Differences in sensitivity of biological functions mediated by epidermal growth factor receptor activation with respect to endogenous and exogenous ligands

A review of electrochemical impedance as a tool for examining cell biology and subcellular mechanisms: merits, limits, and future prospects

Herein the development of cellular impedance biosensors, electrochemical impedance spectroscopy, and the general principles and terms associated with the cell-electrode interface is reviewed. This family of techniques provides quantitative and sensitive information into cell responses to stimuli in real-time with high temporal resolution. The applications of cell-based impedance biosensors as a readout in cell biology is illustrated with a diverse range of examples. The current state of the field, its limitations, the possible available solutions, and the potential benefits of developing biosensors are discussed.

Cabazitaxel suppresses colorectal cancer cell growth via enhancing the p53 antitumor pathway

There were approximately 1.93 million new cases and 940 000 deaths from colorectal cancer in 2020. The first‐line chemotherapeutic drugs for colorectal cancer are mainly based on 5‐fluorouracil, although the use of these drugs is limited by the development of drug resistance. Consequently, there is a need for novel chemotherapeutic drugs for the efficient treatment of colorectal cancer patients. In the present study, we screened 160 drugs approved by the Food and Drug Administration and identified that cabazitaxel (CBT), a microtube inhibitor, can suppress colony formation and cell migration of colorectal cancer cells in vitro. CBT also induces G2/M phase arrest and apoptosis of colorectal cancer cells. Most importantly, it inhibits the growth of colorectal cancer cell xenograft tumors in vivo. Transcriptome analysis by RNA‐sequencing revealed that Tub family genes are abnormally expressed in CBT‐treated colorectal cancer cells. The expression of several p53 downstream genes that are associated with cell cycle arrest, apoptosis, and inhibition of angiogenesis and metastasis is induced by CBT in colorectal cancer cells. Overall, our results suggests that CBT suppresses colorectal cancer by upregulating the p53 pathway, and thus CBT may have potential as an alternative chemotherapeutic drug for colorectal cancer.

H2S-Releasing Polymer Micelles for Studying Selective Cell Toxicity

We report the preparation of S-aroylthiooxime (SATO) functionalized amphiphilic block copolymer micelles that release hydrogen sulfide (H₂S), a gaseous signaling molecule of relevance to various physiological and pathological conditions. The micelles release H₂S in response to cysteine with a half-life of 3.3 h, which is substantially slower than a related small molecule SATO. Exogenous administration of H₂S impacts growth and proliferation of cancer cells; however, the limited control over H₂S generation from inorganic sulfide sources results in conflicting reports. Therefore, we compare the cellular cytotoxicity of SATO-functionalized micelles, which release H₂S in a sustained manner, to Na₂S, which releases H₂S in a single dose. Our results show that H₂S-releasing micelles significantly reduce the survival of HCT116 colon cancer cells relative to Na₂S, GYY4137, and a small molecule SATO, indicating that release kinetics may play an important role in determining toxicity of H₂S toward cancer cells. Furthermore, H₂S-releasing micelles are well tolerated by immortalized fibroblasts (NIH/3T3 cells), suggesting a selective toxicity of H₂S toward cancer cells.

Synthetic genistein glycosides inhibiting EGFR phosphorylation enhance the effect of radiation in HCT 116 colon cancer cells

The need to find new EGFR inhibitors for use in combination with radiotherapy in the treatment of solid tumors has drawn our attention to compounds derived from genistein, a natural isoflavonoid. The antiproliferative potential of synthetic genistein derivatives used alone or in combination with ionizing radiation was evaluated in cancer cell lines using clonogenic assay. EGFR phosphorylation was assessed with western blotting. Genistein derivatives inhibited clonogenic growth of HCT 116 cancer cells additively or synergistically when used in combination with ionizing radiation, and decreased EGFR activation. Our preclinical evaluation of genistein-derived EGFR inhibitors suggests that these compounds are much more potent sensitizers of cells to radiation than the parent isoflavonoid, genistein and indicate that these compounds may be useful in the treatment of colon cancer with radiation therapy.

