Nuclear accumulation of epidermal growth factor in cultured rat pituitary cells.

Epidermal growth factor (EGF) is a mitogen for epidermal cells in vivo and for a wide variety of cells in culture. Recently, we and others have reported that EGF can also regulate the cellular levels of various hormones and fibronectin at concentrations which only minimally influence cell division. In addition, EGF treatment of GH3 cells affects chromatin structure such that isolated nuclei from treated cells have an increased capacity to bind bacterial RNA polymerase in initiation site complexes.

Permissive effect of the extracellular matrix on cell proliferation in vitro.

Corneal endothelial cells maintained in tissue culture retain the ability to synthesize and secrete an extracellular matrix (ECM) along their basal cell surface. Treatment of confluent cultures with 0.5% Triton X-100 results in the removal of the cell monolayer, thereby exposing the ECM, which adheres strongly to the tissue culture dish.

Role of the degradation process in the mitogenic effect of epidermal growth factor.

The protease inhibitor leupeptin inhibits the degradation process of (125)I-labeled epidermal growth factor ((125)I-EGF) by cultured bovine granulosa cells. At 80 mug/ml, leupeptin inhibited the appearance of degradation products of (125)I-EGF in the medium by 95% during 1 hr of incubation and by 90% during 24 hr of incubation when the cells were exposed to 5 ng of (125)I-EGF per ml. In contrast, cultures exposed to either saturating (10 ng/ml) or nonsaturating (0.

Morphological appearance, growth behavior and migratory activity of human tumor cells maintained on extracellular matrix versus plastic.

Growth of human tumor cells (hepatocarcinoma, Ewing's sarcoma) on an extracellular matrix (ECM) produced by bovine corneal endothelial cells is associated with the adoption of a morphological appearance and growth properties that are not expressed when the cells are maintained on plastic. Within minutes after seeding cell aggregates onto an ECM, the aggregates attached firmly. Active cell migration leading to the formation of flattened and nonoverlapping cell clusters was subsequently observed.

The extracellular matrix and the control of proliferation of vascular endothelial and vascular smooth muscle cells.

In this short review we describe the observations which have led us to conclude that one of the most important components involved in modulating cell proliferation in vitro, and probably in vivo as well, may be the extra-cellular matrix upon which cells rest.

Epidermal growth factor and expression of specific genes: effects on cultured rat pituitary cells are dissociable from the mitogenic response.

Cultured rat pituitary tumor cells, GH3/D6, which synthesize both growth hormone and prolactin, have cell-surface epidermal growth factor (EGF) receptor sites (34,000 per cell) that bind 125I-labeled EGF with a high affinity (Kd approximately 1 nM). Prolonged treatment of the cells with EGF did not stimulate cell division but did inhibit thyroid hormone-stimulated cell growth. In addition, EGF altered the morphology of the cells from a rounded to an elongated conformation.

Vascular endothelial cells maintained in the absence of fibroblast growth factor undergo structural and functional alterations that are incompatible with their in vivo differentiated properties.

Vascular endothelial cells cultured in the presence of fibroblast growth factor (FGF) adopt at confluence a morphological appearance similar to that of the vascular endothelium in vivo. Similarly, their apical cell surface is, as in vivo, nonthrombogenic. In contrast, when the cultures are maintained in the absence of FGF, the cells undergo within two to three passages structural and functional alterations that are incompatible with their in vivo morphological appearance and physiological function.

Characteristics of chylomicron binding and lipid uptake by endothelial cells in culture.

Bovine vascular endothelial cells bind chylomicrons via a high affinity membrane receptor site. Subsequent to binding, the chylomicron apoprotein was neither internalized nor degraded by either sparse or confluent (contact-inhibited) cells. However, the adsorption of chylomicrons was associated with interiorization of chylomicron cholesteryl ester and triglyceride and the hydrolysis of these lipids to free cholesterol and unesterified fatty acids by a lysosome-dependent pathway.

Inhibition of low density lipoprotein uptake in confluent endothelial cell monolayers correlates with a restricted surface receptor redistribution.

