Epidermal growth factor promotes the chemotactic migration of cultured rat intestinal epithelial cells

The RIE-1 cell line is an untransformed, epithelial cell line derived from the rat small intestine. We report that epidermal growth factor (EGF), which regulates the proliferation of RIE-1 cells, also directs their movement. We measured cell migration through gelatin-coated filters in blind-well Boyden chambers. The migration of RIE-1 cells was stimulated up to approximately 100-fold by EGF, with a half-maximal response at 1-2 ng/ml and a maximal effect at 10 ng/ml. Further analysis showed that the RIE-1 cells responded directionally to a gradient of EGF in solution. Other growth factors tested did not stimulate RIE-1 cell migration, and EGF did not stimulate the migration of fibroblasts in this assay. We conclude that EGF is a potent and specific chemo-attractant for RIE-1 intestinal epithelial cells and suggest that EGF might influence epithelial cell migration in vivo.     

The anti-proliferative action of transforming growth factor-β1 on a rat intestinal epithelial cell line (rie-1) is dependent on cell population density and culture passage number

• 1.1. The proliferation of RIE-1 rat intestinal epithelial cells was potently but reversibly inhibited by transforming growth factor-β₁ (TGF-β₁). In early-passage cultures, complete growth arrest was observed when sparse cultures were treated with TGF-β₁ (1 ng/ml).
• 2.2. However, increasing the initial cell culture density resulted in decreased TGF-β₁-mediated inhibition of cell proliferation.
• 3.3. Independent of this population density effect, RIE-1 cells also exhibit a marked phenotypic transition around passage-8 to -10, such that later-passage cells were less responsive to growth inhibition by TGF-β₁].

     

Density-dependent growth control of adult rat hepatocytes in primary culture

Adult rat hepatocytes in primary culture, which show various liver functions, did not show any mitosis at confluent cell density, although they entered the S phase and remained in the G2 phase, judging by cytofluorometry, when insulin and epidermal growth factor (EGF) were added to 2-day cultures (Tomita, Y., Nakamura, T., & Ichihara, A. (1981) Exp. Cell Res. 135, 363-371). However, when the cell density was decreased by half or one third, the number of nuclei and cell number increased to 1.5-2.0 times that after culture for 35 h with insulin and EGF. Moreover, at these lower densities, DNA synthesis started much earlier, although at the usual high density DNA synthesis with these two hormones did not start until the hepatocytes had been cultured for over 40 h. These results suggest that proliferation of mature rat hepatocytes is regulated by the cell density. First, cells in G0 enter the G1 phase density-dependently; then cells in the G1 phase seem to be stimulated to enter the S phase by insulin and EGF, and a low cell density may permit cells after DNA synthesis to enter the M phase. DNA synthesis of rat hepatocyte cultures at low cell density was strongly inhibited by co-culture with a dense culture. Therefore, the density-dependent mechanism of hepatocyte proliferation seems to involve regulation by a soluble inhibitor(s) secreted by the hepatocytes into the culture medium.     

Epidermal growth factor dependence and TGF alpha autocrine growth regulation in primary rat tracheal epithelial cells.

We have examined dependence of primary rat tracheal epithelial (RTE) on exogenous epidermal growth factor (EGF) and determined whether a TGF alpha autocrine pathway is operating in these cells. Primary RTE cells plated in serum free media (SFM) without EGF and bovine pituitary factor (BPE) show little proliferation compared to cultures propagated in media containing EGF/BPE (CSFM). Removal of EGF/BPE shortly after plating, however, results in significant proliferation, although plateau cell densities are reduced and cell morphology is significantly altered compared to cells propagated in CSFM. Addition of EGF and/or BPE to cultures propagated in SFM minus EGF/BPE restores maximum cell density. The concentration of TGF alpha peptide in media conditioned by cells propagated without EGF/BPE is lower than the concentration in the media of CSFM cultures. TGF alpha mRNA and protein levels are also significantly lower in cells late in culture compared to logarithmically growing cells regardless of the presence or absence of EGF/BPE. The proliferation of primary RTE cells propagated without EGF/BPE is inhibited by neutralizing TGF alpha antiserum and by a tyrphostin compound that blocks TGF alpha/EGF receptor tyrosine kinase activity. These results indicate that primary RTE cells utilize TGF alpha as an autocrine growth factor and that the autocrine pathway is regulated as a function of growth state of the cells. However, this pathway does not provide growth autonomy to primary RTE cells, since cultures remain dependent on exogenous EGF/BPE for sustained proliferation.     

