Expression of antisense epidermal growth factor receptor RNA downmodulates the malignant behavior of human colon cancer cells

Biomarker-driven EGFR therapy improves outcomes in patients with metastatic colorectal cancer

As new data from randomized studies comparing EGFR-targeting therapies with VEGF inhibitors emerge, the treatment landscape for metastatic colorectal cancer is expected to change. Although both the VEGF inhibitor bevacizumab and the anti-EGFR antibody cetuximab are approved in the first-line setting, they have not until recently been compared directly in randomized studies. Unlike targeted therapy in the EGFR pathway, there are no biomarkers guiding VEGF treatment. Recent data, discussed in this review, demonstrate that patients with KRAS/NRAS wild-type tumors benefit from anti-EGFR therapy in the first-line setting and that anti-EGFR therapy may be superior when compared with anti-VEGF approaches. This review focuses on the clinical utility of targeting EGFR by revisiting the biologic rationale for EGFR inhibition in metastatic colorectal cancer and providing new insight on the advancements in biomarker analyses with the potential to change practice.

Ki-67, p53 and epidermal growth factor receptor expression in early glottic cancer involving the anterior commissure treated with radiotherapy

OBJECTIVE

TNM staging system is not a sufficiently accurate method for predicting the response of an individual patient to a course of radiotherapy. After irradiation, it can become very difficult to assess data obtained by imaging and endoscopy for the diagnosis of both minimal persistent disease and early recurrence. The search for biological parameters that could be used to identify patients who will respond to radiotherapy is crucial. At this study we aimed at evaluating the prognostic significance of immunohistochemical expression of Ki-67, p53 and epidermal growth factor receptor (EGFR) in laryngeal glottic cancer involving the anterior commissure and treated with radiotherapy.

METHODS

From January 1995 to August 2005, 24 patients with glottic cancer involving the anterior commissure were primary treated with radiotherapy. Six patients presented with T1a, 12 patients with T1b and 6 patients with T2. Biopsies were taken before the radiotherapy treatment started. Radiotherapy was done with the same technique for all patients using a linear accelerator device with beam energy of 4-MV photons. Immunohistochemical staining was performed using avidine-biotin-peroxidase technique with antibodies to Ki-67, p53 and EGFR.

RESULTS

p53 and EGFR positive expression values and labeling indices were greater in radioresistant than in radiosensitive tumors but without significant differences. On the other hand, Ki-67 was expressed in all radiosensitive tumors and Ki-67 labeling indices were significantly higher in radiosensitive tumors than radioresistant tumors (p=0.01).

CONCLUSION

We identified overexpression of Ki-67 as predictive marker of radiosensitivity in glottic cancer involving the anterior commissure, with the results showing significant difference between radiosensitive and radioresistant tumors.

Neurotensin stimulates expression of early growth response gene-1 and EGF receptor through MAP kinase activation in human colonic epithelial cells

Neurotensin (NT) is a highly expressed gastrointestinal (GI) neuropeptide, which modulates GI motility, secretion and cell growth as well as intestinal inflammation. Since EGF receptor is highly expressed in human colon cancer cells, we sought to examine whether NT stimulation contributes to the EGFR overexpression using nontransformed colonocyte NCM460 cells. The results show that NT treatment caused a significant increase in EGFR protein expression and gene transcription. Pretreatment with MAP kinase pathway inhibitor PD98059 blocked NT-induced EGFR expression. As the EGFR promoter has a functional Egr-1 site, previously shown to mediate its transcription in response to hypoxia, we examined the role of Egr-1 in the NT response. We first show that NT stimulated Egr-1 expression, which can be inhibited by PD98059. We also determined whether NT increases Egr-1 binding to its site within the EGFR promoter. The data indicate that NT enhanced the amount of Egr-1 binding to the EGFR Egr-1 site and that this binding was significantly decreased by PD98059. To verify that Egr-1 mediated NT-induced EGFR transcription, Egr-1 siRNA was used to knock down its expression. The data show that transfection of Egr-1 siRNA significantly inhibited NT-stimulated EGFR transcription. Together, our results suggest that NT can stimulate MAP kinase-mediated Egr-1 and EGFR gene expression in human colonocytes. Our results may be relevant to the mechanisms by which NT participates in the development of colon cancer.

Epidermal growth factor receptor in adult retinal neurons of rat, mouse, and human

During development, the epidermal growth factor receptor (EGFR) regulates proliferation and differentiation of many types of cells, including precursors of neurons and glia. In the adult, EGFR continues to drive the growth and differentiation of epithelial cells but is absent from glia in the CNS. However, the localization and functions of EGFR in adult neurons are not well defined. By using immunohistochemistry and Western blotting, we have identified EGFR and its ligands in adult retinal ganglion cells in the normal rat, mouse, and human retina. EGFR and its ligands were also present in certain other adult retinal neurons, for example, horizontal cells and amacrine cells, and had different distribution patterns among these species. In addition, we found that EGFR was expressed in the rat retinal ganglion cell line RGC-5. One of the EGFR ligands, EGF, caused a cell shape change and increased neurofilament phosphorylation in RGC-5 cells. The expression of EGFR in postmitotic, terminally differentiated adult retinal neurons suggests that EGFR has pleiotropic functions. In addition to the conventional mitogenic role in adult epithelial cells, EGFR must serve a different, nonmitogenic function in adult neurons. Our work localizes EGFR and its ligands in the adult retinas of several species as a step toward investigating the nonmitogenic functions of EGFR in adult neurons.

