Role of microexudate carpet in cell division

Self-assembled composite matrix in a hierarchical 3-D scaffold for bone tissue engineering

It is of high clinical relevance in bone tissue engineering that scaffolds promote a high seeding efficiency of cells capable of osteogenic differentiation, such as human bone marrow-derived mesenchymal stem cells (hMSCs). We evaluated the effects of a novel polycaprolactone (PCL) scaffold on hMSC seeding efficiency, proliferation, distribution and differentiation. Porous PCL meshes prepared by fused deposition modeling (FDM) were embedded in matrix of hyaluronic acid, methylated collagen and terpolymer via polyelectrolyte complex coacervation. Scaffolds were cultured statically and dynamically in osteogenic stimulation medium for up to 28 days. Compared to naked PCL scaffolds, embedded scaffolds provided a higher cell seeding efficiency (t-test, P<0.05), a more homogeneous cell distribution and more osteogenically differentiated cells, verified by a more pronounced gene expression of the bone markers alkaline phosphatase, osteocalcin, bone sialoprotein I and bone sialoprotein II. Dynamic culture resulted in higher amounts of DNA (day 14 and day 21) and calcium (day 21 and day 28), compared to static culture. Dynamic culture and the embedding synergistically enhanced the calcium deposition of hMSC on day 21 and day 28. This in vitro study provides evidence that hybrid scaffolds made from natural and synthetic polymers improve cellular seeding efficiency, proliferation, distribution and osteogenic differentiation.

Delayed growth and maturation of astrocytic cultures following exposure to ethanol: electron microscopic observations

This investigation examined the effects of ethanol on the morphologic features of cultured rat astrocytes using a treatment paradigm that provided consistent exposure to ethanol at concentrations of 0.2%, 0.5%, or 1.0% (w/v). Cultures were assessed between 4 and 8 days in vitro during the logarithmic phase of growth; differences in culture growth, cell profile area and ultrastructural configuration were found. A dose-dependent inhibition of culture growth was observed after 48 and 96 h of ethanol exposure. In control cultures, the consequences of culture growth included the progressive crowding of cells, a concomitant reduction in the cell profile area, and increased cell-cell contact. On culture day 8, electron microscopic examination of control cultures demonstrated a complex stratified cellular layer, the junction of cells by puncta adhaerentia and the acquisition of intermediate filament bundles. In contrast, the impaired growth in ethanol-exposed cultures was associated with the retention of an extensive cell profile area suggesting restrained morphologic development. At the electron microscopic level, ethanol-exposed cultures showed a dose-dependent attenuation in both the depth and complexity of the cell layer. These findings indicated that the growth kinetics and morphologic development of astrocytic cultures are vulnerable to ethanol exposure at moderate and high levels. These findings were attributed to both ethanol cytotoxicity and a deprivation of cellular interaction resulting from the restricted population size.

Morphological and immunocytochemical studies of fibronectin-coated, plasma membrane-limited vesicles in the early chicken embryo

Vesticles with a mean outside diameter of 32.8 nm have been observed in the early chicken embryo after fixation with a mixture of glutaraldehyde and tannic acid. Densitometric tracing has revealed that the vesicles are limited by a unit membrane. The presence of complex carbohydrates is suggested by the increased electron density of the vesticles after addition of tannic acid to the fixative. Immunocytochemical staining with a monoclonal antibody directed against chicken cellular fibronectin demonstrated the presence of this glycoprotein along the surface of the vesicles. These results suggest a cellular origin of the vesicles, since their surface shares morphological and biochemical similarities with the cell surfaces of the embryonic tissue layers. Recycling of plasma-membrane vesicles may occur, as vesicles were found in the vicinity of coated vesicles. We postulate that extracellular materials of the cell surface, which may affect cell and tissue interactions, are shed in the environment together with plasma-membrane vesicles. The difficulties encountered in observing the vesicles stems from the facts that an adequate visualization method is necessary and that they are few in number. The latter reason suggests their transient nature. The vesicles probably rapidly disintegrate in the extracellular milieu or are recycled by the cell surface.

