Chemical recovery and browning of Nova Scotia surface waters in response to declining acid deposition.

Declining emissions of sulfur and nitrogen have curtailed acid deposition across large areas of North America and Europe. This has allowed many lakes to recover from acidification, with decreases in sulfate, increases in pH, and increases in alkalinity. But reduced acid deposition has not always coincided with chemical lake recovery. Surface waters in Nova Scotia did not exhibit clear evidence of recovery as recently as 2007, due in part to increasing organic acidity and slow replenishment of base cations. In an updated assessment with data collected as recently as 2019, we analyze water chemistry representing 81 lakes and rivers and two precipitation monitoring stations over up to 41 years. We find that Nova Scotia surface waters are now exhibiting signs of chemical recovery. We estimated the linear decrease in precipitation sulfate and nitrate yield at up to 0.31 and 0.18 kg ha-1 year-2, respectively, and the linear increase in precipitation pH at up to 0.014 year-1. Sulfate decreased in 60 of 62 lakes and 14 of 17 rivers (-0.0051 to -0.23 mg L-1 year-1), while pH increased in 55 of 64 lakes and 11 of 17 rivers (0.0015-0.072 year-1). Apparent colour increased in 54 of 62 lakes and 13 of 17 rivers (0.0026-3.9 Pt-Co year-1). We identified increasing aluminum trends in 46 of 61 lakes, and we show using size-exclusion chromatography that binding to organic and iron-based colloids may help to explain these trends. To the extent that increases in apparent colour are explained by chromophoric dissolved organic matter (DOM), they imply greater binding capacity for metals in surface waters, and greater capacity for DOM to stabilize metal (oxyhydr)oxide colloids.

Development and evaluation of high throughput functional assay methods for HERG potassium channel.

Three functional hERG channel assay methods have been developed and evaluated. The methods were tested against five known hERG channel inhibitors: dofetilide, terfenadine (Seldane), sertindole (Serdolect), astemizole (Hismanal), and cisapride (Propulsid). The DiBAC4(3)-based assays were found to be the most economical but had high false-hit rates as a result of the interaction of dye with the test compounds. The membrane potential dye assay had fewer color-quenching problems but was expensive and still gave false hits. The nonradioactive Rb+ efflux assay was the most sensitive of all the assays evaluated and had the lowest false-hit rate.

Automated assay optimization with integrated statistics and smart robotics.

The transition from manual to robotic high throughput screening (HTS) in the last few years has made it feasible to screen hundreds of thousands of chemical entities against a biological target in less than a month. This rate of HTS has increased the visibility of bottlenecks, one of which is assay optimization. In many organizations, experimental methods are generated by therapeutic teams associated with specific targets and passed on to the HTS group. The resulting assays frequently need to be further optimized to withstand the rigors and time frames inherent in robotic handling. Issues such as protein aggregation, ligand instability, and cellular viability are common variables in the optimization process. The availability of robotics capable of performing rapid random access tasks has made it possible to design optimization experiments that would be either very difficult or impossible for a person to carry out. Our approach to reducing the assay optimization bottleneck has been to unify the highly specific fields of statistics, biochemistry, and robotics. The product of these endeavors is a process we have named automated assay optimization (AAO). This has enabled us to determine final optimized assay conditions, which are often a composite of variables that we would not have arrived at by examining each variable independently. We have applied this approach to both radioligand binding and enzymatic assays and have realized benefits in both time and performance that we would not have predicted a priori. The fully developed AAO process encompasses the ability to download information to a robot and have liquid handling methods automatically created. This evolution in smart robotics has proven to be an invaluable tool for maintaining high-quality data in the context of increasing HTS demands.

An ultra-high throughput screening approach for an adenine transferase using fluorescence polarization.

