The plant alkaloid and anti-leukemia drug homoharringtonine sensitizes resistant human colorectal carcinoma cells to TRAIL-induced apoptosis via multiple mechanisms.

TNF-related apoptosis-inducing ligand (TRAIL) is a pro-apoptotic ligand from the TNF-alpha family that is under consideration, along with agonistic anti-TRAIL receptor antibodies, as a potential anti-tumor agent. However, most primary human tumors are resistant to monotherapy with TRAIL apoptogens, and thus the potential applicability of TRAIL in anti-tumor therapy ultimately depends on its rational combination with drugs targeting these resistances. In our high-throughput screening for novel agents/drugs that could sensitize TRAIL-resistant colorectal cancer cells to TRAIL-induced apoptosis, we found homoharringtonine (HHT), a cephalotaxus alkaloid and tested anti-leukemia drug, to be a very effective, low nanomolar enhancer of TRAIL-mediated apoptosis/growth suppression of these resistant cells. Co-treatment of TRAIL-resistant RKO or HT-29 cells with HHT and TRAIL led to the effective induction of apoptosis and the complete elimination of the treated cells. HHT suppressed the expression of the anti-apoptotic proteins Mcl-1 and cFLIP and enhanced the TRAIL-triggered activation of JNK and p38 kinases. The shRNA-mediated down-regulation of cFLIP or Mcl-1 in HT-29 or RKO cells variably enhanced their TRAIL-induced apoptosis but it did not markedly sensitize them to TRAIL-mediated growth suppression. However, with the notable exception of RKO/sh cFLIP cells, the downregulation of cFLIP or Mcl-1 significantly lowered the effective concentration of HHT in HHT + TRAIL co-treatment. Combined HHT + TRAIL therapy also led to the strong suppression of HT-29 tumors implanted into immunodeficient mice. Thus, HHT represents a very efficient enhancer of TRAIL-induced apoptosis with potential application in TRAIL-based, anti-cancer combination therapy.

Major Improvements in Robustness and Efficiency during the Screening of Novel Enzyme Effectors by the 3-Point Kinetics Assay.

The throughput level currently reached by automatic liquid handling and assay monitoring techniques is expected to facilitate the discovery of new modulators of enzyme activity. Judicious and dependable ways to interpret vast amounts of information are, however, required to effectively answer this challenge. Here, the 3-point method of kinetic analysis is proposed as a means to significantly increase the hit success rates and decrease the number of falsely identified compounds (false positives). In this post-Michaelis-Menten approach, each screened reaction is probed in three different occasions, none of which necessarily coincide with the initial period of constant velocity. Enzymology principles rather than subjective criteria are applied to identify unwanted outliers such as assay artifacts, and then to accurately distinguish true enzyme modulation effects from false positives. The exclusion and selection criteria are defined based on the 3-point reaction coordinates, whose relative positions along the time-courses may change from well to well or from plate to plate, if necessary. The robustness and efficiency of the new method is illustrated during a small drug repurposing screening of potential modulators of the deubiquinating activity of ataxin-3, a protein implicated in Machado-Joseph disease. Apparently, intractable Z factors are drastically enhanced after (1) eliminating spurious results, (2) improving the normalization method, and (3) increasing the assay resilience to systematic and random variability. Numerical simulations further demonstrate that the 3-point analysis is highly sensitive to specific, catalytic, and slow-onset modulation effects that are particularly difficult to detect by typical endpoint assays.

Retinoic acid is a negative regulator of matrix Gla protein gene expression in teleost fish Sparus aurata.

Matrix Gla protein (MGP) is an extracellular mineral-binding protein expressed in several tissues while accumulated only in bone and cartilage under physiological conditions. Although the precise molecular mechanism of action of MGP remains unknown, all available evidence indicates that it acts as a physiological inhibitor of mineralization. This work presents the cloning of gilthead seabream MGP gene (SaMGP) and the functional analysis of its promoter. SaMGP gene was found to be organized in five exons and to be under control of a distal and a proximal promoter, both, capable of activating SaMGP transcription in transient transfections. Furthermore, we present strong evidence that retinoic acid down-regulates SaMGP gene transcription by interacting, through binding of its receptor, with a specific region within distal promoter. Interestingly, the presence of repetitive motifs in the proximity of SaMGP gene regulatory regions suggests that they may modulate promoter accessibility to transcription machinery, as already seen for other genes. This work provides additional evidence of the usefulness of non-mammalian model systems to elucidate the complex regulation of MGP gene transcription.