In vitro growth potential of fibroblasts isolated from pigs with radiation-induced fibrosis

Degenerative processes were studied in pig muscles irradiated with single doses of 30 or 40 Gy. Damaged muscle was gradually replaced by an invasive fibrotic tissue. As a control, surgical muscle exeresis was performed of the same size as the radiation-induced lesions at the same anatomical site. Primary cultures were set up comprising cells freshly extracted from normal dermis, or from tissue exhibiting either normal wound fibrosis or radiation-induced fibrosis. The growth potential of cells taken from the latter region far exceeded that of the two other types; attachment efficiency was higher, and fibronectin was detected early by immunofluorescence. These in vivo and in vitro observations imply that a pathological repair process occurs after localized irradiation.

Primary glial cells and brain fibroblasts: interactions in culture

Primary glial-enriched cultures were prepared from newborn mouse cerebral hemispheres. The cultures were grown in Dulbecco's Modified Eagle Medium in which L-valine was substituted with D-valine; this medium selectively inhibits the growth of fibroblasts. Using glutamine synthetase and glial fibrillary acidic protein as immunocytochemical markers, cultures in D-valine medium were characterized as being over 80% astrocytic. However, these cultures exhibited a suppressed growth rate and lagged behind in their differentiation as assessed biochemically using DNA content and glutamine synthetase activity as markers for growth and differentiation. Growth was restored when D-valine cultures were grown in medium containing conditioned medium derived from brain fibroblast cultures when grown on matrix or killed substrata derived from brain fibroblast cultures. This in vitro approach offers the possibility of purifying factors and developing immunological probes to investigate the possible role of brain fibroblasts in influencing glial cell function.

Plasma membrane potential of murine erythroleukemia cells: approach to measurement and evidence for cell-density dependence

The plasmamembrane potential (delta psi p) of murine erythroleukemia (MEL) cells has been determined by measuring the distribution of the lipophilic cation tetraphenylphosphonium (TPP+) across the plasmamembrane. TPP+ accumulation within the cells (experimental accumulation ratio, AR exp) was measured by adding 2 microM TPP+ directly to the culture flasks, avoiding any other perturbation of the experimental system. The mitochondrial contribution to AR exp, evaluated by adding carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) or 2,4-dinitrophenol (DNP), was apparently negligible in standard cultures, AR exp being substantially the same in either the absence or presence of these uncouplers. However, the addition of oligomycin produced a strong AR exp enhancement, which was abolished by FCCP, suggesting that MEL cell mitochondria are in state 3. The aspecific TPP+ binding was estimated by a new mathematical approach worked out to fit AR exp values measured in the presence of valinomycin at various extracellular K+ concentrations and plotted against the ratio of intracellular to extracellular K+ concentration ([K+]i/[K+]e). This binding was found to be close to zero in MEL cells. By applying the Nernst equation directly to AR exp values, delta psi p of these cells was then measured; this potential varying from -65 mV to -16 mV (inside negative) is inversely related to the cell density on the culture surface on which the cells sediment (cells/cm2; CD). The dependence of delta psi p on CD is practically eliminated by valinomycin and appears to be related to a cell interaction with the culture surface of the flasks, suggesting that in the immediate environment of MEL cells one or more factors are produced that modulate the K+ plasma membrane permeability (PK).

Paracrine regulation of mammary gland growth

The growth and differentiation of the mammary gland is a complex process involving the interactions of various steroid and polypeptide hormones. The mammary growth occurs in a discontinued way during five distinct phases, i.e. fetal, prepubertal, postpubertal, pregnancy, and early lactation periods. The gland expresses its differentiated function by producing milk during the period of lactation. Although the mammary gland has been regarded as one of the well-known target tissues for various types of hormones, evidence has been accumulating in recent years indicating the involvement of other factors and substances in the process of mammary growth and differentiation. In this chapter the importance of the mesenchymal component in mammary epithelial cell growth has been documented. This component, including embryonic mesenchyme and adipocytes in adult tissue, play an essential role by not only serving as a structural entity of the gland but also by producing extracellular matrix substances and various factors that promote the growth, morphologic development and differentiation of mammary epithelium in a paracrine fashion. Other possible paracrine peptide factors for mammary cell growth have been isolated from several other sources including mammary tumors and milk. Thus, it is possible that paracrine growth factors play a role in mammary tumorigenesis. Since most of these factors are present in minute amounts, it is difficult to obtain pure forms of these factors in sufficient amounts for detailed physicochemical characterization. Moreover, further studies are needed to assess the physiological importance of these growth factors, their mode of action, and the mechanism of regulation relating to their production. It is conceivable that some mammary paracrine agents interact with each other or with endocrine agents in promoting the normal and neoplastic growth of mammary cells. Furthermore, the possibility exists that the production and release of paracrine factors are under the endocrine control. In view of the rapid progress and great interest in this area, these questions may be answered before long, along with the discovery of some other new growth regulating agents in this system. Clearly such information is important for understanding the complex process of normal and neoplastic growth of the mammary gland.

