Shc regulates epidermal growth factor-induced activation of the JNK signaling pathway

ErbBs in Lens Cell Fibrosis and Secondary Cataract

Purpose

TGFβ-induced epithelial-to-myofibroblast transition (EMyT) of lens cells has been linked to the most common vision-disrupting complication of cataract surgery-namely, posterior capsule opacification (PCO; secondary cataract). Although inhibitors of the ErbB family of receptor tyrosine kinases have been shown to block some PCO-associated processes in model systems, our knowledge of ErbB signaling in the lens is very limited. Here, we investigate the expression of ErbBs and their ligands in primary cultures of chick lens epithelial cells (dissociated cell-derived monolayer cultures [DCDMLs]) and how TGFβ affects ErbB function.

Methods

DCDMLs were analyzed by immunofluorescence microscopy and Western blotting under basal and profibrotic conditions.

Results

Small-molecule ErbB kinase blockers, including the human therapeutic lapatinib, selectively inhibit TGFβ-induced EMyT of DCDMLs. Lens cells constitutively express ErbB1 (EGFR), ErbB2, and ErbB4 protein on the plasma membrane and release into the medium ErbB-activating ligand. Culturing DCDMLs with TGFβ increases soluble bioactive ErbB ligand and markedly alters ErbBs, reducing total and cell surface ErbB2 and ErbB4 while increasing ErbB1 expression and homodimer formation. Similar, TGFβ-dependent changes in relative ErbB expression are induced when lens cells are exposed to the profibrotic substrate fibronectin. A single, 1-hour treatment with lapatinib inhibits EMyT in DCDMLs assessed 6 days later. Short-term exposure to lower doses of lapatinib is also capable of eliciting a durable response when combined with suboptimal levels of a mechanistically distinct multikinase inhibitor.

Conclusions

Our findings support ErbB1 as a therapeutic target for fibrotic PCO, which could be leveraged to pharmaceutically preserve the vision of millions of patients with cataracts.

Interleukin-1β Induces Tissue Factor Expression in A549 Cells via EGFR-Dependent and -Independent Mechanisms

Tissue factor (TF) plays an important role in the progression and angiogenesis of tumor cells. The present study investigated the mechanism of interleukin-1β (IL-1β)-induced TF expression in A549 lung cancer cells. Based on mRNA and protein analyses, including appropriate inhibitor experiments, IL-1β was shown to induce TF expression in a time-dependent manner, mediated by IL-1 receptor-dependent phosphorylation of the mitogen-activated protein kinases (MAPK) p38, p42/44 and c-jun N-terminal kinase (JNK), as well as the Src kinase and the epidermal growth factor receptor (EGFR). Thereby, inhibition of EGFR transactivation by the Src inhibitor PP1 or direct EGFR inhibition by the EGFR tyrosine kinase inhibitor (TKI) erlotinib led to a reduction of IL-1β-induced TF expression and to a suppression of p42/44 MAPK and EGFR activation, while IL-1β-induced p38 MAPK and JNK activation remained unchanged. A knockdown of EGFR by siRNA was associated with decreased IL-1β-mediated p42/44 MAPK activation, which was no longer inhibitable by erlotinib. Concentration-dependent inhibition of IL-1β-induced TF expression was also observed in the presence of gefitinib and afatinib, two other EGFR TKIs. In summary, our results suggest that IL-1β leads to increased TF formation in lung cancer cells via both Src/EGFR/p42/44 MAPK-dependent and EGFR-independent signaling pathways, with the latter mediated via p38 MAPK and JNK.

PLCγ1‑dependent invasion and migration of cells expressing NSCLC‑associated EGFR mutants

The increased tyrosine kinase activity of non‑small cell lung cancer (NSCLC)‑associated epidermal growth factor receptor (EGFR) mutants results in deregulated pathways that contribute to malignant cell survival, tumor progression and metastasis. Previous studies investigating lung cancer‑associated EGFR have focused on the prognostic implications of receptor kinase mutations in patients with NSCLC; however, the role of EGFR mutations in tumor cell invasion and migration remains undetermined. The present study was designed to investigate the role of NSCLC‑associated mutant EGFR‑driven signaling pathways in cell proliferation and invasion. Non‑endogenous EGFR‑expressing 293 cells stably expressing EGFR mutants that are sensitive or resistant to Food and Drug Administration (FDA)‑approved EGFR‑targeted tyrosine kinase inhibitors (TKIs) were used in the present study. The experiments demonstrated an increased phosphorylation of phospholipase (PLC)γ1, c‑Cbl, signal transducer and activator of transcription (Stat), extracellular regulated kinase (Erk)1/2, Akt, Shc and Gab1 proteins in cells expressing a mutant form, rather than the wild‑type receptor. As PLCγ1 is a known regulator of metastatic development, mutant receptor‑mediated PLCγ1 activation was further evaluated. To examine the effects of EGFR and PLCγ1 phosphorylation, the metastatic potential of cells expressing mutants was investigated using wound healing, Transwell cell migration and invasion assays. The inhibition of receptor phosphorylation with the 1st, 2nd and 3rd generation TKIs, gefitinib, afatinib, osimertinib, respectively, reduced PLCγ1 phosphorylation, and reduced the invasive and migratory potential of 293 cells, confirming PLCγ1 as one of the probable downstream effectors of mutant EGFR signaling. However, the PLC inhibitor, U73122, inhibited cell migration and invasion without affecting EGFR signaling and PLCγ1 phosphorylation. Notably, U73122 reduced Akt and Erk1/2 phosphorylation within 25 min of its application; however, 100% cell viability was recorded even after 48 h. Upon further investigation, proliferative signaling pathways remained active at 48 h, in accordance with cell viability. Therefore, the present study concludes that mutant receptor‑mediated PLCγ1 activation may play a significant role in the migration and invasion of NSCLC tumors; however, its regulatory role in tumor cell proliferation warrants further investigation and validation in lung tumor cell lines harboring EGFR mutations.

