The fms-like tyrosine kinase (Flt) is a transmembrane receptor in the tyrosine kinase family. Expression of flt complementary DNA in COS cells conferred specific, high-affinity binding of vascular endothelial growth factor, also known as vascular permeability factor (VEGF-VPF), a factor that induces vascular permeability when injected in the guinea pig skin and stimulates endothelial cell proliferation. Expression of Flt in Xenopus laevis oocytes caused the oocytes to release calcium in response to VEGF-VPF. These findings show that flt encodes a receptor for VEGF-VPF.

https://science.sciencemag.org/content/sci/255/5047/989.full.pdf

The fms-Like Tyrosine Kinase, a Receptor for Vascular Endothelial Growth Factor

Vascular permeability factor (VPF) is an Mr 40-kD protein that has been purified from the conditioned medium of guinea pig line 10 tumor cells grown in vitro, and increases fluid permeability from blood vessels when injected intradermally. Addition of VPF to cultures of vascular endothelial cells in vitro unexpectedly stimulated cellular proliferation. VPF promoted the growth of new blood vessels when administered into healing rabbit bone grafts or rat corneas. The identity of the growth factor activity with VPF was established in four ways: (a) the molecular weight of the activity in preparative SDS-PAGE was the same as VPF (Mr approximately 40 kD); (b) multiple isoforms (pI greater than or equal to 8) for both VPF and the growth-promoting activity were observed; (c) a single, unique NH2-terminal amino acid sequence was obtained; (d) both growth factor and permeability-enhancing activities were immunoadsorbed using antipeptide IgG that recognized the amino terminus of VPF. Furthermore, 125I-VPF was shown to bind specifically and with high affinity to endothelial cells in vitro and could be chemically cross-linked to a high-molecular weight cell surface receptor, thus demonstrating a mechanism whereby VPF can interact directly with endothelial cells. Unlike other endothelial cell growth factors, VPF did not stimulate [3H]thymidine incorporation or promote growth of other cell types including mouse 3T3 fibroblasts or bovine smooth muscle cells. VPF, therefore, appears to be unique in its ability to specifically promote increased vascular permeability, endothelial cell growth, and angio-genesis.

/pdf/tumor-vascular-permeability-factor-stimulates-endothelial-2rfp9vtvt6.pdf

Tumor vascular permeability factor stimulates endothelial cell growth and angiogenesis.

I. Introduction BASIC AND acidic fibroblast growth factors (FGFs) are closely related molecules that show a similar range of biological activities. They differ, however, in some of their physical and chemical properties and in their tissue distribution (1). Basic FGF [bFGF isoelectric point (pi) 9.6] was first identified by its ability to cause the proliferation and phenotypic transformation of BALB/c 3T3 fibroblasts (2, 3). Acidic FGF (aFGF, pi 5.6) was first identified by its ability to cause proliferation and delayed differentiation of myoblasts (4); it was later rediscovered on the basis of its ability to stimulate endothelial cell proliferation (5, 6). As expected from their structural relationship, both FGF and aFGF interact with the same receptor (7), thereby having similar, if not identical, properties. In contrast to aFGF, which has a cellular distribution more restricted than bFGF, many different cells synthesize bFGF, and essentially all have a specific high affinity receptor for this peptide. ...

Structural characterization and biological functions of fibroblast growth factor

The ability of heparin or that of hexuronyl hexosaminoglycan sulfate (HHS-4) to protect basic or acidic fibroblast growth factor (FGF) from acid or heat inactivation has been analyzed. Both freshly prepared basic and acidic FGF stimulate the growth of baby hamster kidney (BHK-21) cells exposed to medium supplemented with transferrin and insulin. Freshly prepared basic FGF was 10 fold more potent than acidic FGF. The addition of heparin to the medium decreased the potency of basic FGF while it potentiated that of acidic FGF. Upon storage of FGF at -80 degrees C, a decline in potency of both basic and acidic FGF was observed. Heparin, when added to the medium, potentiated their activities, which became similar to that of freshly prepared basic FGF. In order to test whether heparin could protect basic or acidic FGF from inactivation, both mitogens were exposed to acid conditions (1% trifluoroacetic acid, pH 1.08, 2 h) or heat (65 degrees C, 5 min) which inactivate basic or acidic FGF. When exposed to such treatment in the presence of heparin or HHS-4, basic and acidic FGF retained their potency. The effect of heparin and HHS-4 on the bioactivity of basic and acidic FGF is truly of a protective nature, since they had no effect when added after inactivation of the mitogens. Potentiation of the bioactivity of the protected mitogens or of the inactivated one could only be observed when cells were exposed to high heparin or HHS-4 concentrations. This indicates that heparin and HHS-4, in addition to protecting FGF from inactivation, also acts at another locus, as yet unidentified.

