Total Epidermal Growth Factor Receptor Levels Research Articles

Abstract 6135: Dynamics of ligand-induced epidermal growth factor receptor internalization in cancer cell lines

Abstract Antibody-drug conjugates (ADCs), comprised of cancer cell-specific antibodies linked to cytotoxic drugs, represent an innovative and promising class of anticancer agents. Due to its amplified expression in various tumor types, the epidermal growth factor receptor (EGFR) presents an attractive target for ADC therapy, and three anti-EGFR ADCs are currently studied in clinical trials. As ADCs depend on receptor internalization for intracellular release of drugs in the targeted cancer cells, studying the dynamics of receptor internalization can aid in their development and optimization. We studied the internalization of EGFR induced by its ligand EGF, as a mimic of ADCs, in cell lines with different surface receptor densities. BxPC-3 (pancreas) and RT-112 (bladder) cancer cells were seeded in 6-well plates and allowed to adhere for 24 hours. Cells were serum-starved overnight, followed by stimulation with 150 ng/mL EGF for 2, 4, 6, 24 and 48 hours. Internalization was studied by quantification of the number of surface-expressed receptors using flow cytometry with Quantibrite PE beads and EGFR-PE antibody. Moreover, incorporation of the ligand-receptor complex into acidic endo-lysosomes was studied using EGF conjugated to the fluorescent pH sensor pHrodo™ Green. Total EGFR and EGFR phosphorylation levels were assessed by western blot analysis. RNA was isolated and converted into cDNA to perform TaqMan qPCR. Unstimulated BxPC-3 cells showed higher numbers of EGFR per cell compared to unstimulated RT-112 cells. Since high receptor expression is key for some ADCs to induce effective endocytosis, this may indicate BxPC-3 cells as a more attractive model to study EGFR internalization. Stimulation with EGF induced a strong decrease in surface receptor density for both BxPC-3 and RT-112 cells during the first two hours, suggesting receptor internalization. Accordingly, treatment of BxPC-3 cells with pHrodo™ Green EGF demonstrated the incorporation of ligand-receptor complexes into endo-lysosomes. During following hours, the cell surface expression of EGFR remained stable, whereas it partially recovered after 24 to 48 hours. In contrast, the lysosomal incorporation of EGF-EGFR complexes was not decreased at 24 or 48 hours, suggesting that the increase in surface EGFR may be due to de novo protein synthesis rather than recycling. No increase of EGFR mRNA was, however, detected. Finally, increased phosphorylation of EGFR was observed after two to six hours of stimulation, whereas total EGFR levels were highest in unstimulated and 24- or 48-hour-stimulated cells, which is in concordance with the flow cytometry data. In conclusion, both BxPC-3 and RT-112 cells show dynamic changes in EGFR internalization upon EGF stimulation, despite differences in EGFR expression levels. These cell lines can therefore successfully be used for internalization studies, which may contribute to future ADC development. Citation Format: Mandy W. Smeets, Eef F. Smits, Janneke J. Melis, Dimitri Pappaioannou, Guido J. Zaman. Dynamics of ligand-induced epidermal growth factor receptor internalization in cancer cell lines. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6135.

GOLPH3 Regulates EGFR in T98G Glioblastoma Cells by Modulating Its Glycosylation and Ubiquitylation.

Protein trafficking is altered when normal cells acquire a tumor phenotype. A key subcellular compartment in regulating protein trafficking is the Golgi apparatus, but its role in carcinogenesis is still not well defined. Golgi phosphoprotein 3 (GOLPH3), a peripheral membrane protein mostly localized at the trans-Golgi network, is overexpressed in several tumor types including glioblastoma multiforme (GBM), the most lethal primary brain tumor. Moreover, GOLPH3 is currently considered an oncoprotein, however its precise function in GBM is not fully understood. Here, we analyzed in T98G cells of GBM, which express high levels of epidermal growth factor receptor (EGFR), the effect of stable RNAi-mediated knockdown of GOLPH3. We found that silencing GOLPH3 caused a significant reduction in the proliferation of T98G cells and an unexpected increase in total EGFR levels, even at the cell surface, which was however less prone to ligand-induced autophosphorylation. Furthermore, silencing GOLPH3 decreased EGFR sialylation and fucosylation, which correlated with delayed ligand-induced EGFR downregulation and its accumulation at endo-lysosomal compartments. Finally, we found that EGF failed at promoting EGFR ubiquitylation when the levels of GOLPH3 were reduced. Altogether, our results show that GOLPH3 in T98G cells regulates the endocytic trafficking and activation of EGFR likely by affecting its extent of glycosylation and ubiquitylation.