Targeted Therapies Against Growth Factor Signaling in Breast Cancer

Breast cancer is the most prevalent female malignancy throughout the world. Conventional treatment strategies for breast cancer consist of chemotherapy, radiation, surgery, chemoradiation, hormone therapy, and targeted therapies. Among them, targeted therapies show advantages to reduce cost and toxicity for being possible for individualized treatments based on the intrinsic subtypes of breast cancer. With deeper understanding of key signaling pathways concerning tumor growth and survival, growth factor-controlled signaling pathways are frequently dysregulated in the development and progression of breast cancer. Thus, targeted therapies against growth factor-mediated signaling pathways have been shown to have promising efficacy in both preclinical animal models and human clinical trials. In this chapter, we will briefly introduce inhibitors and monoclonal antibodies that target the main growth factor-modulated scenarios including epidermal growth factor receptor (EGFR), transforming growth factor beta (TGF-β), insulin-like growth factor 1 receptor (IGF1R), and fibroblast growth factor receptor (FGFR) signaling pathways in breast cancer therapy.

Predicting high-risk endometrioid carcinomas using proteins

Background

The lethality of endometrioid endometrial cancer (EEC) is primarily attributable to advanced-stage diseases. We sought to develop a biomarker model that predicts EEC surgical stage at the time of clinical diagnosis.

Results

PSES was significantly correlated with surgical stage in the TCGA cohort (P < 0.0001) and in the validation cohort (P = 0.0003). Even among grade 1 or 2 tumors, PSES was significantly higher in advanced than in early stage tumors in both the TCGA (P = 0.005) and MD Anderson Cancer Center (MDACC) (P = 0.006) cohorts. Patients with positive PSES score had significantly shorter progression-free survival than those with negative PSES in the TCGA (hazard ratio [HR], 2.033; 95% CI, 1.031 to 3.809; P = 0.04) and validation (HR, 3.306; 95% CI, 1.836 to 9.436; P = 0.0007) cohorts. The ErbB signaling pathway was most significantly enriched in the PSES proteins and downregulated in advanced stage tumors.

Methods

Using reverse-phase protein array expression profiles of 170 antibodies for 210 EEC cases from TCGA, we constructed a Protein Scoring of EEC Staging (PSES) scheme comprising 6 proteins (3 of them phosphorylated) for surgical stage prediction. We validated and evaluated its diagnostic potential in an independent cohort of 184 EEC cases obtained at MDACC using receiver operating characteristic curve analyses. Kaplan-Meier survival analysis was used to examine the association of PSES score with patient outcome, and Ingenuity pathway analysis was used to identify relevant signaling pathways. Two-sided statistical tests were used.

Conclusions

PSES may provide clinically useful prediction of high-risk tumors and offer new insights into tumor biology in EEC.

Proteomics reveals novel protein associations with early endosomes in an epidermal growth factor-dependent manner

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is an integral component of proliferative signaling. EGFRs on the cell surface become activated upon EGF binding and have an increased rate of endocytosis. Once in the cytoplasm, the EGF·EGFR complex is trafficked to the lysosome for degradation, and signaling is terminated. During trafficking, the EGFR kinase domain remains active, and the internalized EGFR can continue signaling to downstream effectors. Although effector activity varies based on the EGFR's endocytic location, it is not clear how this occurs. In an effort to identify proteins that uniquely associate with the internalized, liganded EGFR in the early endosome, we developed an early endosome isolation strategy to analyze their protein composition. Post-nuclear supernatant from HeLa cells stimulated with and without EGF were separated on an isotonic 17% Percoll gradient. The gradient was fractionated, and early endosomal fractions were pooled and immunoisolated with an EEA1 mAb. The isolated endosomes were validated by immunoblot using antibodies against organelle-specific marker proteins and transmission EM. These early endosomes were also subjected to LC-MS/MS for proteomic analysis. Five proteins were detected in endosomes in a ligand-dependent manner: EGFR, RUFY1, STOML2, PTPN23, and CCDC51. Knockdown of RUFY1 or PTPN23 by RNAi indicated that both proteins play a role in EGFR trafficking. These experiments indicate that endocytic trafficking of activated EGFR changes the protein composition, membrane trafficking, and signaling potential of the early endosome.