The effect of prolactin on human BPH epithelial cell proliferation

Epithelial cell monolayers derived from specimens of human benign prostatic hyperplasia (BPH) tissue by an explant culture technique were cultured with prolactin in the presence and absence of androgens. Proliferation of the cells was measured by both autoradiographic assessment of [3H]-thymidine uptake and stathmokinetic procedures. Prolactin significantly stimulated the growth of these cells in the concentration range 0.5 mIU/ml to 10 mIU/ml but was inhibitory at a concentration of 100 mIU/ml. In the presence of testosterone (1 X 10(-7) M), prolactin at low concentrations (greater than 1 mIU/ml) but not at 10 mIU/ml, the concentration at which all other experiments were performed, produced a further stimulation in the proliferation. The increase in growth seen with cells cultured with 5 alpha-dihydrotestosterone (1 X 10(-7) M) was reduced with addition of prolactin at high concentrations (10-100 mIU). When the fetal calf serum used in the cultures was stripped of endogenous steroids, prolactin still increased cell proliferation, although to a reduced extent. This indicated that the effects of prolactin were not dependent on the presence of androgens.

3T3-L1 adipocytes promote the growth of mammary epithelium

Murine mammary epithelium grows in association with predominantly adipocyte stroma in vivo. To investigate potential growth-promoting effects of adipocytes on mammary epithelium, we developed a co-culture system of mammary epithelium and adipocytes by taking advantage of the 3T3-L1 cell line. These cells undergo adipocyte differentiation when the culture reaches confluence and growth ceases. Mid-pregnant murine mammary epithelium was plated on lethally irradiated feeder layers of 3T3-L1 adipocytes, undifferentiated 3T3-L1 cells, 3T3-C2 fibroblasts (a subclone of 3T3 cells that does not undergo adipocyte differentiation), or tissue culture plastic. Mammary epithelial colony size on adipocyte feeder layers was 2-fold larger than colonies on 3T3-C2 cells and 4-fold larger than colonies on tissue culture plastic. Measurement of tritiated thymidine [3H]TdR incorporation and labelling index in mammary cells was significantly higher on adipocytes than on other feeder layers or plastic. There was a 6-fold increase in mammary cell number after 5 days in culture when mammary epithelium was plated on substrate-attached material ('extracellular matrix') derived from 3T3-L1 cells and a 4-fold increase in cell number when plated on plastic in conditioned medium derived from 3T3-L1 adipocytes compared with growth on plastic in unconditioned medium. We conclude that interaction of mammary epithelium with adipocytes results in a marked increase in proliferation of mammary epithelium and that extracellular components may mediate this effect.

Growth factors and their action in vivo and in vitro

The molecular nature and mechanism of action of several of the growth factors including epidermal growth factor, fibroblast growth factor and platelet-derived growth factor is reviewed. The ectopic production of growth factors may be important in the growth development of certain tumours. In addition, attention is directed to the importance of the extracellular matrix in controlling cell proliferation and differentiation.

Haploid plants from in vitro anther culture of Annona squamosa Linn

Haploid plants were induced from anther callus of Annona squamosa Linn. (Custard apple) on a Nitsch basal medium supplemented with 6-benzyl-aminopurine and naphthalene acetic acid. When naphthalene acetic acid was replaced by indole-3-acetic acid only multiple shoots were obtained. Pretreatment (chilling, centrifugation, reduced atmospheric pressure etc.) of the flowers was not effective but dissection of the flowers in a suspension of activated charcoal and sucrose was found essential. The anthers required an initial dark period and a high sucrose medium followed by light and lowered sucrose levels. Root tip squashes of the regenerated plantlets revealed the haploid (n = 7) nature of the plantlets.