The metastasis suppressor NDRG1 down-regulates the epidermal growth factor receptor via a lysosomal mechanism by up-regulating mitogen-inducible gene 6

The metastasis suppressor, N-Myc downstream-regulated gene-1 (NDRG1) inhibits a plethora of oncogenic signaling pathways by down-regulating the epidermal growth factor receptor (EGFR). Herein, we examined the mechanism involved in NDRG1-mediated EGFR down-regulation. NDRG1 overexpression potently increased the levels of mitogen-inducible gene 6 (MIG6), which inhibits EGFR and facilitates its lysosomal processing and degradation. Conversely, silencing NDRG1 in multiple human cancer cell types decreased MIG6 expression, demonstrating the regulatory role of NDRG1. Further, NDRG1 overexpression facilitated MIG6-EGFR association in the cytoplasm, possibly explaining the significantly (p <0.001) increased half-life of MIG6 from 1.6 ± 0.2 h under control conditions to 7.9 ± 0.4 h after NDRG1 overexpression. The increased MIG6 levels enhanced EGFR co-localization with the late endosome/lysosomal marker, lysosomal-associated membrane protein 2 (LAMP2). An increase in EGFR levels after MIG6 silencing was particularly apparent when NDRG1 was overexpressed, suggesting a role for MIG6 in NDRG1-mediated down-regulation of EGFR. Silencing phosphatase and tensin homolog (PTEN), which facilitates early to late endosome maturation, decreased MIG6, and also increased EGFR levels in both the presence and absence of NDRG1 overexpression. These results suggest a role for PTEN in regulating MIG6 expression. Anti-tumor drugs of the di-2-pyridylketone thiosemicarbazone class that activate NDRG1 expression also potently increased MIG6 and induced its cytosolic co-localization with NDRG1. This was accompanied by a decrease in activated and total EGFR levels and its redistribution to late endosomes/lysosomes. In conclusion, NDRG1 promotes EGFR down-regulation through the EGFR inhibitor MIG6, which leads to late endosomal/lysosomal processing of EGFR.

Functional cooperation between HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR

ObjectiveHypoxia-inducible factor 1 (HIF-1) and activator protein 1 (AP-1) are important transcription factors regulating expression of genes involved in cell survival. HIF-1α and c-Jun are key components of HIF-1 and AP-1, respectively, and are regulated by epidermal growth factor receptor (EGFR)-mediated cell signaling and tumor microenvironmental cues. The roles of HIF-1α and c-Jun in development of resistance to EGFR tyrosine kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC) with activating mutation of EGFR have not been explored. In this study, we investigated the roles of HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR. Materials and methodsChanges in HIF-1α protein and in total and phosphorylated c-Jun levels in relation to changes in total and phosphorylated EGFR levels before and after gefitinib treatment were measured using Western blot analysis in NSCLC cells sensitive or resistant to gefitinib. The impact of overexpression of a constitutively expressed HIF-1α (HIF-1α/ΔODD) or a constitutively active c-Jun upstream regulator (SEK1 S220E/T224D mutant) on cell response to gefitinib was also examined. The effect of pharmacological inhibition of SEK1-JNK-c-Jun pathway on cell response to gefitinib was evaluated. ResultsDownregulation of HIF-1α and total and phosphorylated c-Jun levels correlated with cell inhibitory response to gefitinib better than decrease in phosphorylated EGFR did in NSCLC cells with intrinsic or acquired resistance to gefitinib. Overexpression of HIF-1α/ΔODD or SEK1 S220E/T224D mutant conferred resistance to gefitinib. There exists a positive feed-forward regulation loop between HIF-1 and c-Jun. The JNK inhibitor SP600125 sensitized gefitinib-resistant NSCLC cells to gefitinib. ConclusionsHIF-1α and c-Jun functionally cooperate in development of resistance to gefitinib in NSCLC cells. The translational value of inhibiting HIF-1α/c-Jun cooperation in overcoming resistance to EGFR TKI treatment of NSCLC cells with activating mutation of EGFR deserves further investigation.

Significant increase in hEGF uptake is correlated with formation of EGFR dimers induced by the EGFR tyrosine kinase inhibitor gefitinib

PurposeThe epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor gefitinib (ZD1839, Iressa) is approved for cancer treatment. We investigated whether gefitinib treatment can enhance human EGF (hEGF) uptake in vitro, thereby increasing the potential of hEGF as a vehicle for EGFR-targeted therapy.MethodsWestern blotting was used to detect the effect of gefitinib on EGFR signaling. Different EGFR-expressing tumor cells (SCC-1, 22B, A549, and HT-29) were pretreated with gefitinib, and then with 125I-hEGF or 125I-Vectibix (an anti-EGFR monoclonal antibody). Cell-associated activity was then measured. A cross-linking assay detected increased EGFR dimer formation in gefitinib-treated cells.ResultsTotal EGFR levels were not changed, but EGFR phosphorylation was reduced in cells pretreated with gefitinib. Gefitinib mediated formation of EGFR dimers; binding of 125I-hEGF to cells pretreated with gefitinib significantly increased. In contrast, binding of 125I-Vectibix to tumor cells did not increase. Although total EGFR levels did not increase, binding of hEGF to EGFR + tumors was significantly enhanced after gefitinib treatment, because of increased hEGF binding to gefitinib-induced EGFR dimers.ConclusionThese results suggest that hEGF could enhance EGFR-targeting when used with gefitinib.

