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PubMed1981

A comparative study of the in vitro polymerization of tubulin in the presence of the microtubule-associated proteins MAP2 and tau.

At concentrations of microtubule-associated proteins MAP2 and tau inducing maximal microtubule formation, MAP2 promotes higher rates and higher levels of microtubule nucleation that tau. Microtubules polymerized to steady state by tau show a 2-fold higher rate of tubulin loss compared to microtubules polymerized by MAP2. Microtubules polymerized in the presence of both MAP2 and tau contain lower levels of MAP2 (0.06 mol/mol of tubulin) and tau (0.07 mol/mol of tubulin) than microtubules polymerized in the exclusive presence of MAP2 (0.2 mol/mol of tubulin) or tau (0.25 mol/mol of tubulin). Addition of tau to microtubules polymerized by MAP2 results in incorporation of tau into microtubules (0.047 mol/mol of tubulin) and loss of MAP2 (0.1 mol/mol of tubulin). Similarly, incubation of microtubules polymerized by tau in the presence of MAP2 results in microtubule incorporation of MAP2 (0.1 mol/mol of tubulin) and loss of tau (0.08 mol/mol of tubulin). Microtubules and their ribbon precursor contain comparable levels of MAP2. Cross-sectional views of microtubules show no difference in the number of protofilaments (13 to 15) forming the MAP2 and tau microtubules. Fingerprints of cysteine-labeled tryptic peptides of two tau polypeptides (tau 4 and tau 6) are very similar and differ totally from similar fingerprints of MAP2.

Animals↗
PubMed1981

[Polymerization of bacterial flagellar flagellin in the presence of polyethyleneglycol].

Polymerization of flagellin from the flagella of Bacillus brevis in the presence of polyethyleneglycol (PEG) with molecular weight varying from 400 to 40 000 was studied. When 10% PEG2000-6000 was used, polymerization was completed within 5 min. When PEG with higher molecular weights were used, their higher concentrations were necessary. Polymerization of flagellin in the presence of PEG400-600 did not practically differ from that without PEG. At flagellin concentrations up to 0.1 mg/ml the polymerization process with PEG also occurred at a very high rate. Polymerization of flagellin obtained by heating of bacterial flagella in the presence of PEG did not require exogenous primer. A possible mechanism of flagellin polymerization in the presence of PEG is discussed.

Bacillus↗
PubMed1980

[Origin and pathogenesis of polymeric dipyrrilmethenes].

By means of the silicagel thin layer chromatography and spectrophotometry the qualitative differences of the polymeric dipyrryl methenes in the bile and in the urine in normal and pathological conditions were demonstrated. The differences between the polymeric dipyrryl methenes of fresh hepatic bile and the polymeric dipyrryl methenes of the older hepatic and fresh duodenal bile were found. The same differences were found in the urine between the normal urinary polymeric dipyrryl methenes and the polymeric dipyrryl methenes in the hyperhemolytic state and in the bile duct obstruction. An entirely different quality of the polymeric dipyrryl methenes in the urine is to be admitted in the liver diseases.

Anemia, Megaloblastic↗
PubMed1981

The effect of erythrocyte membrane preparations on the polymerization of sickle hemoglobin.

We have investigated the effect of erythrocyte membrane preparations on the rate of polymerization and the solubility of deoxyhemoglobin S. The kinetics of polymerization was monitored by measuring changes in turbidity of hemoglobin S solutions as a function of time in a temperature-controlled cuvette. The solubility of deoxyhemoglobin S, an equilibrium measurement, was determined by measuring the hemoglobin concentration of the supernatant following centrifugation of the polymerized hemoglobin S solution. The solubility of deoxyhemoglobin S was unaffected by the presence of red cell membrane ghosts, inside-out red cell vesicles, or inside-out vesicles enriched in erythrocyte spectrin and actin (Bands 1, 2, and 5) in the hemoglobin solution. Furthermore, inside-out vesicles had no significant effect on kinetics of polymerization. The addition of erythrocyte membrane ghosts to the hemoglobin solution, in ratios approximating that of the intact red cell, increased the rate of polymerization up to 8-fold. However, when corrections were made for the excluded volume contributed by the membrane ghosts, the enhancement of the rate of polymerization was reduced to less than 3-fold. These results fail to show significant facilitation of intracellular sickling by nucleation sites on the red cell membrane.

