⁺/H⁺ antiporter

Background

Calcium (Ca²⁺) signalling is fundamental for host cell invasion, motility, in vivo synchronicity and sexual differentiation of the malaria parasite. Consequently, cytoplasmic free Ca²⁺ is tightly regulated through the co-ordinated action of primary and secondary Ca²⁺ transporters. Identifying selective inhibitors of Ca²⁺ transporters is key towards understanding their physiological role as well as having therapeutic potential, therefore screening systems to facilitate the search for potential inhibitors are a priority. Here, the methodology for the expression of a Calcium membrane transporter that can be scaled to high throughputs in yeast is presented.

Methods

The Plasmodium falciparum Ca²⁺/H⁺ antiporter (PfCHA) was expressed in the yeast Saccharomyces cerevisiae and its activity monitored by the bioluminescence from apoaequorin triggered by divalent cations, such as calcium, magnesium and manganese.

Results

Bioluminescence assays demonstrated that PfCHA effectively suppressed induced cytoplasmic peaks of Ca²⁺, Mg²⁺ and Mn²⁺ in yeast mutants lacking the homologue yeast antiporter Vcx1p. In the scalable format of 96-well culture plates pharmacological assays with a cation antiporter inhibitor allowed the measurement of inhibition of the Ca²⁺ transport activity of PfCHA conveniently translated to the familiar concept of fractional inhibitory concentrations. Furthermore, the cytolocalization of this antiporter in the yeast cells showed that whilst PfCHA seems to locate to the mitochondrion of P. falciparum, in yeast PfCHA is sorted to the vacuole. This facilitates the real-time Ca²⁺-loading assays for further functional and pharmacological studies.

Discussion

The functional expression of PfCHA in S. cerevisiae and luminescence-based detection of cytoplasmic cations as presented here offer a tractable system that facilitates functional and pharmacological studies in a high-throughput format. PfCHA is shown to behave as a divalent cation/H⁺ antiporter susceptible to the effects of cation/H⁺ inhibitors such as KB-R7943. This type of gene expression systems should advance the efforts for the screening of potential inhibitors of this type of divalent cation transporters as part of the malaria drug discovery initiatives and for functional studies in general.

Conclusion

The expression and activity of the PfCHA detected in yeast by a bioluminescence assay that follows the levels of cytoplasmic Ca²⁺ as well as Mg²⁺ and Mn²⁺ lend itself to high-throughput and quantitative settings for pharmacological screening and functional studies.

NFAT-induced histone acetylation relay switch promotes c-Myc-dependent growth in pancreatic cancer cells

BACKGROUND & AIMS

Induction of immediate early transcription factors (ITF) represents the first transcriptional program controlling mitogen-stimulated cell cycle progression in cancer. Here, we examined the transcriptional mechanisms regulating the ITF protein c-Myc and its role in pancreatic cancer growth in vitro and in vivo.

METHODS

Expression of ITF proteins was examined by reverse-transcription polymerase chain reaction and immunoblotting, and its implications in cell cycle progression and growth was determined by flow cytometry and [(3)H]-thymidine incorporation. Intracellular Ca(2+) concentrations, calcineurin activity, and cellular nuclear factor of activated T cells (NFAT) distribution were analyzed. Transcription factor complex formations and promoter regulation were examined by immunoprecipitations, reporter gene assays, and chromatin immunoprecipitation. Using a combination of RNA interference knockdown technology and xenograft models, we analyzed the significance for pancreatic cancer tumor growth.

RESULTS

Serum promotes pancreatic cancer growth through induction of the proproliferative NFAT/c-Myc axis. Mechanistically, serum increases intracellular Ca(2+) concentrations and activates the calcineurin/NFAT pathway to induce c-Myc transcription. NFAT binds to a serum responsive element within the proximal promoter, initiates p300-dependent histone acetylation, and creates a local chromatin structure permissive for the inducible recruitment of Ets-like gene (ELK)-1, a protein required for maximal activation of the c-Myc promoter. The functional significance of this novel pathway was emphasized by impaired c-Myc expression, G1 arrest, and reduced tumor growth upon NFAT depletion in vitro and in vivo.

CONCLUSIONS

Our study uncovers a novel mechanism regulating cell growth and identifies the NFAT/ELK complex as modulators of early stages of mitogen-stimulated proliferation in pancreatic cancer cells.

