Effect of magnesium on secretion of platelet-derived growth factor by cultured human arterial smooth muscle cells

Two conditioned media were prepared by culturing human umbilical artery smooth muscle cells (SMC) in 75 cm2 flasks with minimum essential medium (MEM) under magnesium (Mg) sufficient (900 microM) or deficient (100 microM) conditions for 72 h ([900]- and [100]-MEM), respectively. A third conditioned medium was obtained by adjusting the Mg concentration of half of the [100]-MEM to 900 microM ([100-900]-MEM). SMC in 12-well plates were incubated in one of the three conditioned media and the growth rates of SMC were determined by [3H]-thymidine incorporation and cell counting. The growth rate in [100-900]-MEM was significantly higher than in [900]- and [100]-MEM. When platelet derived growth factor (PDGF) was neutralized by the addition of a mixture of anti-PDGF-AA and -BB antibodies, [3H]-thymidine incorporation in [100-900]-MEM decreased by 23.3 per cent, but only by 7.0 per cent in [900]-MEM. The quantity of PDGF in the Mg-deficient media was greater than in the magnesium-sufficient media at all indicated times, as shown by radioimmunoassay for PDGF-BB or -AB. These results indicate that Mg deficiency increases the secretion of PDGF by SMC.

NMR studies of the effects of the 5'-phosphate group on conformational properties of 5-methylaminomethyluridine found in the first position of the anticodon of Escherichia coli tRNA(Arg)4

5-Methylaminomethyluridine (mnm5U) exists in the first position of the anticodon (position 34) of Escherichia coli tRNA4Arg for codons AGA/AGG. In the present study, the temperature dependence of the ribose-puckering equilibrium of pmnm5U was analyzed by proton NMR spectroscopy. Thus, the enthalpy difference (delta H) between the C2'-endo and C3'-endo forms was obtained at 0.65 kcal.mol-1. By comparison of the delta H values of pU and pmnm5U, the 5-substitution was found to increase the relative stability of the C3'-endo form over the C2'-endo form significantly (by 0.56 kcal.mol-1). Furthermore, this conformational "rigidity" was concluded to depend on the 5'-phosphate group, because nucleoside U exhibits only a negligible change in the ribose-puckering equilibrium upon the 5-methylaminomethyl substitution. Further NMR analyses and molecular dynamics calculations revealed that interactions between the 5-methylaminomethyl and 5'-phosphate groups of pmnm5U restrict the conformation about the glycosidic bond to a low anti form, enhancing steric repulsion between the 2-carbonyl and 2'-hydroxyl groups in the C2'-endo form. This intrinsic conformational rigidity of the mnm5U residue in position 34 may contribute to the correct codon recognition.

Effects of bradykinin on lymphatic pumping in rat mesentery

The effects of bradykinin on lymphatic pump activity of rat mesenteric collecting duct were studied, and the receptor subtype responsible for the bradykinin response was evaluated. Rats were anesthetized with intraperitoneal alpha-chloralose and urethan, and exteriorized mesenteries were studied using intravital microscopic techniques. The diameter of the collecting lymph vessels (approximately 100 microns) was continuously monitored and lymphatic pump parameters (end diastolic diameter, end systolic diameter, stroke volume index, ejection fraction, contraction frequency, and pump flow index) were calculated. Bradykinin (0.1-1.0 nM) did not affect end diastolic diameter, end systolic diameter, stroke volume index, and ejection fraction. Bradykinin increased lymphatic contraction frequency and pump flow index in a dose-dependent manner. Des-Arg9-[Leu8]bradykinin (B1 antagonist, 0.1 microM) had no effect on baseline lymphatic pumping but completely inhibited the bradykinin-induced increase in contraction frequency. N-acetyl-D-Arg-[Hyp3,Thi5,8,D-Phe7] bradykinin (B2 antagonist, 0.1 microM) significantly depressed lymphatic contraction frequency in baseline conditions but had no effect on bradykinin-induced increases in contraction frequency. These results indicate that bradykinin induces positive chronotropic but not inotropic effects on lymphatic pump activity through the stimulation of B1 receptors.