Erythrocyte Membrane↗
PubMed1995

A novel polymeric spermine conjugate inhibits polyamine transport in pulmonary artery smooth muscle cells.

The polyamines putrescine, spermidine and spermine (SPM) are low molecular weight organic cations that play essential intracellular regulatory roles in cell growth and differentiation. Whereas both de novo polyamine synthesis and transmembrane transport regulate cell polyamine contents, exploitation of pathways as pharmacologic targets has been limited by the lack of agents which specifically block polyamine transport. We now report the synthesis and biologic activity of novel polymeric glutaraldehyde conjugates of putrescine, spermidine and SPM which act at the cell membrane to inhibit polyamine uptake in cultured bovine pulmonary artery smooth muscle cells. Each conjugate caused dose-related inhibition of [14C]polyamine transport in pulmonary artery smooth muscle cells with the polymeric SPM conjugate being most effective in inhibiting the uptake of all three polyamines. Polymeric SPM failed to impair uptake of neutral or charged amino acids or to associate with pulmonary artery smooth muscle cells in a temperature-dependent manner. The polymeric SPM conjugate caused substantial decreases in cell polyamine contents which were associated with concentration-dependent cytotoxicity. Spectroscopic analyses of the polymeric SPM conjugate indicated that its molecular weight was 25 +/- 0.5 kDa, which is equivalent to approximately 90 monomeric--HN(CH2)3NH(CH2)4NH(CH2)3NH(CH2)5--units. These findings indicate that reduced polymeric glutaraldehyde conjugates of the polyamines may function as specific inhibitors of polyamine transport and thus provide a basis for examination of polyamine transport as a pharmacologic target in disorders characterized by dysregulated cell growth and differentiation.

Animals↗
PubMed1994

[Inhibition effects of adenosine and its analogues on actin polymerization in pig platelets and the possible mechanism].

The effects of adenosine and its analogues on the polymerization of actin in pig platelets and the possible mechanism were investigated. The results show that: Thrombin (0.5 U/ml) and ADP (50 mumol/L) stimulate actin polymerization in pig platelets: Adenosine, 5'-chloro-5'-deoxyadenosine, 2'-deoxyadenosine strongly inhibit thrombin- and/or ADP-induced actin polymerization. Adenosine and 5'-chloro-5'-deoxyadenosine strongly inhibit the phosphorylation of phosphatidylinositol in dose-dependent manner, and adenosine reverses the formation of thrombin-stimulated inositol bisphosphate, which has proved to promote the polymerization of actin in saponin-permeated platelets. These suggest that the inhibition of adenosine and its analogues on phosphatidylinositol turnover might involve in their inhibition on actin polymerization in platelets, and phosphatidylinositol turnover might play an important role in actin polymerization during cell activation.

Actins↗
PubMed1994

In vivo polymerization of sickle-cell hemoglobin: a theoretical study.

Several studies on the gelation and oxygenation state of sickle red blood cells have been done under conditions of equilibrium. The kinetics of sickle hemoglobin (HbS) polymerization have also been studied extensively in fully deoxygenated HbS solutions. The issue of the relevance of these investigations to the physiological in vivo situation has not been addressed. Here, we use a theoretical model to compare theoretical equilibrium predictions of HbS polymer concentration and cellular oxygen content, previously validated against equilibrium data, with the corresponding values under physiologic oxygen unloading conditions. We also use the model to simulate polymerization in almost completely deoxygenated sickle erythrocytes, validate the theoretical polymerization curves against published data, and compare them with the corresponding curves from the dynamic oxygen unloading analyses. Our model shows that equilibrium predictions severely overestimate intracellular polymer concentrations and underestimate cellular oxygen content, during the unloading of oxygen. Also, the delay times to significant polymerization in the physiologic situation are substantially longer than the corresponding values measured in completely deoxygenated HbS solutions. These results indicate that in vivo HbS polymerization is strongly influenced by the rate of oxygen desaturation. Equilibrium estimates of intracellular polymer content, or polymerization kinetic data from fully deoxygenated solutions, could be misleading and should be used in the proper perspective.