The use of aequorins to record and visualize Ca(2+) dynamics: from subcellular microdomains to whole organisms

In this chapter, we describe the practical aspects of measuring [Ca(2+)] transients that are generated in a particular cytoplasmic domain, or within a specific organelle or its periorganellar environment, using bioluminescent, genetically encoded and targeted Ca(2+) reporters, especially those based on apoaequorin. We also list examples of the organisms, tissues, and cells that have been transfected with apoaequorin or an apoaequorin-BRET complex, as well as of the organelles and subcellular domains that have been specifically targeted with these bioluminescent Ca(2+) reporters. In addition, we summarize the various techniques used to load the apoaequorin cofactor, coelenterazine, and its analogs into cells, tissues, and intact organisms, and we describe recent advances in the detection and imaging technologies that are currently being used to measure and visualize the luminescence generated by the aequorin-Ca(2+) reaction within these various cytoplasmic domains and subcellular compartments.

Reporter proteins in whole-cell optical bioreporter detection systems, biosensor integrations, and biosensing applications

Whole-cell, genetically modified bioreporters are designed to emit detectable signals in response to a target analyte or related group of analytes. When integrated with a transducer capable of measuring those signals, a biosensor results that acts as a self-contained analytical system useful in basic and applied environmental, medical, pharmacological, and agricultural sciences. Historically, these devices have focused on signaling proteins such as green fluorescent protein, aequorin, firefly luciferase, and/or bacterial luciferase. The biochemistry and genetic development of these sensor systems as well as the advantages, challenges, and common applications of each one will be discussed.

Essential role of Pyk2 and Src kinase activation in neuropeptide-induced proliferation of small cell lung cancer cells

Neuropeptide hormones like bombesin/gastrin-releasing peptide, galanin or bradykinin, acting via auto and paracrine growth loops, represent the principal mitogens of small cell lung cancer (SCLC). These mitogenic neuropeptides activate G(q/11)-coupled receptors which stimulate phospholipase Cbeta activity, followed by rises of the intracellular calcium concentration ([Ca2+](i)) and activation of protein kinase C (PKC). We report here that proline-rich tyrosine kinase Pyk2 is highly expressed in SCLC cells and provides a functional link between neuropeptide-induced increases in [Ca2+](i) and tumor cell proliferation. Activation of Pyk2 and its association with Src kinases critically depends on the elevation of [Ca2+](i), but is independent of PKC. Src kinase activities are crucial for neuropeptide-mediated GTP-loading of Ras and activation of extracellular signal-regulated kinases in SCLC cells. Pyk2 and Src kinases essentially contribute to anchorage-independent proliferation of SCLC cells. Inhibition of either Pyk2 or Src kinases by lentiviral RNAi or pharmacological inhibition with PP2, respectively, attenuated basal and neuropeptide-elicited survival and proliferation of SCLC cells in liquid culture and in soft agar. Thus, neuropeptides stimulate anchorage-independent survival and proliferation of SCLC cells via pathways involving Pyk2 and Src kinases. Therefore, Ca2+-induced Pyk2/Src complex formation may be a rewarding molecular target for novel therapeutic strategies in SCLC cells.

Photoprotein aequorin as a novel reporter for SNP genotyping by primer extension-application to the variants of mannose-binding lectin gene

Mannose-binding lectin (MBL) is a key component of the innate immune system, and its deficiency is associated with increased susceptibility to various infections and autoimmune disorders. Since several nucleotide variations in the mannose-binding lectin 2 gene (MBL2) have been associated with the functional deficiency of MBL, there is a growing need to screen its allelic variants and develop genotyping methods for MBL2. In this context we propose a rapid, robust, cost-efficient, and automatable method for detecting all known allelic variants of MBL2. This report introduces for the first time the photoprotein aequorin as a reporter in genotyping by primer extension (PEXT) reactions. The method involves a single PCR amplification of a genomic region that spans all six variant nucleotide sites, i.e., three structural mutations in exon 1 (c.154C>T, pArg52Cys; c.161A>G, p.Gly54Asp; and c.170A>G, p.Gly57Glu), two single nucleotide polymorphisms (SNPs) at positions c.-619G>C and c.-290G>C (promoter region), and one SNP at position c.-66C>T of the 5' untranslated region. PCR is followed by PEXT reactions for each site. Biotin-dUTP is incorporated in the extended primer. The genotyping primers contain a poly(dA) segment at their 5' end. The products are captured by hybridization on the surface of microtiter wells that are coated with a poly(dT)-albumin. The extended primers only are detected by reaction with a streptavidin-aequorin conjugate. The bound photoprotein aequorin is measured within 3 sec by simply adding Ca2+. We carried out extensive optimization studies of the PEXT reaction and genotyped the six nucleotide variant sites using blood specimens from 27 normal DNA samples. The results of the proposed method agreed entirely with the sequencing data.

