Platelet-derived growth factor is not chemotactic for human peripheral blood monocytes

PDGF is a mitogenic protein stored in platelets and released upon platelet degranulation. Recent evidence indicates that PDGF plays an important role in both physiologic and pathophysiologic processes, particularly in tumorigenesis, wound healing, pulmonary fibrosis, and atherogenesis. In addition to its mitogenic potential, it has been reported that PDGF stimulates monocyte chemotaxis. Since the recruitment of monocytes from the peripheral vasculature is an important event in vivo, the potential role of PDGF as a monocyte chemoattractant has significant biologic implications. However, we now report that homogeneous human PDGF from platelets and a recombinant PDGF-2 homodimer do not stimulate monocyte chemotaxis. In contrast to previous reports these results indicate that PDGF is not a monocyte chemoattractant.     

Cultured primate aortic smooth muscle cells express both the PDGF-A and PDGF-B genes but do not secrete mitogenic activity or dimeric platelet-derived growth factor protein

Proliferation of smooth muscle cells (SMC) in the arterial intima of man and experimental animals is important in the pathogenesis of atherosclerosis. Vascular SMC proliferation in vitro is stimulated by a number of agents, including the potent protein mitogen, platelet-derived growth factor (PDGF). Recent studies on rat arterial SMC indicate that these cells may, under certain circumstances, synthesize PDGF protein mitogens, suggesting that the regulation of SMC proliferation in vivo may have an autocrine or paracrine component. In this study we demonstrate that cultured nonhuman primate (baboon) aortic SMC transcribe both the PDGF-A and PDGF-B genes but do not secrete detectable mitogenic activity characteristic of native PDGF. The absence of this activity was not due to the presence in the cell conditioned medium of factors inhibitory for PDGF-mediated mitogenic activity. Metabolic labeling of the cells and immunoprecipitation with specific antibodies to human PDGF did not detect a dimeric (30 kDa) PDGF protein in either the intracellular or extracellular compartments, but instead identified PDGF-related proteins of molecular weight 12 kDa and 100 kDa. These data suggest the presence in vascular SMC of a mechanism regulating the translation of PDGF mRNA that may play an important role in the control of SMC proliferation in vivo.     

Inhibitor binding to isolated chloroplast cytochrome bf complex

Effects of three inhibitors of quinol oxidation in the chloroplast cytochrome bf complex (stigmatellin, tridecylstigmatellin and dibromothymoquinone) were studied in an isolated system comprising Photosystem I (PS I) particles, plastocyanin (PC) and cytochrome bf complex, in the absence of quinol or quinone. Addition of these inhibitors increased the extent of cytochrome f oxidation after a laser flash created oxidised PS I reaction centre (P700) and PC, and decreased somewhat the extent of PC oxidation. The re-reduction of oxidised P700 was more complete than when inhibitor was absent. The data were simulated with reactions which included the putative reduction of cytochrome f by the Rieske centre (FeS) and different rate-coefficients according as to whether inhibitor was bound to the bf complex or not. It was concluded that under the conditions studied the Rieske centre donated electrons to oxidised cytochrome f and plastocyanin with an average rate coefficient of 35 s^–1. This electron transfer was prevented by any of the three inhibitors, which also increased the equilibrium coefficient for the cytochrome f/PC reaction by a maximum factor of two. This increase corresponded to a decrease in the back reaction coefficient and an increase in the forward rate. The equilibrium coefficient for the reduction of oxidised P700 by PC was about 2 in the absence of inhibitor but increased to about 20 in their presence, but only if cytochrome bf complex was additionally present. This was attributed to the transient formation of complexes between P700 with bound plastocyanin, and bf complex. The operative mid-point potential of FeS, if that of cytochrome f is 370 mV, was 390 mV. Deviations in midpoint potentials (P700/plastocyanin) from solution values were attributed to the bound state of the reactants. Estimates were made of the binding coefficient of each of the three inhibitors to p-sites in the cytochrome bf complex in the absence of competing quinol. A stoichiometry of two inhibitors per bf dimer was necessary to cause the above changes in reduction potential of cyt f and PC. A result of one inhibitor per dimer was statistically unlikely, particularly in the case of tridecylstigmatellin.Abbreviations Cyt- cytochrome - DBMIB(H₂)- 2,5-dibromo-3--ethyl-6-isopropyl-p-benzoquinone (reduced) - E _m- midpoint reduction potential of a couple relative to the standard hydrogen electrode - e-t- electron transfer - FeS (or R)- Rieske iron-sulphur centre - HEPES- N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - Mega-9- nonoyl-N-methylglucamide - n-site (Q_r-site)- quinone reduction site in cytochrome bf complex - PC- plastocyanin - p-site (Q_o-site)- quinol oxidation site in cytochrome bf complex - PQ- plastoquinone - PSI- Photosystem I - P700- reaction centre in Photosystem I - TDS- tridecyl stigmatellin     