Epidermal growth factor receptor expression and signaling are essential in glutamine's cytoprotective mechanism in heat-stressed intestinal epithelial-6 cells

Epidermal growth factor receptor (EGFR) expression and signaling can induce cellular protection after intestinal inflammation. L-Glutamine (GLN) is known to prevent apoptosis after intestinal injury by activating MAPK and phosphatidylinositol 3-kinase (PI3-K)/Akt pathways. However, the role of EGFR expression and signaling in GLN-mediated cellular protection in intestinal epithelial-6 (IEC-6) cells after heat stress (HS) is unknown. To address the role of EGFR in GLN-mediated protection, IEC-6 cells were treated with GLN in the presence or absence of EGFR small interfering RNA, the EGFR tyrosine kinase inhibitor AG1478, the ERK1/2 inhibitor PD98059, the p38MAPK inhibitor SB203580, or the PI3-K/Akt inhibitor LY294002 under basal and HS conditions. GLN-mediated cell survival was measured using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Phosphorylated and/or total levels of EGFR, cleaved caspase-3, poly(ADP-ribose) polymerase-1, ERK1/2, p38MAPK, and Akt were assessed by Western blotting. We showed that HS induced a decrease in total, cytoplasmic, and nuclear EGFR levels in IEC-6 cells, which was prevented by GLN supplementation, leading to attenuated apoptosis via EGFR small interfering RNA. Furthermore, the protective effect of GLN was lessened by AG1478, PD98059, and LY294002 but was not affected by SB203580. AG1478 attenuated GLN-mediated increases in ERK1/2 and decreases in p38MAPK phosphorylation. However, AG1478 had no effect on GLN-mediated augmentations in Akt phosphorylation. In summary, EGFR expression was important in the protective mechanism of GLN, as well as GLN-mediated activation of EGFR tyrosine kinase activity. GLN-mediated EGFR signaling activated ERK1/2 and decreased p38MAPK signaling. However, GLN-mediated Akt phosphorylation after HS seems to be independent of EGFR signaling.

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Introduction: Epidermal growth factor receptor (EGFR) expression and signaling can induce cellular protection after intestinal inflammation. L-glutamine (GLN) is known to prevent apoptosis after intestinal injury (e.g. heat stress (HS)) by activating mitogen activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-K)/ Akt pathways. Hypothesis: We assessed if EGFR expression and signaling are essential in GLN’s cell protective mechanism in intestinal epithelial-6 (IEC-6) cells after HS, and investigated whether PI-3K and MAPK pathways are involved in GLN-mediated EGFR signaling. Methods: GLN-starved IEC-6 cells were treated with GLN with/ without EGFR siRNA (20nM), EGFR tyrosine kinase inhibitor AG1478 (20µM), ERK1/2 inhibitor PD98059 (50µM), p38MAPK inhibitor SB203580 (1µM), or PI3-K/ Akt inhibitor LY294002 (25µM). GLN-mediated cell survival was measured via MTS assay 24h post-HS (44°Cx50min). Total, cytoplasmatic and nuclear levels of EGFR were determined via Western blot under basal and stressed conditions (37°Cx45min; 43°Cx45min). Furthermore, phosphorylated and/or total levels of cleaved caspase-3, PARP1, ERK1/2, p38 MAPK, and Akt were assessed by Western blots under basal conditions (37°Cx45min) and non-lethal HS (43°Cx45min). Statistics were calculated via student’s t-test. Results: Here, we show that HS attenuated total, cytoplasmatic, and nuclear EGFR levels in IEC-6 cells. GLN prevented the decrease of total, cytoplasmatic and nuclear EGFR levels, which attenuated apoptosis, shown via siEGFR. Furthermore, EGFR kinase activity inhibition by AG1478, ERK1/2 kinase inhibition by PD98059 and PI-3 kinase inhibitor LY294002 lessened GLN’s protective effect, but not p38MAPK inhibitor SB203580. AG1478 attenuated GLN-mediated increases in ERK1/2 and decreases in p38MAPK phosphorylation. However, AG1478 had no effect on GLN-mediated augmentations in Akt phosphorylation. Conclusions: In summary, not only EGFR expression was important in GLN’s protective mechanism, but also GLN’s activation of EGFR tyrosine kinase activity. GLN-mediated EGFR signaling activated ERK1/2 and decreased p38MAPK signaling. However, GLN-mediated Akt phosphorylation after HS seems not to be activated via EGFR signaling.