We have developed a novel assay for measuring the activity of an enzyme that transfers multiple adenine-containing groups to an acceptor protein. The assay is based on fluorescence polarization (FP) technology in a 1536-well plate format. In the assay, a long wavelength fluorescence tracer, Texas Red (Rhodamine), was covalently conjugated to adenine of the donor substrate through a C(6) spacer arm. As a result of the transfer of the adenine-containing moieties to the acceptor protein substrate, the rotational correlation time of the Texas Red conjugate increased, hence increasing the degree of fluorescence polarization. The pharmacological profile and kinetics of the enzyme measured according to the FP method were consistent with those determined previously by conventional analysis. We have successfully executed a 250,000-compound high throughput screening program based on the FP assay method. The quality and validity of the assay were verified by a variety of statistical analyses.

SH2-Containing protein tyrosine phosphatase-1 (SHP-1) association with Jak2 in UT-7/Epo cells.

We have investigated the interaction of the SH2-containing protein tyrosine phosphatase-1 (SHP-1) and Jak2 in an erythropoietin (Epo)-dependent human leukemia cell line, UT-7/Epo, using reciprocal immunoprecipitation and immunoblotting. The Epo-induced kinetics and dose response on phosphorylated Jak2 in anti-SHP-1 precipitates of UT-7/Epo cell lysates were similar to those in direct anti-Jak2 precipitates, suggesting that Jak2 coprecipitated with SHP-1. Furthermore, immunoblotting with anti-Jak2 and anti-SHP-1 antibodies indicated that SHP-1 appeared to be constitutively associated with non-tyrosine-phosphorylated Jak2 in UT-7/Epo cells in the absence of Epo and without phosphorylation of the Epo receptor (EpoR). Competition studies with C-terminal SHP-1 and Jak2 peptides decreased the amounts of SHP-1 and Jak2 detected in immunoprecipitates supporting the specific coprecipitation of SHP-1 and Jak2. In the presence of a recombinant GST-fusion protein containing both the N-terminal and C-terminal SH2 domains of SHP-1, anti-GST precipitated the fusion protein but not cellular Jak2. These studies suggest that SHP-1 and Jak2 are constitutively associated in UT-7/EPO cells. The association is not dependent upon Epo and is not mediated via SHP-1 SH2 binding. Sequential double immunoprecipitation demonstrated that only a small portion of intracellular Jak2 and SHP-1 molecules are constitutively associated. This partial association pattern may allow a more flexible and diverse regulation of Jak2 and SHP-1 activities. Whether Jak2 and SHP-1 are directly associated with each other or are part of a larger complex needs further investigation.

Screening for high-affinity ligands to the Src SH2 domain using capillary isoelectric focusing-electrospray ionization ion trap mass spectrometry.

A solution-based microscale approach for determination of high-affinity noncovalent complexes from mixtures of compounds is presented, based on capillary isoelectric focusing coupled on-line with electrospray ionization ion trap mass spectrometry. The studies are performed using the src homology 2 domain and tyrosine-phosphorylated peptide ligands as a model system. Tight complexes are formed in solution, preconcentrated up to 2 orders of magnitude and separated on the basis of their isoelectric points. The complexes are then dissociated in the mass spectrometer and the freed ligands identified. Picomole or less amounts of protein reagent are consumed per experiment. Structural information for the ligands involved in tight complex formation may be obtained using the MSn capabilities of the ion trap. The methodology can potentially be used to screen rapidly combinatorial mixtures of compounds for high-affinity ligands.

Structure-activity studies of rapamycin analogs: evidence that the C-7 methoxy group is part of the effector domain and positioned at the FKBP12-FRAP interface.