Epidermal growth factor and thyrotropin-releasing hormone act similarly on a clonal pituitary cell strain. Modulation of hormone production and inhbition of cell proliferation

GH(4)C(1) cells are a clonal strain of rat pituitary cells that synthesize and secrete prolactin and growth hormone. Chronic treatment (longer than 24 h) of GH(4)C(1) cells with epidermal growth factor (EGF) (10(-8) M) decreased by 30-40 percent both the rate of cell proliferation and the plateau density reached by cultures. Inhibition of cell proliferation was accompanied by a change in cellular morphology from a spherical appearance to an elongated flattened shape and by a 40-60 percent increase in cell volume. These actions of EGF were qualitatively similar to those of the hypothalamic tripeptide thyrotropin-releasing hormone (TRH) (10(-7) M) which decreased the rate of cell proliferation by 10-20 percent and caused a 15 percent increase in cell volume. The presence of supramaximal concentrations of both EGF (10(-8)M) and TRH (10(-7)M) resulted in greater effects on cell volume and cell multiplication than either peptide alone. EGF also altered hormone production by GH(4)C(1) cells in the same manner as TRH. Treatment of cultures with 10(-8) M EGF for 2-6 d increased prolactin synthesis five- to ninefold compared to a two- to threefold stimulation by 10(-7) M TRH. Growth hormone production by the same cultures was inhibited 40 percent by EGF and 15 percent by TRH. The half- maximal effect of EGF to increase prolactin synthesis, decrease growth hormone production, and inhibit cell proliferation occurred at a concentration of 5 x 10 (-11) M. Insulin and multiplication stimulating activity, two other growth factors tested, did not alter cell proliferation, cell morphology, or hormone production by GH(4)C(1) cells, indicating the specificity of the EGF effect. Fibroblast growth factor, however, had effects similar to those of EGF and TRH. Of five pituitary cell strains tested, all but one responded to chronic EGF treatment with specifically altered hormone production. Acute chronic EGF treatment with specifically altered hormone production. Acute treatment (30 min) of GH(4)C(1) cells with 10(-8) M EGF caused a 30 percent enhancement of prolactin release compared to a greater than twofold increase caused by 10(-7) M TRH. Therefore, although EGF and TRH have qualitatively similar effects on GH(4)C(1) cells, their powers to affect hormone release acutely or hormone synthesis and cell proliferation chronically are distinct.     

Effects of transforming growth factor beta and epidermal growth factor on cell proliferation and the formation of bone nodules in isolated fetal rat calvaria cells

When cells enzymatically isolated from fetal rat calvaria (RC cells) are cultured in vitro in the presence of ascorbic acid and Na beta-glycerophosphate, discrete three-dimensional nodules form with the histologic, immunohistochemical, and ultrastructural characteristics of bone (Bellows et al; Calcified Tissue International 38:143-154, 1986; Bhargava et al., Bone, 9:155-163, 1988). Quantitation of the number of bone nodules that forms provides a colony assay for osteoprogenitor cells present in the RC population (Bellows and Aubin, Develop. Biol., 133:8-13, 1989). Continuous culture with either epidermal growth factor (EGF) or transforming growth factor beta (TGF-beta) results in dose-dependent inhibition of bone nodule formation; however, the former causes increased proliferation and saturation density, while the latter reduces both parameters. Addition of EGF (48 h pulse, 2-200 ng/ml) to RC cells at day 1 after plating results in increased proliferation and population saturation density and an increased number of bone nodules formed. Similar pulses at confluence and in postconfluent multilayered cultures when nodules first begin forming (approx. day 11) inhibited bone nodule formation and resulted in a smaller stimulation of cell proliferation. Forty-eight hour pulses of TGF-beta (0.01-1 ng/ml) reduced bone nodule formation and proliferation at all times examined, with pulses on day 1 causing maximum inhibition. The effects of pulses with TGF-beta and EGF on inhibition of nodule formation are independent of the presence of serum in the culture medium during the pulse. The data suggest that whereas EGF can either stimulate or inhibit the formation of bone nodules depending upon the time and duration of exposure, TGF-B inhibits bone nodule formation under all conditions tested. Moreover, these effects on osteoprogenitor cell differentiation do not always correlate with the effects of the growth factors on RC cell proliferation.     