B7-H1 expression is associated with poor prognosis in colorectal carcinoma and regulates the proliferation and invasion of HCT116 colorectal cancer cells

Background And Objective

The investigation concerning the B7-H1 expression in colorectal cancer cells is at an early stage. It is unclear whether B7-H1 expression may have diagnostic or prognostic value in colorectal carcinoma. Additionally, how B7-H1 is associated with the clinical features of colorectal carcinoma is not known. In order to investigate the relationship between B7-H1 and colorectal cancer, we analyzed B7-H1 expression and its effect in clinical specimens and HCT116 cells.

Methods

Paraffin-embedded specimens from 143 eligible patients were used to investigate the expression of CD274 by immunohistochemistry. We also examined whether B7-H1 itself may be related to cell proliferation, apoptosis, migration and invasion in colon cancer HCT116 cells.

Results

Our results show that B7-H1 was highly expressed in colorectal carcinoma and was significantly associated with cell differentiation status and TNM (Tumor Node Metastasis) stage. Patients with positive B7-H1 expression showed a trend of shorter survival time. Using multivariate analysis, we demonstrate that positive B7-H1 expression is an independent predictor of colorectal carcinoma prognosis. Our results indicate that B7-H1 silencing with siRNA inhibits cell proliferation, migration and invasion. Furthermore, cell apoptosis was also increased by B7-H1 inhibition.

Conclusions

Positive B7-H1 expression is an independent predictor for colorectal carcinoma prognosis. Moreover, knockdown of B7-H1 can inhibit cell proliferation, migration and invasion.

Neuropilin-1-dependent regulation of EGF-receptor signaling

Neuropilin-1 (NRP1) is a coreceptor for multiple extracellular ligands. NRP1 is widely expressed in cancer cells and in advanced human tumors; however, its functional relevance and signaling mechanisms are unclear. Here, we show that NRP1 expression controls viability and proliferation of different cancer cells, independent of its short intracellular tail. We found that the extracellular domain of NRP1 interacts with the EGF receptor (EGFR) and promotes its signaling cascade elicited upon EGF or TGF-α stimulation. Upon NRP1 silencing, the ability of ligand-bound EGFR to cluster on the cell surface, internalize, and activate the downstream AKT pathway is severely impaired. EGFR is frequently activated in human tumors due to overexpression, mutation, or sustained autocrine/paracrine stimulation. Here we show that NRP1-blocking antibodies and NRP1 silencing can counteract ligand-induced EGFR activation in cancer cells. Thus our findings unveil a novel molecular mechanism by which NRP1 can control EGFR signaling and tumor growth.

Role of protein kinase C and epidermal growth factor receptor signalling in growth stimulation by neurotensin in colon carcinoma cells

Background

Neurotensin has been found to promote colon carcinogenesis in rats and mice, and proliferation of human colon carcinoma cell lines, but the mechanisms involved are not clear. We have examined signalling pathways activated by neurotensin in colorectal and pancreatic carcinoma cells.

Methods

Colon carcinoma cell lines HCT116 and HT29 and pancreatic adenocarcinoma cell line Panc-1 were cultured and stimulated with neurotensin or epidermal growth factor (EGF). DNA synthesis was determined by incorporation of radiolabelled thymidine into DNA. Levels and phosphorylation of proteins in signalling pathways were assessed by Western blotting.

Results

Neurotensin stimulated the phosphorylation of both extracellular signal-regulated kinase (ERK) and Akt in all three cell lines, but apparently did so through different pathways. In Panc-1 cells, neurotensin-induced phosphorylation of ERK, but not Akt, was dependent on protein kinase C (PKC), whereas an inhibitor of the β-isoform of phosphoinositide 3-kinase (PI3K), TGX221, abolished neurotensin-induced Akt phosphorylation in these cells, and there was no evidence of EGF receptor (EGFR) transactivation. In HT29 cells, in contrast, the EGFR tyrosine kinase inhibitor gefitinib blocked neurotensin-stimulated phosphorylation of both ERK and Akt, indicating transactivation of EGFR, independently of PKC. In HCT116 cells, neurotensin induced both a PKC-dependent phosphorylation of ERK and a metalloproteinase-mediated transactivation of EGFR that was associated with a gefitinib-sensitive phosphorylation of the downstream adaptor protein Shc. The activation of Akt was also inhibited by gefitinib, but only partly, suggesting a mechanism in addition to EGFR transactivation. Inhibition of PKC blocked neurotensin-induced DNA synthesis in HCT116 cells.