Prognostic impact of p53, c-erbB-2 and epidermal growth factor receptor on head and neck carcinoma

CONTEXT

p53, c-erbB-2 and epidermal growth factor receptor (EGFR) are cancer-related proteins that are usually expressed in head and neck squamous cell carcinoma (SCC). Their prognostic value remains controversial.

OBJECTIVE

To evaluate the prognostic impact of p53, c-erbB-2 and EGFR expression in head and neck SCC.

TYPE OF STUDY

Prospective.

SETTING

Head and Neck Surgery Department, Hospital AC Camargo, São Paulo.

METHODS

Fifty-four patients were studied for p53, c-erbB-2 and EGFR expression in head and neck SCC and adjacent mucosa, via immunohistochemistry. These data were correlated with histoclinical data and survival.

RESULTS

There was a direct association of p53 expression in SCC and mucosa (p = 0.001); loss of c-erbB-2 expression (-) from normal mucosa to SCC (p = 0.04); lower frequency of association of c-erbB-2 (+) with EGFR (-) in SCC (p = 0.02); and a direct association of EGFR (+) expression in SCC and mitotic index (p = 0.03). The 60-month actuarial survival rates for patients presenting lymph node metastasis were higher when there was no capsule rupture by SCC (48.3%; p = 0.02), no more than one positive lymph node (52.3%; p = 0.004) or clear surgical margins (47.0%; p = 0.01), in comparison with patients presenting capsule rupture (20.2%), two or more positive lymph nodes (18.7%) or compromised surgical margins (0.0%), respectively. Patients presenting SCC p53 (+) and EGFR (-) demonstrated greater survival (75.0%; p = 0.03) than for the remaining group (33.1%). Multivariate analysis confirmed the positive impact of p53 (+) and EGFR (-) on survival (p = 0.02).

DISCUSSION

Associations were found for p53, c-erbB-2 and EGFR expression with histoclinical data and prognosis. Interestingly, these results suggest that loss of mucosal c-erbB-2 expression could be involved in SCC carcinogenesis; EGFR expression in SCC is related to tumor mitotic index; and presence of p53 with absence of EGFR expression in head and neck SCC may be a prognostic factor for survival.

CONCLUSIONS

Further prospective studies should be conducted to confirm the influence of p53, c-erbB-2 and EGFR on histoclinical data and prognosis.

Effects of epidermal growth factor and its signal transduction inhibitors on apoptosis in human colorectal cancer cells

AIM: The study investigated if EGF signaling inhibitors, EGF antibody and tyrphostin 51 (a tyrosine kinase inhibitor), mediated the action of EGF on apoptosis and the expression of EGF receptors and p21 (a cyclin-dependent kinase inhibitor) of human colorectal cancer cells.

METHODS: Human colorectal adenocarcinoma cells (SW480) were incubated with 0.6 mL/L dimethyl sulfoxide (DMSO, the control group), 225 ng/mL (37.5 nmol/L) EGF in 0.6 mL/L DMSO, 225 ng/mL EGF + 2.5 μg/mL (17 nmol/L) EGF antibody in 0.6 mL/L DMSO, or 225 ng/mL EGF+215 ng/mL (0.8 μmol/L) tyrphostin 51 in 0.6 mL/L DMSO.

RESULTS: After 48 h incubation, the levels of EGF in medium significantly increased (P < 0.05) in the EGF-treated groups. The numbers of apoptotic cells were significantly fewer (P < 0.05) in the EGF + EGF antibody and EGF + tyrphostin 51 groups than those in the control and EGF groups after 12 h treatments. The expression of phosphorylated EGF receptors in the EGF, EGF + EGF antibody, and EGF + tyrphostin 51 groups was 176.8%, 62.4%, and 138.1% of the control group, respectively. The expression of p21 protein in the EGF, EGF + EGF antibody, and EGF + tyrphostin 51 groups was 115.7%, 4.8%, and 61.5% of the control group, respectively.

CONCLUSION: The data suggest that EGF antibody and tyrphostin 51 can inhibit the action of EGF on apoptosis in human colorectal cancer cells through down-regulation of EGF receptor and p21 expression.

