The platelet-derived growth factor receptor.
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Animals↗
Biomedical subjects
R Ross
Publications and source records attributed to R Ross.
Irvine H. Page lecture 1981. The lesions of atherosclerosis.
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Animals↗
Management of the postmenopausal woman with hypertension. Case presentation and panel discussion.
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Antihypertensive Agents↗
Isolation, characterization, and propagation in vitro of human glomerular endothelial cells.
Human glomerular endothelial cells have been isolated, cloned, and characterized. They appeared as the first outgrowth from human glomeruli in the presence of platelet-derived growth factor, which was also a requirement for continuous growth. By phase microscopy they appeared as monolayers of polygonal cells. Von Willebrand's factor (VWF) was detected in the cytoplasm of all clones. Their intermediate filaments differed antigenically from that present in human umbilical vein endothelial cells. Like other endothelial cells, they demonstrated high levels of membrane-associated angiotensin-converting enzyme (ACE).
Cell Division↗
Ganglioside-mediated modulation of cell growth, growth factor binding, and receptor phosphorylation.
Glycosphingolipids added exogenously in cell culture are slowly incorporated into plasma membranes, inhibit cell growth, and modify growth behavior ( Laine , R. A., and Hakomori, S. (1973) Biochem. Biophys. Res. Commun. 54, 1039-1045; Keenan , T. W., Schmid, E., Franke , W. W., and Wiegandt , H. (1975) Exp. Cell Res. 92, 259-270). With the availability of purified growth factors and serum-free culture conditions in recent years, we have been able to examine this phenomenon in mouse Swiss 3T3 cells in greater detail with the following results. 1) Cell growth (cell number increase) in serum-free medium was specifically inhibited by the presence of GM1 and to a lesser extent by GM3, but not by NeuAcnLc4 , although the gangliosides were incorporated equally well into cell membranes. GM3 inhibited both platelet-derived growth factor (PDGF)- and epidermal growth factor-stimulated mitogenesis determined by thymidine incorporation, while GM1 could only inhibit PDGF-stimulated mitogenesis. NeuAcnLc4 had no effect on mitogen-stimulated thymidine incorporation. 2) The concentration-dependent binding of 125I-PDGF binding to cells indicated that cells whose growth was inhibited by GM1 or GM3 showed an increased affinity for PDGF as compared to cells grown without addition of ganglioside, while the total number of receptors stayed the same. Addition of ganglioside did not affect the binding of 125I-EGF. 3) No direct interaction was observed between gangliosides and growth factors as evidenced by the lack of competition by ganglioside-containing liposomes for cellular binding of 125I growth factors. 4) GM1 and GM3, but neither NeuAcnLc4 nor Gb4 , inhibited the PDGF-stimulated tyrosine phosphorylation by membrane preparations of a 170,000 molecular weight protein, which is probably the PDGF receptor. Thus, the level of gangliosides GM1 and GM3 in membranes may modulate PDGF receptor function by affecting the degree of tyrosine phosphorylation and may alter the affinity of the receptor for PDGF.
Animals↗
Platelet-derived growth factor: morphologic and biochemical studies of binding, internalization, and degradation.
Kinetic studies of binding and internalization of 125I-platelet-derived growth factor (PDGF) demonstrate that up to 15% of membrane-associated radioactivity is internalized within 2 minutes after warming to 37 degrees C in a variety of cell types. The T 1/2 for internalization is approximately 20 minutes. The T 1/2 for the subsequent appearance of degradation products in the culture medium is between 60-90 minutes following initiation of internalization. Internalization and lysosomal association of 125I-PDGF were confirmed by EM autoradiography. Quantitative studies using PDGF adsorbed to colloidal gold (gold-PDGF) demonstrate that 17% of the cell-associated sites are along coated regions of the plasma membrane (1.0 sites/micron), while 82% are associated with noncoated membrane (0.2 sites/micron). There is a significant redistribution of the gold-PDGF complexes upon warming. Within 1-2 minutes at 37 degrees C, gold particles are found within endocytic vesicles, endosomes (0.09-0.3 micron diameter), and lysosomes (greater than 0.2 micron diameter). At this time the vesicle/endosome compartment comprises 15% of the total sites and contains 0.9 sites per micron2 of surface area. The lysosomes account for 8% of the total sites and contain 0.8 sites per micron2 of surface area. Simultaneously, there is an increase in the number of gold-PDGF binding sites within coated-pits (1.6 sites/micron, 18% of the total sites) and a decrease along noncoated regions of the membrane (0.11 sites/micron, 58% of the total sites). After 15 minutes at 37 degrees C, 26% of the total sites (1.4 sites/micron2) are highly concentrated within lysosomes, while sites in the vesicle/endosome compartment remain constant. At the same time, binding sites within coated pits decrease substantially (0.5 sites/micron, 4% of the total sites), while the number of sites along noncoated regions of the membrane remain constant. Gold-PDGF was not observed associated with the Golgi complex at any time up to 120 minutes following warming. We conclude that gold-PDGF is processed via both receptor-mediated and nonspecific endocytosis and follows an intracellular pathway comparable to that followed by some other protein ligands.