Comparison of the ability of basic and acidic fibroblast growth factor to stimulate the proliferation of an established keratinocyte cell line: modulation of their biological effects by heparin, transforming growth factor beta (TGF beta), and epidermal growth factor (EGF)

The bioactivity of both bFGF and aFGF in the BALB/MK-1 cell line has been compared to that of EGF. Our results indicate that, for that cell type, aFGF was far more potent than bFGF in inducing cell proliferation. In the presence of heparin, aFGF was as potent as EGF. In addition, excess bFGF has an inhibitory effect on the proliferation of MK cells exposed to a saturating concentration of aFGF, therefore acting as a partial agonist of aFGF. Surprisingly, bFGF, although it had low biological activity, was capable of synergizing the effect of EGF. In its presence, cultures exposed to saturating concentration of EGF have a final cell density 3- to 4-fold higher than that of counterpart cultures exposed to EGF alone. TGF beta, which in previous studies has been shown to inhibit the growth of keratinocytes, also inhibited the growth of BALB/MK-1 cells in response to either bFGF or aFGF. These studies suggest a role for FGF in regulating BALB/MK proliferation. aFGF provides positive growth signals which can be negatively modulated by excess bFGF or TGF beta, while bFGF, although a poor mitogen, could act by potentiating the effect of subsaturating concentrations of EGF.     

Stimulation of embryonic mouse limb bud mesenchymal cell growth by peptide growth factors

The possible role of peptide growth factors in mammalian intrauterine cell growth has been investigated using primary cultures of undifferentiated mesenchymal cells from 11-day mouse embryo limb buds. When grown as monolayer cultures, proliferation is greatly favored by high cell densities. In medium containing 0.2% serum, purified epidermal growth factor (EGF), fibroblast growth factor (FGF), multiplication stimulating activity (MSA), insulin, and somatomedin-C (Sm-C) do not increase cell growth, but a 30-40,000 molecular weight component of mouse fetal liver conditioned medium is stimulatory. On the other hand, when limb bud cells are grown as high density or micromass cultures, a method which better approximates in vivo growth conditions, all of the purified growth factors tested stimulate cell growth significantly. These growth factors have additive effects when used in combination, the best stimulation being observed with liver medium (10% v/v), EGF (10 ng/ml), FGF (200 ng/ml), and either insulin (1 microgram/ml) or Sm-C (20 ng/ml). We conclude that the response of limb bud cells to growth stimulation is influenced by the manner in which the cells are cultured and that at least four different growth factors are required for optimal in vitro proliferation. One of these, the active component of liver medium, appears to be a previously uncharacterized growth factor.     

Transforming growth factor-beta,basic fibroblast growth factor,and platelet-derived growth factor-BB interact to affect proliferation of clonally derived porcine satellite cells

Transforming growth factor beta-1 (1GF-β) stimulated porcine satellite cell proliferation in basal serum-free medium by 25%, but inhibited growth in serumcontaining medium by 58%. The effect of TGF-β on cell proliferation in serumfree medium was examined in combination with the following human recombinant growth factors: platelet-derived growth factor-BB (PDGF), basic fibroblast growth factor (FGF), insulin-like growth factor I (IGF-I), and epidermal growth factor (EGF). TGF-β inhibited PDGF-stimulated proliferation, enhanced FGF-stimulated proliferation, and had no effect on proliferation stimulated by IGF-I. The response of satellite cells to EGF and TGF-β in serum-free medium was not different than TGF-β alone. TGF-β depressed proliferation stimulated by the following combinations of two growth factors: PDGF and IGF-I, PDGF and EGF, PDGF and FGF, and IGF-I and EGF. In combination with IGF-I and FGF, TGF-β did not affect proliferation. TGF-β inhibited proliferation stimulated by the combination of PDGF, EGF, and IGF-I, but had no effect on proliferation stimulated by combinations of three growth factors that included FGF. FGF stimulated proliferation in Minimum Essential Medium containing 10% porcine serum (MEM-10% PS) by 13% above control. When the combination of TGF-β and FGF was added to MEM-10% PS, a 78% increase in proliferation was observed. Polyclonal antihuman PDGF-AB (this form neutralizes PDGF-AA, AB, and BB) reduced proliferation in MEM-10% PS by 44%. The combination of TGF-β and anti-PDGF-AB reduced proliferation by 59%, indicating the effects were not additive. These data indicate that: (1) FGF and TGF-β interact to increase proliferation of clonally derived porcine satellite cells, and (2) the inhibitory effect of TGF-β on proliferation of clonally derived porcine satelite cells can be primarily attributed to a reduction in the mitogenic effects of PDGF. © 1993 Wiley-Liss, Inc.     

