Epidermal growth factor stimulates the synthesis of cell-attachment proteins in the human breast cancer cell line PMC42

Gelatin-methacryloyl hydrogels containing turnip mosaic virus for fabrication of nanostructured materials for tissue engineering

Current tissue engineering techniques frequently rely on hydrogels to support cell growth, as these materials strongly mimic the extracellular matrix. However, hydrogels often need ad hoc customization to generate specific tissue constructs. One popular strategy for hydrogel functionalization is to add nanoparticles to them. Here, we present a plant viral nanoparticle the turnip mosaic virus (TuMV), as a promising additive for gelatin methacryloyl (GelMA) hydrogels for the engineering of mammalian tissues. TuMV is a flexuous, elongated, tubular protein nanoparticle (700–750 nm long and 12–15 nm wide) and is incapable of infecting mammalian cells. These flexuous nanoparticles spontaneously form entangled nanomeshes in aqueous environments, and we hypothesized that this nanomesh structure could serve as a nanoscaffold for cells. Human fibroblasts loaded into GelMA-TuMV hydrogels exhibited similar metabolic activity to that of cells loaded in pristine GelMA hydrogels. However, cells cultured in GelMA-TuMV formed clusters and assumed an elongated morphology in contrast to the homogeneous and confluent cultures seen on GelMA surfaces, suggesting that the nanoscaffold material per se did not favor cell adhesion. We also covalently conjugated TuMV particles with epidermal growth factor (EGF) using a straightforward reaction scheme based on a Staudinger reaction. BJ cells cultured on the functionalized scaffolds increased their confluency by approximately 30% compared to growth with unconjugated EGF. We also provide examples of the use of GelMA-TuMV hydrogels in different biofabrication scenarios, include casting, flow-based-manufacture of filaments, and bioprinting. We envision TuMV as a versatile nanobiomaterial that can be useful for tissue engineering.

Spontaneous Cell Detachment and Reattachment in Cancer Cell Lines: An In Vitro Model of Metastasis and Malignancy

There is an unmet need for simplified in vitro models of malignancy and metastasis that facilitate fast, affordable and scalable gene and compound analysis. "Adherent" cancer cell lines frequently release "free-floating" cells into suspension that are viable and can reattach. This, in a simplistic way, mimics the metastatic process. We compared the gene expression profiles of naturally co-existing populations of floating and adherent cells in SW620 (colon), C33a (cervix) and HeLa (cervix) cancer cells. We found that 1227, 1367 and 1333 genes were at least 2-fold differentially expressed in the respective cell lines, of which 122 were shared among the three cell lines. As proof of principle, we focused on the anti-metastatic gene NM23-H1, which was downregulated both at the RNA and protein level in the floating cell populations of all three cell lines. Knockdown of NM23-H1 significantly increased the number of floating (and viable) cells, whereas overexpression of NM23-H1 significantly reduced the proportion of floating cells. Other potential regulators of these cellular states were identified through pathway analysis, including hypoxia, mTOR (mechanistic target of rapamycin), cell adhesion and cell polarity signal transduction pathways. Hypoxia, a condition linked to malignancy and metastasis, reduced NM23-H1 expression and significantly increased the number of free-floating cells. Inhibition of mTOR or Rho-associated protein kinase (ROCK) significantly increased cell death specifically in the floating and not the adherent cell population. In conclusion, our study suggests that dynamic subpopulations of free-floating and adherent cells is a useful model to screen and identify genes, drugs and pathways that regulate the process of cancer metastasis, such as cell detachment and anoikis.