The invasive phenotype in HMT-3522 cells requires increased EGF receptor signaling through both PI 3-kinase and ERK 1,2 pathways

We studied the invasion of HMT-3522 breast epithelial cells in response to epidermal growth factor (EGF), and the associated signaling pathways. HMT-3522 T4-2 cells were shown to invade Matrigel-coated Transwell membranes in response to EGF while HMT-3522 S-1 cells failed to invade when treated with EGF. Studies utilizing specific molecular inhibitors showed the importance of beta1 integrin, phosphatidylinositol 3 kinase (PI 3-kinase), p38, extracellular regulated kinase 1, 2 (Erk 1,2) MAP kinases, and metalloproteinases in invasion and motility. T4-2 cell invasion was shown to be time-dependent and also gene transcription-dependent as shown by inhibition with Actinomycin D. T4-2 cells exhibited an increased activation of MAP kinases Erk 1,2 (2-fold), EGF receptor (3-fold), and PI 3-kinase (3- to 4-fold) when compared to the S-1 cells. In response to EGF, T4-2 cells showed a 5-fold greater secretion of matrix metalloproteinase-9 (MMP-9) as compared to S-1 cells, and this increase was largely dependent on the activity of PI 3-kinase. These findings indicate that expression of the invasive phenotype in these breast epithelial cells requires increased EGF receptor signaling, involving both PI 3-kinase and Erk 1,2 activities, which leads to multiple downstream effects, including enhanced secretion of MMP-9 and transcription of invasion-related genes.

Beta-catenin--a linchpin in colorectal carcinogenesis?

An important role for beta-catenin pathways in colorectal carcinogenesis was first suggested by the protein's association with adenomatous polyposis coli (APC) protein, and by evidence of dysregulation of beta-catenin protein expression at all stages of the adenoma-carcinoma sequence. Recent studies have, however, shown that yet more components of colorectal carcinogenesis are linked to beta-catenin pathways. Pro-oncogenic factors that also release beta-catenin from the adherens complex and/or encourage translocation to the nucleus include ras, epidermal growth factor (EGF), c-erbB-2, PKC-betaII, MUC1, and PPAR-gamma, whereas anti-oncogenic factors that also inhibit nuclear beta-catenin signaling include transforming growth factor (TGF)-beta, retinoic acid, and vitamin D. Association of nuclear beta-catenin with the T cell factor (TCF)/lymphoid enhancer factor (LEF) family of transcription factors promotes the expression of several compounds that have important roles in the development and progression of colorectal carcinoma, namely: c-myc, cyclin D1, gastrin, cyclooxygenase (COX)-2, matrix metalloproteinase (MMP)-7, urokinase-type plasminogen activator receptor (aPAR), CD44 proteins, and P-glycoprotein. Finally, genetic aberrations of several components of the beta-catenin pathways, eg, Frizzled (Frz), AXIN, and TCF-4, may potentially contribute to colorectal carcinogenesis. In discussing the above interactions, this review demonstrates that beta-catenin represents a key molecule in the development of colorectal carcinoma.

Cancer cell motility--on the road from c-erbB-2 receptor steered signaling to actin reorganization

Cell migration depends mainly on actin polymerization and intracellular organization, which are influenced by a vast variety of actin binding proteins (ABPs). Regulation of ABP activity is mediated by second messengers such as phosphoinositides and calcium. Signaling via these second messengers is initiated and regulated by membrane receptors, e.g., receptor tyrosine kinases (RTKs), and by adhesion molecule interactions (e.g., integrins and selectins) and focal adhesion kinases. A major role in steering second-messenger signaling and thus in actin cytoskeleton reorganization and motility of cancer cells is played by the RTK c-erbB-2. This occurs through a number of signaling pathways which involve mainly enzymes, e.g., phospholipase Cgamma1 and GTPases, which modify signaling molecules. Furthermore large multiprotein complexes including actin-related protein 2/3, Wiskott-Aldrich syndrome protein, profilin, and capping protein among others play an important role in regulating actin reorganization. The complex picture of the mode of actin reorganization, which is involved in tumor cell migration, is slowly emerging from the mists of cellular signaling pathways, but this is still by no means a clear view.

Epidermal growth factor (EGF)-like repeats of human tenascin-C as ligands for EGF receptor

Signaling through growth factor receptors controls such diverse cell functions as proliferation, migration, and differentiation. A critical question has been how the activation of these receptors is regulated. Most, if not all, of the known ligands for these receptors are soluble factors. However, as matrix components are highly tissue-specific and change during development and pathology, it has been suggested that select growth factor receptors might be stimulated by binding to matrix components. Herein, we describe a new class of ligand for the epidermal growth factor (EGF) receptor (EGFR) found within the EGF-like repeats of tenascin-C, an antiadhesive matrix component present during organogenesis, development, and wound repair. Select EGF-like repeats of tenascin-C elicited mitogenesis and EGFR autophosphorylation in an EGFR-dependent manner. Micromolar concentrations of EGF-like repeats induced EGFR autophosphorylation and activated extracellular signal-regulated, mitogen-activated protein kinase to levels comparable to those induced by subsaturating levels of known EGFR ligands. EGFR-dependent adhesion was noted when the ligands were tethered to inert beads, simulating the physiologically relevant presentation of tenascin-C as hexabrachion, and suggesting an increase in avidity similar to that seen for integrin ligands upon surface binding. Specific binding to EGFR was further established by immunofluorescence detection of EGF-like repeats bound to cells and cross-linking of EGFR with the repeats. Both of these interactions were abolished upon competition by EGF and enhanced by dimerization of the EGF-like repeat. Such low affinity behavior would be expected for a matrix-"tethered" ligand; i.e., a ligand which acts from the matrix, presented continuously to cell surface EGF receptors, because it can neither diffuse away nor be internalized and degraded. These data identify a new class of "insoluble" growth factor ligands and a novel mode of activation for growth factor receptors.