Oncogenic MCT-1 activation promotes YY1-EGFR-MnSOD signaling and tumor progression

Tumor cells often produce high levels of reactive oxygen species (ROS) and display an increased ROS scavenging system. However, the molecular mechanism that balances antioxidative and oxidative stress in cancer cells is unclear. Here, we determined that oncogenic multiple copies in T-cell malignancy 1 (MCT-1) activity promotes the generation of intracellular ROS and mitochondrial superoxide. Overexpression of MCT-1 suppresses p53 accumulation but elevates the manganese-dependent superoxide dismutase (MnSOD) level via the YY1-EGFR signaling cascade, which protects cells against oxidative damage. Conversely, restricting ROS generation and/or targeting YY1 in lung cancer cells effectively inhibits the EGFR-MnSOD signaling pathway and cell invasiveness induced by MCT-1. Significantly, MCT-1 overexpression in lung cancer cells promotes tumor progression, necrosis and angiogenesis, and increases the number of tumor-promoting M2 macrophages and cancer-associated fibroblasts in the microenvironment. Clinical evidence further confirms that high expression of MCT-1 is associated with an increase in YY1, EGFR and MnSOD expression, accompanied by tumor recurrence, poor overall survival and EGFR mutation status in patients with lung cancers. Together, these data indicate that the MCT-1 oncogenic pathway is implicated in oxidative metabolism and lung carcinogenesis.

Endophilin-1 regulates blood-brain barrier permeability via EGFR-JNK signaling pathway

Endophilin-1 (Endo1), a multifunctional protein, is essential for synaptic vesicle endocytosis. However, the role and mechanism of endophilin-1 in blood-brain barrier (BBB) function are still unclear. This study was performed to determine whether endophilin-1 regulated BBB permeability via the EGFR-JNK signaling pathway. In the present study, we found that endophilin-1 over-expression in human cerebral microvascular endothelial cell (hCMEC/D3) increased BBB permeability and meanwhile reduced the expression levels of epidermal growth factor receptor (EGFR), phosphorylated c-Jun N-terminal kinase (p-JNK). While endophilin-1 knockdown led to the contrary results. After JNK inhibitor SP600125 was administered to the endophilin-1 silenced hCMEC/D3 cells, the transendothelial electrical resistance (TEER) value was decreased and the permeability coefficient values to 4kDa and 40kDa FITC-dextran were increased. Results observed by Transmission electron microscopy (TEM) showed that tight junctions (TJs) were opened. Moreover, immunofluorescence and Western blot assays revealed the discontinuous distribution of TJ-associated proteins ZO-1, occludin on cell-cell boundaries and a significant decrease in protein expressing levels. Therefore, these results indicated that endophilin-1 positively regulated BBB permeability via the EGFR-JNK signaling pathway in hCMEC/D3 cells, which would provide an experimental basis for further research on endophilin-1 mediated the opening of BBB.

Fetal wound healing biomarkers

Fetal skin has the intrinsic capacity for wound healing, which is not correlated with the intrauterine environment. This intrinsic ability requires biochemical signals, which start at the cellular level and lead to secretion of transforming factors and expression of receptors, and specific markers that promote wound healing without scar formation. The mechanisms and molecular pathways of wound healing still need to be elucidated to achieve a complete understanding of this remodeling system. The aim of this paper is to discuss the main biomarkers involved in fetal skin wound healing as well as their respective mechanisms of action.

Anti-inflammatory mechanism of polyunsaturated fatty acids in Helicobacter pylori-infected gastric epithelial cells

Helicobacter pylori is an important risk factor for gastric inflammation, which is mediated by multiple signaling pathways. The aim of this study was to investigate the effects of polyunsaturated fatty acids (PUFAs), such as linoleic acid (LA), alpha-linolenic acid (ALA), and docosahexaenoic acid (DHA), on the expression of the proinflammatory chemokine interleukin-8 (IL-8) in H. pylori-infected gastric epithelial AGS cells. To investigate whether PUFAs modulate H. pylori-induced inflammatory signaling, we determined the activation of epidermal growth factor receptor (EGFR), protein kinase C-δ (PKC δ), mitogen-activated protein kinases (MAPKs), nuclear factor-kappa B (NF- κB), and activator protein-1 (AP-1) as well as IL-8 expression in H. pylori-infected gastric epithelial cells that had been treated with or without PUFAs. We found that PUFAs inhibited IL-8 mRNA and protein expression in H. pylori-infected cells. ω-3 fatty acids (ALA, and DHA) suppressed the activation of EGFR, PKC δ, MAPK, NF- κB, and AP-1 in these infected cells. LA did not prevent EGFR transactivation and exhibited a less potent inhibitory effect on IL-8 expression than did ALA and DHA. In conclusion, PUFAs may be beneficial for prevention of H. pylori-associated gastric inflammation by inhibiting proinflammatory IL-8 expression.