Conclusions

While acting predominantly through PKC in Panc-1 cells and via EGFR transactivation in HT29 cells, neurotensin used both these pathways in HCT116 cells. In these cells, neurotensin-induced activation of ERK and stimulation of DNA synthesis was PKC-dependent, whereas activation of the PI3K/Akt pathway was mediated by stimulation of metalloproteinases and subsequent transactivation of the EGFR. Thus, the data show that the signalling mechanisms mediating the effects of neurotensin involve multiple pathways and are cell-dependent.

EGFR-targeted drugs for colorectal cancer: current status and future challenges

Colorectal cancer is a common gastrointestinal malignancy. The effects of traditional chemotherapy and radiation therapy against colorectal cancer are not satisfactory. The epidermal growth factor receptor (EGFR) signaling pathway plays an important role in tumor proliferation, angiogenesis, invasion, and metastasis in colorectal cancer. EGFR-targeted drugs have been developed and applied to the treatment of colorectal cancer. This paper provides a literature review on the current status and future challenges of EGFR-targeted therapy of colorectal cancer.

A novel role of ERK5 in integrin-mediated cell adhesion and motility in cancer cells via Fak signaling

In metastatic cancer, high expression levels of vitronectin (VN) receptors (integrins), FAK, and ERK5 are reported. We hypothesized that integrin-mediated ERK5 activation via FAK may play a pivotal role in cell adhesion, motility, and metastasis. ERK5 and FAK phosphorylation when metastatic MDA-MB-231 and PC-3 cells were plated on VN was enhanced. Further experiments showed co-immunoprecipitation of integrins beta1, alpha V beta 3, or alpha V beta 5 with ERK5 and FAK. To gain better insight into the mechanism of ERK5, FAK, and VN receptors in cell adhesion and motility, we performed loss-of-function experiments using integrin blocking antibodies, and specific mutants of FAK and ERK5. Ectopic expression of dominant negative ERK5/AEF decreased ERK5 and FAK (Y397) phosphorylation, cell adhesion, and haptotactic motility (micromotion) on VN. Additionally, DN FAK expression attenuated ERK5 phosphorylation, cell adhesion, and motility. This study documents the novel finding that in breast and prostate cancer cells, ERK5 is a critical target of FAK in cell adhesion signaling. Using different cancer cells, our experiments unveil a novel mechanism by which VN receptors and FAK could promote cancer metastasis via ERK5 activation.

Characterization of HCT116 human colon cancer cells in an orthotopic model

BACKGROUND

Colorectal cancer metastases result in a significant number of cancer related deaths. The molecular mechanisms underlying this complex, multi-step pathway are yet to be completely elucidated. In the absence of any transgenic models of colon cancer metastases, an in vivo model system that fulfills the rate limiting steps of metastasis (local invasion and distant colony formation) is needed. The purpose of this study was to characterize the behavior of a human colon cancer cell line, HCT116 in an orthotopic model.

MATERIALS AND METHODS

HCT116 cells were transfected with green fluorescence protein and subcutaneously injected into BALB/c nude male mice. Once xenografts were established, they were excised and orthotopically implanted into 32 other male BALB/c nude mice using microsurgical techniques. Animals were serially imaged and euthanized at 6-8 weeks post-implantation. Tissues were procured and processed for hematoxylin and eosin analysis.

RESULTS

All 32 animals demonstrated primary tumor growth, invasion and peritoneal spread. Liver metastases were identified in 15/32 (47%), and lung metastases were confirmed in 13/32 (41%). In total, 19/32 (59%) animals demonstrated distant metastatic colony formation.

CONCLUSIONS

This orthotopic model of colon cancer fulfills the rate limiting steps of local invasion and distant colony formation in the process of metastases. HCT116 human colon cancer cell line in this in vivo model system provides a tool to dissect the molecular mechanism involved in the metastatic cascade.

