Showing papers on "Growth factor receptor inhibitor published in 1979"

Biologically active phorbol esters specifically alter affinity of epidermal growth factor membrane receptors

Abstract: TPA (12-O-tetradecanoyl-phorbol-13-acetate) reversibly inhibits the binding of 125I-labelled epidermal growth factor (EGF) to treated mouse and human cells, but does not affect the binding of various other ligands to their membrane receptors. It alters the affinity of the receptors for EGF without changing the total number of available receptors per cell. Those phorbol esters which stimulate cell growth in culture and have tumour-promoting activity in vivo alter the EGF-receptor affinity, while the biologically inactive derivatives fail to change the affinity of EGF for its receptors.

Local aggregation of hormone-receptor complexes is required for activation by epidermal growth factor.

Abstract: An analogue of epidermal growth factor (EGF) which is virtually devoid of biological activity retains receptor binding activity but cannot form cell surface clusters or patches. Bivalent anti-EGF antibodies restore both bioactivity and patch formation. The sensitivity of fibroblasts to native EGF can also be enhanced greatly by these antibodies, especially in hormone-resistant cell lines.

Thrombin and epidermal growth factor become linked to cell surface receptors during mitogenic stimulation.

Abstract: THERE is much evidence that interaction with specific cell surface receptors is a key event in the action of polypeptide hormones and growth factors. Many analyses of hormone–receptor interactions have been carried out based on the assumption that hormone binding to the cell receptors is a reversible reaction1–3. Indeed, many studies have demonstrated that bound hormones dissociate from their receptors. However, in most systems the possibility could not be excluded that a significant fraction of the hormone molecules that bind to cells become linked to their receptors. Our present studies with the polypeptide mitogens 125I-thrombin and 125I-epidermal growth factor (125I-EGF) show that a significant percentage of the molecules that are specifically bound on human fibroblasts become linked to cell surface receptors. This finding has broad implications for the way in which these molecules might stimulate cell division. It also raises the question of whether linkage of polypeptide hormones to their receptors is a general phenomenon.

Epidermal growth factor receptors increase during the differentiation of embryonal carcinoma cells.

Abstract: Mouse teratocarcinoma stem cells (embryonal carcinoma, or EC cells) bind very small amounts of mouse epidermal growth factor (EGF) and the latter hormone seems to have no stimulatory effect on the growth of two cloned lines of EC cells. However, when EC cells are induced to differentiate into large flat endodern-like cells (END cells), EGF receptors increase in number reaching a plateau in 6 to 8 days. At 8 to 10 days after induction, END cells multiply very slowly, but when EGF is added (3×10−10 M) to the medium, cell division is stimulated and a further change in morphology occurs. This letter describes the binding characteristics and numbers of the EGF receptors on EC and END cells and shows that exogenous retinoic acid increases the numbers of EGF receptors on END cells. We were unable to find endogenous competing factors produced by EC cells. Such factors could account for the lack of detectable binding of EGF on these cells. As EC cells differentiate to END cells, so the ability of the cells to form tumours is reduced1,2. Since this change is accompanied by an increase in the number of EGF receptors there may be a relationship between these two events.

Direct linkage of epidermal growth factor to its receptor.

Abstract: EPIDERMAL GROWTH FACTOR (EGF), a potent polypeptide mitogen, has been studied intensively by those concerned with the molecular events leading to cell proliferation1–4. The initial, reversible interaction of EGF with a specific cell surface receptor and the subsequent internalisation and degradation of EGF, and by inference the EGF–receptor complex, are well documented, although the role of these events in mitogenesis is unknown4–6. In an attempt to define this role, we used photoaffinity probes to specifically cross-link radiolabelled EGF to its receptor, a 185,000-dalton polypeptide on the surface of murine 3T3 cells7. These probes also enabled us to follow the metabolic fate of this receptor8. We have since noted that a small portion of the underivatised radiolabelled EGF that binds specifically to 3T3 cells or isolated 3T3 cell membranes becomes directly and irreversibly linked to a polypeptide of molecular weight (MW) 185,000. Here, we document this association and show that the resulting complex has properties identical to those of the EGF-receptor complex originally identified by photoaffinity labelling.