Coelenterazine (marine bioluminescent substrate): a source of inspiration for the discovery of novel antioxidants

Coelenterazine and derivatives were initially considered in the scientific community for their (bio)luminescent properties. Now, another interest of such hetero-bicycles has been pointed out by the discovery of remarkable antioxidative properties, and an unique mode of action as a "cascade": the mother-compound (imidazolopyrazinone) is transformed by ROS into a daughter-compound (2-amino-pyrazine) also endowed with antioxidative properties. This review illustrates the therapeutic potential of synthetic imidazolopyrazinones (coelenterazine analogues): chemical reactivity assays with singulet oxygen, radical anion superoxide, peroxynitrite, and radicals formed during lipid and LDL peroxidation, cellular tests of protection against oxidative stress using keratinocyte, hepatocyte, neuronal and erythrocyte cells, and finally in vivo evaluation in a hamster model of ischemia-reperfusion, are fully described.

A cell-based cGMP assay useful for ultra-high-throughput screening and identification of modulators of the nitric oxide/cGMP pathway

We have established a rapid, homogeneous, cell-based, and highly sensitive assay for guanosine 3'-5'-cyclic monophosphate (cGMP) that is suitable for fully automated ultra-high-throughput screening. In this assay system, cGMP production is monitored in living cells via Ca2+ influx through the olfactory cyclic nucleotide-gated cation channel CNGA2, acting as the intracellular cGMP sensor. A stably transfected Chinese hamster ovary (CHO) cell line was generated recombinantly expressing soluble guanylate cyclase, CNGA2, and aequorin as a luminescence indicator for the intracellular calcium concentration. This cell line was used to screen more than 900,000 compounds in an automated ultra-high-throughput screening assay using 1536-well microtiter plates. In this way, we have been able to identify BAY 58-2667, a member of a new class of amino dicarboxylic acids that directly activate soluble guanylate cyclase. The assay system allows the real-time cGMP detection within living cells and makes it possible to screen for activators and inhibitors of enzymes involved in the nitric oxide/cGMP pathway.

Bright fluorescence of a novel protein from Vibrio vulnificus depends on NADPH and the expression of this protein is regulated by a LysR-type regulatory gene

A blue fluorescent protein, BfgV, belonging to the short-chain dehydrogenase/reductase superfamily, was found in a non-bioluminescent pathogen Vibrio vulnificus CKM-1. This protein has fluorescence spectra with two excitation peaks at 283 and 352 nm, and one emission peak at 456 nm. BfgV fluoresces through effectively augmenting the intrinsic fluorescence of NADPH bound to it. Escherichia coli transformants expressing this protein can emit eye-detectable fluorescence. A LysR-type transcriptional regulator gene bfgR was found at the vicinal upstream region of bfgV in CKM-1 genome. The clues that products of bfgR can specifically bind to bfgR-bfgV intergenic promoter region and the deletion of bfgR significantly decreases the expression of bfgV reveal bfgR is a repressor gene of bfgV in V. vulnificus CKM-1.

Imaging reversal of multidrug resistance in living mice with bioluminescence: MDR1 P-glycoprotein transports coelenterazine

Coelenterazine is widely distributed among marine organisms, producing bioluminescence by calcium-insensitive oxidation mediated by Renilla luciferase (Rluc) and calcium-dependent oxidation mediated by the photoprotein aequorin. Despite its abundance in nature and wide use of both proteins as reporters of gene expression and signal transduction, little is known about mechanisms of coelenterazine transport and cell permeation. Interestingly, coelenterazine analogues share structural and physiochemical properties of compounds transported by the multidrug resistance MDR1 P-glycoprotein (Pgp). Herein, we report that living cells stably transfected with a codon-humanized Rluc show coelenterazine-mediated bioluminescence in a highly MDR1 Pgp-modulated manner. In Pgp-expressing Rluc cells, low baseline bioluminescence could be fully enhanced (reversed) to non-Pgp matched control levels with potent and selective Pgp inhibitors. Therefore, using coelenterazine and noninvasive bioluminescence imaging in vivo, we could directly monitor tumor-specific Pgp transport inhibition in living mice. While enabling molecular imaging and high-throughput screening of drug resistance pathways, these data also raise concern for the indiscriminate use of Rluc and aequorin as reporters in intact cells or transgenic animals, wherein Pgp-mediated alterations in coelenterazine permeability may impact results.