Keratinocyte growth factor-transfection-stimulated adhesion of colorectal cancer cells to extracellular matrices

The keratinocyte growth factor (KGF) regulates cell growth and behavior in an autocrine or paracrine manner. In colorectal cancer tissues, KGF is expressed in tumor cells and adjacent stromal fibroblasts. We have constructed a KGF-gene-transfected cell line (HCT15-KGF) from a colorectal cancer cell line, HCT-15, that expresses the KGF receptor, and studied the effects of KGF on cell behavior, particularly growth and adhesion to extracellular matrices (ECMs). The amount of KGF secreted from HCT15-KGF was significantly higher than that from a mock-transfected cell line (HCT15-MOCK). The modes of growth of these cell lines were similar. The degree of adhesion of HCT15-KGF to ECMs, including type-IV collagen and fibronectin was higher than that of HCT15-MOCK. The expressions of integrins in both cell lines were not significantly different. However, extracellular-regulated kinase-1 and -2 (ERK1/2) phosphorylation and focal adhesion kinase (FAK) expression that regulate the adhesive functions of integrin families were enhanced in HCT15-KGF. U0126, an inhibitor of the ERK upstream regulator MEK, attenuated the adhesion and spreading of HCT15-KGF cells to type-IV collagen. These results indicate that KGF enhances the adhesion of colorectal cancer cells to type-IV collagen through ERK and FAK signaling pathways.

Does the EGFR and VEGF expression predict the prognosis in colon cancer?

BACKGROUND/AIM

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF) are frequently encountered with aggressive tumor phenotype and poor prognosis, but the relationship between EGFR/VEGF expression and survival remains unclear. The aim of our study was to further investigate the prognostic value of EGFR and VEGF expression in colon cancer.

MATERIALS AND METHODS

The pathological specimens of 60 colon carcinoma patients were retrospectively evaluated and grouped according to EGFR and VEGF staining intensity and percentage of stained neoplastic cells. A final score was assigned to each case by multiplying percentage and staining score. The patients were stratified into the following categories: negative (score 0), low expression (score 1 or 2), and high expression (score 4). The remaining patient data were filtered out from the institutional cancer database.

RESULTS

The mean survival time was 28.93 +/- 14.1 (range 2-52) months in the EGFR-negative group, 23.92 +/- 14.0 (range 6-46) months in the group with a low EGFR expression, and 17.00 +/- 12.8 (range 10-40) months in the group with a high EGFR expression. The median survival time was 27.50 +/- 14.7 (range 4-52) months in the VEGF-negative group, 29.33 +/- 12.8 (range 6-48) months in the group with a low VGEF expression, and 14.50 +/- 14.2 (range 2-40) months in the group with a high VGEF expression. The expression of EGFR and VEGF was not an independent factor that affects survival.

CONCLUSIONS

The EGFR and VEGF expression rates of colon tumors do not predict the survival. In addition, the EGFR expression in the primary tumor was not predictive of metastatic lymph nodes. The prognostic value of EGFR/VEGF staining may be further questioned.

Integrin alpha2-mediated ERK and calpain activation play a critical role in cell adhesion and motility via focal adhesion kinase signaling: identification of a novel signaling pathway

Higher levels of focal adhesion kinase (FAK) are expressed in colon metastatic carcinomas. However, the signaling pathways and their mechanisms that control cell adhesion and motility, important components of cancer metastasis, are not well understood. We sought to identify the integrin-mediated mechanism of FAK cleavage and downstream signaling as well as its role in motility in human colon cancer GEO cells. Our results demonstrate that phosphorylated FAK (tyrosine 397) is cleaved at distinct sites by integrin signaling when cells attach to collagen IV. Specific blocking antibodies (clone P1E6) to integrin alpha2 inhibited FAK activation and cell motility (micromotion). Ectopic expression of the FAK C-terminal domain FRNK attenuated FAK and ERK phosphorylation and micromotion. Calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal blocked FAK cleavage, cell adhesion, and micromotion. Antisense approaches established an important role for mu-calpain in cell motility. Expression of wild type mu-calpain increased cell micromotion, whereas its point mutant reversed the effect. Further, cytochalasin D inhibited FAK phosphorylation and cleavage, cell adhesion, locomotion, and ERK phosphorylation, thus showing FAK activation downstream of actin assembly. We also found a pivotal role for FAK Tyr(861) phosphorylation in cell motility and ERK activation. Our results reveal a novel functional connection between integrin alpha2 engagement, FAK, ERK, and mu-calpain activation in cell motility and a direct link between FAK cleavage and enhanced cell motility. The data suggest that blocking the integrin alpha2/FAK/ERK/mu-calpain pathway may be an important strategy to reduce cancer progression.

Reg IV activates the epidermal growth factor receptor/Akt/AP-1 signaling pathway in colon adenocarcinomas

BACKGROUND & AIMS

Reg IV, a secreted protein and member of the Reg multigene family, is up-regulated in malignancies of the human gastrointestinal tract, including colorectal carcinoma (CRC). However, in vitro signal transduction pathway(s) utilized by Reg IV are not yet known.