Animals↗
Platelet-derived growth factor.
Platelet-derived growth factor (PDGF) is a basic (pI congruent to 10) 30 000 molecular weight protein circulating in normal blood sequestered within the platelet alpha-granules. It binds with high affinity (Kd = 10(-11) M) to a specific cell-surface receptor found on many connective tissue cell types in culture. It is active in stimulating the metabolism and multiplication of connective tissue cells at very low concentrations (ED50 = 10(-11) M). It is likely that PDGF is released from platelets at sites of vascular damage and that it contributes toward the cell proliferation and connective tissue formation seen in healing wounds and in arteriosclerotic lesions. PDGF which does not bind to responsive cells at the wound site is largely inactivated by a plasma binding protein and is rapidly cleared from the circulation.
Adult↗
Plasma binding proteins for platelet-derived growth factor that inhibit its binding to cell-surface receptors.
Evidence is presented that the binding of platelet-derived growth factor (PDGF) to plasma constituents inhibits the binding of PDGF to its cell-surface mitogen receptor. Approximately equivalent amounts of PDGF-binding activity were found in plasma from a number of different species known by radioreceptor assay to contain PDGF homologues in their clotted blood. Activation of the coagulation cascade did not significantly alter the PDGF-binding activity of the plasma components. Three molecular weight classes of plasma fractions that inhibit PDGF binding to its cell-surface receptor were defined by gel filtration: approximately equal to 40,000, 150,000, and greater than 500,000. Specific binding of 125I-labeled PDGF to the highest molecular weight plasma fraction could also be demonstrated by gel filtration. The binding of PDGF to these plasma components was reversible under conditions of low pH or with guanidine X HCl, and active PDGF could be recovered from the higher molecular weight fractions. Immunologic and functional evidence is presented that the highest molecular weight plasma fraction may be alpha 2-macroglobulin. A model is proposed in which the activity of PDGF released in vivo may be regulated by association with these plasma binding components and by high-affinity binding to cell-surface PDGF receptors.
Carrier Proteins↗
Production of platelet-derived growth factor-like molecules and reduced expression of platelet-derived growth factor receptors accompany transformation by a wide spectrum of agents.
A series of nontransformed human and murine cells and derivative cell lines transformed by methylcholanthrene; by simian virus 40, Kirsten and Moloney murine sarcoma viruses, simian sarcoma virus, and adenovirus; and by a "spontaneous" event in culture were examined for the expression of receptors for the platelet-derived growth factor (PDGF) and for production of substances able to compete with 125I-labeled PDGF for binding to the cell-surface PDGF receptor. In each case, transformation resulted in a 50-100% decrease in available PDGF receptors. All transformed cells except the methylcholanthrene-transformed mouse cells produce a PDGF competitor into the conditioned medium. Levels of PDGF competitor in conditioned medium at the end of a 48-hr collection were as high as 2 ng/ml--high enough to be measured by radioreceptor assay diluted 1:30 and to maximally stimulate [3H]thymidine incorporation by human fibroblasts. The PDGF competitor activity detected in a radioreceptor assay does not reflect irreversible (e.g., proteolytic) damage to the receptor of test cells since its effects are reversed by acetic acid dissociation. Antiserum against human PDGF neutralizes 20-80% of the PDGF competitor found in conditioned medium from different transformed human cells and 100% of the activity from normal human endothelial cells. The possibility that induction of expression of the cellular PDGF gene may be involved in the mechanism of transformation of PDGF-responsive mesenchymal cells is discussed.