Induction of angiogenesis by hyperplastic colonic mucosa adjacent to colon cancer

We determined whether hyperplastic mucosa adjacent to colon cancer contributes to neoplastic angiogenesis. Surgical specimens of human colon cancer (40 Dukes' stage B and 34 Dukes' stage C) were analyzed by immunohistochemistry for expression of proliferative and angiogenic molecules. The mucosa adjacent to Dukes' stage C tumors (but not Dukes' stage B tumors) had a higher Ki-67 labeling index and a higher expression of epidermal growth factor receptor and transforming growth factor-alpha than distant mucosa. The expression levels of vascular endothelial growth factor, basic fibroblast growth factor, interleukin-8, and the vascular density in the adjacent mucosa were similar to those in the tumor lesions and significantly higher than those in the distant mucosa. The expression of interferon-beta inversely correlated with the level of pro-angiogenic molecules and the vascular density. The injection of metastatic human colon cancer cells and murine colon cancer cells into the cecal wall of mice induced hyperplastic changes in the adjacent mucosa which expressed higher levels of epidermal growth factor receptor, basic fibroblast growth factor, and vascular endothelial growth factor, and lower levels of interferon-beta than did the control mucosa, which directly correlated with the degree of hyperplasia. These data suggest that metastatic human colon cancer cells can induce hyperplasia in the adjacent mucosa, which in turn produces angiogenic molecules that contribute to neoplastic angiogenesis.

Repopulation of tumour cells between cycles of chemotherapy: a neglected factor

Repopulation of clonogenic tumour cells during fractionated radiation treatment is recognised as an important factor affecting local control. Given the longer intervals between cycles and longer total duration of treatment, the impact of repopulation is likely to be greater following chemotherapy. Limited data from experimental models suggest that, after chemotherapy, there is a 'lag period', followed by variable but rapid rates of repopulation of tumour cells, possibly accelerating between cycles. Modelling of these properties indicates that after the initial response, accelerated repopulation between cycles can lead to tumour regrowth without any change in the drug sensitivity of the tumour cells. The importance of repopulation may be comparable with that of intrinsic or acquired cellular resistance in determining the effective resistance of tumours to chemotherapy. Biological agents with rapid onset and short duration of action, which can selectively inhibit tumour-cell repopulation, administered between cycles of chemotherapy, might improve the therapeutic index.

Mammary gland specific hEGF receptor transgene expression induces neoplasia and inhibits differentiation

The epidermal growth factor receptor (EGFR) is overexpressed in about 48% of human breast cancer tissues. To analyse the role of the EGFR in mammary tumor development we generated transgenic mice expressing the human EGFR under the control of either the MMTV-LTR (MHERc) or the beta-lactoglobulin promoter (BLGHERc). The BLGHERc-transgene was expressed exclusively in the female mammary gland, whereas the MHERc transgene was expressed more promiscuously in other organs, such as ovary, salivary gland and testis. Female virgin and lactating transgenic mice of both strains have impaired mammary gland development. Virgin EGFR transgenic mice developed mammary epithelial hyperplasias, whereas in lactating animals progression to dysplasias and tubular adenocarcinomas was observed. In both strains the number of dysplasias increased after multiple pregnancies. The transgene expression pattern was heterogeneous, but generally restricted to regions of impaired mammary gland development. Highest EGFR transgene expression was observed in adenocarcinomas. By using a whole mount organ culture system to study the differentiation potential of the mammary epithelium, we observed a reduced number of fully developed alveoli and a decrease in whey acidic protein expression. Taken together, EGFR overexpression results in a dramatic effect of impaired mammary gland development in vitro as well as in vivo, reducing the differentiation potential of the mammary epithelium and inducing epithelial cell transformation.