METHODS

To determine the signaling pathway(s) responsive to Reg IV, we examined the effects of purified recombinant human Reg IV (rhR4) on HCT116 and HT29 colon adenocarcinoma cells.

RESULTS

Addition of rhR4 to cultures led to a dose-dependent increase in cell number similar to that observed after treatment with epidermal growth factor (EGF). In addition, rhR4 treatment resulted in rapid phosphorylation of EGF receptor at Tyr992 and Tyr1068 and Akt at Thr308 and Ser473. Using luciferase reporter gene assays, we demonstrated that Reg IV signaling through EGF receptor and Akt results in increased activator protein-1 (AP-1) transcription factor activity. Real-time reverse-transcription polymerase chain reaction and Western blot analyses revealed quantitative increases in c-Jun, JunB, JunD, and FosB expression associated with increased AP-1 activity. Electrophoretic mobility shift assay further revealed significant increases in AP-1 binding activity in rhR4-treated cells, with increased supershift in the presence of antibodies to JunB, JunD, and FosB. Furthermore, rhR4 treatments led to the increased expression of Bcl-2, Bcl-XL, survivin, and matrilysin, genes associated with a poor prognosis in advanced CRC.

CONCLUSIONS

Reg IV is a potent activator of the EGF receptor/Akt/AP-1 signaling pathway in CRC. Disruption of Reg signaling may have utility as a therapeutic intervention for human gastrointestinal adenocarcinomas.

Molecular mechanism of epidermal growth factor receptor pathway mediated adhesion and invasion of Caco-2 cell line

AIM: To investigate the effect of epidermal growth factor receptor (EGFR) pathway on proliferation, adhesion and invasion of Caco-2 cell line and its molecular mechanism.

METHODS: Tetrazolium-based colorimetric assay was used to evaluate the effect of EGF, AG1478 or PD98059 on proliferation and growth of cultured human colon carcinoma Caco-2 cells. Matrigel experiment and cell adhesion assay were used to examine the invasiveness of Caco-2 cells. The transcription of MMP-2, MMP-9, TIMP-1 and TIMP-2 of Caco-2 cells was detected by reverse transcription polymerase chain reaction (RT-PCR). The expression of P-EGFR protein in Caco-2 cells was determined by Western-blot.

RESULTS: Exogenous EGF significantly enhanced the growth and proliferation of Caco-2 cells. The growth ratio was increased by 23.4% at 24 h (P<0.01). AG1478 (20 mmol/L, 48 h) and PD98059 (40 mmol/L, 72 h) inhibited the growth and proliferation of Caco-2 cells in a time-independent manner, and the growth rates were decreased by 45.7% and 54.6%, respectively (P<0.01). Matrigel experiment showed that EGF increased the adhesion (P<0.05) and invasion (P = 0.001) ability of Caco-2 cells in vitro at the concentration of 10 mg/L. AG1478 or PD98059 inhibited EGF-induced adhesion and invasion of Caco-2 cells (P<0.01) by blocking the activity of EGFR and ERK1/2. After treatment with EGF the protein of P-EGFR was increased, which was abolished by AG1478. RT-PCR assays revealed that exogenous EGF up-regulated mRNA levels of MMP-2 and MMP-9 and down-regulated mRNA levels of TIMP-1 and TIMP-2. Meanwhile AG1478 and PD98059 reversed the effect of EGF by decreasing the levels of MMP-2, MMP-9 mRNA and increasing the levels of TIMP-1 and TIMP-2 mRNA. The MMP-2 to TIMP-2 ratio and the MMP-9 to TIMP-1 ratio were decreased significantly by AG1478 or PD98059(P <0.001).

CONCLUSION: In human colon carcinoma, EGFR changes MMP-2, MMP-9, TIMP-1 and TIMP-2 transcription via MAPK signal pathway, which may contribute to the invasiveness and metastasis of Caco-2 cells.