The kinetics of reactions around the cytochrome bf complex studied in an isolated system

The kinetics of oxidation and reduction of P700, plastocyanin, cytochrome f and cytochrome b-563 were studied in a reconstituted system consisting of Photosystem I particles, cytochrome bf complex and plastocyanin, all derived from pea leaf chloroplasts. Decyl plastoquinol was the reductant of the bf complex. Turnovers of the system were initiated by laser flashes. The reaction between oxidised P700 and plastocyanin was non-homogeneous in that a second-order rate coefficient of c. 5×10^–7 M^–1 s^–1 applied to 80% of the P700⁺ and c. 0.7×10⁷ M^–1 s^–1 to the remainder. In the presence of bf complex, but without quinol, the electron transfer between cytochrome f and oxidised plastocyanin could be described by a second-order rate coefficient of c. 4×10⁷ M^–1 s^–1 (forward), and c. 1.6×10⁷ M^–1 s^–1 (reverse). The equilibrium coefficient was thus 2.5. Unexpectedly, there was little reduction of cytochrome f ⁺ or plastocyanin⁺ by electrons from the Rieske centre. With added quinol, reduction of cytochrome b-563 occurred. Concomitantly, electrons appeared in the oxidised species. It was inferred that either the Rieske centre was not involved in the high-potential chain of electron transfer events, or that, only in the presence of quinol, electrons were quickly passed from the Rieske centre to cytochrome f ⁺. Additionally, the presence of quinol altered the equilibrium coefficient for the cyt f/PC interaction from 2.5 to c. 5. The reaction between quinol and the bf complex was describable by a second-order rate coefficient of about 3×10⁶ M^–1 s^–1. The pattern of the redox reactions around the bf complex could be simulated in detail with a Q-cycle model as previously found for chloroplasts.Abbreviations AQS anthraquinone sulphonate - cyt cytochrome - cyt b-563(H) high-potential cyt b-563 - cyt b-563(L) low potential cyt b-563 - FeS(R) the Rieske protein of the cyt bf complex, containing an Fe₂S₂ centre - PC plastocyanin - PS photosystem - P700 reaction centre in PS I     

Effects of pH on the kinetics of redox reactions in and around the cytochromebf complex in an isolated system

Rate-coefficients describing the electron transfer reactions between P700 and plastocyanin, between cytochromef in cytochromebf complexes and plastocyanin, and between decyl plastoquinol and cytochromebf complexes were determined as a function of pH in the range 4–10 from flash-induced absorbancy changes at four wavelengths. The reactions between P700 and plastocyanin, and between cytochromef and plastocyanin were optimised when there was electrostatic interaction between ionised acidic groups in plastocyanin with a pK_a of 4.3–4.7 and ionised basic constituents in P700 (assumed to be in the PSI-F subunit) and in cytochromef, with a pK_b of 8.9–9.4. The basic groups are thought to be lysine rather than arginine. This mechanism agrees with that inferred from effects of ionic strength changes on rate-coefficients. The relation between the second-order rate-coefficient for decyl plastoquinol oxidation by thebf complex and pH was characterised by a pK_a of 6.1. This is interpreted as showing that the anion radical form of that quinol, which has a pK_a of 6, and which becomes progressively protonated when pH is changed from 7 to 5, is essential to reduce cytochromeb-563 (low potential) during quinol oxidation. Above pH 9, permanent effects were observed on this rate-coefficient, which were absent in the reactions between P700, plastocyanin and cytochromef.     

Modulation of the heart rate by thyroid hormone in the newborn rat

Confirming the literature data the authors describe that the heart rate is smaller in the newborn rats than in adult ones and increases until the adult values during the first two weeks of life. On the other hand, the blood thyroid hormone exhibits the same pattern, showing an early postnatal increment. As, according the Adolph's data (1967), the heart rate enhancement is not due to the catecholamines, the authors suppose that such enhancement might conceivably depend on thyroid hormone increment.     