Anacardic acid inhibits gelatinases through the regulation of Spry2, MMP-14, EMMPRIN and RECK

Earlier studies from our laboratory have identified Anacardic acid (AA) as a potent inhibitor of gelatinases (MMP-2 and 9), which are over-expressed in a wide variety of cancers (Omanakuttan et al., 2012). Disruption of the finely tuned matrix metalloproteinase (MMP) activator/inhibitor balance plays a decisive role in determining the fate of the cell. The present study demonstrates for the first time, that in addition to regulating the expression as well as activity of gelatinases, AA also inhibits the expression of its endogenous activators like MMP-14 and Extracellular Matrix MetalloProteinase Inducer (EMMPRIN) and induces the expression of its endogenous inhibitor, REversion-inducing Cysteine-rich protein with Kazal motifs (RECK). In addition to modulating gelatinases, AA also inhibits the expression of various components of the Epidermal Growth Factor (EGF) pathway like EGF, Protein Kinase B (Akt) and Mitogen-activated protein kinases (MAPK). Furthermore, AA also activates the expression of Sprouty 2 (Spry2), a negative regulator of EGF pathway, and silencing Spry2 results in up-regulation of expression of gelatinases as well as MMP-14. The present study thus elucidates a novel mechanism of action of AA and provides a strong basis for utilizing this molecule as a template for cancer therapeutics.

Novel approaches with targeted therapies in bladder cancer. Therapy of bladder cancer by blockade of the epidermal growth factor receptor family

The improved understanding of the molecular biology of urothelial malignancies is helping to define the role of new targets and prognostic indices that can direct the most appropriate choice of treatment for advanced disease. Many human tumors express high levels of growth factors and their receptors that can be used as potential therapeutical targets. Tyrosine-kinase receptors, including many growth factor receptors such the receptors for epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and Her2/neu, have been found overexpressed in urothelial tumors. For many of these growth factor receptors, the degree of expression has been associated with the progression of cancer and a poor prognosis. Among the best studied growth factor receptors are the two members of EGF receptor familiy EGFr (ErbB-1), and Her2/neu (ErbB-2). Several preclinical studies in bladder cancer models, have confirmed that systemic administration of growth factor inhibitors inhibits the growth and metastasis of human transitional cell carcinoma established in the bladder wall of athymic nude mice. Additional studies indicate that therapy with EGFR inhibitors enhances the activity of conventional cytoreductive chemotherapeutic agents, in part by inhibiting tumor cell proliferation, angiogenesis, and inducing apoptosis. Novel targeted therapy hold promise to improve the current results of bladder cancer treatment. Based on the success seen with anti-HER2 monoclonal antibodies (Herceptin) and the promising results with EGFR targeted agents (IMC-C225 Cetuximab, ZD1389 Iressa, OSI-774 Tarceva, GW 57016) in other tumor types, and based on the results obtained in preclinical models, there is a great interest in assessing these agents in patients with bladder cancer. Several trials are now ongoing testing these new agents alone or in combination with chemotherapy in bladder cancer patients. The integration of these newer biologic agents, probably to supplement rather than to supplant chemotherapeutic drugs, should be a primary direction of research with the objective to interfere with multiple aspects of bladder cancer progression. However, the value of integration of biologically targeted agents into combined modality treatment for patients with bladder cancer has still to be proven.

Epidermal growth factor-induced epithelio-mesenchymal transition in human breast carcinoma cells

PMC42-LA cells display an epithelial phenotype: the cells congregate into pavement epithelial sheets in which E-cadherin and beta-catenin are localized at cell-cell borders. They abundantly express cytokeratins, although 5% to 10% of the cells also express the mesenchymal marker vimentin. Stimulation of PMC42-LA cells with epidermal growth factor (EGF) leads to epithelio-mesenchymal transition-like changes including up-regulation of vimentin and down-regulation of E-cadherin. Vimentin expression is seen in virtually all cells, and this increase is abrogated by treatment of cells with an EGF receptor antagonist. The expression of the mesenchyme-associated extracellular matrix molecules fibronectin and chondroitin sulfate proteoglycan also increase in the presence of EGF. PMC42-LA cells adhere rapidly to collagen I, collagen IV, and laminin-1 substrates and markedly more slowly to fibronectin and vitronectin. EGF increases the speed of cell adhesion to most of these extracellular matrix molecules without altering the order of adhesive preference. EGF also caused a time-dependent increase in the motility of PMC42-LA cells, commensurate with the degree of vimentin staining. The increase in motility was at least partly chemokinetic, because it was evident both with and without chemoattractive stimuli. Although E-cadherin staining at cell-cell junctions disappeared in response to EGF, beta-catenin persisted at the cell periphery. Further analysis revealed that N-cadherin was present at the cell-cell junctions of untreated cells and that expression was increased after EGF treatment. N- and E-cadherin are not usually coexpressed in human carcinoma cell lines but can be coexpressed in embryonic tissues, and this may signify an epithelial cell population prone to epithelio-mesenchymal-like responses.