Binding of either low density lipoprotein (LDL) or Concanavalin A (ConA) to actively growing vascular endothelial cells is associated with a redistrubution of the appropriate cell surface receptor sites which form patches and caps. This receptor lateral mobility is greatly restricted when endothelial cells reach confluence and adopt the configuration of a cell monolayer composed of closely apposed and non-overlapping cells. In this case, although the cells still exhibit specific LDL binding to the appropriate cell surface receptor sites, neither the binding of LDL nor of ConA induces a receptor redistribution.

Appearance in confluent vascular endothelial cell monolayers of a specific cell surface protein (CSP-60) not detected in actively growing endothelial cells or in cell types growing in multiple layers.

The formation of a highly organized vascular and corneal endothelial cell monolayer is associated with the appearance of a 60,000-dalton cell surface protein (CSP-60) (30,000 daltons after reduction with dithiothreitol) which is not detectable in rapidly growing endothelial cells and in subconfluent cultures that do not yet exhibit the strict morphology of a confluent monolayer. It is also absent from vascular smooth muscle cells and from endothelial cultures that are maintained in the absence of fibroblast growth factor and grow on top of each other at confluence. After disorganization of cells in a confluent endothelial monolayer by urea, EDTA, or trypsin, CPS-60 is no longer exposed on the cell surface, but it reappears as soon as the cells readopt their characteristic two-dimensional configuration.

Effect of contact inhibition on the regulation of cholesterol metabolism in cultured vascular endothelial cells.

Cholesterol synthesis in actively growing bovine vascular endothelial cells is regulated by low density lipoprotein (LDL) at a step prior to mevalonate formation, in a manner comparable to that found in aortic smooth muscle cells. LDL uptake by these cells is associated with induction of cholesterol esterification, an increase in total cell cholesterol, and an inhibition of endogenous sterol synthesis. In contrast, cholesterol metabolism in confluent contact-inhibited endothelial cultures was not significantly affected by LDL even though the cells bind the lipoprotein at high affinity receptor sites.

Structural and functional alterations in the surface of vascular endothelial cells associated with the formation of a confluent cell monolayer and with the withdrawal of fibroblast growth factor.

Vascular endothelial cells cultured in the presence of fibroblast growth factor (FGF) divide actively when seeded at low or clonal cell densities and upon reaching confluence adopt a morphologic appearance and differentiated properties similar to those of the vascular endothelium in vivo. In this review, we present some of our recent observations regarding the characteristics (both structural and functional) of these endothelial cells and the role of FGF in controlling their proliferation and normal differentiation. At confluence the endothelial cells form a monolayer of closely apposed and nondividing cells that have a nonthrombogenic apical surface and can no longer internalize bound ligands such as low-density lipoprotein (LDL).

Epidermal growth factor induced membrane changes in 3T3 cells.

Epidermal growth factor (EGF) is a mitogen for Swiss 3T3 cells. Short incubation periods with physiological concentrations of EGF induced increased binding of Swiss 3T3 cells to Con A-coated nylon fibers. This effect was not induced in an EGF non-responsive 33 variant, in the transformed murine XC cells or in Swiss SV3T3 cells.

Role of contact inhibition in the regulation of receptor-mediated uptake of low density lipoprotein in cultured vascular endothelial cells.

Bovine vascular endothelial cells during logarithmic growth bind, internalize, and degrade low density lipoprotein (LDL) via a receptor-mediated pathway. However, contact-inhibited (confluent) monolayers bind but do not internalize LDL. This is in contrast to aortic smooth muscle cells or endothelial cells that have lost the property of contact inhibition.

Control of normal differentiation of myeloid leukemic cells. X. Glucose utilization, cellular ATP and associated membrane changes in D+ and D- cells.

Glucose utilization, energy metabolism and associated membrane changes, have been studied in D+ myeloid leukemic cells that can be induced to undergo cell differentiation to mature granulocytes by incubation with the appropriate conditioned medium (CM) and in D- myeloid leukemic cells that cannot be induced to differentiate to mature cells. Before incubation with CM, glycolysis and the glycolytic production of ATP were lower and the activity of the pentose cycle was higher in D+ than in D- cells. ATP depletion induced a higher degree of agglutination by concanavalin A in D- than in D+ cells, indicating a difference in their surface membrane.