A Potential Peptide Therapeutic Derived from the Juxtamembrane Domain of the Epidermal Growth Factor Receptor

The epidermal growth factor receptor (EGFR) is involved in many cancers and EGFR has been heavily pursued as a drug target. Drugs targeting EGFR have shown promising clinical results for several cancer types. However, resistance to EGFR inhibitors often occurs, such as with KRAS mutant cancers, therefore new methods of targeting EGFR are needed. The juxtamembrane (JXM) domain of EGFR is critical for receptor activation and targeting this region could potentially be a new method of inhibiting EGFR. We hypothesized that the structural role of the JXM region could be mimicked by peptides encoding a JXM amino acid sequence, which could interfere with EGFR signaling and consequently could have anti-cancer activity. A peptide encoding EGFR 645–662 conjugated to the Tat sequence (TE-64562) displayed anti-cancer activity in multiple human cancer cell types with diminished activity in non-EGFR expressing cells and non-cancerous cells. In nude mice, TE-64562 delayed MDA-MB-231 tumor growth and prolonged survival, without inducing toxicity. TE-64562 induced non-apoptotic cell death after several hours and caspase-3-mediated apoptotic cell death with longer treatment. Mechanistically, TE-64562 bound to EGFR, inhibited its dimerization and caused its down-regulation. TE-64562 reduced phosphorylated and total EGFR levels but did not inhibit kinase activity and instead prolonged it. Our analysis of patient data from The Cancer Genome Atlas supported the hypothesis that down-regulation of EGFR is a potential therapeutic strategy, since phospho- and total-EGFR levels were strongly correlated in a large majority of patient tumor samples, indicating that lower EGFR levels are associated with lower phospho-EGFR levels and presumably less proliferative signals in breast cancer. Akt and Erk were inhibited by TE-64562 and this inhibition was observed in vivo in tumor tissue upon treatment with TE-64562. These results are the first to indicate that the JXM domain of EGFR is a viable drug target for several cancer types.

Thyroid-specific knockout of the tumor suppressor mitogen-inducible gene 6 activates epidermal growth factor receptor signaling pathways and suppresses nuclear factor-κB activity

Mitogen-inducible gene 6 (Mig-6) is a putative tumor suppressor gene and prognostic biomarker in papillary thyroid cancer. We hypothesized that Mig-6 knockout would activate pro-oncogenic signaling in mouse thyrocytes. We performed a thyroid-specific knockout using the Cre/loxP recombinase system. Four knockout and 4 control mouse thyroids were harvested at 2 months of age. Immunoblotting confirmed Mig-6 ablation in knockout mice thyrocytes. Epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK) phosphorylation levels were increased in Mig-6 knockout compared to wild-type mice. Total EGFR levels were similar in knockout and wild-type mice. However, EGFR was absent in the caveolae-containing membrane fraction of knockout mice, indicating that Mig-6 depletion is associated with a change in the membrane distribution of EGFR. Although p65 localized to the nucleus in wild-type mice, it was distributed in both cytoplasm and nucleus in knockouts, suggesting that Mig-6 loss decreases p65 activity. Our results confirm the feasibility of targeted, thyroid-specific gene knockout as a strategy for studying the relevance of specific genes in thyroid oncogenesis. We suggest that the loss of Mig-6 alters the membrane distribution of EGFR, which may limit receptor degradation and activate this oncogenic signaling pathway.

P130Cas Attenuates Epidermal Growth Factor (EGF) Receptor Internalization by Modulating EGF-Triggered Dynamin Phosphorylation

BackgroundEndocytosis controls localization-specific signal transduction via epidermal growth factor receptor (EGFR), as well as downregulation of that receptor. Extracellular matrix (ECM)-integrin coupling induces formation of macromolecular complexes that include EGFR, integrin, Src kinase and p130Cas, resulting in EGFR activation. In addition, cell adhesion to ECM increases EGFR localization at the cell surface and reduces EGFR internalization. The molecular mechanisms involved are not yet well understood.Methodology/Principal FindingsWe investigated the molecular mechanism by which p130Cas affects the endocytic regulation of EGFR. Biochemical quantification revealed that cell adhesion to fibronectin (FN) increases total EGFR levels and its phosphorylation, and that p130Cas is required for this process. Measurements of Texas Red-labeled EGF uptake and cell surface EGFR revealed that p130Cas overexpression reduces EGF-induced EGFR internalization, while p130Cas depletion enhances it. In addition, both FN-mediated cell adhesion and p130Cas overexpression reduce EGF-stimulated dynamin phosphorylation, which is necessary for EGF-induced EGFR internalization. Coimmunoprecipitation and GST pull-down assays confirmed the interaction between p130Cas and dynamin. Moreover, a SH3-domain-deleted form of p130Cas, which shows diminished binding to dynamin, inhibits dynamin phosphorylation and EGF uptake less effectively than wild-type p130Cas.Conclusions/SignificanceOur results show that p130Cas plays an inhibitory role in EGFR internalization via its interaction with dynamin. Given that the EGFR internalization process determines signaling density and specificity in the EGFR pathway, these findings suggest that the interaction between p130Cas and dynamin may regulate EGFR trafficking and signaling in the same manner as other endocytic regulatory proteins related to EGFR endocytosis.