Epidermal growth factor receptor signaling and the invasive phenotype of ovarian carcinoma cells

BACKGROUND

Most (70%-100%) ovarian carcinomas express high levels of the epidermal growth factor receptor (EGFR). To examine the relationship between EGFR and the invasive phenotype, we assessed integrin expression, adhesion, matrix metalloproteinase (MMP) activity, and migration in ovarian cancer cells in which EGFR expression was modified.

METHODS

NIH:OVCAR-8 human ovarian carcinoma cells were transfected with an expression vector containing the human EGFR complementary DNA in an antisense orientation (EGFR-antisense cells) or the vector alone (vector control cells). We compared vector control and EGFR-antisense cells for cell morphology and adhesion by light microscopy, expression of alpha(6)- and alpha(3)-integrin subunits by flow cytometry, MMP and tissue inhibitor of MMP (TIMP) activity by zymography, and migration by a wound migration assay. In some experiments, EGFR kinase activity in parental cells was inhibited by treatment with PD153035. All statistical tests were two-sided.

RESULTS

EGFR-antisense cells were morphologically distinct from vector control cells and had a selective decrease in adhesion to laminin-1 that was not observed with vector control cells (P = .008) or on other extracellular matrix substrates. Compared with vector control cells, cell surface alpha(6)-integrin expression decreased by approximately 80% (difference = 78.7%; 95% confidence interval [CI] = 77.8% to 79.6), MMP-9 activity decreased by approximately 50%, and TIMP activity increased by approximately 50% in EGFR-antisense cells. Vector control cells were highly motile (5.51 arbitrary distance unit; 95% CI = 4.98 to 6.04), whereas the EGFR-antisense cells were not (0.99 arbitrary distance units; 95% CI = 0.38 to 1.60). The morphology and integrin profile of NIH:OVCAR-8 parental cells treated with PD153035 were similar to those of the EGFR-antisense cells.

CONCLUSIONS

Reduced EGFR expression in ovarian carcinoma cells decreased their adhesion to laminin-1, expression of the alpha(6)-integrin subunit (a well-characterized laminin-1 receptor), and MMP-9 activity. These data support the hypothesis that EGFR overexpression in ovarian cancer cells results in multiple phenotypic changes that enhance the invasive phenotype.

Phospholipase C-gamma inhibition prevents EGF protection of intestinal cytoskeleton and barrier against oxidants

Loss of intestinal barrier integrity is associated with oxidative inflammatory GI disorders including inflammatory bowel disease. Using monolayers of human intestinal epithelial (Caco-2) cells, we recently reported that epidermal growth factor (EGF) protects barrier integrity against oxidants by stabilizing the microtubule cytoskeleton, but the mechanism downstream of the EGF receptor (EGFR) is not established. We hypothesized that phospholipase C (PLC)-gamma is required. Caco-2 monolayers were exposed to oxidant (H2O2) with or without pretreatment with EGF or specific inhibitors of EGFR tyrosine kinase (AG-1478, tyrphostin 25) or of PLC (L-108, U-73122). Other Caco-2 cells were stably transfected with a dominant negative fragment for PLC-gamma (PLCz) to inhibit PLC-gamma activation. Doses of EGF that enhanced PLC activity also protected monolayers against oxidant-induced tubulin disassembly, disruption of the microtubule cytoskeleton, and barrier leakiness as assessed by radioimmunoassay, quantitative Western blots, high-resolution laser confocal microscopy, and fluorometry, respectively. Pretreatment with either type of inhibitor abolished EGF protection. Transfected cells also lost EGF protection and showed reduced PLC-gamma phosphorylation and activity. We conclude that EGF protection requires PLC-gamma signaling and that PLC-gamma may be a useful therapeutic target.