Are factors originating from serum, plasma, or cultured cells involved in the growth-promoting effect of the extracellular matrix produced by cultured bovine corneal endothelial cells?

The possibilities that the growth-promoting effect of the extracellular matrix (ECM) produced by cultured bovine corneal endothelial (BCE) cells could be due to: (1) adsorbed cellular factors released during the cell lysis process leading to the denudation of the ECM; (2) adsorbed serum or plasma factors: or (3) adsorbed exogenous growth factors have been examined. Exposure of confluent BCE cultures to 2 M urea in medium supplemented with 0.5% calf serum denudes the ECM without cell lysis. The ECM prepared by this procedure supports cell growth just as well as ECM prepared by denudation involving cell lysis. Thus, it is unlikely that the growth-promoting properties of ECM are due to adsorbed cellular factors. When the ECM produced by BCE cells grown in defined medium supplemented with high-density lipoprotein, transferrin, and insulin was compared to the ECMs produced by cells grown in the presence of serum- or plasma-supplemented medium, all were found to be equally potent in stimulating cell growth. It is therefore unlikely that the growth-promoting ability of the ECM is due to adsorbed plasma or serum components. When fibroblast growth factor (FGF)-coated and ECM-coated plastic dishes were submitted to a heat treatment (70 degrees C, 30 min) which results in the inactivation of FGF, the growth-supporting ability of FGF-coated dishes was lost, while the comparable ability of ECM-coated dishes was not affected significantly. This observation tends to demonstrate that the active factor present in the ECM is not FGF. Nor is it platelet-derived growth factor (PDGF), since treatment known to destroy the activity of PDGF, such as exposure to dithiothreitol (0.1 M, 30 min, 22 degrees C) or to beta-mercaptoethanol (10%) in the presence or absence of 6 M urea for 30 min at 22 degrees C, does not affect the growth-promoting activity of ECM. It is therefore unlikely that the growth-promoting effect of ECM is due to cellular growth-promoting agents or to plasma or serum factors adsorbed onto the ECM.

Effect of substrata and fibroblast growth factor on the proliferation in vitro of bovine aortic endothelial cells

The hypothesis that, in the case of clonal or low-density cultures, cells which do not readily proliferate are those that do not produce an extracellular matrix (ECM), while those that proliferate actively are cells that have retained their ability to produce it, has been tested using low-density vascular endothelial cell cultures maintained on either plastic or ECM-coated dishes and exposed to various combinations of media and sera. Proliferation of low-density vascular endothelial cell cultures seeded on plastic and exposed to DMEM, RPMI-1640, or medium 199 plus thymidine is a function of the batch of calf serum used to supplement the various media. In all three cases, such cultures proliferated at a slow rate and fibroblast growth factor (FGF) greatly accelerated their proliferation. In contrast, when similar cultures were seeded on ECM-coated dishes, they actively proliferated regardless of the batch of calf serum to which they were exposed. FGF was no longer required in order for cultures to become confluent. In the case of cultures exposed to RPMI-1640 or medium 199 plus thymidine, it was even toxic. When cultures were exposed to either medium 199 or Waymouth medium, cells did not proliferate, regardless of the substrate (either plastic or ECM) upon which they were maintained and of the batch of serum to which they were exposed. Addition of FGF to such media had no effect. It is therefore likely that nutrient limitations in both of these media restrict the ability of low-density vascular endothelial cells to respond to the mitogenic stimuli provided by either serum or FGF. These restrictions cannot be relieved by maintaining cells on ECM-coated dishes, and modifications of the nutrient composition of both media is required in order to allow cells to respond to either FGF or serum when maintained on plastic or to serum alone when maintained on ECM. These results suggest that, when low-density cell cultures are maintained on plastic and exposed to an adequate medium, their proliferation will be a function of both serum and FGF. When maintained on ECM, their proliferation will depend only on serum. It is therefore possible that the inability of serum to stimulate optimal cell proliferation when cells are maintained on plastic results from an inability of the cells to produce an ECM, and that FGF could induce such production.