Molecular detection of epidermal growth factor receptor in colorectal cancer: does it still make sense?

The aim of the study was to detect and compare the epidermal growth factor receptor (EGFr) content using different methods, to establish whether the quantitative detection and functional study of EGFr in colorectal cancer, using methods other than immunohistochemistry (IHC), are appropriate. Analysis of EGFr by IHC was performed in 230 colorectal cancer patients using monoclonal anti-EGFr. Total and activated EGFr (pY1068) contents were determined in 92 patients and real-time PCR, to determine the level of EGFr messenger RNA, was carried out in 60 patients. There was no association between EGFr IHC groups and the mean total EGFr levels measured using ELISA. The study shows that the results of different EGFr detection methods do not correlate with each other. Hence, the real role of EGFr in colorectal cancer remains unsettled. Clinically, the receptor itself does not seem to be important and it would be better to focus on EGFr signalling in downstream pathways.

Epidermal Growth Factor Receptor Expression and Activity In Acute Myeloid Leukemia

AbstractAbstract 3144It was previously described that Epidermal Growth Factor Receptor (EGFR) inhibitors can induce a clinical response in AML patients (Boehrer et al., 2008; Chan and Pilichowska, 2007; Pitini et al., 2008). In contrast, it was reported that EGFR is not expressed in AML cells both at protein and mRNA level and that the phenotypic effects of the EGFR inhibitors are off-target effects on the spleen tyrosine kinase (SYK) (Lindhagen et al., 2008; Stegmaier et al., 2005; Hahn et al., 2009). We have, however, detected EGFR mRNA expression in gene expression array data of 534 publicly available adult AML patient samples and 132 publicly available pediatric AML patient samples (obtained from the Gene Expression Omnibus (www.ncbi.nlm.nih.gov/geo, accession number GSE6891 for adult AML patients and GSE22056 for pediatric AML patients) (Fig. A, and B). EGFR kinase activity was measured in four AML samples using the PamChip® tyrosine kinase microarray system and EGFR phosphorylation measured using Phospho-receptor tyrosine kinase antibody microarray (R&D). EGFR kinase activity could be detected in 2 of 4 of the samples (Fig. C) In addition, protein expression of EGFR and phosphorylated (Tyr-992) EGFR was measured using Reverse Phase Protein Array in 511 cases of newly diagnosed AML. Total EGFR levels were equivalent to normal bone marrow CD34+ cells in 72% and above and below normal in 13.5 and 13.7% of AML patient samples respectively (Fig. D). The phosphorylation of the EGF receptor was equivalent to that observed in normal bone marrow CD34+ cells in 80% and above and below normal in 8 and 11.7% of cases respectively (Fig. E). EGFR protein expression was correlated with the level of NF2, CIAP, Survivin, Stat5p694, CyclinD1, Her3, NRP1, PLAC1, CateninA, IGF1, TAZ, SMAD6, YAP, NF2 and PI3Kp110. The level of phospho-EGFR was correlated with the level of expression of P53, RB, pRB, Cyclin B1 and E, BCLXL, BIM, Cleaved caspase 7 and 9, GATA3, Stat1p701 and ODC. Levels of EGFR protein expression and phosphorylation did not correlate with FAB classification, cytogenetics, or the presence of FLT3-ITD or NPM1 or RAS mutation or with age, gender, or the presence of an antecedent hematological disorder. Neither total or phospho-EGFR levels were prognostic for remission attainment, remission duration, overall or event free survival. These results indicate that EGFR is expressed at both the mRNA and the protein level in AML. In addition, EGFR is commonly phosphorylated and active in primary AML patient samples. Activity of EGFR receptor was correlated with higher expression of proliferation regulating genes (Cyclins, P53, RB) and anti-apoptotic proteins suggesting that signaling through the EGFR axis might be affecting proliferation and apoptosis sensitivity in AML blasts. This suggests that modulation of the EGFR axis in different settings could be used to stimulate proliferation and sensitivity to cell cycle specific agents or inhibited to inhibit proliferation or to reduce anti-apoptotic forces. Future experiments to correlate the responsiveness of AML blasts to therapy with EGFR activators/inhibitors with the endogenous activity of the EGFR receptor and to determine the optimal way to target cells through this pathway are underway. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Association of Phosphorylated Epidermal Growth Factor Receptor with Survival in Patients with Locally Advanced Non-small Cell Lung Cancer Treated with Radiotherapy