Epidermal growth factor receptor-stimulated intestinal epithelial cell migration requires phospholipase C activity

BACKGROUND & AIMS

Ulceration of intestinal mucosa is rapidly followed by enterocyte migration via restitution. The aim of this study was to investigate signaling mechanisms of epidermal growth factor (EGF) receptor-stimulated monolayer restitution in a mouse intestinal epithelial cell line.

METHODS

EGF-stimulated cell migration was determined using a wound model in the presence of agonists and/or antagonists of tyrosine kinase, phospholipase C, phosphatidylinositol 3-kinase, or protein kinase C. The tyrosine phosphorylation state of the EGF receptor, phosphatidylinositol phospholipase C gamma1 (PLCgamma1), focal adhesion kinase, and cellular lysates was determined by immunodetection.

RESULTS

EGF stimulated cell migration twofold at 4, 8, and 24 hours. Inhibition of EGF receptor tyrosine kinase activity, phospholipase C, or phosphatidylinositol 3-kinase attenuated EGF-induced intestinal cell migration. Pretreatment of cells with phorbol 12-myristate 13-acetate, known to down-regulate protein kinase C expression, blocked EGF-induced cell migration. Increased tyrosine phosphorylation of the EGF receptor and PLCgamma1 was detected within 5 minutes after wounding.

CONCLUSIONS

EGF-stimulated intestinal cell migration requires intact EGF receptor tyrosine kinase, phospholipase, and protein kinase C activities. PLCgamma1 may be a key regulatory molecule in the initial EGF receptor signal transduction pathway of EGF-stimulated cell migration.

Rho proteins play a critical role in cell migration during the early phase of mucosal restitution

In the intestine, several growth factors stimulate migration of epithelial cells, contributing to the maintenance of tissue integrity. The Ras-like GTPase Rho regulates a signal transduction pathway linking growth factor receptors to the formation of actin stress fibers and focal adhesions, presumed to be important for motility. Using an in vitro wound-induced migration assay, we have examined the role of Rho GTPases in the migration of IEC-6 and Caco-2 cells, and provide evidence that the Rho GTPases play an essential role in the initial phase of mucosal wound healing. Treatment of the cells with Clostridium difficile toxins A and B, inhibitors of the Rho family GTPases inhibited migration in a dose-dependent fashion. Microinjection of the inhibitory exchange factor Rho-guanine nucleotide dissociation inhibitor (GDI), or Clostridium botulinum C3 ADP-ribosyl transferase (C3) toxin, a Rho-ADP-ribosylating exoenzyme, potently inhibited migration. Microinjection of RhoT19N, a dominant negative form of RhoA, or in vitro ADP-ribosylated RhoA impaired the ability of cells to migrate. Rho-GDI and C3 exoenzyme also inhibited EGF-induced migration of IEC-6 cells. These results demonstrate that Rho is required for endogenous and EGF-induced migration of small intestinal crypt cells, and that Rho proteins are essential elements of a mechanism by which growth factors induce cell migration to restitute mucosal integrity.

Cytokines in tumour growth, migration and metastasis

A wide variety of cytokines are involved at every stage of tumour growth and dissemination. Primary tumour growth is helped by growth factors and angiogenic factors. These may either be produced by tumour cells themselves or be provided by one of the infiltrating cell populations, such as vascular endothelium or leukocytes. The influx of these cells is, in turn, under the control of the chemokines, a chemoattractant subfamily of cytokines. Autocrine motility factors, in conjunction with cytokines that regulate the production and activity of proteases capable of breaking down components of the extracellular matrix, are involved in the dispersal of cells from primary tumours, leading to the formation of metastases. The development of metastases may also be under the control of circulating cytokines released from the primary tumour. The ways in which cytokines and allied growth factors regulate tumour growth and development are both complex and controversial. However, the study of this system will provide a more profound understanding of tumour biology and may lead the way for the development of novel therapeutic approaches.