Biopolymers↗
PubMed1994

Induction of actin polymerization in permeabilized neutrophils. Role of ATP.

We have used streptolysin-O (SO)-permeabilized neutrophils to investigate the signal transduction pathway through which chemoattractants induce actin polymerization. Chemoattractants stimulate phosphorylation of various proteins and lipids but whether these phosphorylations are required for actin polymerization is not known. Addition of guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) to SO-permeabilized neutrophils induced a doubling of the F-actin. This induction of F-actin, assayed by TRITC-labeled phalloidin binding, did not require the addition of ATP. Neither addition of apyrase to deplete residual ATP nor addition of ADP or UDP to compete with residual endogenous ATP inhibited significantly the GTP gamma S-induced polymerization. Addition of ATP on its own caused no increase in F-actin and did not affect the time course or concentration dependence of GTP gamma S-induced F-actin. Addition of ATP did increase the maximal amount of F-actin induced by GTP gamma S by about 20%. N-Formylnorleucylleucylphenalanine (formyl-peptide) in the presence of GTP, but not in its absence, also stimulated an increase in F-actin in SO-permeabilized cells. The F-actin induced by formyl-peptide plus GTP was inhibited by pertussis toxin. The induction did not require addition of ATP and addition of ADP to compete with residual ATP only slightly decreased the level of actin. However, addition of UDP significantly reduced the response to formyl-peptide plus GTP. Addition of ATP enhanced the increase in F-actin induced by optimal concentrations of GTP with formyl-peptide. ATP also lowered the apparent Km for GTP, but not for N-formyl peptide. The non-hydrolyzable ATP analog, adenosine 5'-(beta, gamma-imino)triphosphate, did not enhance the actin polymerization. Rather its presence inhibited the response induced by formyl-peptide plus GTP. The data suggest that actin polymerization can be induced by GTP gamma S in an manner that is largely ATP-independent. A role for ATP cannot be ruled out in the induction of actin polymerization by formyl-peptide plus GTP.

Actins↗
PubMed1994

[The effect of different liner materials on the polymerization of composites].

It has been shown that the polymerization of certain composite filling materials are inhibited by eugenol containing temporary filling materials. The aim of this study was to evaluate the influence of different lining materials (Ketac-Bond, Vitrebond, Dropsin, Dycal, Alkaliner, Super EBA [= control]) on the degree of polymerization of different composites (Brilliant Lux, Brilliant, Herculite, Dual-Cement). The degree of polymerization was characterized by Knoop hardness measurements. The data were analysed by the Wilcoxon test. All lining materials decreased the hardness of the adjacent zone of the tested composites. Brilliant Lux showed a significant decrease (p < 0.01) in hardness until a distance of 200 microns from all lining materials. The chemical curing composite (Brilliant) was generally less influenced in its polymerization by the tested lining materials. Light-activated glass ionomer materials influenced the polymerization at least. It was concluded that light-activated composites seemed to be more influenced in their polymerization by adjacent lining materials than chemically activated ones.

Composite Resins↗
PubMed1993

Regulatory factors for polymerization of melanin monomers within coated vesicles and premelanosomes in melanoma cells.