Presence of epidermal growth factor receptors and influence of epidermal growth factor on proliferation and aging in cultured smooth muscle cells

Epidermal growth factor (EGF) at nanomolar concentrations stimulated DNA synthesis in confluent, serum-starved cultures of calf aorta and human uterine smooth muscle cells. Stimulation of DNA synthesis in lens epithelial cells was studied for comparison. L and D-ascorbic acid potentiated the effect of serum and EGF on DNA synthesis in calf aorta cells. In contrast L-ascorbic acid had minimal potentiating effect with serum and no effect with EGF present along with serum on DNA synthesis in human uterine smooth muscle and rabbit lens epithelial cells. EGF and ascorbic acid increased cell number when added to stationary phase cultures. Specific binding of 125I-labelled EGF to smooth muscle cells was demonstrated. Receptor concentration in calf-aorta smooth muscle cells was higher in dense cultures compared to sparse cultures. The time course of binding and dissociation of 125I-labelled EGF was similar in "dense" and "sparse" cultures. Human uterine smooth muscle cells in culture exhibited a finite lifespan. There was no stimulation of DNA synthesis in response to serum and EGF in cells of high population doubling level (PDL); although 125I-labeled EGF binding was higher in old cells (high PDL) compared to young cells (low PDL). This increase in binding was shown to be due to changes in the concentration of receptors without changes in their affinity for EGF.

In vitro studies on the self-differentiating capacities of quail adenohypophysis epithelium

Isolated epithelial rudiments of 3--4 days quail embryo adenohypophysis were cultivated in vitro. Differentiation of glandular cells occurred when culture conditions allowed the formation of explants characterized by the presence of a fibroblastic sheet and of an epithelial roof surrounding a central cavity. Differentiation did not occur when culture conditions did not allow the fibroblastic sheet to be established or resulted in the absence of a cavity. The importance of the explant structure in differentiation is also indicated by the location of glandular cells. In vitro they differentiate near the cavity derived from Rathke's pouch lumen while in situ they first appear at the periphery of the rudiment, near the basement membrane. The results of this study show that the adenohypophyseal primordium can differentiate without any mesenchymal influence. The observed differentiation seems to be correlated with fibroblast-secreted material, and this hypothesis is discussed.

Glycoproteins and human cancer. 1. Circulating levels in cancer serum

Total protein and sialic acid levels were determined in the supernatant of serum treated with perchloric acid. Patients with either localized or advanced metastatic malignancy have significantly elevated mean serum values. The highest levels occur in patients with lung, GI, GYN cancer, lymphoma and malignant melanoma. Patients with leukemia and multiple myeloma have slightly elevated values, but they were not significantly different from normal. Patients following curative surgery have normal values while patients in clinical remission following chemotherapy have elevated mean serum protein and NANA levels. Elevated values also occur in patients with benign tumors and 12% of patients with nonmalignant disease. Tumor cells appear to shed macromolecules which contribute to the observed elevation of serum protein and sialic acid levels.

Two functionally distinct pools of glycosaminoglycan in the substrate adhesion site of murine cells