Modulation of the response of prostate cancer cell lines to cisplatin treatment using small interfering RNA

Cisplatin is one of the most effective and widely used chemotherapeutic agents against several types of human cancers. However, the underlying mechanisms of action are not fully understood. We aimed to investigate the possible molecular mechanism(s) of acquired chemoresistance observed in prostate cancer cells treated with cisplatin. Human LNCaP cells (bearing wild-type p53) and PC-3 cells (lacking p53) were used. The expression levels of protein were determined by western blotting, and the mRNA levels were determined by reverse transcription-polymerase chain reaction (RT-PCR). Cell viability was measured by MTT assay, and the transcriptional effect of small interfering RNA (siRNA) was measured by luciferase reporter gene. We showed that cisplatin treatment increased JNK-1 and JNK-2 activity and expression in both LNCaP and PC-3 cells. In addition, the knockdown of JNK-1 expression by siRNA-JNK-1 or siRNA-JNK-2 significantly impaired the upregulation of AP-1 luciferase reporter gene, but failed to decrease the levels of AP-1 reporter gene expression induced by TPA treatment. Our observations indicate that JNK-1 and JNK-2 may be involved in the chemoresistance observed in prostate cancer cells treated with cisplatin and that blocking the stimulation of Jun kinase (JNK) signaling may be important for regulating the susceptibility to cisplatin of prostate cancer.

Chlamydia trachomatis co-opts the FGF2 signaling pathway to enhance infection

The molecular details of Chlamydia trachomatis binding, entry, and spread are incompletely understood, but heparan sulfate proteoglycans (HSPGs) play a role in the initial binding steps. As cell surface HSPGs facilitate the interactions of many growth factors with their receptors, we investigated the role of HSPG-dependent growth factors in C. trachomatis infection. Here, we report a novel finding that Fibroblast Growth Factor 2 (FGF2) is necessary and sufficient to enhance C. trachomatis binding to host cells in an HSPG-dependent manner. FGF2 binds directly to elementary bodies (EBs) where it may function as a bridging molecule to facilitate interactions of EBs with the FGF receptor (FGFR) on the cell surface. Upon EB binding, FGFR is activated locally and contributes to bacterial uptake into non-phagocytic cells. We further show that C. trachomatis infection stimulates fgf2 transcription and enhances production and release of FGF2 through a pathway that requires bacterial protein synthesis and activation of the Erk1/2 signaling pathway but that is independent of FGFR activation. Intracellular replication of the bacteria results in host proteosome-mediated degradation of the high molecular weight (HMW) isoforms of FGF2 and increased amounts of the low molecular weight (LMW) isoforms, which are released upon host cell death. Finally, we demonstrate the in vivo relevance of these findings by showing that conditioned medium from C. trachomatis infected cells is enriched for LMW FGF2, accounting for its ability to enhance C. trachomatis infectivity in additional rounds of infection. Together, these results demonstrate that C. trachomatis utilizes multiple mechanisms to co-opt the host cell FGF2 pathway to enhance bacterial infection and spread.

Chlamydia trachomatis is an obligate intracellular bacterium that is an important cause of human disease, including sexually transmitted diseases and acquired blindness in developing countries. The inability to carry out conventional genetic manipulations limits our understanding of the mechanisms of C. trachomatis binding, entry, and spread. Previous studies have shown that heparan sulfate proteoglycans (HSPGs) play a role in early binding events. As cell surface HSPGs facilitate the interactions of many growth factors with their receptors, we investigated whether HSPG-associated growth factors affect C. trachomatis binding or entry. Here, we report the novel finding that Fibroblast Growth Factor 2 (FGF2), a ubiquitously expressed growth factor, enhances C. trachomatis binding to host cells in an HSPG-dependent manner. Furthermore, C. trachomatis infection stimulates production and release of FGF2 through distinct signaling pathways. Released FGF2 is sufficient to enhance the subsequent rounds of infection. Together, these results demonstrate that C. trachomatis utilizes multiple mechanisms to co-opt the host cell FGF2 pathway that sets up a positive feedback loop to enhance bacterial infection and spread.

Mitogen-activated protein kinases in mammalian oxidative stress responses

All aerobic organisms are exposed to oxidative stress during their lifetime and are required to respond appropriately for maintenance of their survival and homeostasis. Sustained exposure to oxidative stress has devastating effects in organisms, and, not surprisingly, oxidative stress has been implicated in numerous human diseases. Therefore, an understanding of how mammals respond to oxidative stress is crucial both biologically and clinically. Intracellular signaling pathways, which are activated in response to excessive oxygen radicals, play essential roles in overcoming oxidative stress. The mitogen-activated protein kinase (MAPK) signaling pathways are involved in diverse physiological processes, and are critical for induction of oxidative stress responses. In this review, we will discuss the physiological roles of MAPKs in oxidative stress, the upstream signaling pathways leading to MAPK activation, their regulation, and the MAPK downstream substrates, with a focus on mammalian systems.