Hydrogen Peroxide Induces a Long-Lasting Inhibition of the Ca2+-Dependent Glutamate Release in Cerebrocortical Synaptosomes Without Interfering with Cytosolic Ca2+

Abstract: We studied the action of H₂O₂ on the exocytosis of glutamate by cerebrocortical synaptosomes. The treatment of synaptosomes with H₂O₂ (50–150 µ M ) for a few minutes results in a long-lasting depression of the Ca²⁺-dependent exocytosis of glutamate, induced by KCl or by the K⁺-channel inhibitor 4-aminopyridine. The energy state of synaptosomes, as judged by the level of phosphocreatine and the ATP/ADP ratio, was not affected by H₂O₂, although a transient decrease was observed after the treatment. H₂O₂ did not promote peroxidation, as judged by the formation of malondialdehyde. In indo-1-loaded synaptosomes, the treatment with H₂O₂ did not modify significantly the KCl-induced increase of [Ca²⁺]_i. H₂O₂ inhibited exocytosis also when the latter was induced by increasing [Ca²⁺]_i with the Ca²⁺ ionophore ionomycin. The effects of H₂O₂ were unchanged in the presence of superoxide dismutase and the presence of the Fe³⁺ chelator deferoxamine. These results appear to indicate that H₂O₂, apparently without damaging the synaptosomes, induces a long-lasting inhibition of the exocytosis of glutamate by acting directly on the exocytotic process.     

Distribution of transposable elements in neotropical species of Drosophila

The phylogenetic distribution of transposable families, P, gypsy, hobo, I, and mariner has been analyzed in 33 species of 11 groups of neotropical Drosophila and a Drosophilidae species Zygotrica vittimaculosa, using squash blot and dot blot. Genomic DNA of almost all neotropical species tested hybridized with gypsy probe and some species showed a particularly strong hybridization signal, as D. gaucha, D. virilis, and species of flavopilosa group. The hobo element was restricted to melanogaster group and some strains of D. willistoni. Only D. simulans DNA showed hybridization to mariner probe in all species tested and D. simulans and D. melanogaster showed hybridization with I element probe. P element homologous sequence was present in D. melanogaster and all species and strains of the willistoni and saltans groups tested. The presence of at least one P-homologous sequence was detected in Drosophila mediopunctata. This one was the only P-bearing species of all six tested from the tripunctata group. Four different pairs of primers homologous to segments of the canonical sequence of D. melanogaster's P were used to amplify specific sequences from D. mediopunctata DNA, showing the occurrence of seemingly well-conserved P-homologous sequences. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hair structure of the Woolly mammoth, Mammuthus primigenius and the modern elephants, Elephas maximus and Loxodonta africana

The structure of overhairs from a Wooly mammoth, Mammuthus primigenius , 10–13 thousand years old, is compared with that of its living relatives, Elephas maximus and Loxodonta africana . The hair profile, cross-sectional appearance, wholeamount and cuticular scale cast of the haris of the three species were examined and a selected array of photographs representing the hair structure of each species are presented. In general there is little variation between the three in the gross structure of the overhairs.     

Post-translational modification of a monocyte-specific chemoattractant synthesized by glioma, osteosarcoma, and vascular smooth muscle cells

Chemotaxis is an important step in monocyte recruitment in inflammation, wound healing, and tumor growth. We reported previously that monocyte chemotactic activity secreted by malignant cells and normal smooth muscle cells is associated with a protein or family of proteins that are related to the monocyte-specific smooth muscle cell-derived chemotactic factor (SMC-CF) (Graves, D. T., Jiang, Y. L., Williamson, M. J., and Valente, A. J. (1989) Science 245, 1490-1493). Similar monocyte chemotactic proteins (MCP-1) produced by U-105MG human glioma cells have also been identified (Yoshimura, T., Robinson, E. A., Tanaka, S., Appella, E., Kuratsu, J., and Leonard, E. J. (1989) J. Exp. Med. 169, 1449-1459). We now report that the MCP-1 gene is expressed in MG-63 human osteosarcoma and vascular smooth muscle cells and that SMC-CF antiserum specifically immunoprecipitates proteins synthesized by U-105MG glioma cells. Experiments were undertaken to elucidate the processing pathway of MCP-1/SMC-CF-like proteins in each of these cell types. These experiments demonstrate that larger MCP-1/SMC-CF-like proteins are derived from a Mr = 9000 precursor. Post-translational modification involves the addition of O-linked carbohydrates and sialic acid residues. Differences in carbohydrate processing account for the heterogeneity in MCP-1/SMC-CF-like proteins produced by different cell types. Secretion of these proteins occurs rapidly following processing events in the endoplasmic reticulum-Golgi compartment.