Footpad adhesion sites pinch off from the rest of the cell surface during EGTA-mediated detachment of normal or virus-transformed murine cells from their tissue culture substrates. In these studies, highly purified trypsin and testicullar hyaluronidase were used to investigate the selective destruction or solubilization of proteins and polysaccharides in this substrate-attached material (SAM). Trypsin-mediated detachment of cells or trypsinization of SAM after EGTA-mediated detachment of cells resulted in the following changes in SAM composition: (a) solubilization of 50-70% of the glycosaminoglycan polysaccharide with loss of only a small fraction of the protein, (b) selective loss of one species of glycosaminoglycan-associated protein in longterm radiolabeled preparations, (c) no selective loss of the LETS glycoprotein or cytoskeletal proteins in longterm radiolabeled preparations, and (d) selective loss of one species of glycosaminoglycan-associated protein, a protion of the LETS glycoprotein, and proteins Cd (mol wt 47,000 and Ce' (mol wt 39,000) in short term radiolabeled preparations. Digestion of SAM with testicular hyaluronidase resulted in: (a) almost complete solubilization of the hyaluronate and chondroitin sulfate moieties from long term radiolabeled SAM with minimal loss of heparan sulfate, (b) solubilization of a small portion of the LETS glycoprotein and the cytoskeletal proteins from longterm radiolabeled SAM, (c) resistance to solubilization of protein and polysaccharide in reattaching cell SAM which contains principally heparan sulfate, and (d) complete solubilization of the LETS glycoprotein in short term radiolabeled preparations with no loss of cytoskeletal proteins. Thus, there appear to be two distinct pools of LETS in SAM, one associated in some unknown fashion with hyaluronate-chondroitin sulfate complexes, and a second associated with some other component in SAM, perhaps heparan sulfate. These data, together with other results, suggest that the cell-substrate adhesion process may be mediated principally by a heparan sulfate--LETS complex and that hyaluronate-chondroitin sulfate complexes may be important in the detachability of cells from the serum-coated substrate by destabilizing LETS matrices at posterior footpad adhesion sites.

High molecular weight, cell surface-associated glycoprotein (fibronectin) lost in malignant transformation

Fibronectin is a polymorphic glycoprotein found in blood and tissues of vertebrates and in cultures of adherent vertebrate cells. There are several forms of fibronectin is composed of two high molecular weight subunits held together by forms found in tissues and on and around the surfaces of cultured cells. Soluble fibronectin is composed of two high molecular weight subunits held together by disulfide bonds. Insoluble fibronectin may be covalently cross-linked in larger complexes. Fibronectin has affinities for collagen, fibrin, heparin, and cell surfaces. In culture, fibronectin in growth medium may mediate attachment of cells to substratum, and fibronectin synthesized by cells may mediate adhesion to substratum. The widespread occurrence of fibronectin in basal lamina indicates that may different cell types in vivo abut against a fibronectin-containing matrix. Cultured transformed cells usually lack cell-surface fibronectin, also called large, external transformation-sensitive (LETS) protein. The failure of transformed cells to synthesize or bind fibronectin is paralleled (at least in some systems) by failures to synthesize or bind collagen and proteoglycans. Abnormal synthesis of fibronectin and other matrix components and abnormal interactions with the tissue matrix may account for several phenotypic characteristics of transformed cultured cells and for some of the malignant behavior of neoplastic cells in vivo.

The substrate attached material synthesized by clonal cell lines of nerve, glia, and muscle

A large number of clonal cell lines were examined for the deposition of proteins (substrate attached material, SAM) on the substratum of culture dishes. Of the many cell types examined, only nerve, muscle, and glia synthesized SAM containing a predominant species of protein with a apparent molecular weight of 55,000. This 55,000 molecular weight protein is distinguishable from actin, tubulin, and collagen.

The synthesis of macromolecular 3-hydroxyproline by attaching and confluent cultures of human fibroblasts

The synthesis of collagen has been studied during the attachment of freshly trypsinized human fibroblasts to culture vessels by measurement of the incorporation of radioactive proline into macromolecular hydroxyproline. Collagenous protein(s) was found to be a component of a substrate-attached material ('microexudate carpet') synthesized rapidly during cell attachment in the absence of serum. The ratio of 3-hydroxyproline/4-hydroxyproline in the collagenous proteins synthesized during cell attachment was found to be 4-5 fold higher than that of normal type I collagen. The synthesis of 3-hydroxyproline by confluent cultures was diminished by serum deprivation, and was shown to require higher concentrations of ascorbate than the synthesis of the 4-hydroxy isomer.

Stimulation of clonal growth of normal fibroblasts with substrata coated with basic polymers

Improved media have reduced the amount of serum protein required for clonal growth of normal human and chicken fibroblast-like cells. In the presence of limiting amounts of serum protein, attachment of colonies to tissue culture plastic surfaces is weak. Treatment of the culture surface with polylysine or other basic polymers causes the cells to adhere much more tightly. Growth is also improved on the surfaces treated with basic polymers, and further reductions in the concentration of serum as possible. At sufficiently low protein concentrations, growth of some types of cells is totally dependent on the use of a treated surface. Several different types of normal human and chicken fibroblast-like cells show improved growth on polylysine-coated surfaces, but no improvement was obtained in growth of a line of SV-40 transformed WI-38 cells. Acidic and neutral polymers are generally inactive. Collagen and gelatin improve growth slightly, but the effect is much less than that obtained with basic polymers. Both natural and synthetic polymers with an excess of basic groups are active, including histone, polyarginine, polyhistidine, polylysine, polyornithine, and protamine. The only critical requirement appears to be a polymer that carries a positive charge at a physiological pH.