Affinity capture-facilitated preparation of aequorin- oligonucleotide conjugates for rapid hybridization assays

We report a general procedure for the preparation of biomolecular conjugates that combine the molecular recognition properties of oligonucleotides with the high detectability of the photoprotein aequorin. Central to the conjugation protocols is the use of recombinant aequorin fused to a hexahistidine tag. In one protocol, an amino-modified oligonucleotide was treated with a homobifunctional cross-linker carrying two N-hydroxysuccinimide ester groups, and the derivative was allowed to react with (His)(6)-aequorin. A second strategy involved the introduction of protected sulfhydryl groups into (His)(6)-aequorin and subsequent reaction with a heterobifunctional linker containing a N-hydroxysuccinimide and a maleimide group. The strong, but reversible, binding of (His)(6)-aequorin to Ni(2+)-nitrilotriacetic acid agarose enabled the rapid and effective removal of the unreacted oligonucleotide, which otherwise diminishes the performance of the hybridization assay by competing with the conjugate for the complementary target sequence. Aequorin-oligo conjugates prepared by affinity capture showed similar performance with those purified by anion-exchange HPLC. The conjugates were applied to the development of rapid bioluminometric hybridization assays. The analytical range extended from 2 to 2000 pmol/L of target DNA. The reproducibility was less than 10%. The conjugate obtained from a reaction of 10 nmol of (His)(6)-aequorin is sufficient for about 5000 hybridization assays. The proposed conjugation strategy is general because a variety of reporter proteins can be fused to hexahistidine tag by using suitable vectors that are commercially available.

Bioluminescence immunoassay for cortisol using recombinant aequorin as a label

The analysis of hormones in saliva is a powerful tool in the assessment of a patient's endocrine function, since it allows multiple noninvasive samplings. Since salivary levels of most hormones are 10 to 50 times lower than plasma levels, accurate and highly sensitive assays are needed for saliva measurements. Herein, we describe the development of a solid-phase competitive immunoassay for cortisol in saliva, in which a mutant of the photoprotein aequorin has been used as a label. We have chemically conjugated cortisol to aequorin at different molar ratios. The various cortisol-aequorin conjugates were characterized in terms of bioluminescent activity and affinity for the anti-cortisol antibody. The conjugate that gave the best analytical performance was used for the development of the immunoassay and the analysis of cortisol in saliva samples. The conjugates were stable for at least 6 months when stored at 4 degrees C. The method fulfilled all the standard requirements of precision and accuracy. The optimized immunoassay gave a detection limit of 300 fmol/tube, corresponding to 3 nmol/L, with a linear dynamic range of 10-1000 nmol/L. Therefore, cortisol can be detected down to 0.1 ng in 100 microl of saliva sample using this assay, without any sample pretreatment. This detection limit is almost one order of magnitude lower than the physiological levels of salivary cortisol, which are reported to be 10-25 nmol/L. This allows the quantification of salivary cortisol to be performed in the linear range of the calibration curve, which is most reliable for quantification purposes.

A novel photoprotein from oceanic squid (Symplectoteuthis oualaniensis) with sequence similarity to mammalian carbon-nitrogen hydrolase domains

A 60-kDa photoprotein was selectively extracted from squid photogenic organ with 0.6 M KCl solution at pH 6 as luminescence-active forms. The photoprotein with fluorescence chromophore was eluted from size-exclusion HPLC mainly as oligomeric forms (about 200 kDa or more) with a trace amount of monomeric form of about 60 kDa. A limited tryptic digestion of the KCl-extract induced the cleavage into a 40-kDa fragment and a 16-kDa N-terminal fragment and the conversion to the monomeric form which still retained luminescence activity. Under UV light the 60-kDa protein and its 40-kDa fragment emitted fluorescence. Immunoblot analysis using specific antibody showed specific expression of the 60-kDa protein in the photogenic organ. Amino acid sequences of the 60-kDa photoprotein, its 40- and 16-kDa fragments, and six peptides from the Lys-C digest revealed no sequence similarity to known photoproteins but significant similarity to the carbon-nitrogen hydrolase domain found in mammalian biotinidase and vanin (pantetheinase).