Shaping up for shipping out: PLCgamma signaling of morphology changes in EGF-stimulated fibroblast migration

For effective migration, cells must establish an asymmetry in cell/substratum biophysical interactions permitting cellular protrusive and contractile motive forces to produce net cell body translocation; often this is superficially manifested as a polarized cell shape. This change is most easily noted for epithelial cells, which typically undergo a mesenchymal transition prior to rapid motility, and for hematopoietic cells, which must transition from non-adherent to adherent states. These two situations entail dramatic changes that also involve cell-cell contact and differentiation-related changes, and thus introduce confounding events and signals in defining control elements. Hence, a simpler biochemical and biophysical model system may be useful for gaining fundamental insights into the underlying mechanisms. Fortunately, even relatively "uniform" fibroblasts also undergo an initial shape change to commence locomotion. Investigators have recently begun to probe underlying signals that contribute to the reorganization of the actin cytoskeleton. We describe here a model for fibroblast shape changes involved in epidermal growth factor (EGF) stimulation of motility, focusing on signals through EGF receptor (EGFR) -mediated pathways influencing cytoskeletal organization and cell/substratum adhesion. We present new data addressing specifically phospholipase C-gamma (PLCgamma) pathway activation of actin-modifying proteins, including gelsolin, that contributes to these changes and promotes cell migration by increasing the fraction of cells in a motility-permissive morphology and the time spent in such a state.

Tumor invasion: role of growth factor-induced cell motility

Cancer progression to the invasive and metastatic stage represents the most formidable barrier to successful treatment. To develop rational therapies, we must determine the molecular bases of these transitions. Cell motility is one of the defining characteristics of invasive tumors, enabling tumors to migrate into adjacent tissues or transmigrate limiting basement membranes and extracellular matrices. Invasive tumor cells have been demonstrated to present dysregulated cell motility in response to extracellular signals from growth factors and cytokines. Recent findings suggest that this growth factor receptor-mediated motility is one of the most common aberrations in tumor cells leading to invasiveness and represents a cellular behavior distinct from-adhesion-related haptokinetic and haptotactic migration. This review focuses on the emerging understanding of the biochemical and biophysical foundations of growth factor-induced cell motility and tumor cell invasiveness, and the implications for development of targeted agents, with particular emphasis on signaling from the epidermal growth factor (EGF) and hepatocyte growth factor (HGF) receptors, as these have most often been associated with tumor invasion. The nascent models highlight the roles of various intracellular signaling pathways including phospholipase C-gamma (PLC gamma), phosphatidylinositol (PI)3'-kinase, mitogen-activated protein (MAP) kinase, and actin cytoskeleton-related events. Development of novel agents against tumor invasion will require not only a detailed appreciation of the biochemical regulatory elements of motility but also a paradigm shift in our approach to and assessment of cancer therapy.

Altered expression of the suppressors PML and p53 in glioblastoma cells with the antisense-EGF-receptor

Gene amplification and enhanced expression of the epidermal growth factor receptor (EGFR) represent the major molecular genetic alteration in glioblastomas and it may play an essential role in cell growth and in the carcinogenic process. On the other hand, the nuclear suppressor proteins PML and p53 are also known to play critical roles in cancer development and in suppressing cell growth. Here we report that, in glioblastoma cells with defective EGFR function, the expressions of both promyelocytic leukaemia (PML) and p53 were altered. Cells that were transfected with the antisense-cDNA of EGFR were found to have more cells in G1 and fewer cells in S phase. In addition, the transfected cells were found to be non-responsive to EGF-induced cell growth. Interestingly, the expression of the suppressors p53 and PML were found to be significantly increased by immunohistochemical assay in the antisense-EGFR cells. Moreover, the PML expression in many of the cells was converted from the nuclear dot pattern into fine-granulated staining pattern. In contrast, the expressions of other cell cycle regulated genes and proto-oncogene, including the cyclin-dependent kinase 4 (cdk4), retinoblastoma, p16INK4a and p21H-ras, were not altered. These data indicate that there are specific inductions of PML and p53 proteins which may account for the increase in G1 and growth arrest in antisense-EGFR treated cells. It also indicates that the EGF, p53 and PML transduction pathways were linked and they may constitute an integral part of an altered growth regulatory programme. The interactions and cross-talks of these critical molecules may be very important in regulating cell growth, differentiation and cellular response to treatment in glioblastomas.

Efficacy and specificity of antisense laminin chain-specific expression vectors in blocking laminin induction by TGFbeta1: effect of laminin blockade on TGFbeta1-mediated cellular responses