The epidermal growth factor receptor (EGFR) and its downstream effector kinases are thought to have important roles in lung cancer cell proliferation and response to treatment. In a prospective cohort of patients with locally advanced non-small cell lung cancer (NSCLC) undergoing high-dose radiotherapy with or without chemotherapy, we examined by immunohistochemistry (IHC) the tumor levels of EGFR and phosphorylated/ activated-EGFR (P-EGFR), P-Erk, P-Akt, P-Stat3, and the cell cycle marker Ki67. We examined the relationships among marker expression, at the plasma membrane (M), cytoplasm (C) and nucleus, as well as the radiologic tumor response, and overall survival (OS). Fifty patients were recruited in this study. Their median survival was 18.3 months. No correlation was detected between total EGFR and P-EGFR levels in any subcellular compartment. M P-EGFR correlated positively with C P-Akt (p = 0.01). C P-Erk correlated negatively with radiologic response (p = 0.022), and on univariate regression analysis, this approached significance (p = 0.059). M and C P-EGFR correlated negatively with OS (p = 0.020), and on univariate analysis higher M P-EGFR predicted for poor OS (p = 0.001). Patients with high M P-EGFR levels had median survival of 7.8 months versus 17.7 months for patients with low M P-EGFR. Our results support a role of activated M P-EGFR, (but not total EGFR), as a predictor of OS in locally advanced-NSCLC. It is suggested that detailed evaluation of the subcellular distribution and activation state of EGFR and its downstream effectors is required to unravel the predictive value of these markers in NSCLC.

TNK2 preserves epidermal growth factor receptor expression on the cell surface and enhances migration and invasion of human breast cancer cells

IntroductionAmplification of the TNK2 gene in primary tumours correlates with poor prognosis. In accordance, TNK2 overexpression was shown to promote invasion of cancer cells – but the mechanism by which TNK2 mediates these effects is unresolved. TNK2 was suggested to regulate Cdc42-driven migration by activation of breast cancer antioestrogen resistance 1 (BCAR1); however, distinct from this effect is evidence for a role of TNK2 in the regulation of epidermal growth factor receptor (EGFR) endocytosis and degradation. In the present study we sought to investigate whether negative targeting of TNK2 by siRNA could be used to inhibit cancer cell invasion, to establish the contribution of its effect on the EGFR and to consequently attempt to resolve the issue of TNK2's mechanism of action.MethodsWe used siRNA to knockdown expression of TNK2 and its proposed effector BCAR1 in order to analyse the effect of this knockdown on cancer cell behaviour in vitro. We examined morphological changes using phase-contrast microscopy and immunohistochemistry. Functional parameters examined included apoptosis, proliferation, migration and invasion. We also performed flow cytometry analysis to examine EGFR cell surface expression and carried out western blot to examine the total EGFR levels.ResultsWe observed that targeting of TNK2 by siRNA in breast cancer cells resulted in distinct morphological changes characterised by a stellate appearance and an absence of protrusions at membrane edges. These changes were not recapitulated upon siRNA targeting of BCAR1. We thus hypothesised that a component of the effects induced by TNK2 may be independent of BCAR1. Consistent with the idea of an alternative mechanism for TNK2, we observed that TNK2 associates with activated EGFR in breast cancer cells in a TNK2-kinase-independent manner. Furthermore, we demonstrated that TNK2 functions to maintain EGFRs on the cell surface. We could demonstrate that the main functional effect of activating these surface EGFRs in breast cancer cells is stimulation of migration. In accordance, TNK2 silencing by siRNA led to a significant reduction in cell surface EGFR and to a concomitant decrease in the migratory and invasive capacity of breast cancer cells.ConclusionOur data suggest that TNK2 can enhance migration and invasion of breast cancer cells via preservation of EGFR expression, notwithstanding its previously reported signalling via BCAR1, explaining its oncogenic behaviour in vitro and correlation with metastatic human breast cancer in vivo.