Isolation of the human placenta receptor for epidermal growth factor-urogastrone.

Abstract: EPIDERMAL growth factor-urogastrone (EGF-URO), a singlechain polypeptide of molecular weight ∼6,000, found both in the mouse1–3 and in man4–7, is both a potent stimulant of cell proliferation and an inhibitor of gastric acid secretion. Specific membrane receptors for EGF-URO can be detected in various tissues including human placenta8–11. Although the mouse and human polypeptide sequences differ at 16 positions, they can share the same receptor site in human tissues3,12. There has been considerable recent interest in EGF-URO and its receptor, not only because of the potent mitogenic and acid-inhibitory actions of the polypeptide, but also because of the association of viral13, chemical14 and spontaneous15 cell transformation with a specific reduction in cell receptors for EGF-URO. It is also believed that EGF-URO and its receptor may be involved in the development, maintenance, and differentiation of tissues as diverse as the lens16, the palate17 and the keratin layer of skin18. In experiments aimed at the isolation of the membrane receptor for EGF-URO, we have observed that, unlike the receptor for insulin19, but like the muscarinic receptor for acetylcholine20, the EGF-URO receptor loses its ligand recognition property following solubilisation with detergents. We therefore developed an affinity-labelling technique using glutaraldehyde, that can covalently crosslink the receptor with 125I-labelled EGF-URO before solubilisation21. Independently, Das and coworkers have developed a photoaffinity-labelling technique that can also be used to radiolabel the EGF-URO receptor before solubilisation22. Here we report the success of both our previously described glutaraldehyde crosslinking technique21 (using 125I-EGF-URO for receptor labelling) and of a newly developed photoaffinity-labelling technique (using a photolabile 125I-EGF-URO crosslinking reagent) to identify the EGF-URO receptor in human placenta membranes and to effect the isolation of the affinity-labelled receptor by affinity chromatography using lectin and murine EGF-URO antibody–Agarose columns.

Antitubulin agents enhance the stimulation of DNA synthesis by polypeptide growth factors in 3T3 mouse fibroblasts

Abstract: Colchicine and other antitubulin agents markedly enhanced the stimulation of DNA synthesis by combinations of various growth factors such as epidermal growth factor, insulin, fibroblast-derived growth factor, and vasopressin in serum-free cultures of several quiescent 3T3 mouse fibroblast cell lines. Enhancing effects were observed based on continuous incorporation of [3H]thymidine into DNA as well as by autoradiographic labeling of cell nuclei. The concentration of colchicine and podophyllotoxin required to produce half-maximal enhancement of DNA synthesis stimulated by epidermal growth factor and insulin was 25-50 nM. Lumicolchicine did not produce enhancing effects. The disassembly of microtubules resulting from the action of colchicine, Colcemid, and vinblastine did not inhibit the stimulation of DNA synthesis in quiescent Swiss 3T3 fibroblasts by fetal bovine serum. We conclude that the cytoplasmic microtubule network in 3T3 mouse fibroblasts does not exert a positive regulatory function in the initiation of DNA synthesis but rather can produce a constraint on the initial action of the peptide growth factors in serum-free media.

Binding, internalization, and degradation of epidermal growth factor by balb 3T3 and BP3T3 cells: relationship to cell density and the stimulation of cell proliferation.