Animals↗
Atherosclerosis.
The lesions of atherosclerosis are proliferative smooth-muscle lesions which may result from various forms of endothelial injury or dysfunction associated with the different risk factors for atherosclerosis. These lesions have been associated with interactions between platelets, macrophages, and with substances released from these cells, including growth factors. Approaches toward lesion prevention should include: protection of the endothelium, particularly in relation to maintenance of its nonthrombogenic character: inhibition of platelet interactions; and understanding of the nature of growth factors that may be involved to permit development of approaches to prevent growth-factor activity, including binding of growth factors derived from platelets and macrophages upon other cells, in particular, smooth muscle.
Animals↗
Analysis of reference transactions using packaged computer programs.
Motivated by a continuing education class attended by the authors on the measurement of reference desk activities, the reference department at Scott Memorial Library initiated a project to gather data on reference desk transactions and to analyze the data by using packaged computer programs. The programs utilized for the project were SPSS (Statistical Package for the Social Sciences) and SAS (Statistical Analysis System). The planning, implementation and development of the project are described.
Computers↗
Platelet-derived growth factor in vivo: levels, activity, and rate of clearance.
Platelet-derived growth factor (PDGF) is a potent mitogen for many cultured connective tissue cells. It is present in concentrated form within the platelet alpha-granules and is believed to be released during platelet degranulation at sites of vascular injury. We have used a sensitive radioreceptor assay to measure PDGF levels in whole blood serum from normal humans [17.5 +/- 3.1 (SD) ng/mL] and baboons (2.7 +/- 1.2 ng/mL). PDGF was not detected in plasma from either species. In addition, plasma was found to substantially reduce the ability of added purified PDGF to bind to the cell surface PDGF receptor on cultured cells, suggesting that plasma may contain a PDGF-binding protein that would serve to inactivate PDGF released into plasma. Calculations of PDGF concentrations in serum have been corrected for the effects of the binding protein. 125I-PDGF injected intravenously into normal baboons was cleared rapidly from the plasma (t1/2 = two minutes). The rapid clearance of 125I-PDGF did not result from iodination damage, as purified unlabeled PDGF was cleared with comparable kinetics. The rapid clearance of purified and iodinated PDGF did not result from changes in PDGF structure during purification or from removal of PDGF-associated proteins during purification, as PDGF present in freeze-thaw lysates of fresh platelets was cleared equally rapidly. We conclude that release of PDGF at sites of vascular injury would greatly increase the local concentration of PDGF and that PDGF not localized to the site of injury would be rapidly cleared from the circulation.
Animals↗
Multiple responses of connective tissue cells to mitogenic stimulation with platelet-derived growth factor.
A number of important properties are held by mitogenic substances such as platelet derived growth factor for cells that can respond to such a mitogen. These include responses that occur early after exposure of the cells to the mitogens. Such responses include increases in endocytosis, binding of low density lipoprotein to high affinity cell surface receptors and increased uptake and degradation of LDL, increases in phospholipid metabolism, sodium and potassium ion flux, increases in protein and RNA synthesis, and chemotaxis. It is not yet clear whether some of these properties can be separated from the stimulus to enter DNA synthesis and mitosis, or whether they are tightly coupled to the latter. Nevertheless, they all precede DNA synthesis by many hours before the cells enter into S and go on to divide. It is highly probable that a number of other biological events will be found to be stimulated by exposing cells to mitogens, such as the platelet derived growth factor. Elucidation of these events and determination of the interrelation of each of these biological responses to the subsequent multiplication of the cells in a given set of circumstances will help to provide a basis for understanding how these mitogens work, and potentially how it may be possible to prevent some of the proliferative responses that represent such an inherent part of many disease processes.
Chemotaxis↗
The role of endothelial injury and platelet and macrophage interactions in atherosclerosis.
