Cellular localization and regulation of gene expression for components of the insulin-like growth factor ternary binding protein complex

Insulin-like growth factors (IGFs) are present in the circulation, largely as part of a high mol wt complex including IGF-binding protein-3 (IGFBP-3) and an acid-labile subunit (ALS). This study used in situ hybridization to investigate the cellular sites of synthesis of these factors in the rat and to evaluate changes in transcript levels during development and after hypophysectomy and GH treatment. IGFBP-3 transcripts are considerably more abundant and widely expressed than ALS at birth, but both are present in liver and kidney. Hepatic IGFBP-3 gene expression increases slightly, whereas ALS increases dramatically in the first few weeks after birth. IGFBP-3 mRNA is concentrated in portal venous and sinusoidal endothelium, but is not detected in hepatocytes, whereas ALS mRNA is diffusely expressed by hepatocytes, but is not detected in nonparenchymal cells. Both transcripts are localized in the renal cortex; however, IGFBP-3 mRNA is concentrated in interstitial cells, whereas ALS is expressed in proximal tubule epithelium. Hypophysectomy results in a 90% reduction in hepatic ALS and an approximately 50% decrease in IGFBP-3 mRNA level. ALS, but not IGFBP-3, transcripts were also reduced in the kidney. GH receptor mRNA is coexpressed with ALS in liver and kidney, suggesting that the effects of GH on ALS gene expression may be direct. In summary, the fact that IGFBP-3 gene expression is far more widespread than that of ALS in both spatial and temporal parameters suggests that IGFBP-3 has a role apart from contribution to the ternary complex. We have also shown that IGFBP-3 and ALS are synthesized by distinct hepatic cell types in an anatomical organization that may serve to ensure efficient formation of the ternary complex in the blood passing through the sinusoids. Finally, the present data suggest that regulation of ALS synthesis may be the primary site of GH regulation of ternary complex formation.

Purification and characterization of the acid-labile subunit of rat serum insulin-like growth factor binding protein complex

Circulating insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), when occupied by IGF-I or IGF-II, combines with an acid-labile glycoprotein subunit (ALS) to form a high molecular weight complex. In this study, ALS from rat serum has been purified and its properties investigated. Purification involved ion-exchange chromatography, and affinity chromatography on an IGF-I-IGFBP-3 column, yielding almost 1 mg ALS from 100 ml serum. Amino-terminal sequencing confirmed the prediction from previous complementary DNA analysis but indicated that the protein may circulate in a truncated form. Rat ALS was almost as potent as human ALS in binding to human IGF-I-IGFBP-3 complex (association constant, 2.3 nM-1). A sensitive RIA was developed, with high specificity for rodent ALS. Serum ALS rose from 3 micrograms/ml in 2-day-old rats to more than 40 micrograms/ml at 10 weeks, with no sex difference. GH-deficient rats showed 60-75% lower values than controls. This study shows rat ALS to have similar binding properties, and age and GH dependence, to human ALS. The new RIA will facilitate studies of IGF and IGFBP regulation in the rat.

[Quality of rhizoma Anemarrhenae grown for different periods of time and gathered in different seasons]

The experimental results have shown that except the stem and leaves all kinds of Rhizoma Anemarrhenae and all parts of the herb contain sarsasapogenin, but the contents are different. Furthermore, the root and peel of Rhizoma Anemarrhenae may be used as drug instead of Rhizoma Anemarrhenae.

[Change in calcium transport as a factor in causing dysfunction of myocardial mitochondria during hypoxia]

During normoxic incubation of isolated myocardial mitochondria, there were marked increases in mitochondrial calcium when free calcium concentration in the incubation medium was enhanced. The increases were concomitant with rises increase in the rate of state 4 respiration. Moreover, there is a positive correlation between the mitochondrial calcium and the rate of state 4 respiration. During hypoxic incubation, when the calcium concentration of the incubation medium was enhanced, there was no significant increase in mitochondrial calcium and the rises in the rate of state 4 respiration were much lower than the rises during normoxia. Hypoxic incubation in medium of low calcium concentration (pCa 8.0) resulted in slight rises in rate of state 4 respiration. The above results suggest that in myocytes, the mitochondrial dysfunction under hypoxia may be caused indirectly by changes in cytoplasm rather than directly by hypoxia. It seems that the change of cellular free calcium concentration is an important factor in the mitochondrial dysfunction.