In vitro invasiveness of DU-145 human prostate carcinoma cells is modulated by EGF receptor-mediated signals

Prostate carcinomas often present an autocrine stimulatory loop in which the transformed cells both express the EGF receptor (EGFR) and produce activating ligands (TGF alpha and EGF forms). Up-regulated EGFR signalling has been correlated with tumor progression in other human neoplasia; however, the cell behaviour which is promoted remains undefined. To determine whether an EGFR-induced response contributes to cell invasiveness, we transduced DU-145 human prostate carcinoma cells with either a full-length (WT) or a mitogenically-active but motility-deficient truncated (c'973) EGFR. The DU-145 Parental and two transgene sublines all produced EGFR and TGF alpha, but the transduced WT and c'973 EGFR underwent autocrine downregulation to a lesser degree, with more receptor remaining intact. DU-145 cells transduced with WT EGFR transmigrated a human amniotic basement membrane matrix (Amgel) to a greater extent than did Parental DU-145 cells (175 +/- 22%). Cells expressing the c'973 EGFR invaded through the Amgel only to about two thirds the extent of the Parental cells (62 +/- 23%). A monoclonal antibody which prevents ligand-induced activation of EGFR decreased the invasiveness of WT-expressing cells by half and Parental cells by a fifth, but had little effect on the invasiveness of c'973-expressing cells; with the result that in the presence of antibody, all three cell lines transmigrated the Amgel to the same extent. The different levels of invasiveness between the three sublines were independent of cell proliferation. These findings demonstrated that EGFR-mediated signals increase tumor cell invasiveness and suggested that domains in the carboxy-terminus are required to signal invasiveness. As an initial investigation into the mechanisms underlying the EGFR-mediated enhanced invasiveness, we determined whether these cells presented different collagenolytic activity, as the major constituents of Amgel are collagen types I and IV. All three sublines secreted easily detectable levels of gelatin-directed proteases and TIMP-1, with WT cells secreting equivalent or lower levels of proteases. The proteolytic balance in these cells did not correlate with invasiveness. These data suggest that the TGF alpha-EGFR autocrine loop promotes invasiveness and that this is accomplished by signalling cell properties other than differential secretion of collagenolytic activity.

Cell movement elicited by epidermal growth factor receptor requires kinase and autophosphorylation but is separable from mitogenesis

The EGF receptor (EGFR) upon activation signals increased cell movement. However, the domains within the receptor, and the pathway which trigger movement are undefined. We expressed EGFR mutants at physiologic levels in receptor-devoid NR6 cells to investigate this biologic response. The receptors possessed kinase activity and underwent autophosphorylation as predicted by primary amino acid sequence. EGF-induced cell motility was assessed in vitro by excess migration into an acellular area and colony scatter in the presence of saturating concentrations of EGF. Wild-type (WT)-EGFR signaled increased motility. However, replacing the conserved lysine721 with methionine resulted in a kinase-inactive receptor which did not elicit movement. Removal of the entire terminus by truncation (c'973) also abrogated ligand-induced motility. Thus, we concentrated on the carboxy-terminal domains. EGF-induced movement was seen with a less-truncated mutant (c'1000) that contained a single autophosphorylated tyrosine (tyrosine992). Other mutants, c'991 and c'1000F992, in which this tyrosine was removed did not signal motility. Fusion mutants which presented other autophosphorylated tyrosine domains also exhibited EGF-induced movement. These findings suggested that the presence of both an autophosphorylated tyrosine signaling domain and the kinase activity are necessary for this biologic response. All kinase-positive mutants signaled cell proliferation but only those that contained autophosphorylatable tyrosines induced movement. The motility responses mediated by these EGFR were identical in the presence or absence of mitomycin-C, at a dose (0.5 micrograms/ml) which completely inhibited cell proliferation. On the other side, D-actinomycin (50 ng/ml) blocked EGF-induced motility but did not affect thymidine incorporation. Thus, EGF-induced mitogenesis and cell motility are mediated through different pathways.