Enhanced synthesis and extracellular accumulation of hyaluronic acid during stimulation of quiescent human fibroblasts by mouse epidermal growth factor

The effect of mouse epidermal growth factor (mEGF) on the synthesis of glycosaminoglycans and glycoproteins by human fibroblasts has been studied. The addition of physiological concentrations (10(-9)M) of mEGF to quiescent cultures preincubated in the absence of serum was found to elicit an increased incorporation of 3H-glucosamine into the glycosaminoglycans and glycoproteins of both the cellular and extracellular fractions. Although the growth response to the factor, as measured by DNA replication, was minimal under these conditions as compared with the effect of serum, the mEGF-induced incorporation of glucosamine into these cellular constituents and into the extracellular glycoproteins was comparable to that elicited by serum shift-up. Serum, however, caused a significantly larger incorporation of glucoasimine into extracellular, acid-soluble glycosaminoglycans, which were shown to contain hyaluronic acid as the major component. As previously demonstrated, the growth response to mEGF can be enhanced several fold by an mEGF-binding arginine esterase, which is normally associated with the factor in vivo, and by ascorbate. The esterase was found to increase markedly the mEGF-induced incorporation of glucosamine into extracellular hyaluronic acid, while the addition of ascorbic acid did not significantly alter glucosamine incorporation.

Electrophoretic analysis of substrate-attached proteins from normal and virus-transformed cells

The proteins which have been left tightly bound to the tissue culture substrate after ethylenebis (oxyethyl-enenitrilo) tetraacetic acid (EGTA)-mediated removal of normal, virus-transformed, and revertant mouse cells and which have been implicated in the substrate adhesion process have been analyzed by slab sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Three size classes of hyaluronate proteoglycans were resolved in the 5% well gel; approximately half of the protein in the substrate-attached material coelectrophoresed with these polysaccharides-so-called glycosaminoglycan-associated protein(GAP). A portion of the GAP was shown to be highly heterogeneous and displaced from the polysaccharide by preincubation with calf histone before electrophoresis. The relative proportions of the proteoglycans varied in material deposited during a variety of cellular attachment and growth conditions. The remainder of the cellular protein in substrate-attached material was resolved as several major and distinct protein bands in 8 or 20% separating gels (a limited number of distinct serum proteins have also been identified as substrate bound). Protein C0 (molecular weight 220 000) was a prominent component in the material from a variety of normal and virus-transformed cells and resembled the so-called LETS or CSP glycoprotein in several respects; protein Ca was myosin-like in several respects; protein C2 was shown to be actin; and protein C1 (molecular weight 56 000) does not appear to be tubulin. Histones were also present in most preparations of substrate-attached material, particularly at high levels in transformed cell meterial, and may result from EGTA-mediated leakiness of the cell and subsequent binding to the negatively charged polysaccharide. These substrate-attached proteins were (a) prominent in substrate-attached material from many cell types in characteristic relative proportions, (b) deposited by EGTA-subcultured cells during the first hour of attachment to fresh substrate, (c) deposited by cells growing on plastic or glass substrates (three additional) components were also prominent in glass-attached material), and (d) deposited during long-term growth on or initial attachment to substrates coated wit 3T3 substrate-attached material. Pulse-chase analyses with radioactive leucine indicated that these proteins exhibit different turn-over behaviors. These results are discussed with regard to the possible involvement of these substrate-attached proteins in the substrate adhesion process, with particular interest in the interaction of cytoskeletal microfilaments with other surface membrane components and with regard to alteration of substrate adhesion by virus transformation.