Transforming growth factorbeta1 (TGFbeta1) elicits a multitude of cellular responses from the epithelial-derived human colon cancer Moser cells. TGFbeta1 induces the expression of laminin and fibronectin, and previous studies show that the induction of fibronectin is functionally associated with the regulation of carcinoembryonic antigen (CEA) expression by TGFbeta1 (Huang and Chakrabarty, 1994, J Biol Chem 269:28764-28768). In this study we constructed antisense laminin chain-specific expression vectors and determined their efficacy in blocking the expression and the induction of the large multichain laminin molecule by TGFbeta1. We also determined the functional role of laminin in several TGFbeta1-mediated responses: growth inhibition, downmodulation of anchorage-independent growth, and cellular invasion. Expression of either antisense laminin chain A, B1, or B2 RNA resulted in a downmodulation of endogenous laminin mRNA expression and blocked the induction of laminin protein by TGFbeta1 without affecting the induction of other adhesion molecules such as fibronectin or CEA. It is concluded that antisense RNA directed to only one of the laminin chains was sufficient to disrupt the induction of the complex laminin molecule in quite a specific manner. Expression of antisense laminin RNA downregulated cellular adhesion to extracellular matrix (ECM) laminin and blocked the ability of TGFbeta1 to upmodulate adhesion to ECM laminin. Expression of antisense laminin RNA, however, did not alter the downregulating effect of TGFbeta1 on cellular proliferation, anchorage-independent growth, or cellular invasion, suggesting that the induction of laminin did not play a significant functional role in these TGFbeta1-mediated cellular responses. It is likely that other adhesion pathways may be involved in mediating the action of TGFbeta1 in this cell line.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Differentiation-promoting effect of 1-O (2 methoxy) hexadecyl glycerol in human colon cancer cells

Alkylglycerols are naturally occurring bioactive ether lipids found in great abundance in the livers of many marine species. In this study, we evaluated the differentiation-promoting potential of a methoxy substituted alkylglycerol--1-O (2 methoxy) hexadecyl glycerol (MHG)--to promote a more benign or differentiated phenotype in human colon cancer cells. Three cell lines with different biological and phenotypic properties were used. They were the moderately differentiated and growth factor-responsive Moser, the growth factor-unresponsive and malignant HT29, and the poorly differentiated and growth factor-unresponsive HCT116. Treatment of these cell lines with MHG resulted in a downmodulation of cellular proliferation, a reduced propensity for anchorage-independent growth, and a reduced capacity in cellular invasion. Induction of the colon-associated and differentiation-related molecule carcinoembryonic antigen was also observed in the three cell lines. Induction of the transformation-sensitive and differentiation-related glycoprotein fibronectin was observed in the HT29 cells. It is concluded that MHG was biologically active and promoted a more benign or differentiated phenotype in these colon cancer cells. Since differentiation-inducing agents may possess chemoprevention properties, the use of MHG and the alkylglycerols in inducing differentiation or in chemoprevention of malignant diseases warrants further investigation.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Epidermal growth factor receptor-mediated motility in fibroblasts

Cell motility is induced by many growth factors acting through cognate receptors with intrinsic tyrosine kinase activity (RPTK). However, most of the links between receptor activation and the biophysical processes of cell motility remain undeciphered. We have focused on the mechanisms by which the EGF receptor (EGFR) actuates fibroblast cell motility in an attempt to define this integrated process in one system. Our working model is that divergent, but interconnected pathways lead to the biophysical processes necessary for cell motility: cytoskeleton reorganization, membrane extension, formation of new adhesions to substratum, cell contraction, and release of adhesions at the rear. We postulate that for any given growth factor some of the pathways/processes will be actively signaled and rate-limiting, while others will be permissive due to background low-level activation. Certain couplings have been defined, such as PLCgamma and actin modifying proteins being involved in cytoskeletal reorganization and lamellipod extension and MEK being implicated in detachment from substratum. Others are suggested by complementary investigations in integrin-mediated motility, including rac in membrane protrusion, rho in new adhesions, myosin II motors in contraction, and calpain in detachment, but have yet to be placed in growth factor-induced motility. Our model postulates that many biochemical pathways will be shared between chemokinetic and haptokinetic motility but that select pathways will be activated only during RPTK-enhanced motility.

Antisense epidermal growth factor receptor RNA transfection in human malignant glioma cells leads to inhibition of proliferation and induction of differentiation

The epidermal growth factor receptor (EGFR) is a protooncogene that is frequently observed with alterations in late stage gliomas, suggesting an important role of this gene in glial tumorigenesis and progression. In this study we evaluated an antisense EGFR approach as an alternative therapeutic modality for glioblastomas. We transfected U-87MG cells with an antisense EGFR construct and obtained several clones stably expressing lower or undetectable levels of EGFR protein. These clones were found to have impaired proliferation as well as a reduced transforming potential to grow in soft agarose. The number of cells positive for the cell cycle-specific nuclear antigen Ki-67 was also significantly decreased (P < 0.05) in antisense EGFR-transfected clones compared with parental or empty vector-transfected cells. Flow cytometric analysis revealed that the proportion of cells in G0/G1 phases of the cell cycle in the antisense clones increased by up to 31% compared with control cells, whereas the proportion of cells in S phase decreased by up to 58%. In addition, the antisense EGFR-transfected cells showed higher expression of glial fibrillary acidic protein and a more differentiated form, with smaller cell bodies possessing fine tapering cell processes. These results suggest that EGFR plays a major role in modulating cell growth and differentiation in glioblastoma cells. Our experimental model of antisense EGFR provides a basis for future development of antisense EGFR oligodeoxynucleotides in treatment of glioblastomas.