Hypoxia-reoxygenation impairs endothelium-dependent relaxation in isolated rat aorta

The effects of hypoxia followed by reoxygenation on endothelium-dependent relaxation in isolated rat aorta were investigated. Acetylcholine (ACh, 3 nM-10 microM) and calcium ionophore A-23187 (3 nM-300 nM)-induced endothelium-dependent vasorelaxation of isolated rate aortic vessel rings was impaired after 15 min of hypoxia followed by 30 min of reoxygenation. Impairment of ACh-induced relaxation was prevented by pretreatment with the combination of superoxide dismutase (200 U/ml) and catalase (1,000 U/ml). Hypoxia-reoxygenation did not affect sodium nitroprusside (0.1 nM-1 microM)-induced endothelium-independent relaxation nor the dissociation constant of ACh to endothelial M3 muscarinic receptors. Propidium iodide staining of the vascular endothelium revealed a significant increase in the number of dead endothelial cells on the aortic vessel rings following hypoxia-reoxygenation, but not on those pretreated with superoxide dismutase and catalase. These results suggest that hypoxia-reoxygenation impairs endothelium-dependent relaxation of rat aorta by a mechanism that involves oxidant-mediated endothelial cell death.

Large-scale perfusion culture process for suspended mammalian cells that uses a centrifuge with multiple settling zones

A high-cell-density perfusion culture process, using a novel centrifuge, was developed. The centrifuge has spiral multiple settling zones to separate cells from culture medium. Because of the multiple zones, the separation area can be efficiently increased without enlarging the diameter of the centrifuge. The centrifuge used in this study had a separation capacity of 2600 ml culture medium min -1 at 100 g of the centrifugal force. A new cell separation and withdrawal method was also developed. The cells separated in the centrifuge can be withdrawn easily from the centrifuge with no cell clogging by feeding a liquid carrier such as a perfluorocarbon into the centrifuge and pushing the cells out with the liquid carrier. By this culture process, monoclonal antibodies were produced with mouse-human hybridoma X87X at a cell density of about 8 x 10(6) cells ml -1 for 25 days. This centrifuge culture shows promise as a large-scale perfusion culture process. (Himmelfarb et al. 1969; Feder and Tolbert 1983) usually have the problem of filter clogging, and perfusion culture processes with gravitational cell settling (Tokashiki and Arai 1989) are limited in scale-up because of low separation efficiency. Recently centrifugal separation of cells from culture medium has been used for perfusion culture processes (Hamamoto et al. 1989; Tokashiki et al. 1990; Apelman 1992; Jäger 1992). This process essentially has a high separation efficiency and can avoid further operational problems, such as filter clogging, by the type of filtration. To investigate the scale-up feasibility of the centrifuge culture system, we have developed a new type of centrifuge with four layers of spiral cell-settling zones to increase the separation area, and a novel cell separation and withdrawal method using a perfluorocarbon.

An RNA fragment consisting of the P7 and P9.0 stems and the 3'-terminal guanosine of the Tetrahymena group I intron

On the basis of the nucleotide sequence of Tetrahymena group I intron, we constructed a 31 residue RNA that has the P7 stem and the 3'-terminal guanosine residue (3'-G) with a putative stem-loop structure (P9.0) intervening between them. For this model RNA (P7/P9.0/G), four residues around the guanosine binding site (GBS) in the P7 stem were found to exhibit much lower sensitivities to ribonuclease V1 than those of a variant RNA having adenosine in place of the 3'-G, suggesting that the 3'-G contacts around the GBS. NMR analyses of the imino proton resonances of the P7/P9.0/G RNA indicated that the base pairing in the GBS is retained on the interaction with the 3'-G, and that the two base pairs of the putative P9.0 stem-loop are definitely formed. Comparison of the RNA with its variants with either A (3'-A) or a deletion in place of the 3'-G suggested that the stability of the P9.0 stem-loop is affected by the GBS-3'-G interaction. The melting temperatures of the P9.0 stem-loop were determined from the UV absorbances of these RNAs, which quantitatively indicated that the P9.0 stem-loop is significantly stabilized by the interaction of the GBS with the 3'-G, rather than the 3'-A, and also by direct interaction with divalent cations (Mg2+, Ca2+ or Mn2+). Upon replacement of the G-C base pair by C-G in the GBS of the P7/P9.0/G RNA, the specificity was switched from 3'-G to 3'-A, as in the case of the intact intron.

Activation of human plasma cholesteryl ester transfer protein by human apolipoprotein A-IV

Function of apolipoprotein (apo) A-IV was studied for its role in cholesteryl ester transfer protein (CETP; lipid transfer protein, LTP) reaction between lipid microemulsions having the diameter of low density lipoprotein, being compared to apoA-I. CETP hardly catalyzed lipid transfer without apolipoproteins. ApoA-IV bound to the surface of the microemulsion in equilibrium with a similar affinity to that of other helical apolipoproteins, and activated the transfer reaction by CETP of cholesteryl ester, triacylglycerol and phosphatidylcholine between the emulsions. The rate of the transfer reaction of cholesteryl ester and triacylglycerol was directly proportional to the amount of the bound apoA-IV to the surface of the emulsion. For phosphatidylcholine, activation was less effective until 40% of total binding capacity of lipid emulsion was occupied by the apolipoprotein. Cholesteryl ester was highly preferred by CETP over triacylglycerol when equal amount of these lipids was present in the core of the apoA-IV-activated emulsion, resulting in almost no triacylglycerol transfer. However, when the emulsion has the core exclusively of triacylglycerol, triacylglycerol was transferred by CETP with the rate in the same order as that of cholesteryl ester transfer. These findings were all comparable to the results with apoA-I, and also consistent with our previous observation for other amphiphilic helical apolipoproteins such as apoA-II, E and C-III.