Coated vesicles (CV) and premelanosomes (PMS) differ in the amount of melanin monomers produced from 2-carboxy-2,3-dihydroindole-5,6-quinone (dopachrome) in vitro. CV convert dopachrome preferentially to 5,6-dihydroxy-indole-2-carboxylic acid (DHI2C) and PMS mainly to 5,6-dihydroxyindole (DHI). We examined the effect of CV and PMS on in vitro spontaneous polymerization of DHI and DHI2C. The polymerization of DHI is accelerated by addition of extracts from both CV and PMS, while polymerization of DHI2C is suppressed. Factors associated with these two regulatory activities have been separated on concanavalin A-Sepharose. The ConA-adhesive glycoproteins isolated from PMS enhance polymerization of not only DHI but also DHI2C. The latter effect is stimulated by dopa. Both accelerating activities can be inhibited by phenylthiourea (PTU). In contrast to glycoproteins, the non-glycoprotein subfraction suppresses spontaneous polymerization of both melanin monomers. Our data suggest that the absence of in vivo melanin polymer formation within CV can be explained by formation by these organelles of relatively stable DHI2C rather than easily polymerizing DHI.

Animals↗
PubMedDate not supplied

A novel surface photo-graft polymerization method for fabricated devices.

This paper presents a new photo-graft polymerization method that permits surface modification of complex shaped devices. The principle is based on photochemistry of the dithiocarbamate group, as a polymerization initiator-transfer agent-terminator (iniferter), which is capable of photochemical dissociation into a radical pair. The procedure is as follows: first, coating of a photosensitive polymer on a substrate, and subsequent ultraviolet (UV) light irradiation in the presence of a monomer. The photosensitive polymer prepared was a radical copolymer of styrene and vinylbenzyl N,N-diethyldithiocarbamate. Surface graft polymerization of a water soluble monomer (N,N-dimethylacrylamide) on poly(ethylene terephthalate) pre-coated with the photosensitive polymer was achieved. Because the photopolymerization proceeded via a living radical polymerization, the control of molecular weight of the grafted polymer was feasible. This was quantitatively observed by graft polymerization on a quartz crystal microbalance (QCM) that can detect the weight increase with the sensitivity of ng-order. Two-dimensional patterning of cultured cells was demonstrated to show how surface grafted polymerization is limited on UV light irradiation portions with dimensionally micron order precision.

Animals↗
PubMed1993

Effects of beta 6 aromatic amino acids on polymerization and solubility of recombinant hemoglobins made in yeast.

Valine, leucine, tryptophan, and phenylalanine substitutions at the beta 6 position of hemoglobin (Hb) were made using a yeast expression system coupled with a polymerase chain reaction-based mutagenesis strategy. The oxygen affinity and absorption spectra of these mutants were similar to recombinant Hb A except for Hb beta E6W which had a higher absorbance at approximately 280 nm. The deoxy forms of Hb beta E6L and Hb S showed characteristic delay times prior to polymerization. Tetrameric deoxy-Hbs containing tryptophan or phenylalanine at the beta 6 position had higher solubilities and polymerized less readily compared with deoxy-Hb S. However, when oversaturated, these Hbs polymerized without a delay time. These results suggest that Hb beta E6W and Hb beta E6F form polymers upon deoxygenation by a linear polymerization mechanism without nuclei formation. During polymerization, bulky hydrophobic amino acids, like phenylalanine and tryptophan at the beta 6 position, might interact with the acceptor pocket on the surface of an adjacent Hb molecule but may not be able to form stable hydrophobic interactions like beta 6 valine and leucine. Difficulty in insertion of the bulky side chains of these aromatic amino acids into the hydrophobic acceptor pocket on an adjacent tetramer may inhibit nuclei formation prior to polymerization.

Amino Acids↗
PubMed2002

The human polymeric immunoglobulin receptor facilitates invasion of epithelial cells by Streptococcus pneumoniae in a strain-specific and cell type-specific manner.