Role of epidermal growth factor receptor degradation in gemcitabine-mediated cytotoxicity

We have recently reported that treatment with gemcitabine, a potent chemotherapeutic agent and radiation sensitizer, stimulates phosphorylation of the epidermal growth factor receptor (EGFR). Because phosphorylation of EGFR is known to precede receptor degradation, we hypothesized that gemcitabine treatment may also result in EGFR degradation. In two human head and neck cancer cell lines, UMSCC-1 and UMSCC-6, we demonstrated an approximately 80% decrease in total EGFR levels at 72 h after a 2-h treatment with 1 muM gemcitabine. Neither cisplatin nor 5-fluorouracil, which are used to treat head and neck cancer, caused EGFR degradation. EGFR downregulation did not occur at the level of transcription, as assessed by reverse transcription-polymerase chain reaction (RT-PCR), but instead occurred via phosphorylation and ubiquitination of the receptor along a proteosome/lysosome-mediated pathway. Inhibition of EGFR degradation, by either pretreatment with the EGFR tyrosine kinase inhibitor gefitinib or by exposure to the proteosome/lysosome inhibitor MG132, significantly reduced gemcitabine-induced cell death. These results suggest that EGFR degradation may be a novel mechanism for gemcitabine-mediated cell death. These findings also indicate that caution should be exercised when combining gemcitabine with agents that may prevent EGFR degradation, such as EGFR tyrosine kinase inhibitors administered in a suboptimal sequence or proteosome inhibitors.

The role of autocrine transforming growth factor alpha in Epidermal Growth Factor receptor mediated tumorigenicity

Introduction: Transforming Growth Factor-α (TGFα), a member of the Epidermal Growth Factor ligand family binds to and activates the Epidermal Growth Factor Receptor (EGFR) resulting in a positive growth stimulus. The impact of TGFα in the malignant progression of human cancer is not entirely clear. The purpose of this study was to determine the role of ectopic TGFα expression on EGFR and its downstream effectors and subsequent tumorigenicity in FET, a human colon cancer cell line that makes only transitory tumors and is growth factor dependent. Methods: FET cells maintained in supplemental McCoy’s media were transfected with a full length TGFα construct with a tetracycline repressible vector. This cell line is referred to as FETα. Thus, with the addition of tetracycline to culture media or drinking water, TGFα can be turned “off.” Protein extracts from the cell lines treated with and without tetracycline were generated for Western blots to assess levels of EGFR, pEGFR, Akt, pAkt, Erk and pErk. PARP cleavage assays were performed to compare apoptosis between FET and FETα. BALB/c nude mice were subcutaneously injected with 5×106 cells of FETα cells. Experimental mice had 2mg/ml of tetracycline added to the drinking water on days 7- 21 post injection. Xenograft growth curves were generated and compared for animals with and without tetracycline in drinking water. On day 21 animals were sacrificed and xenografts were formalin fixed and paraffin embedded for HematoxylinsEosin (H&E) and immunohistochemical (IHC) analysis. FETα xenografts were generated and orthotopically implanted (subserosally) using microsurgical techniques into colons of other BALB/c nude mice. The experimental group received 2mg/ml of tetracylcine in the drinking water 1 week post implantation. Results: Western blots of FETα cells demonstrated increased levels of pEGFR, pAkt, pErk compared to FETα cells treated with tetracycline. Total EGFR, Akt and Erk levels for both groups were the same (see figure). PARP cleavage assays showed FETα to be resistant to growth factor deprivation stress induced apoptosis. Xenograft growth curves showed tumor regression in FETα animals treated with tetracycline (see figure). Immunohistochemical analysis of the xenografts showed that with the addition of tetracycline, TGFα was not produced and levels of activated EGFR, Akt, Erk were decreased as compared to control xenografts with no tetracycline treatment. Animals orthotopically implanted with FETα and treated with tetracyline failed to invade the bowel as compared with the no tetracyline control animals. Conclusions: Transfection of TGFα to generate constitutive EGFR activation into FET transforms a non-tumorigenic cell line into a tumorigenic one. The Western, in vivo xenograft, orthotopic implantation and IHC data show that this tumorigenicity is related to TGFα’s activation of EGFR and its downstream effectors Akt and Erk. Understanding the pathologic nature of such growth regulatory disruptions may lead to the development of novel therapeutic interventions in cancer treatment.

Decorin Evokes Protracted Internalization and Degradation of the Epidermal Growth Factor Receptor via Caveolar Endocytosis

Decorin inhibits the epidermal growth factor receptor (EGFR) by down-regulating its tyrosine kinase activity, thereby blocking the growth of a variety of transformed cells and tumor xenografts. In this study we provide evidence that decorin directly binds to the EGFR causing its dimerization, internalization, and ultimately its degradation. Using various pharmacological agents to disrupt clathrin-dependent and -independent endocytosis, we demonstrate that decorin evokes a protracted internalization of the EGFR primarily via caveolar-mediated endocytosis. In contrast to EGF, decorin targets the EGFR to caveolae, but not to early or recycling endosomes. Ultimately, however, both EGF- and decorin-induced pathways converge into late endosomes/lysosomes for final degradation. Thus, we have discovered a novel biological mechanism for decorin that could explain its anti-proliferative and anti-oncogenic mode of action.