EGF receptor in neoplasia and metastasis

EGFR is a member of the tyrosine kinase family of cell surface receptors with a wide range of expression throughout development and in a variety of different cell types. The receptor can transmit signals to cells: i) upon interaction with ligands such as EGF, TGF alpha, amphiregulin or heparin binding EGF, ii) upon truncation or mutation of extracellular and/or intracellular domains, iii) upon amplification of a basal receptor activity (in the absence of ligand) through cooperation with other cellular signaling pathways or nuclear events (e.g. expression of v-erbA). The activated EGFR can exert pleiotropic functions on cells, depending on their tissue origin and state of differentiation. Under certain conditions it can also contribute to neoplasia and development of metastases. Such conditions can exist upon aberrant receptor/ligand expression and activation (e.g. in the wrong cell; at the wrong time; in the wrong amounts). Aberrant signalling can also occur through constitutive EGFR activation. Oncogenic potential of EGFR has been demonstrated in a wide range of experimental animals. EGFR is also implicated in human cancer, where it may contribute both to the initiation (glioblastoma) and progression (epithelial tumors) of the disease. EGFR may influence key steps in the processes of tumor invasion and dissemination. Involvement of EGFR in tumor spread may indicate a potential use of this receptor as a target for antimetastatic therapy.

Trophic actions of transforming growth factor alpha on mesencephalic dopaminergic neurons developing in culture

Transforming growth factor alpha messenger RNA and protein levels are highest in the striatum, the target area of mesencephalic dopaminergic neurons of the substantia nigra, suggesting a role as a target-derived neurotrophic factor for these cells. To test this hypothesis, we characterized the actions of transforming growth factor alpha on fetal rat dopaminergic neurons in culture. Transforming growth factor alpha promoted dopamine uptake in a dose- and time-dependent manner. Administration of transforming growth factor alpha at the time of plating for 2 h produced a significant increase in dopamine uptake after five days of growth in vitro. As cultures aged they became less responsive to transforming growth factor alpha, such that longer times of exposure were required to elicit a similar, but weaker, response. Dopaminergic cell survival was selectively promoted by transforming growth factor alpha, since there was an increase in the number of tyrosine hydroxylase-immunostained cells without a parallel increase in the total number of neuron-specific enolase-immunopositive cells. Neurite length, branch number and soma area of tyrosine hydroxylase-immunopositive cells also were enhanced by transforming growth factor alpha treatment. Increases in each of the dopaminergic parameters due to transforming growth factor alpha were accompanied by a rise in glial cell number, making it possible that these effects were mediated by this cell population. The neurotrophin antagonist, K252b, failed to inhibit the transforming growth factor alpha-induced increase in dopamine uptake, indicating that transforming growth factor alpha's effects were not mediated by neurotrophin mechanisms. The actions of transforming growth factor alpha on the differentiation of dopaminergic neurons only partially overlapped with those of epidermal growth factor. Thus, while transforming growth factor alpha and epidermal growth factor are believed to share the same receptor they differentially affect dopaminergic cell development in vitro. These results indicate that transforming growth factor alpha is a trophic factor for mesencephalic cells in culture and suggests that transforming growth factor alpha plays a physiological role in the development of these cells in vivo.

A hepatic invasive human colorectal xenograft model

A hepatic invasive human colorectal xenograft model was derived in nude mice by selection through the liver of the parental cell line, C170. Following intraperitoneal injection, tumours selectively grew on the liver in > 80% of the animals within 15-20 days. The liver-invading xenograft line, renamed C170HM2, had a significantly greater expression of the Lewisx antigen compared to C170 (mean linear fluorescence per cell > 1000 compared with 500 for C170, P < 0.02). C170HM2 had significantly elevated proliferation (when compared with C170) in the presence of epidermal (P < 0.001) and basic fibroblast growth factor (P < 0.001). C170HM2 also mitogenically responded to type I collagen (derived from rat tails), unlike C170. C170HM2 tumours when invading the liver expressed both interstitial collagenase and gelatinase activity at the invading edge.