Calcium Ionophore, Calcimycin, Kills Leishmania Promastigotes by Activating Parasite Nitric Oxide Synthase.

Leishmaniasis is an infectious disease caused by protozoan parasites of the genus Leishmania. There is no vaccine against human leishmaniasis and the treatment of the disease would benefit from a broader spectrum and a higher efficacy of leishmanicidal compounds. We analyzed the leishmanicidal activity and the mechanism of action of the calcium ionophore, calcimycin. L. major promastigotes were coincubated with calcimycin and the viability of the cells was assessed using resazurin assay. Calcimycin displayed dose-dependent effect with IC50 = 0.16 µM. Analysis of propidium iodide/LDS-751 stained promastigotes revealed that lower concentrations of calcimycin had cytostatic effect and higher concentrations had cytotoxic effect. To establish the mechanism of action of calcimycin, which is known to stimulate activity of mammalian constitutive nitric oxide synthase (NOS), we coincubated L. major promastigotes with calcimycin and selective NOS inhibitors ARL-17477 or L-NNA. Addition of these inhibitors substantially decreased the toxicity of calcimycin to Leishmania promastigotes. In doing so, we demonstrated for the first time that calcimycin has a direct leishmanicidal effect on L. major promastigotes. Also, we showed that Leishmania constitutive Ca2+/calmodulin-dependent nitric oxide synthase is involved in the parasite cell death. These data suggest activation of Leishmania nitric oxide synthase as a new therapeutic approach.

Characterization of Sparus aurata osteonectin cDNA and in silico analysis of protein conserved features: evidence for more than one osteonectin in Salmonidae.

Osteonectin is a matricellular protein involved in various cellular mechanisms but its exact function remains unclear despite numerous studies. We present here the cloning of Sparus aurata partial osteonectin cDNA and the reconstruction of 15 other sequences from both vertebrates and invertebrates, almost doubling the set of available sequences (a total of 35 sequences is now available). Taking advantage of the resulting large amount of data, we have created multiple sequence alignments and identified osteonectin putative conserved features (intra- and inter-disulfide bonds, collagen- and calcium-binding domains and phosphorylation sites) likely to be important for protein structure and function. This work also provides the first evidence for the presence of more than one osteonectin in some species. Finally, S. aurata osteonectin gene expression has been shown to initiate during larval development shortly after gastrulation, and to be high in bone-derived cell lines while down-regulated during extracellular matrix mineralization, further emphasizing the important role of osteonectin in skeletal development and bone formation.

Cubozoan genome illuminates functional diversification of opsins and photoreceptor evolution.

Animals sense light primarily by an opsin-based photopigment present in a photoreceptor cell. Cnidaria are arguably the most basal phylum containing a well-developed visual system. The evolutionary history of opsins in the animal kingdom has not yet been resolved. Here, we study the evolution of animal opsins by genome-wide analysis of the cubozoan jellyfish Tripedalia cystophora, a cnidarian possessing complex lens-containing eyes and minor photoreceptors. A large number of opsin genes with distinct tissue- and stage-specific expression were identified. Our phylogenetic analysis unequivocally classifies cubozoan opsins as a sister group to c-opsins and documents lineage-specific expansion of the opsin gene repertoire in the cubozoan genome. Functional analyses provided evidence for the use of the Gs-cAMP signaling pathway in a small set of cubozoan opsins, indicating the possibility that the majority of other cubozoan opsins signal via distinct pathways. Additionally, these tests uncovered subtle differences among individual opsins, suggesting possible fine-tuning for specific photoreceptor tasks. Based on phylogenetic, expression and biochemical analysis we propose that rapid lineage- and species-specific duplications of the intron-less opsin genes and their subsequent functional diversification promoted evolution of a large repertoire of both visual and extraocular photoreceptors in cubozoans.