Differential structural requirements for interaction of Ras protein with its distinct downstream effectors

Ras proteins have multiple effectors of distinct structures that do not share significant structural homology at their Ras interaction sites. To prove possible differences in their recognition mechanisms of Ras, we screened 44 human Ha-Ras proteins carrying mutations in the effector region and its flanking sequences for interaction with human Raf-1, Schizosaccharomyces pombe Byr2, and Saccharomyces cerevisiae adenylyl cyclase. The Ras binding specificities were largely shared between Raf-1 and Byr2 although Ras mutants, Y32F, T35S, and A59E, had their affinities for Byr2 selectively reduced. The only exception was Ras(D38N), which lost the ability to bind Raf-1 while retaining the activity to bind Byr2 and complement the Byr2- phenotype of S. pombe. On the other hand, adenylyl cyclase had quite distinct requirements for Ras residues; mutations P34G and T58A selectively abolished the ability to bind and activate it without considerably affecting the interaction with Raf-1 and Byr2. Y32F mutant, whereas losing the ability to activate Raf-1 and Byr2, could activate adenylyl cyclase efficiently. In addition, V45E mutation was found to impair the ability of Ras to activate both Raf-1 and adenylyl cyclase without significantly affecting the binding affinities for them. These results demonstrate that significant differences exist in the recognition mechanisms by which the three effector molecules associate with Ras and suggest that a region of Ras required for activation of the effectors in general may exist separately from that for binding the effectors.

Major identity determinants in the "augmented D helix" of tRNA(Glu) from Escherichia coli

By a kinetic analysis of 59 variant transcripts of Escherichia coli tRNA(Glu) with glutamyl-tRNA synthetase (GluRS), the U11.A24 base-pair, the U13.G22..A46 base-triple, and the lack of residue 47 (delta47) were found to serve as major determinants for tRNA(Glu) identity. This is the first system for which major identity determinants are reported to be clustered in the "augmented D helix", consisting of the D stem with some neighboring residues and the variable loop. Other identity determinants are U34, U35, C36 and A37 in the anticodon loop, and G1.C72 and U2.A71 in the acceptor stem. Phosphate-group protection by GluRS from ethylnitrosourea was observed most strongly for the minor groove side of D-stem helix, indicating that GluRs tightly binds to the D stem for recognition, on the minor groove side, of the potent identity-determinant groups of the U11.A24 and U13.G22 base-pairs. A46 is not involved in direct recognition by GluRS; the U13.G22..A46 base-triple is required probably for formation of the structural features that are recognized by GluRS. In this context, the essential role of characteristic delta47 in tRNA(Glu) identity may be to maintain the U13.G22..A46 base-triple.

Expression and secretion of rabbit plasma cholesteryl ester transfer protein by Pichia pastoris

The rabbit cholesteryl ester transfer protein (CETP) was expressed in the methylotrophic yeast Pichia pastoris by introducing the CETP cDNA under the control of the methanol-inducible alcohol oxidase promoter. The cDNA was cloned from in vitro amplified cDNA of rabbit liver mRNA. The nucleotide sequence of the cloned cDNA differed slightly from the previously published sequence that changed the amino acid sequence in six residues. Interestingly, five of these replacements are identical to the corresponding residues in human CEPT. In addition, the encoded mature N-terminal sequence was changed from Cys- to Arg-Glu-Phe- to link the CETP sequence to the yeast acid phosphatase signal peptide. The culture medium of the transformed cells induced with 1% methanol contained both cholesteryl ester and triglyceride transfer activity comparable to that of rabbit plasma. Like rabbit plasma, the lipid transfer activity in the medium could be inhibited by monoclonal antibodies that block CE/TG transfer or TG transfer alone. Immunoblot analysis of M(r) = 80 K and minor species of M(r) = 60-100 K. In spite of these differences, the specific transfer activity of the recombinant CETP was indistinguishable from that of rabbit plasma CETP of M(r) = 74 K. N-Glycosidase F treatment converted both the recombinant and plasma CETP to a single species of M(r) = 55 K. Both the plasma and recombinant CETP lost their activity after removal of N-linked carbohydrate and sialic acid. A single 55 K component was found in the cell-lysates. The intracellular form of the recombinant CETP was not modified by N-glycosidase F treatment. In conclusion, the recombinant CETP is synthesized as an inactive polypeptide that is processed and secreted as a functional glycoprotein. In addition, the N-terminal Cys residue of the plasma CETP is not required for its activity.