Streptococcus pneumoniae is a gram-positive bacterial pathogen that causes invasive life-threatening disease worldwide. This organism also commonly colonizes the upper respiratory epithelium in an asymptomatic fashion. To invade, this pathogen must traverse the respiratory epithelial barrier, allowing it to cause disease locally or disseminate hematogenously throughout the body. Previous work has demonstrated that S. pneumoniae choline-binding protein A, a pneumococcal surface protein, interacts specifically with the human polymeric immunoglobulin receptor, which is expressed by cells in the respiratory epithelium. Choline-binding protein A is required for efficient colonization of the nasopharynx in vivo. Additionally, a recent study showed that the R6x laboratory strain of S. pneumoniae invades a human pharyngeal cell line in a human polymeric immunoglobulin receptor-dependent manner. These findings raised the possibility that the interaction between choline-binding protein A and human polymeric immunoglobulin receptor may be a key determinant of S. pneumoniae pathogenesis. However, the strain used in prior invasion studies, R6x, is an unencapsulated, nonpathogenic strain. In the present study we determined the relative ability of strain R6x or pathogenic strains to invade a variety of human polymeric immunoglobulin receptor-expressing epithelial cell lines. The results of this work suggest that human polymeric immunoglobulin receptor-dependent enhanced invasion of epithelial cells by S. pneumoniae is a limited phenomenon that occurs in a strain-specific and cell type-specific manner.

Cell Line↗
PubMed1998

Combinations of paclitaxel and vinblastine and their effects on tubulin polymerization and cellular cytotoxicity: characterization of a synergistic schedule.

Paclitaxel (PTX) and vinblastine (VBL) represent 2 classes of drugs that target tubulin but have separate binding properties and opposing mechanisms of action. To evaluate the potential use of these agents together in a chemotherapeutic regimen, we investigated their effects on the dynamics of tubulin polymerization and cellular cytotoxicity, when administered singly or in combination. In human epidermoid carcinoma KB cells and MCF-7 breast carcinoma cells, we observed a time- and dose-dependent effect on cytoskeletal dynamics for both PTX and VBL. Tubulin polymerization induced by PTX was stable for more than 24 hr. When PTX treatment was followed by VBL, a time- and dose-dependent reversal of tubulin polymerization was observed. In contrast, rapid tubulin polymerization occurred when VBL was followed by PTX. When both agents were added simultaneously, a diminution of PTX-induced tubulin polymerization was observed with increasing doses of VBL; a maximum reduction was achieved when equal concentrations were used. Examination of the tubulin pattern by immunofluorescence in MCF-7 breast cancer cells confirmed and extended our findings. Bundle formation followed treatment with PTX. Addition of increasing concentrations of VBL prevented bundling; however, the normal cytoskeletal architecture was not restored. Cytotoxicity studies carried out using the median dose effect principles and the combination index analysis showed synergism when VBL and PTX were administered sequentially and antagonism for simultaneous administration. Our results demonstrate changes in tubulin dynamics following drug treatment and provide a rationale for combined PTX/VBL therapy after careful evaluation of the schedule of administration.

Antineoplastic Agents, Phytogenic↗
PubMed1996

Fluid shear stress induces actin polymerization in human neutrophils.

We have previously reported that a physiological range of shear stress induces neutrophil homotypic aggregation mediated by lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-3 (ICAM-3) interactions. To further characterized the homotypic aggregation, actin polymerization was investigated in neutrophils stimulated by shear stress in comparison with formyl-methionyl-leucyl-phenylalanine (fMLP). In fMLP-stimulated neutrophils, actin polymerization was localized in the pseudopods, and this reaction was not mediated by a cytosolic level of Ca2+. In contrast to fMLP stimulation, the actin polymerization induced by shear stress in a cone-plate viscometer was localized in cell-cell contact regions, and this polymerization required the increase of intracellular Ca2+. This shear stress-induced actin polymerization was not observed when neutrophils were pretreated with anti-LFA-1 or anti-ICAM-3 antibody. In conclusion, LFA-1 and ICAM-3 interaction mediated by the increase of [Ca2+]i generated the intercellular signal in order to accumulate F-actin in the cell-cell contact regions.