BACKGROUND: Rapamycin is an immunosuppressant natural product, which blocks T-cell mitogenesis and yeast proliferation. In the cytoplasm, rapamycin binds to the immunophilin FKBP12 and the complex of these two molecules binds to a recently discovered protein, FRAP. The rapamycin molecule has two functional domains, defined by their interaction with FKBP12 (binding domain) or with FRAP (effector domain). We previously showed that the allylic methoxy group at C-7 of rapamycin could be replaced by a variety of different substituents. We set out to examine the effects of such substitutions on FKBP12 binding and on biological activity. RESULTS: Rapamycin C-7-modified analogs of both R and S configurations were shown to have high affinities for FKBP12, yet these congeners displayed a wide range of potencies in splenocyte and yeast proliferation assays. The X-ray crystal structures of four rapamycin analogs in complexes with FKBP12 were determined and revealed that protein and ligand backbone conformations were essentially the same as those observed for the parent rapamycin-FKBP12 complex and that the C-7 group remained exposed to solvent. We then prepared a rapamycin analog with a photoreactive functionality as part of the C-7 substituent. This compound specifically labeled, in an FKBP12-dependent manner, a protein of approximately 250 kDa, which comigrates with recombinant FRAP. CONCLUSIONS: We conclude that the C-7 methoxy group of rapamycin is part of the effector domain. In the ternary complex, this group is situated in close proximity to FRAP, at the interface between FRAP and FKBP12.

Mechanism of action of bicyclic imidazoles defines a translational regulatory pathway for tumor necrosis factor alpha.

Expression of tumor necrosis factor alpha (TNF) by lipopolysaccharide-treated human monocytic cells is inhibited by bicyclic imidazoles. We studied the mechanism of action of a representative inhibitor, SK&F 86002, on synthesis of TNF by THP-1 cells. Levels of TNF protein were lowered by SK&F 86002 under conditions where TNF mRNA accumulation was unaffected, suggesting a post-transcriptional action. No effect of SK&F 86002 was detected on the rate of induction of TNF mRNA or steady state levels over a 5 hr period. The kinetics of SK&F 86002 inhibition of TNF protein synthesis coincided with those of anisomycin, not with actinomycin, suggesting an effect of SK&F 86002 on TNF mRNA translation. By using sucrose gradient sedimentation, we showed that quiescent THP-1 cells contained a substantial amount of TNF mRNA which was primarily associated with 43S pre-ribosomal complexes. Activation of the cells with lipopolysaccharide caused an elevation of the TNF mRNA level and increased the proportion associated with polyribosomes. Treatment with lipopolysaccharide plus SK&F 86002 led to a marked accumulation of TNF mRNA in the 43S complex-containing fractions and a concomitant reduction of polysome-associated TNF message. Neither lipopolysaccharide nor SK&F 86002 affected the amount or distribution of cyclophilin mRNA in the same fractions. The results suggest that lipopolysaccharide activates TNF translation at the initiation step and that SK&F 86002 inhibits this activation.

Pyridinyl imidazoles inhibit IL-1 and TNF production at the protein level.

The mechanism by which SK&F 86002 and other pyridinyl imidazoles inhibit the production of IL-1 and TNF from LPS-stimulated human monocytes was examined. Inhibition of IL-1 and TNF production was found to depend on the time of addition of SK&F 86002, with diminishing effect when added more than 2 h after LPS stimulation. Analysis of Western blots confirmed that both intracellular IL-1 beta and extracellular TNF were significantly reduced in response to SK&F 86002, but these reductions were not paralleled by changes in IL-1 and TNF mRNA. 35S methionine pulse and pulse-chase studies on IL-1 biosynthesis suggest that significant inhibition by SK&F 86002 and related compounds occurs at the translational level.

Antiserum to a novel peptide sequence reacts selectively with epithelial subpopulations.

A synthetic peptide corresponding to a novel protein sequence isolated from bovine kidney was used to immunize rabbits. When applied to Western blots of bovine kidney extracts, antiserum to this peptide recognizes proteins with molecular weights of 23 and 18 KD. Immunohistochemical examination of a variety of bovine and rat tissues with this antiserum revealed a unique distribution of immunoreactivity with the intermediate layers of a variety of stratified epithelia, in addition to renal glomeruli. The pattern of reactivity differed from previously described epithelial markers such as cytokeratins. These results indicate that this antiserum may be useful as a tool for the identification of cells of the intermediate layer of stratified epithelia and, as such, may aid in the study of this differentiating/proliferating tissue compartment.