Heparin protects basic and acidic FGF from inactivation

Angiogenesis, the formation of new capillaries, which is observed in embryonic and injured tissue and is particularly prominent in the vicinity of solid tumours1, involves the migration and proliferation of capillary endothelial cells. It is probably triggered by agents, such as basic fibroblast growth factor (bFGF), thought to be released from tissues adjacent to proliferating capillaries1. As well as being a potent inducer of cell division in capillary endothelial cells in vitro, bFGF can act as an angiogenic agent in vivo2. It is present in a wide variety of richly vascularized tissues including brain, pituitary, retina, adrenal gland, kidney, corpus luteum, placenta and various tumours1–3. So far, however, the normal bFGF-producing cell species in these tissues have not been identified2,4. We report here that capillary endothelial cells express the bFGF gene, that they produce and release bFGF and that bFGF derived from them can stimulate the proliferation of capillary endothelial cells. We conclude that bFGF can act as a self-stimulating growth factor for capillary endothelial cells, and that it is possible that the formation of new capillaries is induced by capillary endothelial cells themselves.

Capillary endothelial cells express basic fibroblast growth factor, a mitogen that promotes their own growth

Bovine adrenal and brain cortex and corpus luteum-derived capillary endothelial cells have been established in culture, taking advantage of their ability to proliferate at clonal density when maintained on extracellular matrix (ECM) coated dishes in the presence of serum supplemented medium. All three cell types formed at confluency a monolayer of small, tightly packed, contact inhibited cells that express factor VIII related antigen. Their proliferative response to basic and acidic FGF when cells were maintained on plastic and exposed to serum supplemented medium was similar to that previously reported for endothelial cells derived from large vessels, with acidic FGF being 30-fold less potent than basic FGF. Their requirement for high density lipoproteins and transferrin in order to proliferate actively when maintained on ECM-coated dishes and exposed to serum-free conditions was also similar to that previously reported for endothelial cells derived from large vessels. Heparin strongly reduced the proliferative response of capillary endothelial cells to either basic or acidic FGF, as well as their response to serum alone, regardless of whether cells were maintained on plastic or on ECM-coated dishes. The present data indicate that bovine endothelial cells derived from large or small vessels are indistinguishable in so far as their response to growth factors, plasma factors, and substrata are concerned.

Effect of fibroblast growth factor and lipoproteins on the proliferation of endothelial cells derived from bovine adrenal cortex, brain cortex, and corpus luteum capillaries.

Bovine pituitary fibroblast growth factor has been purified 222,000-fold to homogeneity by a combination of differential salt extraction, gel filtration, and ion exchange chromatography on Mono S column. Pituitary FGF is a single-chain polypeptide with an apparent molecular mass of 15,800 and an isoelectric point of 9.6. It is highly active in triggering the proliferation of bovine and human vascular endothelial cell [half-maximal stimulation at 23–40 pg/ml (1.5–2.6 pM) and saturation between 140 and 280 pg/ml (9.3–18.6 pM)]. It displays a similar activity on bovine vascular smooth muscle cells, corneal endothelial cells, granulosa and adrenal cortex cells, and rabbit costal chondrocytes.

Isolation of pituitary fibroblast growth factor by fast protein liquid chromatography (FPLC): partial chemical and biological characterization.