Epidermal growth factor alters fibroblast migration speed and directional persistence reciprocally and in a matrix-dependent manner

Growth factors stimulate sustained cell migration as well as inducing select acute motility-related events such as membrane ruffling and disruption of focal adhesions. However, an in-depth understanding of the characteristics of sustained migration that are regulated by growth factor signals is lacking: how the biochemical signals are related to physical processes underlying locomotion, and how these events are coordinately influenced by interplay between growth factor and matrix substratum signals. To address these issues, we studied sustained migration of NR6 fibroblasts on a complex human matrix substratum, Amgel, comparing effects of epidermal growth factor (EGF) treatment across a range of Amgel levels. In the absence of EGF, cell migration speed and directional persistence are relatively independent of Amgel level, whereas in the presence of EGF speed is increased at intermediate Amgel levels but not at low and high Amgel levels while directional persistence is decreased at intermediate but not at low and high Amgel levels. The net effect of EGF is to increase the frequency of changes in the cell direction, and at the same time to slightly increase the path-length and thereby greatly enhance random dispersion of cells. Despite increasing migration speed during long-term sustained migration EGF treatment does not lead to significantly increased absolute rates of membrane extension in contrast to its well-known elicitation of membrane ruffling in the short term. However, EGF treatment does decrease cell spread area, yielding an apparent enhancement of specific membrane extension rate, i.e. normalized to cell spread area. Cell movement speed and directional persistence are thus, respectively, directly related and indirectly related to the increase in specific membrane extension rate (alternatively, the decrease in cell spread area) induced by EGF treatment during sustained migration. These results indicate that growth factor and matrix substrata coordinately regulate sustained cell migration through combined governance of underlying physical processes.

Differential expression of epidermal growth factor receptor in human head and neck cancers

BACKGROUND

Over-expression of human epidermal growth factor receptor (EGFR) is associated with a variety of human malignancies, including head and neck cancer. It has also been studied for its effect on cancer cell responses to chemotherapy. To accurately measure changes in EGFR expression that might be of diagnostic or prognostic importance in head and neck cancers, a quantitative assay for the direct detection of EGFR messenger ribonucleic acid (mRNA) was developed.

METHODS

Our method was based on competitive reverse transcriptase-polymerase chain reaction (RT-PCR) that was able to measure EGFR mRNA levels undetectable by northern-blot analysis. We measured EGFR mRNA by RT-PCR in human head and neck cancers and their corresponding adjacent, histologically normal tissues and in cisplatin-treated and untreated oral epithelial cell lines.

RESULTS

All the tumor samples had higher EGFR mRNA levels than their corresponding adjacent normal tissues. It is also shown that EGFR mRNA levels in normal oral epithelial cells were elevated after exposure to cisplatin. In contrast, EGFR mRNA levels in oral cancer cells were decreased after the exposure, suggesting that increased EGFR expression may have different functions in cancer cells and in normal cells under stress.

CONCLUSIONS

Accurate monitoring of EGFR expression may be a useful marker for diagnosis, treatment, and prognosis of head and neck cancer.

EGFR antisense RNA blocks expression of the epidermal growth factor receptor and partially reverse the malignant phenotype of human breast cancer MDA-MB-231 cells

The effects of human EGFR to the malignant phenotype of human breast cancer cell line MDA-MB-231 were investigated experimentally. A retroviral vector containing a 5'1350bp fragment of the human EGFR cDNA in the antisense orientation was transfected into targeted cells by lipofectamine. The effects on cell proliferation, cell cycle and adherent ability to extracellular matrix (ECM) components were studied after the expression of antisense transcripts to EGFR 5'1350bp fragment in target cells. In vitro studies showed that the growth ability of the transfected cells was partially inhibited in comparison to parental cells and to cells transfected with the plasmid containing the neomycin resistance gene only. It was found that EGF (10 ng/ml) had an argumenation effect on the growth of transfected MDA-AS10 cells but not MDA-MB-231 cells. Flow cytometric analysis showed that the cell cycle of the transfected cells was abnormal with a decrease of cells in G2/M and S phases and an increase of cells in G1 phase, indicating a blockage in phase G1. Immunofluorescence of EGFR expression in transfectants stained with an anti-EGFR antibody was decreased and their growth in soft agarose was also severely impaired. The transfected cells showed less adherence to laminin (LN) and fibronectin (FN). In short, EGFR antisense RNA decreases the expression of EGFR on MDA-MB-231 cells and partially reverses their malignant phenotype as well.