The Rac1/JNK pathway is critical for EGFR-dependent barrier formation in human airway epithelial cells

The airway epithelial barrier provides defenses against inhaled antigens and pathogens, and alterations of epithelial barrier function have been proposed to play a significant role in the pathogenesis of chronic airway diseases. Although the epidermal growth factor receptor (EGFR) plays roles in various physiological and pathological processes on the airway epithelium, the role of EGFR on barrier function in the airway remains largely unknown. In the present study, we assessed the effects of EGFR activation on paracellular permeability in airway epithelial cells (AECs). EGFR activation induced by the addition of EGF increased transepithelial electrical resistance (TER) in AECs. An EGFR-blocking antibody eradicated the development of TER, paracellular influx of dextran, and spatial organization of tight junction. Moreover, the effects of EGFR activation on paracellular permeability were eradicated by knockdown of occludin. To identify the EGFR signaling pathway that regulates permeability barrier development, we investigated the effects of several MAP kinase inhibitors on permeability barrier function. Pretreatment with a JNK-specific inhibitor, but not an ERK- or p38-specific inhibitor, attenuated the development of TER induced by EGFR activation. Rac1 is one of the upstream activators for JNK in EGFR signaling. Rac1 knockdown attenuated the phosphorylation of JNK activation and EGFR-mediated TER development. These results suggest that EGFR positively regulates permeability barrier development through the Rac1/JNK-dependent pathway.

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

The crosstalk between EGF, IGF, and Insulin cell signaling pathways--computational and experimental analysis

BACKGROUND

Cellular response to external stimuli requires propagation of corresponding signals through molecular signaling pathways. However, signaling pathways are not isolated information highways, but rather interact in a number of ways forming sophisticated signaling networks. Since defects in signaling pathways are associated with many serious diseases, understanding of the crosstalk between them is fundamental for designing molecularly targeted therapy. Unfortunately, we still lack technology that would allow high throughput detailed measurement of activity of individual signaling molecules and their interactions. This necessitates developing methods to prioritize selection of the molecules such that measuring their activity would be most informative for understanding the crosstalk. Furthermore, absence of the reaction coefficients necessary for detailed modeling of signal propagation raises the question whether simple parameter-free models could provide useful information about such pathways.

RESULTS

We study the combined signaling network of three major pro-survival signaling pathways: Epidermal Growth Factor Receptor (EGFR), Insulin-like Growth Factor-1 Receptor (IGF-1R), and Insulin Receptor (IR). Our study involves static analysis and dynamic modeling of this network, as well as an experimental verification of the model by measuring the response of selected signaling molecules to differential stimulation of EGF, IGF and insulin receptors. We introduced two novel measures of the importance of a node in the context of such crosstalk. Based on these measures several molecules, namely Erk1/2, Akt1, Jnk, p70S6K, were selected for monitoring in the network simulation and for experimental studies. Our simulation method relies on the Boolean network model combined with stochastic propagation of the signal. Most (although not all) trends suggested by the simulations have been confirmed by experiments.

CONCLUSION

The simple model implemented in this paper provides a valuable first step in modeling signaling networks. However, to obtain a fully predictive model, a more detailed knowledge regarding parameters of individual interactions might be necessary.

Epidermal growth factor receptor-mediated membrane type 1 matrix metalloproteinase endocytosis regulates the transition between invasive versus expansive growth of ovarian carcinoma cells in three-dimensional collagen

The epidermal growth factor receptor (EGFR) is overexpressed in ovarian carcinomas and promotes cellular responses that contribute to ovarian cancer pathobiology. In addition to modulation of mitogenic and motogenic behavior, emerging data identify EGFR activation as a novel mechanism for rapid modification of the cell surface proteome. The transmembrane collagenase membrane type 1 matrix metalloproteinase (MT1-MMP, MMP-14) is a major contributor to pericelluar proteolysis in the ovarian carcinoma microenvironment and is subjected to extensive posttranslational regulation. In the present study, the contribution of EGFR activation to control of MT1-MMP cell surface dynamics was investigated. Unstimulated ovarian cancer cells display caveolar colocalization of EGFR and MT1-MMP, whereas EGFR activation prompts internalization via distinct endocytic pathways. EGF treatment results in phosphorylation of the MT1-MMP cytoplasmic tail, and cells expressing a tyrosine mutated form of MT1-MMP (MT1-MMP-Y(573)F) exhibit defective MT1-MMP internalization. As a result of sustained cell surface MT1-MMP activity, a phenotypic epithelial-mesenchymal transition is observed, characterized by enhanced migration and collagen invasion, whereas growth within three-dimensional collagen gels is inhibited. These data support an EGFR-dependent mechanism for regulation of the transition between invasive and expansive growth of ovarian carcinoma cells via modulation of MT1-MMP cell surface dynamics.