Characterization and partial purification of human epithelial transforming growth factor.

A polypeptide growth factor has been partially purified from medium conditioned by the human adrenocortical carcinoma cell line SW13. This factor, designated h-TGFe, stimulates anchorage-independent growth of the SW13 cells. Similar activity was observed in human milk, and in conditioned media from seven of 14 epithelial cell lines. The SW13-derived activity is stable to low pH and 8M urea but labile to dithiothreitol and 2% sodium dodecyl sulfate. Human TGFe does not bind to heparin and fails to stimulate growth of endothelial cells in monolayer culture. The apparent molecular weight of h-TGFe is 59k by size exclusion chromatography in the presence of 8M urea and the activity binds strongly to cation exchangers. The activity elutes at 15-30% acetonitrile from a C18 reverse-phase column and has been partially purified by using a four-step chromatographic procedure. TGFe appears to be a novel growth factor produced by many epithelial cells and tissues.

Identification of a low molecular weight form of epithelial transforming growth factor.

We have purified a novel form of epithelial transforming growth factor (TGFe) from bovine kidney. Acid ethanol extracts of kidney were fractionated by size exclusion, reverse phase and cation exchange chromatography and activity was monitored by measuring growth of SW13 adrenocortical carcinoma cells in soft agar. The purified material was highly cationic, bound weakly to heparin and gave a band at 13-15000 Mr by SDS-PAGE following Bolton-Hunter iodination. This band correspond to the migration of biological activity extractable from gel slices. The results suggest that we have isolated a truncated form of TGFe which nonetheless retains biological activity.

Stimulation of anchorage independent proliferation of human adrenocortical carcinoma cells by inhibition of cholesterol biosynthesis.

Proliferation of SW13 human adrenocortical carcinoma cells under anchorage independent conditions was stimulated in a dose-dependent manner by treatment with the cholesterol biosynthesis inhibitor mevinolin. Induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was observed in mevinolin treated cultures. The growth stimulatory effect of mevinolin, but not that of epithelial transforming growth factor, a polypeptide growth factor for SW13 cells, was reversed by exogenous mevalonic acid. However, neither dolichol nor low density lipoprotein supplementation affected the response of SW13 cells to mevinolin. The results suggest that mevalonic acid metabolites may participate in the regulation of anchorage independent growth of SW13 cells.

Isolation and properties of cell lines from the metastasising rat mammary tumour SMT-2A.

A new cell line Rat mammary (Rama) 900 was isolated from the ascitic version of the SMT-2A metastasising rat mammary tumour by stepwise adaptation of the tumour cells to tissue culture. The cells grew mainly as loosely-adherent aggregates, and were dependent during the first 18 passages in vitro on a feeder layer of mesothelial-like cells (Rama 950) obtained from the same tumour. Subcutaneous injection of Rama 900 cells in fat pads of syngeneic Wistar Furth rats yielded anaplastic primary tumours and extensive, gross metastases including those in lungs, lymph nodes, liver and bones, similar to the parental transplantable tumour. The extent of metastatic spread from subcutaneous fat pads was increased by passage 17 in vitro for the Rama 900 cells. A similar extent of metastatic spread was achieved at earlier times by injecting the original cells with the non-tumorigenic Rama 950 cells in vivo. Subcutaneous injection of Rama 900 into thymectomised rats or MF1 nu/nu mice yielded fewer tumours, most of which regressed. No metastases occurred in the thymectomised rats and fewer metastases, mainly in lungs but not in lymph nodes, livers or bones, were seen in the nude mice. The ascitic tumours formed by intraperitoneal injection of nude mice contained both anaplastic rat cells similar to Rama 900 and mouse mesothelial-like cells similar to Rama 950. Although these anaplastic ascites cells failed to yield any tumours in syngeneic or thymectomised rats, they still produced tumours and metastases, including those in lymph nodes, in nude mice.