Initial attachment of baby hamster kidney cells to an epoxy substratum. Ultrastructural analysis

In the presence of serum-containing medium, BHK cells attached and spread during a 1-h period onto a 3-5 nm thick serum layer absorbed on the substratum surface. The closest approach of the plasma membrane to the serum layer was observed to be about 9nm, which was determined by tilting the sectioned cells in a goniometer holder. Bundles of microfilaments or other cytoplasmic specializations were not observed in association with the regions of close contact. However, in the space between the plasma membrane and the adsorbed serum layer, a diffusely stained material could be visualized after fixation/staining by the tannic acid-glutaraldehyde technique. This technique also permitted increased clarity of visualization of trilaminar appearance of the plasma membrane. The distribution and mobility of anionic sites on the surfaces of attached and spreading cells was determined by labeling with polycationic ferritin. We observed movement of polycationic ferritin into large clusters on the cell surface, collapse of cell surface microextensions, and endocytosis, all of which were similar to our previous findings utilizing cells in suspension. However, the absolute amount of ferritin bound to the upper cell surface was less than that previously observed when suspended cells were put under similar labeling conditions. Also, polycationic ferritin did not appear to penetrate between the lower cell surface and the substratum.

Substrate-attached serum and cell proteins in adhesion of mouse fibroblasts

The effects of serum and coatings of substrate-attached material (SAM, which remains tightly adherent to the substrate after EGTA-mediated removal of cells) on the kinetics of attachment of DNA-radiolabeled BALB/c 3T3. SV40-transformed 3T3, and concanavalin A-selected revertant cells to glass coverlips were studied. The presence of serum in the medium of attaching cells had a marked effect on (1) the initial time lag before stable attachment of cells, (2) the maximum level of attached cells, (3) the stability of attachment, and (4) pseudopodial spread of the cell over the substrate. These serum effects could be mimicked by measuring attachment in medium without serum and with use of serum-preadsorbed or 3T3 SAM-coated coverslips. Enzymatic treatment of serumpreadsorbed substrates indicated that the factor(s) in serum which affects attachment is very trypsin-sensitive. Serum preadsorption of substrates stimulated attachment of SVT2 cells in medium with serum in a manner very similar to the effects of 3T3 SAM coating, while attachment of 3T3 SAM coating, while attachment of 3T3 or revertant cells was unaffected. Slab gel electrophoretic analysis (PAGE-SDS gels) identified eight major serum proteins by Coomassie blue staining (a) which bind to the substrate in the absence of cells and (b) which persist on the substrate after growth to confluence of 3T3 or SVT2 cells; this suggests that major breakdown or serum-adsorbed components does not occur during growth of normal or transformed cells. Seven radioactive SAM proteins were detected by autoradiography in 3T3 or SVT2 SAM electropherograms -- two of which are high molecular weight components which correspond to the glucosamine-radiolabeled hyaluronate proteoglycans observed previously; the remaining five are newly-identified proteins in SAM (one of these proteins appears to be actin). 3T3 and SVT2 cells have unique proportions of these seven components. The data are consistent with the idea that normal or virus-transformed cells do not attach directly to the culture substrate, but to specific classes of substrate-adsorbed serum proteins via deposition of specific classes of cell surface proteins and polysaccharides.

Induction of human fibroblast proliferation by epidermal growth factor (EGF): enhancement by an EGF-binding arginine esterase and by ascorbate

The effect of mouse epidermal growth factor (mEGF) and an mEGF-binding arginine esterase on the growth of cultured human fibroblasts has been studied. Physiological concentrations (10(-9)-10(-10) M) of the growth factor were found to stimulate DNA replication and cell proliferation in quiescent cultures, and the arginine esterase, which is normally associated with mEGF in vivo, was shown to enhance this growth effect synergistically. The cellular response to mEGF was dependent upon a low, growth-limiting concentration of serum in the extracellular medium. Ascorbic acid, which alone exhibited no growth-promoting effect, could partially replace this requirement, and was found to elicit a rapid and marked increase in proline hydroxylation. Quiescent cultures in serum-free medium containing ascorbic acid were stimulated by the combination of mEGF and the esterase in a manner comparable to that achieved with serum shift-up. The possible requirement of a collagen-containing extracellular matrix for the growth response to mEGF is discussed.