Human enterocyte (Caco-2) migration is modulated in vitro by extracellular matrix composition and epidermal growth factor

The modulation of enterocyte sheet migration was studied using Caco-2 cells, a well-differentiated human colonic cell line. Although Caco-2 cells attached and spread equivalently over collagen types I, III, IV, and V and laminin, migration over laminin was significantly slower than migration over the collagen types. Fibronectin was a poor substrate for attachment, spreading, and migration. Epidermal growth factor (EGF) stimulated migration over laminin but did not alter Caco-2 migration over collagen or fibronectin. This effect was independent of cell proliferation, which was stimulated equivalently on both laminin and collagen I. Expression and organization of cell surface receptors for matrix (integrins) were studied using antibodies specific for beta and alpha integrin subunits. Integrin surface expression was assessed by immunoprecipitation of surface 125iodinated control and EGF-treated cells. Beta 1 surface pools did not change substantially in any condition studied. Alpha 1 subunit pools were decreased after EGF treatment on collagen I but alpha 1 pools increased after EGF treatment on laminin. Surface pools of alpha 2 subunits were increased following EGF treatment whether cells were cultured on laminin or collagen I. However, traditional immunofluorescent and laser confocal imaging demonstrated substantial differences in the character of alpha 2 subunit organization between collagen and laminin in the migrating cell front. Furthermore, a functional antibody to the alpha 2 subunit inhibited EGF stimulation of migration over laminin without substantial effects on basal migration over laminin or collagen I. Thus, EGF appears to exert a matrix-specific effect on enterocyte migration by modulation of integrin expression and organization.

Effects of growth factors on proliferation on basal and luminal cells in human breast epithelial explants in serum-free culture

A method of culturing human breast epithelium is described in which viable explants can be maintained in protein-free medium while retaining the capacity of responding to added hormones and growth factors for at least 7 days. Culture parameters were chosen to provide maximum sensitivity of detection of proliferative responses by autoradiography. Under basal conditions, the mean thymidine labeling index of the explants was 0.08%. After stimulation with insulin, hydrocortisone, and cholera toxin (I,H,CT), a combination known to stimulate proliferation in human breast epithelium in vitro, the mean labeling index was 15.7%. Stimulation of explants with epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha resulted in mean labeling indices of 6.6 and 10.8%, respectively. Autoradiography at the ultrastructural level demonstrated that in I,H,CT-stimulated explants the majority of the labeled cells were luminal, with only 1.5% being basal cells. In contrast, after EGF and TGF-alpha basal cells accounted for 11.5 and 18.5% of the labeled population. These results indicate that this system provides an in vitro assay of proliferative activity in the normal human breast that enables comparisons to be made between both the luminal and the basal cells in the explants and their counterparts in monolayer culture prepared from flow sorted cells. Thus, growth responses dependent on cell-to-cell interactions or stromal modulation can be identified.

Epidermal growth factor receptors and EGF-responsiveness of the human breast-carcinoma cell line PMC42

PMC42 is an early-passage, well-differentiated, pleiomorphic human breast-cancer cell line. It expresses an average of 2.4 x 10(5) EGF receptor (EGFR) sites per cell when cultures are assayed using a radioreceptor assay. This is a relatively high figure for breast-carcinoma cell lines. Its responses to epidermal growth factor (EGF) were analyzed morphologically and by flow cytometry and immunocytochemistry. PMC42 responded in vitro to EGF with morphological changes, inhibition of "doming" and an increase in DNA synthesis in serum-containing medium in confluent or near-confluent cultures. When EGF receptor sites were localized immunocytochemically in PMC42, they were found to be variably expressed on the membrane of cells grown in the absence of EGF, with discrete areas of strong and weak cells of different morphological appearances; flow cytometry indicated a 10-fold range in EGFR levels between individual cells. Cultures maintained in the presence of EGF were less heterogeneous in their morphology and had a predominantly cytoplasmic, relatively uniform localization of EGFR with down-regulation of membrane EGFR levels. EGF-stimulated cultures were stained simultaneously for the presence of EGFR and the proliferation-related antigen Ki-67 and analyzed by both flow cytometry and immunocytochemistry. No correlation was observed between Ki-67 positivity and level of EGFR expression by individual cells. Electron microscopic localization of receptor sites demonstrated that the receptors were concentrated predominantly on the lateral and basal membranes. These results show that the PMC42 line reflects a number of the properties of heterogeneous breast tumours in situ. It may also continue to express growth-factor receptors in a manner that reflects their topographical distribution on normal luminal breast epithelial cells.