Regulation of cellular cholesterol efflux by lecithin:cholesterol acyltransferase reaction through nonspecific lipid exchange

Erythrocyte was found lacking in reactivity to lipid-free apolipoproteins to generate pre-beta-high density lipoprotein (HDL) with the cellular lipid and, therefore, was used to study cellular cholesterol efflux to plasma lipoproteins exclusively by a nonspecific exchange mechanism. Over the range of hematocrit from 1-20% (cellular cholesterol pool of 2.5 micrograms per 250 microliters), the fractional rate of cellular cholesterol efflux to lipoprotein was constant, and, therefore, absolute efflux rate was a linear function of the hematocrit of this range. In the absence of lecithin:cholesterol acyltransferase (LCAT), the cholesterol influx rate from lipoproteins was equal to the efflux rate from erythrocyte resulting in no net transfer of cholesterol, with either HDL or low density lipoprotein. In the presence of LCAT in the mixture of HDL and erythrocyte, cholesterol was esterified exclusively in HDL regardless of the origin. When the hematocrit was low and efflux of cellular cholesterol was slower than cholesterol esterification, the esterification of cell-originating cholesterol did not directly enhance the efflux. With high hematocrit that gives faster cholesterol efflux, the efflux was increased directly by the cholesterol esterification. On the other hand, the LCAT reaction significantly reduced HDL-cholesterol influx. The LCAT reaction thus induces substantial net cholesterol efflux from erythrocytes through a nonspecific cholesterol exchange mechanism.

PCR-LIS-SSCP (Low ionic strength single-stranded conformation polymorphism)--a simple method for high-resolution allele typing of HLA-DRB1, -DQB1, and -DPB1

We have developed a simple and efficient procedure with which to form single-stranded DNA [ssDNA] and then applied HLA-DRB1, -DQB1, and -DPB1 allele typing. This method is referred to as low ionic strength single-stranded conformation polymorphism (LIS-SSCP), and is based on the diversity in the electrophoretic mobility of ssDNA formed by heat denaturation in low ionic strength solutions. This method detected DNA polymorphisms, including point mutations at a variety of positions in the DNA fragments of the HLA-DRB1, -DQB1, and -DPB1 genes. Under our experimental conditions, stable ssDNA could be kept at room temperature > or = 5 hr without having been cooled on ice immediately after heat denaturation. A total of 41 HLA-DRB1, 14 HLA-DQB1, and 17 HLA-DPB1 alleles from 220 healthy people were analyzed using a combination of PCR-LIS-SSCP with group-specific amplification. All of the alleles analyzed were discriminated among the DRB1, DQB1, and DPB1 groups except for DPB1*0402 and 0201. The efficiency of ssDNA formation using the LIS-SSCP procedure was higher than that of the traditional formamide method, and the SSCP profiles were clearer than those of the original SSCP. This procedure is useful for screening new alleles as well as the donor-recipient molecular matching of HLA class II genes. It is simple, rapid, and cost effective, requiring neither radioisotopes nor enzymes to confirm the typing results of other methods.

Quantitative capillary reversed passive latex agglutination test for C-reactive protein (CRP) in the dog

A capillary reversed passive latex agglutination test (capillary RPLA) was developed which allows quantification of serum C-reactive protein (CRP) within approximately 15 min. The logarithmic regression line (calibration curve) obtained after measuring each CRP concentration three times in twofold dilutions of a standard canine serum containing 222 micrograms/ml of CRP was y = 6.394 + 0.030x (r = 0.995). Capillary RPLA permitted quantification of CRP in the range 6.9-222 micrograms/ml. The coefficients of variation ranged from 10.28% to 12.40%. The recovery rates (percentage recovery) of CRP by capillary RPLA were within the range 87% to 106%. On measuring the CRP concentrations in sera from 78 dogs by capillary RPLA, single radial immunodiffusion (SRID) and enzyme-linked immunosorbent assay (ELISA), close correlations were demonstrated between SRID and capillary RPLA (y = 7.250 + 1.109x, r = 0.978), between SRID and ELISA (y = 3.042 + 1.059x, r = 0.967), and between capillary RPLA and ELISA (y = 1.778 + 0.929x, r = 0.962). Capillary RPLA may be considered useful as a routine biochemical technique for measurement of serum CRP concentration in the dog.