Atherosclerotic lesions take two forms, the fatty streak and the fibrous plaque or complicated lesion. The former is a flat, lipid-rich lesion containing variable numbers of foam cells in the form of macrophages and/or smooth muscle. In contrast, the fibrous plaque is a proliferative lesion of smooth muscle containing variable numbers of macrophages. Associated with the smooth muscle proliferative response is the formation of connective tissue matrix and the accumulation of intracellular and extracellular lipid. The response to injury hypothesis of atherogenesis provides and approach to exploring the interactions among substances that alter endothelial function and/or structure and to investigating the relationships among endothelium, smooth muscle, platelets, macrophages, and plasma constituents. Studies of molecules potentially important in lesion development, such as mitogens derived from platelets, macrophages, and endothelium, and of the potential roles of lipids in generating these lesions and in inducing injury to the overlying endothelial cells, have begun to shed light on how these processes may occur and on approaches that may be taken to better understand and possibly prevent them. We still lack an understanding of one of the key events, endothelial injury. The many ways by which endothelial cells may be altered in relation to the hypercholesterolemic environment and to the underlying macrophages in the fatty streaks remain to be explored. Nevertheless, these approaches point the way to the development of new means for prevention, intervention, and diagnosis of atherosclerosis.
Animals↗
Human atherosclerosis. I. Cell constitution and characteristics of advanced lesions of the superficial femoral artery.
This study represents a systematic analysis of the fine-structural characteristics of atherosclerotic lesions of the superficial femoral artery in man together with the growth characteristics in culture of the smooth muscle cells derived from these lesions. Occlusive fibrous atherosclerotic plaques were obtained from 29 male patients at the time of bypass surgery for occlusion of the superficial femoral artery and were studied by light and transmission electron microscopy. The occluded segment of each artery was obtained immediately after removal from the patient and examined with sterile techniques, and representative segments were fixed for light- and electron-microscopic study. Adjacent segments were used for dissection of the lesion away from the underlying media, and smooth muscle cells were cultured from lesion and nonlesion areas and compared in terms of their growth responses to increasing concentrations of a pool of human whole blood serum. The majority of the lesions were fibroproliferative and contained relatively little lipid. The fibrous cap that covered each lesion consisted of a special form of dense connective tissue that contained flat, pancake-shaped smooth muscle cells in a lacunalike space. This space consisted of concentric layers of basement membrane, collagen fibrils, and proteoglycan. The majority of the cells beneath the fibrous cap were smooth muscle cells mixed with small but varying numbers of macrophages. Most of the lesions were occluded by a thrombus, which had undergone organization and recanalization. A small number of the lesions had deep lipid deposits together with foci of degeneration and calcification. The occluded thrombi contained smooth muscle cells and a larger proportion of macrophages than the lesions themselves. The in vitro growth properties of the smooth muscle cells isolated from the lesion and the underlying media suggested that the lesion cells had senesced, compared with the medial smooth muscle cells derived from the same artery.
Aged↗
Is epidermal growth factor present in human blood? Interference with the radioreceptor assay for epidermal growth factor.
Human whole blood serum reduces the binding of [125I]labeled mouse epidermal growth factor to cultured human fibroblasts as well as does 70-100 ng/ml mouse epidermal growth factor. However, at most 1-2% of the binding inhibitor detected in human whole blood serum is related to epidermal growth factor--the remaining consists of other factors released during preparation of serum, predominantly the platelet-derived growth factor, which are capable of altering the binding properties of the epidermal growth factor receptor. This accounts for much of the differences between values reported for epidermal growth factor concentration in blood by investigators using different assay procedures.
Binding, Competitive↗
Characterization of platelet-derived growth factor-stimulated phosphorylation in cell membranes.
Platelet-derived growth factor (PDGF) stimulated the phosphorylation of a 170,000-Mr protein in membranes prepared from parental and several variant lines of Swiss 3T3 cells as well as from diploid human fibroblasts. The intensity of the phosphorylation of the 170,000-Mr protein paralleled the number of PDGF receptors present on the various cells. The enhanced phosphorylation was the result of an increase in the amount of phosphoserine and phosphotyrosine present in the 170,000-Mr protein. PDGF-stimulated phosphorylation of the 170,000-Mr protein was rapid and showed a dose response to PDGF. Down regulation of the PDGF receptor led to a rapid loss in the PDGF-stimulated phosphorylation of the 170,000-Mr protein. In Swiss 3T3 cell membranes, PDGF as well as epidermal growth factor stimulated the phosphorylation of a synthetic, tyrosine-containing peptide. The effects of the two growth factors were additive, indicating that PDGF and epidermal growth factor stimulate peptide phosphorylation through distinct receptors.
Animals↗