Autocrine transforming growth factor alpha regulates cell adhesion by multiple signaling via specific phosphorylation sites of p70S6 kinase in colon cancer cells

Recently, we showed that autocrine transforming growth factor alpha (TGFalpha) controls the epidermal growth factor receptor (EGFR)-mediated basal expression of integrin alpha2, cell adhesion and motility in highly progressed HCT116 colon cancer cells. We also reported that the expression of basal integrin alpha2 and its biological effects are critically controlled by the constitutive activation of the ERK/MAPK pathway (Sawhney, R. S., Sharma, B., Humphrey, L. E., and Brattain, M. G. (2003) J. Biol. Chem. 278, 19861-19869). In the present report, we further examine the downstream signaling mechanisms underlying EGFR/ERK signaling and integrin alpha2 function in HCT116 cells. Selective MEK inhibitors attenuated TGFalpha-mediated basal activation of p70S6K (S6K) specifically at Thr-389, indicating that this S6K site is downstream of ERK/MAPK signaling. Cells were treated with the selective protein kinase C (PKC) inhibitor bisindolylmaleimide to determine the role of PKC in S6K activation. The Thr-421 and Ser-424 phosphorylation sites of S6K were specifically inhibited by bisindolylmaleimide, which also blocked integrin alpha2 expression, cell adhesion, and motility. These data establish a novel cell motility function of S6K via PKC activation in a cancer cell. In addition, we examined whether mammalian target of rapamycin signaling controls S6K activation. Rapamycin inhibited constitutive S6K phosphorylation specifically at Thr-389, Thr-421, and Ser-424 sites. The assignment of these phosphorylation sites on S6K to biological functions was unequivocally confirmed by transfection of cells with specific single phosphorylation site dominant negative mutants. These experiments show for the first time that autocrine TGFalpha regulates cell adhesion function by multiple signaling pathways via specific phosphorylation sites of S6K in cancer cells.

Blockade of epidermal growth factor- or heregulin-dependent ErbB2 activation with the anti-ErbB2 monoclonal antibody 2C4 has divergent downstream signaling and growth effects

Due to heterodimerization and a variety of stimulating ligands, the ErbB receptor system is both diverse and flexible, which proves particularly advantageous to the aberrant signaling of cancer cells. However, specific mechanisms of how a particular receptor contributes to generating the flexibility that leads to aberrant growth regulation have not been well described. We compared the utilization of ErbB2 in response to epidermal growth factor (EGF) and heregulin stimulation in colon carcinoma cells. Anti-ErbB2 monoclonal antibody 2C4 blocked heregulin-stimulated phosphorylation of ErbB2 and ErbB3; activation of mitogen-activated protein kinase (MAPK), phosphatidylinositol 3'-kinase (PI3K), and Akt; proliferation; and anchorage-independent growth. 2C4 blocked EGF-mediated phosphorylation of ErbB2 and inhibited PI3K/Akt and anchorage-independent growth but did not affect ErbB1 or MAPK. Immunoprecipitations showed that ErbB3 and Grb2-associated binder (Gab) 1 were phosphorylated and associated with PI3K activity after heregulin treatment and that Gab1 and Gab2, but not ErbB3, were phosphorylated and associated with PI3K activity after EGF treatment. These data show that monoclonal antibody 2C4 inhibited all aspects of heregulin signaling as well as anchorage-independent and monolayer growth. Furthermore, we identify ErbB2 as a critical component of EGF signaling to the Gab1/Gab2-PI3K-Akt pathway and anchorage-independent growth, but EGF stimulation of MAPK and monolayer growth can occur efficiently without the contribution of ErbB2.

Invasion of normal human fibroblasts induced by v-Fos is independent of proliferation, immortalization, and the tumor suppressors p16INK4a and p53

Invasion is generally perceived to be a late event during the progression of human cancer, but to date there are no consistent reports of alterations specifically associated with malignant conversion. We provide evidence that the v-Fos oncogene induces changes in gene expression that render noninvasive normal human diploid fibroblasts highly invasive, without inducing changes in growth factor requirements or anchorage dependence for proliferation. Furthermore, v-Fos-stimulated invasion is independent of the pRb/p16(INK4a) and p53 tumor suppressor pathways and telomerase. We have performed microarray analysis using Affymetrix GeneChips, and the gene expression profile of v-Fos transformed cells supports its role in the regulation of invasion, independent from proliferation. We also demonstrate that invasion, but not proliferation, is dependent on the activity of the up-regulated epidermal growth factor receptor. Taken together, these results indicate that AP-1-directed invasion could precede deregulated proliferation during tumorigenesis and that sustained activation of AP-1 could be the epigenetic event required for conversion of a benign tumor into a malignant one, thereby explaining why many malignant human tumors present without an obvious premalignant hyperproliferative dysplastic lesion.