Actins↗
PubMed2000

Screw-sense-selective polymerization of aryl isocyanides initiated by a Pd-Pt mu-ethynediyl dinuclear complex: a novel method for the synthesis of single-handed helical poly(isocyanide)s with the block copolymerization technique

Living polymerization of chiral aryl isocyanides, such as m- and p-menthoxycarbonylphenyl isocyanides 2 and 5, initiated by the Pd-Pt mu-ethynediyl dinuclear complex 1, proceeds with a high screw-sense selectivity to give the poly(isocyanide)s 3 and 6, which exhibit a large specific rotation and an intense CD band at lambda = 364 nm as a consequence of a helical chirality. The molar optical rotation and molar circular dichroism of the resulting polymers 3 and 6 reach a constant value at a degree of polymerization (Pn) of more than 30. Screw-sense-selective polymerization of achiral aryl isocyanides that bear very bulky substituents, such as 3,5-di(propoxycarbonyl)phenyl isocyanide (11), 3,5-di(butoxycarbonyl)phenyl isocyanide (13), and 3,5-di(cyclohexyloxycarbonyl)phenyl isocyanide (15), is achieved by the use of chiral oligomer complexes 3(30) and 6(30), prepared from the reaction of 1 with 30 equivalents of 2 or 5, as an initiator to give predominantly single-handed helical polymers. In contrast, smaller aryl isocyanides are also polymerized by 3(30) and 6(30) with screw-sense selectivity in the initial stage of the reaction, but the single-handed helix is not preserved up to high molecular weight. Kinetic studies of the polymerization of (L)- and (D)-2, or (L)- and (D)-5 with chiral oligomer complexes (L)-3(50) or (L)-6(100) suggests that the screw sense of the polymer backbone is not controlled kinetically, but rather that the thermodynamically stable screw sense is produced.

Journal Article↗
PubMed2000

Polymeric micellar paclitaxel phosphorylates Bcl-2 and induces apoptotic regression of androgen-independent LNCaP prostate tumors.

BACKGROUND: Paclitaxel has been difficult to evaluate in preclinical tumor model systems because its poor solubility requires a Cremophor EL formulation, which results in lethal anaphylaxis. We tested the effectiveness of a novel polymeric micellar paclitaxel on androgen-independent tumor growth in the LNCaP tumor model. METHODS: Athymic male mice bearing LNCaP tumors were castrated and allowed to grow until their PSA levels increased to three times above precastration levels. The animals were then treated with 0.5 mg intravenous polymeric micellar paclitaxel once daily for the first 5 days of a 3-week cycle. In total, three cycles were given. Tumor volume and serum PSA levels were measured weekly to monitor tumor progression. RESULTS: In vitro mitogenic assays demonstrated that polymeric micellar paclitaxel was effective in inhibiting LNCaP cell growth with an IC(50) of 5 nM. Paclitaxel precipitated apoptosis in vitro at a concentration of 1 nm and higher, confirmed by DNA laddering. Western blotting demonstrated that paclitaxel treatment phosphorylated and inactivated Bcl-2. In mice bearing LNCaP tumors treated with micellar paclitaxel, tumors regressed rapidly with the commencement of micellar paclitaxel treatment. Tumor size decreased 91% and PSA level decreased 96% after three cycles of treatment. TUNEL immunostaining of the tumor treated with micellar paclitaxel showed marked apoptosis when compared with the control. No significant side effects or mortality was observed in the micellar paclitaxel group (n = 7). In contrast, all (n = 7) mice treated with conventional Cremophor EL paclitaxel died within 1 day of injection. CONCLUSIONS: The polymeric micellar paclitaxel formulation is water-soluble and capable of inducing complete response in mice bearing androgen-independent LNCaP tumors. The lack of toxicity of polymeric micellar paclitaxel permits in vivo preclinical testing of paclitaxel-based combination regimens.

Animals↗
PubMed2002

Ruthenium alkylidenes: modulation of a new class of catalysts for controlled radical polymerization of vinyl monomers.

Air-stable and readily available ruthenium benzylidene complexes of the general type [RuCl2(=CHPh)(L)(L')] (L, L' = PCy3 and/or N-heterocyclic carbene) constitute a new class of catalyst precursors for atom-transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy3 and/or N-heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl2(=CHPh)(L)(L')] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N-heterocyclic carbene ligands remain bound to the metal center. Polymerization of n-butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox-initiated free-radical process.

Journal Article↗