Combination of DNA single strand synthesis with PCR to construct mung bean trypsin inhibitor gene

This paper using the synthesis of mung bean trypsin inhibitor gene as an example, presented a new method for gene synthesis. The principle of the method was based on the combination of the single strand strategy and the PCR technique. The synthesis was very simple, convenient and rapid. The mung bean trypsin inhibitor is a protein composed of 72 amino acid residues. Its amino acid sequence has been determined, but the DNA sequence of gene still unknown. The synthetic mung bean trypsin inhibitor gene was 248 bp in length. It contains the encoded sequence, the start and stop codons, the restriction sites of EcoRI and BamHI at both ends, The codon selection of the synthetic gene was carried out according to the codon usage of other plant protease inhibitor gene or plant gene. The synthetic double-stranded DNA was digested with EcoRI and BamHI or PstI first, then cloned into plasmid pUC19. The synthetic gene was proved to be correct by the restriction map and the sequence analysis using the dideoxy-mediated chain termination method.

Molecular cloning of the acid-labile subunit of the rat insulin-like growth factor binding protein complex

The insulin-like growth factors, IGF-I and IGF-II, circulate in both humans and rats as part of a 125-150 kDa complex comprising IGFs, the IGF binding protein IGFBP-3, and an acid-labile subunit. Clones encoding rat acid-labile subunit have been isolated from a rat liver cDNA library probed with a human acid-labile subunit cDNA. Two overlapping clones encode a leucine-rich protein of 576 amino acids preceded by a 27-residue signal sequence, with 78% homology to the human acid-labile subunit. Northern analysis of mRNA from adult rat brain, kidney, heart, lung, spleen, muscle and liver shows a major species of about 4.4 kb and minor bands of about 2 kb, 1.4 kb and 1 kb. The tissue distribution of this protein may therefore be wider than previously recognized.

Depression of cardiac sarcolemmal phospholipase D activity by oxidant-induced thiol modification

Myocardial phospholipase D (PLD) is primarily localized at the sarcolemmal level and selectively hydrolyzes phosphatidylcholine to form phosphatidic acid as part of the signal transduction mechanisms for regulating Ca2+ movements in the heart. Since the myocardial cell damage induced by oxidative stress is associated with abnormalities in Ca2+ homeostasis and thiol status, we examined the thiol group dependence and the effects of oxidant species on this enzyme. Sarcolemmal membranes isolated from rat heart were exposed to several types of thiol group modifiers. Alkylation with N-ethylmaleimide or methyl methanethiosulfonate, mercaptide formation with p-chloromercuriphenylsulfonic acid, and thiol-disulfide exchange with 5,5'-dithio-bis(2-nitrobenzoate) depressed sarcolemmal PLD activity; in all cases the depression was prevented by dithiothreitol. At different concentrations of N-ethylmaleimide the PLD depression correlated well (r = 0.98) with the decrease in total thiol group content of the membrane. The enzyme activity was not affected by xanthine-xanthine oxidase, a superoxide anion-generating system, but was depressed by hydrogen peroxide (H2O2) in a concentration-dependent manner. This inhibitory effect was prevented by catalase as well as by dithiothreitol, but not by D-mannitol. The effect of a hydroxyl radical-generating system (Fenton reaction) could not be assessed because of an interfering direct inhibition by Fe2+. Dithiothreitol was also able to restore PLD activity in H2O2-pretreated membranes and to prevent a severe deactivation of the enzyme by hypochlorous acid (HOCI). Protection by glutathione and inhibition by its oxidized form were also observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer system for the acquisition and analysis of vascular contractility. Application to a bioassay of endothelial cell function