Transforming growth factor-alpha attenuates N-methyl-D-aspartic acid toxicity in cortical cultures by preventing protein synthesis inhibition through an Erk1/2-dependent mechanism

Transforming growth factor-alpha (TGF-alpha), a ligand of the epidermal growth factor receptor, reduces the infarct size after focal cerebral ischemia in rat, but the molecular basis underlying the protection is unknown. Excitotoxicity and global inhibition of translation are acknowledged to contribute significantly to the ischemic damage. Here we studied whether TGF-alpha can rescue neurons from excitotoxicity in vitro and how it affects calcium homeostasis, protein synthesis, and the associated Akt and extracellular signal-regulated kinase 1/2 (Erk1/2) intracellular signaling pathways in mixed neuron-glia cortical cultures. We found that 100 ng/ml TGF-alpha attenuated neuronal cell death induced by a 30-min exposure to 35 microM N-methyl-D-aspartic acid (NMDA) (as it reduced lactate dehydrogenase release, propidium iodide staining, and caspase-3 activation) and decreased the elevation of intracellular Ca2+ elicited by NMDA. TGF-alpha induced a prompt and sustained phosphorylation of Erk1/2 and prevented the loss of Akt-P induced by NMDA 3 h after exposure. The protective effect of TGF-alpha was completely prevented by PD 98059, an inhibitor of the Erk1/2 pathway. Studies of incorporation of [3H]leucine into proteins showed that NMDA decreased the rate of protein synthesis, and TGF-alpha attenuated this effect. TGF-alpha stimulated the phosphorylation of the eukaryotic initiation factor 4E (eIF4E) but did not affect eIF2 alpha, two proteins involved in translation regulation. PD 98059 abrogated the TGF-alpha effect on eIF4E. Our data demonstrate that TGF-alpha exerts a neuroprotective action against NMDA toxicity, in which Erk1/2 activation plays a key role, and suggest that the underlying mechanisms involve recovery of translation inhibition, mediated at least in part by eIF4E phosphorylation.

Integrin alpha2 and extracellular signal-regulated kinase are functionally linked in highly malignant autocrine transforming growth factor-alpha-driven colon cancer cells

Recently, we have shown that autocrine transforming growth factor-alpha (TGF-alpha) controls the expression of integrin alpha2, cell adhesion to collagen IV and motility in highly progressed HCT116 colon cancer cells (Sawhney, R. S., Zhou, G-H. K., Humphrey, L. E., Ghosh, P., Kreisberg, J. I., and Brattain, M. G. (2002) J. Biol. Chem. 277, 75-86). We now report that expression of basal integrin alpha2 and its biological effects are controlled by constitutive activation of the extracellular signal-regulated/mitogen-activated protein kinase (ERK/MAPK) pathway. Treatment of cells with selective mitogen-activated protein kinase kinase (MEK) inhibitors PD098059 and U0126 showed that integrin alpha2 expression, cell adhesion, and activation of ERK are inhibited in a parallel concentration-dependent fashion. Moreover, autocrine TGF-alpha-mediated epidermal growth factor receptor activation was shown to control the constitutive activation of the ERK/MAPK pathway, since neutralizing antibody to the epidermal growth factor receptor was able to block basal ERK activity. TGF-alpha antisense-transfected cells also showed attenuated activation of ERK. Using a real time electric cell impedance sensing technique, it was shown that ERK-dependent integrin alpha2-mediated cell micromotion signaling is controlled by autocrine TGF-alpha. Thus, this study implicates ERK/MAPK signaling activated by endogenous TGF-alpha as one of the mechanistic features controlling metastatic spread.