Automation of data acquisition and processing in assays for anchorage-independent growth: application to the purification of epithelial transforming growth factor.

We have developed a method for automated data collection from anchorage-independent growth assays by direct interfacing of an Omnicon image analysis system with a VAX mainframe computer network. By use of this interface, data generated with the Omnicon can be acquired and manipulated by the VAX, providing several advantages including high throughput, elimination of operator error, flexibility and speed, and capacity of mainframe data processing. We have applied these techniques to aid in the purification of a novel growth factor for human epithelial cells. Both column elution profiles and dose-response data were processed to graphic formats, and ED50 values for the individual purification steps were obtained by Hill transformation of the dose-response curves. The assay for anchorage-independent growth is widely used for purification of growth factors and testing of chemotherapeutic agents against human tumor cells. The present technique should be useful in facilitating these labor-intensive studies.

Growth factors as novel therapeutic targets in neoplastic disease.

The emerging concept of autocrine/paracrine control of tumour cell proliferation coupled with the identification of several polypeptide mitogens has created new opportunities for the discovery of novel classes of antineoplastic drugs. Growth factors (for example, transforming growth factor alpha, fibroblast growth factor and platelet-derived growth factor) and, in certain cases, their receptors have been identified in a number of human tumours and their expression may contribute to unregulated cell proliferation. Selective antagonists that block the activity of these mediators may have important therapeutic utility in the management of cancer patients, particularly in metastatic disease where patterns of tumour cell dissemination may be strongly influenced by paracrine mediators. However, since many, if not all, of these growth factors are polypeptides with molecular weights over 5 kDa, the discovery of potent antagonists represents an important pharmacological challenge. Advances in understanding protein structure-function relationships will be essential in guiding rational attempts at generating growth factor antagonists through site-directed mutagenesis and peptide synthesis, while better insights into the mechanisms by which growth factors are synthesized, processed, released and exert their mitogenic effects may also reveal new sites for pharmacological assault. The availability of (low molecular weight) potent growth factor antagonists will allow the autocrine/paracrine hypothesis to be clinically tested and in the process will throw considerable light on the function of these growth regulatory molecules in vivo.

Characterization of an animal model of metastatic colon carcinoma.

Although numerous animal tumor models have been used to study colon carcinoma, few display metastatic properties. We have characterized an animal tumor model that has 3 properties essential for the study of metastasis of colon carcinoma cells: epithelial cell origin; a reproducible pattern of metastatic behavior and the ability to be propagated both in vitro and in vivo to facilitate identification of biochemical correlates of metastasis. The K12/TR cell line was derived from a transplantable colon carcinoma induced by dimethylhydrazine in the BD-1X rat strain. Transmission electron microscopy of K12/TR cells demonstrated junctional complexes, desmosomes and surface microvilli characteristic of gastrointestinal epithelial cells. The epithelial cell origin of K12/TR was confirmed by demonstrating the presence of keratin, a marker of epithelial cells, but not vimentin, a constituent of mesenchymal cells. Secretion of CEA and Ca19-9 antigens by K12/TR cells in vitro was below the sensitivity of the assays (1 ng/ml and 6 U/ml respectively). K12/TR cells produced tumors following s.c. injection into syngeneic BD-1X rats, allogeneic RNU/rnuDF rats and xenogeneic CRL:nu/nuBR mice. Macroscopic lung metastases were observed in animals from all 3 groups. Distal lymph node metastases were more frequent in BD-1X rats than in nude rats or mice. The histological appearances of all tumors and metastases were similar, showing a moderate to poorly differentiated glandular carcinoma. Intrasplenic injections of K12/TR cells in nude mice resulted in liver colonization. Preferential growth of tumor cells at sites of trauma was also observed. The results show that the K12/TR system can be used as a model to study metastasis of colon carcinoma cells and may find utility in the testing of chemotherapeutic agents against metastatic lesions.