MDCK Cells seeded on extracellular matrix- (ECM-) coated dishes and exposed to medium supplemented with high density lipoproteins (HDLs, 750 μg protein/ml) and transferrin (10 μg/ml) have a proliferative rate, final cell density, and morphological appearance similar to those of cells grown in serum-supplemented medium. The mitogenic stimulus provided by HDLs is not limited by the initial cell density at which cultures are seeded, nor is it limited in time, since cells grown in medium supplemented with transferrin and HDLs grew for at least 50 generations. The presence of HDLs in the medium is required in order for cells to survive, since cells actively proliferating in the presence of medium supplemented with HDLs and transferrin begin to die within 2 days after being transferred to medium supplemented only with transferrin. Low-density lipoprotein (LDL) is mitogenic for MDCK cells when present at low concentrations (from 2.5 to 100 μg protein/ml). Above 100 μg protein/ml, LDL is cytotoxic and therefore cannot support cell proliferation at an optimal rate. The mitogenic effect of HDLs is also observed when cells are maintained on fibronectin-coated dishes. However, the proliferative rate of the cells is suboptimal and cultures cannot be passaged on this substrate indefinitely, as they can be on ECM-coated dishes.



A close association between the ability of HDLs to support cell proliferation and their ability to induce the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase is observed. HMG CoA reductase activity is 18 times higher (70 pmoles/min /106 cells) in proliferating cells than in confluent, nondividing cells (4 pmoles/min /106 cells). The HMG CoA reductase activity of sparse cells is more sensitive to induction by HDLs (eight-fold higher than control cells) than is the enzyme activity of confluent cells (twofold higher than control levels). The dose-response relationships between the abilities of HDLs to support proliferation and to induce HMG CoA reductase activity are similar. The time course of the stimulation of proliferation and the increase in enzyme activity of sparse, quiescent cells after exposure to HDLs are parallel.



The HMG CoA reductase activity of sparse MDCK cells is induced six-fold by exposure to compactin, a competitive inhibitor of HMG CoA reductase. This induction of HMG CoA reductase is prevented by mevalonic acid, not affected by LDL, and synergistically enhanced by simultaneous exposure to HDLs. HDLs effect a rescue from the cytotoxic effect of compactin, whereas LDL does not. More specifically, cells proliferating in the presence of HDLs are 100 times more resistant to the toxic effects of compactin than are cells exposed to LDL. These results taken together suggest that the induction of HMG CoA reductase activity by HDLs may play a role in mediating the proliferative effect of HDLs. The significance of the increased mevalonate made available by higher levels of HMG CoA reductase appears not to lie in the bulk provision of cellular cholesterol, but rather in the provision of a specific pool of endogenously synthesized sterol, or in one or more of the nonsterol products of mevalonate. In cells that proliferate in response to HDLs, the induction of HMG CoA reductase activity appears to be a consistent and essential feature of a possibly pleiotypic metabolic response to HDLs.

Stimulation of the proliferation of the Madin-Darby canine kidney (MDCK) epithelial cell line by high-density lipoproteins and their induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity.

Monoclonal antibodies (McAbs) were developed that identify the complete (1-146 aa) and the NH2-terminal truncated (des 1-15) form of bovine basic fibroblast growth factor (bFGF). Four McAbs, designated McAbs 6, 8, 38, and 42, bind the complete form of bFGF found in bovine pituitary, brain, and adrenal gland. One of these McAbs, McAbs 42, also binds to the des 1-15 aa form of bFGF found in bovine adrenal gland, kidney, and corpus luteum. None of the McAbs binds bovine-brain-derived acidic FGF (aFGF). McAbs 6, 8, and 38 recognized the same epitope located within the first ten residues of the NH2-terminal of complete bFGF. McAb 42 recognizes a "core" epitope found on both the complete and des 1-15 aa bFGFs. The McAbs are murine IgGs with affinity constants of 10(7)-10(8) liter/M for bovine-pituitary-derived bFGF. McAbs 8 and 42 have been used in a two-site ELISA to detect the complete form of bFGF. The ELISA is sensitive to 38.5 fmole/well of bFGF and is not affected by the presence of calf serum or bovine-brain-derived aFGF. These McAbs should be useful in distinguishing the native and des 1-15 aa forms of bFGF from each other, and from aFGF and other growth factors.

Sharon L. Massoglia

Papers

Effect of fibroblast growth factor and lipoproteins on the proliferation of endothelial cells derived from bovine adrenal cortex, brain cortex, and corpus luteum capillaries.

Isolation of pituitary fibroblast growth factor by fast protein liquid chromatography (FPLC): partial chemical and biological characterization.

Stimulation of the proliferation of the Madin-Darby canine kidney (MDCK) epithelial cell line by high-density lipoproteins and their induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity.

Characterization of murine monoclonal antibodies directed against basic fibroblast growth factor.