Abstract: Epidermal growth factor (EGF) stimulates the growth of both benzo[a]pyrene-transformed Balb 3T3 cells (BP3T3) and untransformed Balb 3T3 cells. We describe here the binding, internalization, and degradation of [125I]-EGF by BP3T3 cells and 3T3 cells. Binding of [125I]-EGF reaches a maximum after 45 to 90 minutes incubation at 37 degrees C. In both BP3T3 and 3T3 cells the extent of EGF binding required to stimulate DNA synthesis is density dependent; sparse cultures require a 15-30% occupancy to elicit a maximal response whereas dense cultures require a 70-85% occupancy. At physiological concentrations the total binding of [125I]-EGF to 3T3 cells is higher than to BP3T3 cells, and this difference increases at higher cell densities. The rate of degradation of [125I]-EGF is directly proportional to the total [125I]-EGF binding in each cell type. This supports the hypothesis that one cause of the diminished serum requirement of BP3T3 cells is a reduced rate of utilization of serum growth factors.

Platelet-derived growth factor prevents G0 growth arrest

Abstract: Baserga1 has summarised evidence that there are two growth states in which cells have a diploid content of DNA; G1—the interval between mitosis and S phase in exponentially growing cultures—and G0, a quiescent state entered only when conditions for growth are suboptimal. G0 can be distinguished from G1 by temporal measurements; for BALB/c 3T3 cells, the lag time between G0 and S phase is never shorter than 12 h (ref. 2), whereas in exponentially growing cells the mean lag time between mitosis and S (G1 by definition) lasts 5–6 h (ref. 3). G0 can also be distinguished from G1 by some biochemical parameters including G0- and G1-specific intracellular proteins4,5. SV40- or polyoma virus-transformed cells cannot enter G0 to become quiescent6–9. Serum induces the growth of BALB/c 3T3 cells in tissue culture. It sustains the growth of exponentially replicating populations, and causes density-inhibited cells to leave G0 and replicate10–12. Serum contains several sets of hormonal growth factors which have recently been defined2,13,14. One of these hormones, the platelet-derived growth factor (PDGF), is released into serum during the clotting process; PDGF is absent in platelet-poor plasma, the liquid portion of unclotted blood15–19. It promotes the growth of G0-arrested cells2,16 by stimulating cells to become ‘competent’ to enter the S phase2; plasma allows these competent cells to progress through G0/G1, synthesise DNA2,20 and divide13. We now show that PDGF has a second function. It prevents replicating cells from entering G0.

Desensitisation of cultured glial cells to epidermal growth factor by receptor down-regulation.

Abstract: Epidermal growth factor (EGF), which can be purified from the mouse submaxillary gland or from pregnant human urine, is a potent multiplication-stimulating factor for several types of cultured cells, including human fibroblasts and glial cells. The molecule binds with high affinity and saturation kinetics to a cell-surface receptor, is subsequently internalised and finally degraded. The binding event is accompanied by a reduction in the number of EGF receptors. This phenomenon--'receptor down-regulation'--has been demonstrated with several hormones and may be a general principle for the modulation of binding groups on the outer cell surface. Further, it has been proposed that receptor loss acts to regulate the cellular response to the binding ligand. The present study provides direct experimental support for this hypothesis. It demonstrates that down-regulation of EGF receptors on glial cells causes desensitisation of the mitogenic response of these cells to subsequent stimulation with EGF.

Epidermal growth factor stimulates proliferation of rat hepatoma cells producing α-fetoprotein

Abstract: Epidermal growth factor stimulated both [3H]thymidine uptake and proliferation of rat AH66 hepatoma cells. However, the increase in cell number was not accompanied by a proportional increase in the levels of α-fetoprotein of the culture media. The effects of EGF on the cell proliferation were antagonized by N6, O2′-dibutyryl cAMP.

Mitogenic effects of murine serum and fibroblast growth factor on EGF nonproliferative variants of 3T3.

Abstract: The enhanced ability of murine serum to support growth of 3T3 cells, when compared with fetal calf serum, is also evident on variants of 3T3 cells lacking the ability to bind epidermal growth factor (EGF). Variant 3T3 cell lines unable to bind EGF also retain a mitogenic response to fibroblast growth factor.