Transcriptional regulation of the human NaPi-IIb cotransporter by EGF in Caco-2 cells involves c-myb

The type IIb sodium-phosphate (NaP(i)-IIb) cotransporter mediates intestinal phosphate absorption. Previous work in our laboratory has shown that EGF inhibited NaP(i)-IIb cotransporter expression through transcriptional regulation. To understand this regulation, progressively shorter human NaP(i)-IIb promoter constructs were used to define the EGF response region, and gel mobility shift assays (GMSAs) were used to characterize DNA-protein interactions. Promoter analysis determined that the EGF response region was located between -784 and -729 base pair (bp) of the promoter. GMSAs and overexpression studies revealed an interaction between this promoter region and c-myb transcription factor. Inhibition of EGF receptor activation restored promoter function. Further studies suggested that MAPK, PKC, and/or PKA pathways are involved in this regulation. In conclusion, these studies suggest that EGF decreases human NaP(i)-IIb gene expression by modifying the c-myb protein such that it inhibits transcriptional activation. We further conclude that this downregulation of promoter function is mediated by EGF-activated PKC/PKA and MAPK pathways. This is the first study that demonstrates involvement of c-myb in the regulation of intestinal nutrient absorption.

Cholinergic agonists transactivate EGFR and stimulate MAPK to induce goblet cell secretion

Conjunctival goblet cells are the primary source of mucins in the mucous layer, the innermost layer of the tear film. Conjunctival goblet cell mucin secretion is under neural control because exogenous addition of parasympathetic agonists stimulates goblet cell secretion. To elucidate the intracellular signal pathways used by cholinergic agonists to stimulate goblet cell mucin secretion, we determined whether p42/p44 mitogen-activated protein kinase (MAPK) is activated during cholinergic agonist-stimulated mucin secretion. Rat conjunctiva was removed, preincubated with or without antagonists, and stimulated with the cholinergic agonist carbachol (10(-4) M). Carbachol statistically significantly stimulated the phosphorylation of MAPK in a time- and concentration-dependent manner. U-0126, an inhibitor of MAPK activation, completely inhibited both the activation of MAPK and goblet cell secretion stimulated by carbachol. The M(1) muscarinic antagonist pirenzepine, the M(2) muscarinic antagonist gallamine, and the M(1)/M(3) muscarinic receptor antagonist N-(3-chloropropyl)-4-piperidinyl diphenylacetate (4-DAMP) also inhibited carbachol-stimulated MAPK activation. Increasing the intracellular Ca(2+) concentration with a Ca(2+) ionophore increased MAPK activation, and chelation of extracellular Ca(2+) inhibited carbachol-stimulated activation. Carbachol also increased tyrosine phosphorylation of Pyk2, p60Src, and the epidermal growth factor receptor (EGFR). The Src inhibitor PP1 and the EGFR inhibitor AG-1478 completely inhibited carbachol-stimulated MAPK activation. AG-1478 also inhibited goblet cell secretion. We conclude that carbachol transactivates the EGFR to activate MAPK, leading to conjunctival goblet cell secretion. In addition, carbachol also activates Pyk2 and p60Src that could play a role in the transactivation of the EGFR.

P53-mediated induction of Cox-2 counteracts p53- or genotoxic stress-induced apoptosis

The identification of transcriptional targets of the tumor suppressor p53 is crucial in understanding mechanisms by which it affects cellular outcomes. Through expression array analysis, we identified cyclooxygenase 2 (Cox-2), whose expression was inducible by wild-type p53 and DNA damage. We also found that p53-induced Cox-2 expression results from p53-mediated activation of the Ras/Raf/MAPK cascade, as demonstrated by suppression of Cox-2 induction in response to p53 by dominant-negative Ras or Raf1 mutants. Furthermore, heparin-binding epidermal growth factor-like growth factor (HB- EGF), a p53 downstream target gene, induced Cox-2 expression, implying that Cox-2 is an ultimate effector in the p53-->HB-EGF-->Ras/Raf/MAPK-->Cox-2 pathway. p53-induced apoptosis was enhanced greatly in Cox-2 knock-out cells as compared with wild-type cells, suggesting that Cox-2 has an abrogating effect on p53-induced apoptosis. Also, a selective Cox-2 inhibitor, NS-398, significantly enhanced genotoxic stress-induced apoptosis in several types of p53+/+ normal human cells, through a caspase-dependent pathway. Together, these results demonstrate that Cox-2 is induced by p53-mediated activation of the Ras/Raf/ERK cascade, counteracting p53-mediated apoptosis. This anti-apoptosis effect may be a mechanism to abate cellular stresses associated with p53 induction.

Emerging molecular markers of cancer

Alterations in gene sequences, expression levels and protein structure or function have been associated with every type of cancer. These 'molecular markers' can be useful in detecting cancer, determining prognosis and monitoring disease progression or therapeutic response. But what is the best way to identify molecular markers and can they be easily incorporated into the clinical setting?