Cysteine-free mutant of aequorin as a photolabel in immunoassay development

The bioluminescent protein aequorin is a sensitive label that has been employed in a number of analytical applications. A mutant of aequorin with enhanced stability produced recombinantly in our laboratory has been employed as a label in the development of an immunoassay for digoxin. Digoxin is a cardiac glycoside used in the treatment of congestive heart failure. This drug has a very narrow therapeutic range of 0.8-2.0 ng/mL (1.0-2.5 nmol/L), thus requiring therapeutic drug monitoring. In this study, a derivative of digoxigenin was chemically conjugated to the mutant aequorin, and the resulting protein-digoxigenin derivative conjugates were characterized in terms of their luminescence properties. A solid-phase immunoassay for digoxin was then developed. The detection limit of the assay for digoxin was 1 x 10(-12) M. To demonstrate the use of this mutant aequorin as a label in biological sample analysis without any need for pretreatment of the samples, the assay was tested in serum spiked with digoxin. Interference from digoxin analogues was also evaluated to determine the specificity of the assay.

Catechol derivatives of aminopyrazine and cell protection against UVB-induced mortality

A series of 5-aryl- and 3,5-bis-aryl-2-amino-1,4-pyrazine derivatives 4 and 6, and related imidazolopyrazinones 7, has been synthesized, the aryl groups of which are catechol and/or phenol substituents. These compounds, tested against human keratinocyte cells stressed by UVB irradiation, showed high antioxidative properties. One compound (6f) was more active than EGCG/ECG (green tea extract) in reducing cell mortality.

Imidazolopyrazinones as potential antioxidants

A series of imidazolopyrazinones 3, substituted at C-2, and C-2/C-6, has been prepared. The compounds behaved as quenchers of superoxide anion. The more active compounds are structurally related to coelenterazine, a natural substrate of marine bioluminescence. Theoretical parameters based on Hartree-Fock instabilities have been examined.

C-Terminal and N-Terminal Fusions of Aequorin with Small Peptides in Immunoassay Development

Aequorin fusion proteins have been used extensively in intracellular Ca2+ measurements and in the development of binding assays. Gene fusions to aequorin for production of fusion proteins have been so far limited to its N-terminus, as previous studies have indicated that aequorin loses its activity upon modification of its C-terminus. To further investigate this, two model peptides, an octapeptide (DTLDDDDL), and leu-enkephalin (TGGFL), an opioid peptide, were fused to the C-terminus of a cysteine-free mutant of aequorin through genetic engineering. The octapeptide was also fused to the N-terminus of the aequorin-leu-enkephalin fusion protein, which enables its affinity purification. Contrary to reports of earlier studies, we found that aequorin retains its bioluminescence activity after modification of the C-terminus. The half-life of light emission and the calibration curves obtained with the fusion proteins were comparable to those of the cysteine-free mutant of aequorin. Dose-response curves for the octapeptide were generated using two aequorin-octapeptide fusion proteins with the octapeptide fused to the N-terminus in one case, and to the C-terminus in the other. Similar detection limits for the octapeptide were obtained using both fusion proteins. The C-terminal fusion system has advantages in cases where antibodies recognize only the C-terminus of the peptide, as well as in cases where the functionality of the peptide lies in its C-terminus. The purification is also simplified as the affinity tag can be engineered at one terminus and the peptide of interest at the other.

An immunoassay for Leu-enkephalin based on a C-terminal aequorin-peptide fusion

Recently we demonstrated that the fusion of an octapeptide to the C-terminus of a cysteine-free mutant of aequorin showed no inhibitory effect on the luminescence activity of the photoprotein. This observation is of particular importance when the use of aequorin as a label in the development of immunoassays for peptides whose activity lies in their C-terminal region or the epitope for antibody recognition is at their C-terminus is desired. In the case of opioid peptides, antibodies are directed toward their C-terminus as they differ from each other at this terminus. The goal of this study was to develop an immunoassay for Leu-enkephalin, a mammalian opioid peptide, using a C-terminal aequorin-peptide fusion protein. For that, the N-terminus of Leu-enkephalin was genetically fused to the C-terminus of a cysteine-free mutant of aequorin. It was observed that the C-terminal conjugated aequorin maintained its luminescence activity. An immunoassay for Leu-enkephalin was then developed using the aequorin-Leu-enkephalin fusion protein as a labeled analyte in a competitive as well as in a sequential binding mode. It was demonstrated that aequorin can be used as a label in peptide assays in which it is critical that the peptide's C-terminus be free for activity and/or for antibody recognition.