Modulation of human breast cancer cell adhesion by estrogens and antiestrogens

In order to study the effect of estrogens and antiestrogens on the adhesive properties of human breast cancer cells, the attachment on endothelial cells (EC), on subendothelial extracellular matrix (ECM) and on ECM components (collagen I and IV, laminin, fibronectin) of estrogen-dependent (MCF-7, ZR75-1) and estrogen-independent (BT-20) breast cancer cell lines was investigated. The cells were grown under conditions of controlled exposure to estrogen [17 beta-estradiol (E2)] and/or antiestrogens [tamoxifen (Tam) or 4-hydroxytamoxifen (OH-Tam)]. Treatment by E2 enhanced the ability of ZR75-1 cells to adhere to the various substrates, which contrasts with the observed absence of effects with the BT-20 cells. Similarly, Tam or OH-Tam induced a reduction of the adhesion of ZR75-1 tumor cell, but not of BT-20 cells. This effect was reversed by competing concentrations of E2. The effects on MCF-7 cell adhesion were similar to those described for ZR75-1 cells, but could not be reproducibly observed. Adhesion assays carried out with ZR75-1 cells grown in the absence or presence of phenol red, a pH indicator which behaves as a weak estrogen, led to a similar pattern of cell attachment. Conditioned media harvested from E2- or Tam-treated ZR75-1 cells failed to induce any effect on adhesion of other ZR75-1 cells grown in E2-deprived medium, suggesting that secretory activities are not required for the control of cell adhesiveness. The results suggest that estrogens and antiestrogens can control the adhesive behavior of breast tumor cells through their hormone responsive structures possibly by regulating expression of cell adhesion proteins and/or their cell surface receptors.

Growth factor control of myoepithelial-cell differentiation in cultures of human mammary gland

The relationship between growth and cytodifferentiation was studied in cultured human mammary myoepithelial cells under serum-free culture conditions. Myoepithelial-cell differentiation was monitored by quantifying cells showing immunoreactivity to the muscle isoform of actin; to the membrane glycoprotein common acute lymphoblastic leukemia antigen (CALLA); and to type IV collagen. Growth was quantified either by measuring the actual increase in cell number, or in a more-sensitive assay using immunoreactivity to the cell-proliferation-associated nuclear antigen Ki-67 as a measurement of the number of cells leaving the G0-phase of the cell cycle. The results showed that: (a) Primary cultures of myoepithelial cells on DME-F12 supplemented with cholera toxin (CT) alone resulted in the formation of quiescent cell islets (in the G0-phase of the cell cycle) showing phenotypic traits preserved from the in vivo situation (actin- and CALLA-positive cells with little or no type-IV-collagen immunoreactivity). (b) After addition of epidermal growth factor (EGF), with an ED50 of 1-10 ng/ml, in the presence of CT, the cells entered the G1-phase of the cell cycle, without further increase in cell number. At the same ED50 of EGF, the frequency of CALLA-positive cells decreased, while the number of cells immunoreactive for type IV collagen increased with a maximal effect of EGF seen after 7-11 days. During the same period, the cells remained fully differentiated with respect to actin immunoreactivity. (c) Further addition of insulin (I) to the medium in the presence of EGF and CT resulted in the cells entering an exponential growth phase associated with simultaneous decrease in actin immunoreactivity with a maximal effect of I after 11 days of exposure. The dose-response curve to I was virtually identical for stimulating cell proliferation and for reducing the frequency of actin-immunoreactive cells (ED50 in the range of 30 ng/ml), suggesting that the two processes were controlled by the same initial I-receptor interaction. (d) Some reduction in the number of actin-positive cells was exerted by I-EGF-CT independently of the mitogenic response, but this reduction was further augmented if the cells were allowed to proliferate. (e) Time-course studies of quiescent (G0-phase) cells stimulated to exponential growth revealed that entrance of cells into the G1-phase of the cell cycle preceded the loss of muscle actin filaments. (f) Exponentially growing actin-negative epithelial cells did not resume a myoepithelial phenotype in density-arrested postconfluent cultures.(ABSTRACT TRUNCATED AT 250 WORDS)