A system for the digital acquisition and subsequent analysis of the tension developed by isolated blood vessels in response to an endothelial cell superfusate is reported. Tension of the isolated rat aortic rings was measured by strain gauge. Strain-gauge output was then amplified, and the analog signal was digitized on a 16-channel A/D board. Lab tech Notebook software was used to display and store the data. The sampling rate was 0.1 Hz, and the data was written concurrently to hard disk and printer. Both disk and printer output were accompanied by a time stamp for subsequent ease of retrieval. The endothelial cell bioassay system allowed measurement of changes in vascular tension after the release of endothelium-dependent relaxing factor, nitric oxide (EDRF-NO) from cultured cells. Cells were cultured on microcarrier beads, formed into columns, and perfused with physiological salt solution. Significant (p < 0.05) relaxant responses occurred after agonist stimulation with bradykinin (10(-8) M; Emax -31.0% +/- 8.2%), acetylcholine (10(-8) M; Emax -33.2% +/- 5.0%), and calcium ionophore A 23187 (10(-6) M; Emax -55.7% +/- 15.4%). These responses were dependent on EDRF-NO, as shown by both the lack of relaxation in the absence of endothelial cells, and that relaxation to A 23187 was overcome by hemoglobin (3 x 10(-6) M). Results were manipulated graphically to allow the superimposition of data and thereby provide a mean and standard error of the mean for the entire time course of each response. Thus, a system was produced where fidelity of data expression was not dependent on measurements made at single points, but on the sampling frequency of the acquisition system.

Structure and functional expression of the acid-labile subunit of the insulin-like growth factor-binding protein complex

Nearly all of the insulin-like growth factor (IGF) in the circulation is bound in a heterotrimeric complex composed of IGF, IGF-binding protein-3, and the acid-labile subunit (ALS). Full-length clones encoding ALS have been isolated from human liver cDNA libraries by using probes based on amino acid sequence data from the purified protein. These clones encode a mature protein of 578 amino acids preceded by a 27-amino acid hydrophobic sequence indicative of a secretion signal. Expression of the cDNA clones in mammalian tissue culture cells results in the secretion into the culture medium of ALS activity that can form the expected complex with IGF-I and IGF-binding protein-3. The amino acid sequence of ALS is largely composed of 18-20 leucine-rich repeats of 24 amino acids. These repeats are found in a number of diverse proteins that, like ALS, participate in protein-protein interactions.

Molecular replacement real-space averaging

Structure determination of macromolecules often depends on phase improvement and phase extension by use of real-space averaging of electron density related by noncrystallographic symmetry. Although techniques for such procedures have been described previously [Bricogne (1976). Acta Cryst. A32, 832–847; Johnson (1978). Acta Cryst. B34, 576–577], modern computer architecture and experience with these methods have suggested changes and improvements. Two unit cells are considered: (1) the p-cell corresponding to the actual crystal structure(s) being determined (there would be more than one of these if the molecule crystallizes in more than one crystal form) and (2) the h-cell corresponding to the molecule in a standard orientation with respect to which the molecular symmetry axes are defined. Averaging can proceed entirely within the p-cell, referring to the h-cell only in as far as knowledge of the molecular symmetry is required. It is also possible to place the averaged molecule back into the h-cell, where it can be used to redefine the molecular envelope or for displaying a suitably chosen asymmetric unit of the molecule. Techniques are discussed for automatically selecting a molecular envelope which is consistent with packing considerations within the p-cell and which retains the symmetry of the molecular point group. The electron density map to be averaged is divided into bricks for storage in virtual memory. Roughly as many bricks as there are noncrystallographic asymmetric units per crystallographic asymmetric unit need to be retained in memory at one time. This procedure minimizes paging problems and avoids double sorting. Use of eight-point interpolation permits storing the map at grid points separated by no more than 1/2.5 of the resolution limit to obtain rapid convergence.