Simultaneous Inhibition of Epidermal Growth Factor Receptor (EGFR) Signaling and Enhanced Activation of Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) Receptor-mediated Apoptosis Induction by an scFv:sTRAIL Fusion Protein with Specificity for Human EGFR

Epidermal growth factor receptor (EGFR) signaling inhibition by monoclonal antibodies and EGFR-specific tyrosine kinase inhibitors has shown clinical efficacy in cancer by restoring susceptibility of tumor cells to therapeutic apoptosis induction. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent with tumor-selective apoptotic activity. Here we present a novel approach that combines EGFR-signaling inhibition with target cell-restricted apoptosis induction using a TRAIL fusion protein with engineered specificity for EGFR. This fusion protein, scFv425:sTRAIL, comprises the EGFR-blocking antibody fragment scFv425 genetically fused to soluble TRAIL (sTRAIL). Treatment with scFv425:sTRAIL resulted in the specific accretion to the cell surface of EGFR-positive cells only. EGFR-specific binding rapidly induced a dephosphorylation of EGFR and down-stream mitogenic signaling, which was accompanied by cFLIP(L) down-regulation and Bad dephosphorylation. EGFR-specific binding converted soluble scFv425:sTRAIL into a membrane-bound form of TRAIL that cross-linked agonistic TRAIL receptors in a paracrine manner, resulting in potent apoptosis induction in a series of EGFR-positive tumor cell lines. Co-treatment of EGFR-positive tumor cells with the EGFR-tyrosine kinase inhibitor Iressa resulted in a potent synergistic pro-apoptotic effect, caused by the specific down-regulation of c-FLIP. Furthermore, in mixed culture experiments binding (L)of scFv425:sTRAIL to EGFR-positive target cells conveyed a potent apoptotic effect toward EGFR-negative bystander tumor cells. The favorable characteristics of scFv425:sTRAIL, alone and in combination with Iressa, as well as its potent anti-tumor bystander activity indicate its potential value for treatment of EGFR-expressing cancers.

EGFR and cancer prognosis

Elevated levels of the epidermal growth factor receptor (EGFR), a growth-factor-receptor tyrosine kinase, and/or its cognate ligands have been identified as a common component of multiple cancer types and appear to promote solid tumour growth. This article examines the relationship between EGFR expression and cancer prognosis based on literature compiled on PubMed between 1985 and September 2000. More than 200 studies were identified that analysed relapse-free-interval or survival data directly in relation to EGFR levels in over 20 000 patients. Analysis of the data showed that 10 cancer types both express elevated levels of EGFR relative to normal tissues and have been studied in sufficient depth to allow sound judgements to be made concerning the association between EGFR and patient outlook. The EGFR was found to act as a strong prognostic indicator in head and neck, ovarian, cervical, bladder and oesophageal cancers. In these cancers, increased EGFR expression was associated with reduced recurrence-free or overall survival rates in 70% (52/74) of studies. In gastric, breast, endometrial and colorectal cancers, the EGFR provided more modest prognostic information, correlating to poor survival rates in 52% (13/25) of studies, while in non-small cell lung cancer (NSCLC), EGFR expression only rarely (3/10 studies) related to patient outlook. However, it is likely that the true prognostic significance of the EGFR has been underestimated as the published studies only assessed total cellular EGFR levels, rather than the activated form of the receptor, and were not standardised with regard to patient populations or assay methods. Finally, it is important to stress that failure to detect a prognostic significance for EGFR in any one cancer type does not necessarily preclude patients from benefiting from anti-EGFR therapies.

Epidermal growth factor receptor expression in primary cultured human colorectal carcinoma cells.

In situ hybridization on human colon tissue demonstrates that epidermal growth factor receptor (EGFR) mRNA expression is strongly increased during tumour progression. To obtain test systems to evaluate the relevance of growth factor action during carcinogenesis, primary cultures from human colorectal carcinomas were established. EGFR distribution was determined in 2 of the 27 primary cultures and was compared with that in well-defined subclones derived from the Caco-2 cell line, which has the unique property to differentiate spontaneously in vitro in a manner similar to normal enterocytes. The primary carcinoma-derived cells had up to three-fold higher total EGFR levels than the Caco-2 subclones and a basal mitotic rate at least fourfold higher. The EGFR affinity constant is 0.26 nmol l(-1), which is similar to that reported in Caco-2 cells. The proliferation rate of Caco-2 cells is mainly induced by EGF from the basolateral cell surface where the majority of receptors are located, whereas primary cultures are strongly stimulated from the apical side also. This corresponds to a three- to fivefold higher level of EGFR at the apical cell surface. This redistribution of EGFR to apical plasma membranes in advanced colon carcinoma cells suggests that autocrine growth factors in the colon lumen may play a significant role during tumour progression.