Diesel exhaust increases EGFR and phosphorylated C-terminal Tyr 1173 in the bronchial epithelium

Background

Epidemiological studies have demonstrated adverse health effects of environmental pollution. Diesel exhaust (DE) is a major contributor to particulate matter pollution. DE exposure has been shown to induce a pronounced inflammatory response in the airways, together with an enhanced epithelial expression of cytokines such as IL-8, Gro-α, IL-13 and activation of redox sensitive transcription factors (NFκB, AP-1), and MAP kinases (p38, JNK). The aim of the present investigation was to elucidate the involvement of the epidermal growth factor receptor (EGFR) signalling pathway in the epithelial response to DE in-vivo.

Results

Immunohistochemical staining was used to quantify the expression of the EGFR, phosphorylated Tyrosine residues, MEK and ERK in the bronchial epithelium of archived biopsies from 15 healthy subjects following exposure to DE (PM₁₀, 300 μg/m³) and air. DE induced a significant increases in the expression of EGFR (p = 0.004) and phosphorylated C-terminal Tyr 1173 (p = 0.02). Other investigated EGFR tyrosine residues, Src related tyrosine (Tyr 416), MEK and ERK pathway were not changed significantly by DE.

Conclusion

Exposure to DE (PM₁₀, 300 μg/m³) caused enhanced EGFR expression and phosphorylation of the tyrosine residue (Tyr 1173) which is in accordance with the previously demonstrated activation of the JNK, AP-1, p38 MAPK and NFkB pathways and associated downstream signalling and cytokine production. No effects were seen on the MEK and ERK pathway suggesting that at the investigated time point (6 hours post exposure) there was no proliferative/differentiation signalling in the bronchial epithelium. The present findings suggest a key role for EGFR in the bronchial response to diesel exhaust.

Effect of aging on EGF-induced proliferative response in primary cultured periportal and perivenous hepatocytes

BACKGROUND/AIMS

Aging relates to declined proliferative capacity of the liver, but the molecular mechanism is not well understood. We examined whether functional changes of epidermal growth factor (EGF) receptor (EGFR) are involved in age-related decline in EGF-induced DNA synthesis using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in the proliferative capacity.

METHODS

Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) in 7-, 30-, and 90-week-old rats were isolated using the digitonin/collagenase perfusion technique. DNA synthesis was assessed by [methyl-(3)H]thymidine incorporation. EGFR binding affinity to EGF was analyzed by Scatchard analysis using [(125)I]EGF. EGFR dimerization and phosphorylation were determined by Western blot analysis.

RESULTS

EGF-induced DNA synthesis was greater in PPH than in PVH from rats of 7 weeks, but the zonal difference disappeared with aging. [(125)I]EGF binding studies indicated that high-affinity EGFR in both subpopulations also disappeared with aging. Furthermore, EGF-induced dimerization in both subpopulations was down-regulated with aging, and the pattern of EGFR phosphorylation was parallel to that of dimerization.

CONCLUSIONS

These data suggest that age-related decline in EGF-induced DNA synthesis of PPH and PVH is caused by down-regulation of EGFR dimerization through the decrease of high-affinity EGFR.

Dok-3 sequesters Grb2 and inhibits the Ras-Erk pathway downstream of protein-tyrosine kinases

Adaptor proteins are essential in coordinating recruitment and, in a few cases, restraint of various effectors during cellular signaling. Dok-1, Dok-2 and Dok-3 comprise a closely related family of adaptor, which negatively regulates mitogen-activated protein kinase Erk downstream of protein-tyrosine kinases (PTKs). Recruitment of p120 rasGAP, a potent inhibitor of Ras, by Dok-1 and Dok-2 appears critical in the negative regulation of the Ras-Erk pathway. However, as Dok-3 does not bind rasGAP, it has been unclear how Dok-3 inhibits Erk downstream of PTKs. Here, we identified Grb2 as a Dok-3-binding protein upon its tyrosine phosphorylation. This interaction required the intact binding motifs of the Grb2 SH2 domain, and a mutant (Dok-3-FF) having a Tyr/Phe substitution at these motifs failed to inhibit Ras and Erk activation downstream of a cytoplasmic PTK Src. Because Grb2 forms a stable complex with Sos, a crucial activator of Ras, these data suggest that Dok-3 restrains Grb2 and inhibits the ability of the Grb2-Sos complex to activate Ras. Indeed, forced expression of Dok-3, but not Dok-3-FF, inhibited the recruitment of the Grb2-Sos complex to Shc downstream of Src, which is an essential event for activation of the Ras-Erk pathway. These findings indicate that Dok-3 sequesters Grb2 from Shc and inhibits the Ras-Erk pathway downstream of PTKs.