In vivo pharmacology and anti-tumour evaluation of the tyrphostin tyrosine kinase inhibitor RG13022

Amplification and increased expression of many growth factor receptors, including the epidermal growth factor receptor (EGFR), has been observed in human tumours. One therapeutic strategy for overcoming EGF autocrine control of tumour growth is inhibition of EGFR protein tyrosine kinase (PTK). A series of low molecular weight molecules have been identified which inhibit the EGFR PTK in vitro and demonstrate antiproliferative activity against human cancer cell lines with high expression of EGFR. A significant growth delay in squamous cancer xenografts has been reported for one of these compounds, the tyrphostin RG13022. Based on these encouraging results, we sought to confirm the activity of RG13022 in vivo and relate the effects to the in vivo plasma disposition. RG13022 and three additional peaks were detected by HPLC following intraperitoneal administration of 20 mg kg-1 RG13022 in MF1 nu/nu mice. RG13022 demonstrated rapid biexponential elimination from plasma with a terminal half-life of 50.4 min. RG13022 plasma concentrations were less than 1 microM by 20 min post injection. A primary product was identified as the geometrical isomer (E)-RG13022. Both RG13022 and its geometrical isomer inhibited DNA synthesis in HN5 cells after a 24 h in vitro incubation (IC50 = 11 microM and 38 microM respectively). Neither RG13022 nor its geometrical isomer displayed significant cytotoxicity. RG13022 had no influence on the growth of HN5 tumours when administered chronically, starting either on the day of tumour inoculation or after establishment of tumour xenografts. The rapid in vivo elimination of RG13022 has potential significance to the development of this and other related tyrphostin tyrosine kinase inhibitors, as plasma concentrations fell below that required for in vitro activity by 20 min post injection. The lack of in vivo tumour growth delay suggests that a more optimal administration schedule for RG13022 would include more frequent injections or continuous administration. An improved formulation for RG13022 is therefore required before further development of this or other similar protein tyrosine kinase inhibitors can be made. Alternative strategies should also be sought which display longer lasting in vivo exposures.

EGF receptor signaling enhances in vivo invasiveness of DU-145 human prostate carcinoma cells

Carcinomas of the prostate and other lineages often present an autocrine stimulatory loop acting via the EGF receptor (EGFR). We have recently shown that EGFR-mediated signals enhance DU-145 prostate carcinoma cell transmigration of an extracellular matrix in vitro, and that this increased invasiveness was independent of proteolytic degradation of the matrix (Xie et al., 1995, Clin Exp Metastasis, 13, 407). To determine whether up-regulated EGFR signaling promotes tumor progression in vivo and to define the EGFR-induced cell property responsible, we inoculated athymic mice with genetically-engineered DU-145 cells. Parental DU-145 cells and those transduced to overexpress a full-length wild type (WT) EGFR formed tumors and metastasized to the lung when inoculated in the prostate and peritoneal cavity. The WT DU-145 tumors were more invasive. DU-145 cells expressing a mitogenically-active, but motility-deficient (c'973) EGFR formed small, non-invasive tumors without evidence of metastasis. All three sublines demonstrated identical, EGFR-dependent rates of cell growth in vitro, suggesting that the differential invasiveness was not due to altered growth rates. To determine whether cell motility may be, in part, responsible for tumor invasiveness, we treated WT DU-145 intraperitoneal tumors with a pharmacologic agent (U73122) which blocks EGFR-mediated cell motility but not mitogenesis. Under this treatment regimen, the WT DU-145 cells formed tumors of similar numbers and size to those formed without treatment; however, these tumors were much less invasive. These data suggest that EGFR-mediated cell motility is an important mechanism involved in tumor progression, and that this cell property may represent a novel target to limit the spread of tumors.

Epidermal growth factor modulates cell attachment to hyaluronic acid by the cell surface glycoprotein CD44

Cell adhesion to and migration through extracellular matrices (ECM) are critical events in tumor invasion and metastasis. Previous work by us had demonstrated that signaling of epidermal growth factor receptor (EGFR) confers an oncogenic phenotype on NR6 cells and that these cells when transfected with holo EGFR demonstrate greater motility and invasiveness than cells carrying a carboxy-terminal truncated EGFR. Recently, a cell surface glycoprotein, CD44, has been implicated in cell-ECM adhesion involved in tumor cell migration, signal transduction, and metastasis. We investigated whether EGF regulates cellular interactions with ECM components, and in particular, hyaluronate, by modulating CD44 expression. In vitro cell attachment assays on hyaluronate-coated plates demonstrated similar basal level of binding (approximately 33%) for murine NR6 parental cells devoid of endogenous EGFR (P) or expressing wild-type EGFR (WT), while a time-dependent increase in binding was observed in WT cells stimulated with EGF. Additionally, utilizing monoclonal antibody blocking assays, CD44, but not EGFR, was shown to be directly involved in this attachment. Both WT and P cells possessed equivalent 95 kDa bands on immunoblots, corresponding to CD44. The existence of CD44 mRNA was verified by RT-PCR using synthetic oligonucleotides in which a 1.1 kb cDNA was detected in both cell lines and confirmed by DNA sequencing. After 24-h exposure to exogenous EGF, an increase in CD44 protein and mRNA expression was found in WT cells, but not in P cells, supporting the contention that a functional EGFR signaling pathway is required for CD44 regulation. Thus, EGF stimulates cell binding to hyaluronate in vitro by regulating CD44 expression.