Pulmonary surfactant migrates into the alveolar capillaries of newborn rats: an immunoelectron microscopic study

The goal of the present study was to elucidate the migration of surfactant-like material into the alveolar capillaries of newborn rats. The lungs of experimental animals were studied by ultrastructural techniques-standard electron microscopy as well as immunoelectron microscopy-using antibodies against synthetic polypeptide complementary to the noncollagenous part of surfactant protein A (SP-A). Antibodies exhibited specific reaction with native rat SP-A in Western blot and immunohistochemical analysis. Surfactant was observed in the alveolar space, type II pneumocytes, macrophages, type I pneumocytes, endothelial cells, the extracellular space of the alveolar septa and in the alveolar capillaries. Lamellar structures observed in all elements of the blood-air barrier as well as in the alveolar capillaries were stained positively with anti-SP-A antibodies. Transport of the pulmonary surfactant into the circulatory system was observed more frequently during the first 6-8 h of extrauterine life of newborn rats, although it was also seen in the blood vessels till 48 h after delivery. The results of our investigation suggest that clearance of surfactant via the circulatory system plays an important role in the early postnatal period.

The connective tissue compartment in the terminal region of the developing rat lung. An ultrastructural study

The present study was designed to analyze the connective tissue compartment in the terminal region of the developing rat lung. Lungs of rat fetuses (at 17, 19 and 21 days of gestation) and of newborns (2, 4, 7, 10, 14 and 21 days after birth) were examined by several ultrastructural techniques; staining with tannic acid for elastic fibers (EFs), collagen fibers (CFs) and basement membranes (BMs); staining with ruthenium red for glycosaminoglycans; and immunoelectron microscopy for visualization of collagen type IV, laminin and fibronectin (FN). Dynamic changes in the levels and distribution of the components of the extracellular connective tissue were observed in parallel with the formation and maturation of the alveoli. The terminal regions of the respiratory tract of the rat fetus and of the lungs of early newborns contained few CFs and EFs, and the Bms in these lungs were incomplete. However, strong immunolabeling of FN was observed (in BMs, CFs and in spaces among fibroblasts). Starting from 4 to 7 days newborns had increasing numbers of Cfs and EFs and BMs became more extensive. In rat newborns, immunolabeling specific for FN was weak and irregularly distributed. Furthermore, the present results provide a summary of the changes in connective tissue that occur in the rat lung during different stages of its development, from the pseudoglandular stage, through the canalicular and saccular stages, to the alveolar stage.

Infectious mononucleosis with pulmonary consolidation

Infectious mononucleosis occurs most commonly among adolescents and young adults. Moreover, intrathoracic involvement by infectious mononucleosis, especially pulmonary consolidation, is uncommon. Thoracic computed tomography (CT) showed a massive pulmonary consolidation in the right lower lobe, multiple mediastinal lymphadenopathy, and pleural effusion in a 41-year-old man with infectious mononucleosis. Histopathology confirmed that lymphocytes and plasma cells had infiltrated the peribronchial areas and alveolar septa, and showed alveolar exudates composed of amorphous fibrinous debris, lymphocytes, and macrophages.

Cysteine-rich region of Raf-1 interacts with activator domain of post-translationally modified Ha-Ras

The interaction between "switch I/effector domain" of Ha-Ras and the Ras-binding domain (RBD, amino acid 51-131) of Raf-1 is essential for signal transduction. However, the importance of the "activator domain" (approximately corresponding to amino acids 26-28 and 40-49) of Ha-Ras and of the "cysteine-rich region" (CRR, amino acids 152-184) of Raf-1 have also been proposed. Here, we found that Raf-1 CRR interacts directly with Ha-Ras independently of RBD and that participation of CRR is necessary for efficient Ras-Raf binding. Furthermore, Ha-Ras carrying mutations (N26G and V45E) in the activator domain failed to bind CRR, whereas they bound RBD normally. On the contrary, Ha-Ras carrying mutations in the switch I/effector domain exhibited severely reduced ability to bind RBD, whereas their ability to bind CRR was unaffected. Mutants that bound to either RBD or CRR alone failed to activate Raf-1. Ha-Ras without post-translational modifications, which lacks the ability to activate Raf-1, selectively lost the ability to bind CRR. These results suggest that the activator domain of Ha-Ras participates in activation of Raf-1 through interaction with CRR and that post-translational modifications of Ha-Ras are required for this interaction.