Phospholipase D activity in subcellular membranes of rat ventricular myocardium

The phospholipase D (PL D), which catalyzes the formation of phosphatidic acid (PA), was studied in rat myocardium using 14C-labelled phosphatidylcholine (PC) as an exogenous substrate. Subcellular distribution experiments indicated the presence of PL D in particulate fractions only. Different procedures for the isolation of purified cardiac subcellular organelles showed the presence of PL D in sarcolemma (SL), sarcoplasmic reticulum (SR) and mitochondria with 14-, 11- and 5-fold enrichment when compared to the homogenate value, respectively. The activity of SL PL D was observed over a narrow acid pH range with an optimum at 6.5, and it showed a high specificity for PC while phosphatidylethanolamine and phosphatidylinositol showed a low rate of hydrolysis. Under optimal conditions, PA formation was linear for a 90-min period of incubation and the reaction rate was constant for 10 to 100 micrograms SL protein in the assay medium. The SR PL D displayed properties similar to those seen with the SL PL D. In membrane fractions PL D was also found to catalyze a transphosphatidylation reaction for the synthesis of phosphatidylglycerol. Assessment of the intramembranal levels of radioactive 1,2-diacylglycerol (DAG) in the absence or presence of KF suggested the presence of an active PA phosphohydrolase activity. This study indicates that a PC-specific PL D activity is localized in different membrane systems of the myocardium and may be associated with PA phosphohydrolase to act in a coordinated manner. The functional significance of PL D-dependent formation of PA in cardiac membranes is discussed.

Role of sulfhydryl groups in phospholipid methylation reactions of cardiac sarcolemma

The effect of reagents that modify sulfur-containing amino acid residues in the phosphatidylethanolamine N-methyltransferase was studied in the isolated rat cardiac sarcolemma by employing S-adenosyl-L-[methyl-3H]methionine as a methyl donor. Dithiothreitol protected the sulfhydryl groups in the membrane and caused a concentration- and time-dependent increase of phospholipid N-methylation at three different catalytic sites. This stimulation was highest (9-fold) in the presence of 1 mM MgCl2 and 0.1 microM S-adenosyl-L-[methyl-3H]methionine at pH 8.0 (catalytic site I), and was associated with an enhancement of Vmax without changes in Km for the methyl donor. Thiol glutathione was less stimulatory than dithiothreitol; glutathione disulfide inhibited the phosphatidylethanolamine N-methylation by 50%. The alkylating reagents, N-ethylmaleimide and methylmethanethiosulfonate, inhibited the N-methylation with IC50 of 6.9 and 14.1 microM, respectively; this inhibition was prevented by 1 mM dithiothreitol. These results indicate a critical role of sulfhydryl groups for the activity of the cardiac sarcolemmal phosphatidylethanolamine N-methyltransferase and suggest that this enzyme system in cardiac sarcolemma may be controlled by the glutathione/glutathione disulfide redox state in the cell.

[Morphological and functional features of endodermal cells in rat yolk sac, with special reference to the fetal macrophage differentiation]

Morphological and functional features of the yolk sac endodermal cells with special reference to the fetal macrophage differentiation were investigated morphologically under the light and electron microscopes and immunologically with the antigen phenotypic analysis and the phagocytic activity-test, using the syngeneic DA rat-embryos from 8 to 16 days of gestation. Based on the staining property with toluidin blue and the ultrastructural features, the endodermal layer from day 8 to 16-yolk sacs has been known to consist of two kinds of cell type; 10% "clear" cells with clear cytoplasm and 90% "dark" cells with dark cytoplasm. Numerous primary lysosomes, phagolysosomes, lipid droplets and coated vesicles distributed preferentially in the supranuclear portion of endodermal cells. A broad intercellular space was found between "clear" cells and "dark" cells, indicating the loose intercellular binding. It was often found that "clear" cells tend to migrate from the endodermal layer into the mesenchymal layer, where the poor development of basement membrane was seen between them. Cells phagocytosing red blood cells, that resemble morphologically "clear" cells, were also observed in the fetal liver. At ten hours after latex-injection into the yolk sac cavity of 14 days embryos, some cells which phagocytosed latex beads in their cytoplasm were found in the endodermal layer, and also in the liver tissue and loose connective tissue of fetus. These cells were stained positively with monoclonal antibody Mar3 which recognizes preferentially rat-mononuclear phagocyte system. In vitro-latex uptake of separated endodermal cells was also demonstrated by the culture-study of endodermal cell suspension. The present findings indicate that the yolk sac-endodermal layer derived from the proximal endoderm consists of at least two kinds of cell-population with a great similarity to tissue macrophages in morphological and functional senses, and support the concept that some cell-populations of endodermal layer may migrate into fetal tissue and are closely related to the differentiation of fetal macrophages and their precursors.