Regulation of MAPKs by growth factors and receptor tyrosine kinases

Multiple growth- and differentiation-inducing polypeptide factors bind to and activate transmembrane receptors tyrosine kinases (RTKs), to instigate a plethora of biochemical cascades culminating in regulation of cell fate. We concentrate on the four linear mitogen-activated protein kinase (MAPK) cascades, and highlight organizational and functional features relevant to their action downstream to RTKs. Two cellular outcomes of growth factor action, namely proliferation and migration, are critically regulated by MAPKs and we detail the underlying molecular mechanisms. Hyperactivation of MAPKs, primarily the Erk pathway, is a landmark of cancer. We describe the many links of MAPKs to tumor biology and review studies that identified machineries permitting prolongation of MAPK signaling. Models attributing signal integration to both phosphorylation of MAPK substrates and to MAPK-regulated gene expression may shed light on the remarkably diversified functions of MAPKs acting downstream to activated RTKs.

Anti-HER-3 MAbs inhibit HER-3-mediated signaling in breast cancer cell lines resistant to anti-HER-2 antibodies

Two members of the EGF receptor family, HER2 and HER3, act as key oncogenes in breast cancer cells. A MAb against HER2, trastuzumab, interferes with HER2 signaling and istherapeutically effective in humans. Here, we explored the biologic effects of an antibody against HER3 (alpha-HER3ECD) in the invasive breast cancer cell lines MCF-7ADR and MDA-MB-468. Pretreating the breast cancer cells with alpha-HER3ECD prior to Heregulin stimulation caused significant reduction of the migratory and proliferative properties. This reduction is due to a substantial decrease in the tyrosine phosphorylation content of HER2 and to a modification of the HER2/HER3 association, which ultimately inhibits the activity of the downstream effectors phosphatidyinositol-3-OH-kinase and c-jun-terminal kinase. Furthermore, HER3 is internalized and not activated by HRG after pretreatment with alpha-HER3ECD. Our data reinforce the notion that HER3 could be a key target in cancer drug design and show the great potential of anti-HER3 antibodies for the therapy of breast cancer and other malignancies characterized by overexpression of HER3.

Expression of the epidermal growth factor receptor and Her-2 are predictors of favorable outcome and reduced complete response rates, respectively, in patients with muscle-invading bladder cancers treated by concurrent radiation and cisplatin-based chemotherapy: a report from the Radiation Therapy Oncology Group

PURPOSE

Erb-1 (epidermal growth factor receptor, EGFR) and Erb-2 (Her-2) are two of the best characterized members in the EGFR pathway. In many tumor types, overexpression of these proteins is associated with enhanced malignant potential. Our objective in this study was to investigate the clinical relevance of EGFR and Her-2 expression in bladder cancer cases from four prospective Radiation Therapy Oncology Group (RTOG) bladder preservation trials using cisplatin-containing chemoradiation (RTOG 8802, 8903, 9506, and 9706).

METHODS AND MATERIALS

Tumors from 73 cases from patients with muscle-invading T2-T4a bladder cancers had slides interpretable for EGFR staining; 55 cases had slides interpretable for Her-2 staining. Additionally, the respective prognostic values of p53, pRB, and p16 immunostaining were concomitantly examined. Staining and interpretation of staining were done in a blinded manner, without knowledge of clinical outcome. Staining was judged as positive or negative. Subsequently, staining was correlated with clinical outcome.

RESULTS

On univariate analysis, EGFR positivity was significantly associated with improved overall survival (p = 0.044); disease-specific survival (DSS) (p = 0.042); and DSS with intact bladder (p = 0.021). There was also a trend for association between EGFR expression and reduced frequency of distant metastasis (p = 0.06). On multivariate analysis adding tumor stage, tumor grade, whether a visibly complete transurethral resection of bladder tumor (TURBT) was done or not, and patient age to the model, EGFR positivity was significantly associated with improved DSS. On univariate analysis, Her-2 positivity was significantly associated with reduced complete response (CR) rates (50% vs. 81%, p = 0.026) after chemoradiation which remained significant on multivariate analysis. The other markers examined in this study were not found to have any prognostic value in this setting.

CONCLUSION

Epidermal growth factor receptor expression appears to correlate significantly with improved outcome in bladder cancer, whereas Her-2 expression is significantly associated only with reduced CR rates after chemoradiation. Further investigations are warranted into how EGFR family members regulate response to chemoradiation in bladder cancer and their potential therapeutic implications.

Oncostatin M-induced activation of stress-activated MAP kinases depends on tyrosine 861 in the OSM receptor and requires Jak1 but not Src kinases

We have investigated the molecular mechanisms involved in the activation process of the stress-activated protein kinases (SAPK) p38 and JNK in response to the interleukin-6-type cytokine oncostatin M (OSM). Interestingly, activation of p38 and JNK originates from tyrosine residue 861 in the OSMR; the same tyrosine residue which we identified before to be involved in the activation of the mitogen-activated kinases Erk1/2 [Hermanns, H. M., Radtke, S., Schaper, F., Heinrich, P. C., and Behrmann, I. (2000) J. Biol. Chem. 275, 40742-40748]. Therefore, activation of members belonging to all three MAPK families is mediated by one tyrosine motif in the cytoplasmic region of the human OSMR. Concomitantly, point mutation of this residue abrogates the phosphorylation of these kinases. The Janus kinase Jak1 is absolutely essential for the activation of p38 in response to OSM, while Src kinase family members appear to be generally dispensable. Finally, we demonstrate that mutation of tyrosine 861 abrogates OSMR-mediated cell proliferation and identify Erk1/2 as mainly responsible for the proliferative effect. Erk1/2 activation is negatively influenced by p38 activation and inhibition of p38 significantly prolongs the half-life of OSM-induced Egr-1.