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.     

Growth inhibition of mitogen-stimulated fibroblasts induced by double-stranded RNA depends on cell density

Polyinosinic-polycytidylic acid [poly(I:C)], a synthetic double-stranded RNA, is an inhibitor of mitogen-induced proliferation of normal fibroblasts. We show that this inhibition depends strongly on cell density. While cultures with densities at or above confluence are completely inhibited by poly(I:C) in their proliferative response to epidermal growth factor (EGF), the proliferation of sparse (subconfluent) cultures is only delayed. Conditioned medium from dense fibroblasts exposed to poly(I:C) inhibits EGF stimulation of sparse cells, indicating that the inhibition is, at least in part, mediated by a factor released from the cells. Preincubation of quiescent cultures with poly(I:C) renders the cells refractory to the inhibitory effects of poly(I:C). This desensitization correlates with a decreased production of the inhibitor. Since the inhibition of mitogenic stimulation by poly(I:C) is completely overcome by antisera recognizing interferon-beta (IFN-beta) and interleukin-6 (IL-6), we tested the effect of IL-6 and IFN-beta on EGF mitogenicity. None of the available IL-6 preparations had any effect on cell cycle entry. IFN-beta caused a dose-dependent delay of cell division but did not affect the density-dependent proportion of cells entering the cell cycle in response to EGF. Thus, IFN-beta cannot be the sole mediator of the poly(I:C)-induced inhibition. In the presence of dexamethasone, poly(I:C) did not inhibit EGF mitogenis. Indeed, the combined presence of poly(I:C) and dexamethasone did more than just restore the density-dependent control levels of EGF stimulation; most cells entered the cell cycle even at extremely high cell densities. Thus, poly(I:C) in combination with dexamethasone could deactivate the cell density-dependent negative control of proliferation.     

Density dependent proliferation of human glia cells stimulated by epidermal growth factor.

Epidermal growth factor (EGF) isolated from mouse salivary glands, enhanced the multiplication and [³H]TdR incorporation of human normal glia cells in serum-free medium supplemented with human serum albumin. Optimal dose was 2 ng/ml for both dense and sparse cultures but dense cultures were stimulated by EGF to a much less extent than sparse cultures. Data are presented that make the possibility unlikely that the density dependent inhibition of the EGF response is due to depletion of EGF in the medium or a local, juxtacellular starvation for the factor.     

Effect of protein and steroidal osteotropic agents on differentiation and epidermal growth factor-mediated growth of the CFK1 osseous cell line.

The effects of factors known to influence bone metabolism were examined using the osseous cell line CFK1. Parathyroid hormone (PTH) and dexamethasone (DEX) appeared to enhance the formation of cell foci of CFK1 cells in culture whereas retinoic acid (RA) caused a marked alteration in individual cell morphology. Bone morphogenetic protein (BMP-2) and PTH increased alkaline phosphatase activity, however, this index of differentiation was suppressed by epidermal growth factor (EGF), DEX, and RA. BMP-2 and EGF each stimulated DNA synthesis in a dose-dependent manner and enhanced cell numbers, but, no synergistic response of EGF and BMP-2 was observed. PTH and DEX failed to significantly alter cell number or EGF-stimulated DNA synthesis or cell proliferation. Although RA treatment of CFK1 cells resulted in a reduction in cell number compared to control, pretreatment with RA enhanced EGF-stimulated DNA synthesis and proliferative effects. At least part of this effect was by increasing the EGF receptor binding capacity of the cells. Furthermore, using cell cycle analysis, addition of EGF stimulated the progression of RA-treated cells into the DNA synthesis (S) phase with a reduced lag time. EGF and BMP-2, therefore, appear to exert a role in the expansion dynamics of the CFK1 population although BMP-2 may also enhance differentiation. PTH and DEX may act primarily to modulate the differentiated function of the CFK1 cells. RA inhibited cell proliferation and may mediate differentiation towards a less established cell population with upregulation of EGF receptors. The CFK1 cell model may, therefore, provide insight into microenvironmental control of growth and differentiation of precursor osseous cells.     

Effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the growth inhibitory and increased phosphatidylinositol (PI) responses induced by epidermal growth factor (EGF) in A431 cells

Epidermal growth factor (EGF) inhibited the growth of A431 human epidermoid carcinoma cells. The tumor promoting, phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) also retarded A431 cell growth. Addition of both TPA and EGF inhibited cell growth in an additive or synergistic manner depending upon the initial plating density of the cultures. EGF increased the production of diacylglycerol (60-70%) and stimulated the synthesis of phosphatidylinositol (PI) from 3H-inositol (three- to fourfold increase). Both of these responses were attenuated in the presence of TPA. TPA alone stimulated the production of diacylglycerol (DG) but had little effect on PI synthesis. The biological effect of TPA appeared to be mediated by the presence of a high-affinity receptor for phorbol esters on A431 cells. Moreover, the binding of 125I-EGF to A431 cells was unaffected by TPA, suggesting that the antagonistic effects of TPA were occurring distal to the EGF receptor. These findings also indicated that although TPA and EGF both inhibited A431 cell growth, this effect could be dissociated from changes in PI synthesis but may be dependent upon transient changes in DG production.     

Growth regulation of ovarian cancer cells by epidermal growth factor and transforming growth factors alpha and beta 1.

Regulation of ovarian cancer growth is poorly understood. In this study, the effects of EGF, TGF alpha and TGF beta 1 on two ovarian cancer cell lines (OVCAR-3 and CAOV-3) were investigated. The results showed that EGF/TGF alpha stimulated cell growth and DNA synthesis in OVCAR-3 cells, but inhibited cell proliferation and DNA synthesis in CAOV-3 cells. TGF beta 1 invariably inhibited cell proliferation and DNA synthesis in both cell lines. These effects on growth factors are dose dependent. The interaction of TGF beta 1 and EGF/TGF alpha was antagonistic in OVCAR-3 cells. In contrast, EGF/TGF alpha and TGF beta 1 had an additive inhibitory effect on CAOV-3 cells. Our results demonstrated that mature and functional EGF receptors are present in both cell lines and that they are capable of ligand binding, internalization, processing and ligand-enhanced autophosphorylation. Both high- and low-affinity binding are present in these cell lines, with CAOV-3 cells having about 2-3-fold higher total receptors than OVCAR-3 cells. These results together with those from our previous studies show that these cells express TGF alpha, TGF beta 1 and EGF receptors and that cell growth may be modulated by these growth factors in an autocrine and paracrine manner. This report presents evidence supporting the important roles of growth factors in ovarian cancer growth and provides a foundation for further study into the mechanism of growth regulation by growth factors in these cell lines.     

Regulation of growth of LNCaP human prostate tumor cells by growth factors and steroid hormones

The mitogenic activity of several growth factors on androgen responsive LNCaP human prostate tumor cells was studied. A two-fold stimulation of cell proliferation was observed after a culture period of 6 days in 1 ng EGF/ml, 10 ng TGF-alpha/ml or 20 ng basic FGF/ml. TGF-beta (0.02 ng/ml), which did not affect cell proliferation when added alone to the culture medium, inhibited the EGF- and TGF-alpha-induced growth. The synthetic androgen R1881 (0.1 nM) stimulated cell proliferation three-fold and increased the number of EGF receptors from 11500 to 28500 sites/cell. One of the mechanisms involved in androgen action on these cells is therefore an increased EGF receptor expression and increased sensitivity to EGF. TGF-beta did not directly affect androgen-responsive growth but inhibited the synergistic effect of EGF. A considerable expression of TGF alpha (precursors) could be demonstrated on the cells by immunohistochemical staining. However the staining intensity was not affected by androgens. These results make it less likely that androgen-responsive growth is mediated by regulation of secretion of an EGF- or TGF alpha-like activity, which in turn acts in an autocrine manner to stimulate growth. Estrogens, progestagens and antiandrogens do not inhibit androgen responsive growth of LNCaP cells but have striking growth stimulatory effects, increase EGF receptor level and increase acid phosphatase secretion. LNCaP cells contain a modified androgen receptor system with respect to both steroid specificity and antiandrogen sensitivity. It has recently been shown that the stimulatory effects are due to a mutated amino acid in the steroid binding domain of the androgen receptor.     