[Determination of glycyrrhetinic acid in radix Glycyrrhizae by TLC densitometry]

A TLC densitometric method for the determination of glycyrrhetinic acid in Radix Glycyrrhizae is described. The method is accurate, sensitive and simple. The recovery of glycyrrhetinic acid is 98.30% and the coefficient of variation of five samplings is 2.20%.

Alteration of lipid methylation by oleic acid in rat heart sarcolemma

Incubation of rat heart sarcolemma with the methyl donor S-adenosyl-L-[methyl-3H] methionine resulted in N-methylation of phosphatidylethanolamine and methylation of a heterogenous fraction of nonpolar lipids in the membrane. Oleic acid reduced the synthesis of N-methylated phospholipids and stimulated the methyl group incorporation into nonpolar lipids in a concentration-dependent manner. Both methylation reactions were not affected when oleic acid was substituted by methyl ester of oleic acid or by the detergents sodium deoxycholate or Triton X-100. This study suggests that the enzymatic biosynthesis of the N-methylated phospholipids may be altered by free fatty acids.

[Studies on ultraweak luminescence of bacteria]

Ultraweak luminescence of Escherichia coli, Bacillus subtilis and Brevibacterium ammoniagenes was measured with high sensitive single photon counting equipment (Made in China). The results obtained from ultraweak luminescence of as above three bacterial strains were as follows: spectral distribution curves, photon emission kinetic curves or emission intensity and its qualitative relationship between intensity and bacterial counts.

Interactions between cyclic AMP-dependent protein phosphorylation and lipid transmethylation reactions in isolated porcine cardiac sarcolemma

Premethylation of purified porcine cardiac sarcolemma (SL) in the presence of 0.15, 10 and 150 microM S-adenosyl-L-methionine (AdoMet) did not change the phosphorylation of SL proteins catalyzed either by intrinsic cyclic AMP-dependent protein kinase (cAK) or by added catalytic (C) subunit of this enzyme. On the other hand, membrane exhibited increased lipid methyltransferase activity after preincubation with MgATP and C subunit. Prephosphorylation of membranes stimulated the total [3H]-methyl incorporation into SL lipids assayed at 0.15 microM [3H]AdoMet due to an enhancement of Vmax and without changes in the Km value for AdoMet. Analysis of the methylated lipid products revealed an increased methyl group incorporation into a nonpolar lipid fraction whereas phosphatidylethanolamine-N-methylation was not affected by phosphorylation. The results suggest that the cyclic AMP-mediated signal transduction at the level of cardiac SL is not affected by methylation-induced modifications of the membrane lipid microdomains. On the other hand, an intrinsic SL lipid methyltransferase activity is apparently not related to the N-methylation of phospholipids, is modulated by cyclic AMP-dependent protein phosphorylation.

Holocene—Late Pleistocene Climatic Ice Core Records from Qinghai-Tibetan Plateau

Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Würm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative delta(18)O ratios, increased dust content, decreased soluble aerosol concentrations, and reduced ice crystal sizes than the Holocene part. These changes occurred rapidly approximately 10,000 years ago. In addition, the last 60 years were apparently one of the warmest periods in the entire record, equalling levels of the Holocene maximum between 6000 and 8000 years ago.