Monensin inhibits canonical Wnt signaling in human colorectal cancer cells and suppresses tumor growth in multiple intestinal neoplasia mice.

The Wnt signaling pathway is required during embryonic development and for the maintenance of homeostasis in adult tissues. However, aberrant activation of the pathway is implicated in a number of human disorders, including cancer of the gastrointestinal tract, breast, liver, melanoma, and hematologic malignancies. In this study, we identified monensin, a polyether ionophore antibiotic, as a potent inhibitor of Wnt signaling. The inhibitory effect of monensin on the Wnt/ß-catenin signaling cascade was observed in mammalian cells stimulated with Wnt ligands, glycogen synthase kinase-3 inhibitors, and in cells transfected with ß-catenin expression constructs. Furthermore, monensin suppressed the Wnt-dependent tail fin regeneration in zebrafish and Wnt- or ß-catenin-induced formation of secondary body axis in Xenopus embryos. In Wnt3a-activated HEK293 cells, monensin blocked the phoshorylation of Wnt coreceptor low-density lipoprotein receptor related protein 6 and promoted its degradation. In human colorectal carcinoma cells displaying deregulated Wnt signaling, monensin reduced the intracellular levels of ß-catenin. The reduction attenuated the expression of Wnt signaling target genes such as cyclin D1 and SP5 and decreased the cell proliferation rate. In multiple intestinal neoplasia (Min) mice, daily administration of monensin suppressed progression of the intestinal tumors without any sign of toxicity on normal mucosa. Our data suggest monensin as a prospective anticancer drug for therapy of neoplasia with deregulated Wnt signaling.

Lipophosphonoxins: new modular molecular structures with significant antibacterial properties.

Novel compounds termed lipophosphonoxins were prepared using a simple and efficient synthetic approach. The general structure of lipophosphonoxins consists of four modules: (i) a nucleoside module, (ii) an iminosugar module, (iii) a hydrophobic module (lipophilic alkyl chain), and (iv) a phosphonate linker module that holds together modules i-iii. Lipophosphonoxins displayed significant antibacterial properties against a panel of Gram-positive species, including multiresistant strains. The minimum inhibitory concentration (MIC) values of the best inhibitors were in the 1-12 µg/mL range, while their cytotoxic concentrations against human cell lines were significantly above this range. The modular nature of this artificial scaffold offers a large number of possibilities for further modifications/exploitation of these compounds.

Development of two bone-derived cell lines from the marine teleost Sparus aurata; evidence for extracellular matrix mineralization and cell-type-specific expression of matrix Gla protein and osteocalcin.

A growing interest in the understanding of the ontogeny and mineralization of fish skeleton has emerged from the recent implementation of fish as a vertebrate model, particularly for skeletal development. Whereas several in vivo studies dealing with the regulation of bone formation in fish have been published, in vitro studies have been hampered because of a complete lack of fish-bone-derived cell systems. We describe here the development and the characterization of two new cell lines, designated VSa13 and VSa16, derived from the vertebra of the gilthead sea bream. Both cell types exhibit a spindle-like phenotype and slow growth when cultured in Leibovitz's L-15 medium and a polygonal phenotype and rapid growth in Dulbecco's modified Eagle medium (D-MEM). Scanning electron microscopy and von Kossa staining have revealed that the VSa13 and VSa16 cells can only mineralize their extracellular matrix when cultured in D-MEM under mineralizing conditions, forming calcium-phosphate crystals similar to hydroxyapatite. We have also demonstrated the involvement of alkaline phosphatase, a marker of bone formation in vivo, and Gla proteins (osteocalcin and matrix Gla protein, MGP) in the process of mineralization. Finally, we have shown that VSa13 and VSa16 cell lines express osteocalcin and MGP in a mutually exclusive manner. Thus, both cell lines are capable of mineralizing in vitro and of expressing genes found in chondrocyte and osteoblast cell lineages, emphasizing the suitability of these new cell lines as valuable tools for analyzing the expression and regulation of cartilage- and bone-specific genes.