Growth regulation of ovarian cancer cells by epidermal growth factor and tranforming growth factors α and β1

Regulation of ovarian cancer growth is poorly understood. In this study, the effects of EGT, TGFα and TGFβ1 on two ovarian cancer cell lines (OVCAR-3 and CAOV-3) were investigated. The results showed that EGF/TGFα stimulated cell growth and DNA synthesis in OVCAR-3 cell, but inhibited cell proliferation and DNA synthesis in CAOV-3 cells. TGFβ1 invariably inhibited cell proliferation and DNA synthesis in both cell lines. These efefects on growth factors are dose dependent. The interaction of TGFβ1 and EGF/TGFα was antagonistic in OVCAR-3 cells. In contrast, EGF/TGFα and TGFβ1 had an additive inhibitory effect on CAOV-3 cells. Our results demonstrated that mature and functional EGF receptors are present in both cell lines and that they are capable of ligand binding, internalization, processing and ligand-enhanced autophosphorylation. Both high- and low-affinity binding are present in these cell lines, with CAOV-3 cells having about 2–3 fold higher total receptors than OVCAR-3 cells. These results together with those from our previous studies show that these cells express TGFα, TGFβ1 and EGF receptors and that cell growth may be modulated by these growth factors in an autocrine can paracrine manner. This report presents evidence supporting the important roles of growth factors in ovarian cancer growth and provides a foundation for futher study into the mechanism of growth regulation by growth factors in these cell lines.     

Differential proliferative response of cultured fetal and regenerating hepatocytes to growth factors and hormones

Upon epidermal growth factor (EGF) stimulation, fetal (20 days of gestation) and regenerating (44-48 h after partial hepatectomy) rat hepatocytes, isolated and cultured under identical conditions, increased DNA synthesis and entered into S-phase and mitosis, measured as [3H]thymidine incorporation and DNA content per nucleus in a flow cytometer, respectively. Fetal hepatocytes consisted of a homogeneous population of diploid (2C) cells. Two different populations of cells were present in regenerating liver, diploid (2C) and tetraploid (4C) cells, that responded to EGF. Glucagon or norepinephrine did not affect EGF stimulation of DNA synthesis in fetal liver cells, but they potentiated EGF response in regenerating hepatocyte cultures. Glucocorticoid hormones (dexamethasone) inhibited DNA synthesis in fetal hepatocyte cultures, an effect potentiated by the presence of glucagon or norepinephrine. In contrast, in regenerating hepatocytes, dexamethasone increased EGF-induced proliferation. EGF-dependent DNA synthesis was inhibited by TGF-beta in both fetal and regenerating cultured hepatocytes. TGF-beta action was partially suppressed by norepinephrine in regenerating hepatocytes, but was without effect in fetal hepatocyte cultures, whereas a synergistic action between TGF-beta and dexamethasone inhibiting growth in fetal but not in regenerating hepatocytes was found. Taken together, these results may suggest that there are significant differences between fetal and regenerating hepatocyte growth in their response to various hormones.     

Inhibition of E-cadherin dependent cell-cell contact promotes MUC5AC mucin production through the activation of epidermal growth factor receptors

Mucin production by epithelial cells is modulated by many soluble factors, including epidermal growth factor (EGF). E-Cadherin promotes EGF receptor (EGFR)-mediated MUC5AC mucin production in airway epithelial cells in dense cultures, suggesting the involvement of E-cadherin in activating EGFRs and mucin production. However, the role of E-cadherin in modulating mucin production is not completely understood. We examined its role in MUC5AC production in a human lung epithelial cell line, NCI-H292. Treatment of low density NCI-H292 cells with an anti-E-cadherin monoclonal antibody (SHE78-7) inhibited cell-cell contact in the dispersed colonies, but promoted MUC5AC production. Furthermore, treatment of the NCI-H292 cells with anti-E-cadherin antibody stimulated phosphorylation of extracellular signal-regulated kinase (ERK). The enhanced production of MUC5AC was inhibited with an EGFR inhibitor and with a MEK inhibitor, but not with a Src family kinase inhibitor. These results suggest that inhibition of E-cadherin activates EGFRs independently of Src and promotes MUC5AC production through the ERK signaling pathway in sparsely cultured NCI-H292 cells.     

The effect of dexamethasone on epidermal growth factor binding and stimulation of proliferation in young and senescent WI38 cells

Addition of 0.14 microM dexamethasone (DEX) to young log-phase WI38 cultures seeded at various densities in serum-free medium containing 4.1 nM epidermal growth factor (EGF) resulted in a synergistic increase in proliferation and final cell density. The action of DEX plus EGF was stimulatory but not synergistic in young confluent cultures. DEX plus EGF had no synergistic effect on senescent cells either during log phase or at confluence. Analysis of the effect of DEX on [125I]EGF binding revealed no statistically significant changes in either the number of binding sites or the apparent dissociation constant of the EGF-receptor complex.