Cooperation and selectivity of the two Grb2 binding sites of p52Shc in T-cell antigen receptor signaling to Ras family GTPases and Myc-dependent survival

Shc proteins participate in a variety of processes regulating cell proliferation, survival and apoptosis. The two ubiquitously expressed isoforms, p52Shc/p46Shc, couple tyrosine kinase receptors to Ras by recruiting Grb2/Sos complexes to a membrane-proximal localization. Tyrosine residues 239/240 and 317 become phosphorylated following receptor engagement and, as such, form two Grb2 binding sites, which have been proposed to be differentially coupled to Myc-dependent survival and to fos-dependent proliferation, respectively. Here, we have addressed the individual function of YY239/240 and Y317 in T-cell antigen receptor (TCR) signaling. We show that p52Shc is phosphorylated on both YY239/240 and Y317 following TCR engagement. Mutation of either YY239/240 or Y317 results in impaired interaction with Grb2 and inhibition of Ras/MAP kinase activation and CD69 induction, supporting a role for both Grb2 binding sites in this function. Substitution of either YY239/240 or Y317 also results in a defective activation of Rac and the coupled stress kinases JNK and p38. Furthermore, mutation of Y317 or, to a larger extent, of YY239/240, results in increased activation-induced cell death, which in cells expressing the FF239/240 mutant is accompanied by impaired TCR-dependent c-myc transcription. The data underline a pleiotropic and nonredundant role of Shc, mediated by both YY239/240 and Y317, in T-cell activation and survival.

Requirement for Ras guanine nucleotide releasing protein 3 in coupling phospholipase C-gamma2 to Ras in B cell receptor signaling

Two important Ras guanine nucleotide exchange factors, Son of sevenless (Sos) and Ras guanine nucleotide releasing protein (RasGRP), have been implicated in controlling Ras activation when cell surface receptors are stimulated. To address the specificity or redundancy of these exchange factors, we have generated Sos1/Sos2 double- or RasGRP3-deficient B cell lines and determined their ability to mediate Ras activation upon B cell receptor (BCR) stimulation. The BCR requires RasGRP3; in contrast, epidermal growth factor receptor is dependent on Sos1 and Sos2. Furthermore, we show that BCR-induced recruitment of RasGRP3 to the membrane and the subsequent Ras activation are significantly attenuated in phospholipase C-gamma2-deficient B cells. This defective Ras activation is suppressed by the expression of RasGRP3 as a membrane-attached form, suggesting that phospholipase C-gamma2 regulates RasGRP3 localization and thereby Ras activation.

Contribution of the Membrane-distal Tyrosine in Intracellular Signaling by the Granulocyte Colony-stimulating Factor Receptor

We have evaluated the contribution of intracellular tyrosine residues of the granulocyte colony-stimulating factor receptor (GCSF-R) to its signaling and cellular outcomes. We began with stable BaF3 cell lines overexpressing wild-type or mutant GCSF-Rs. When all four intracellular tyrosines of the GCSF-R were replaced with phenylalanine (FFFF GCSF-R), cell proliferation and survival were compromised. Replacement of only the membrane-distal tyrosine (YYYF GCSF-R) also showed reduced survival following a GCSF withdrawal/replacement protocol, suggesting a role for this tyrosine. Proliferation by FFFY GCSF-R cells was attenuated by approximately 70%. In evaluating the biochemical steps involved in signaling, we then showed that the membrane-distal tyrosine was necessary and sufficient for c-Jun N-terminal kinase (JNK) activation. With the use of a cell-permeable JNK-inhibitory peptide, JNK was implicated in the proliferation of the FFFY GCSF-R mutant. To further define the events linking the membrane-distal tyrosine and JNK activation, the Src homology 2 domains of Shc, Grb2, and 3BP2 were shown to bind the full-length GCSF-R and a phosphopeptide encompassing the membrane-distal tyrosine. When binding to variant phosphopeptides based on this membrane-distal tyrosine was tested, altering the amino acids immediately following the phosphotyrosine could selectively abolish the interaction with Shc or Grb2, or the binding to both Grb2 and 3BP2. When these changes were introduced into the full-length GCSF-R and new cell lines created, only the mutant that did not interact with Grb2 and 3BP2 did not activate JNK. Our results suggest that direct binding of Shc by the GCSF-R is not essential for JNK activation.

Shc-dependent pathway is redundant but dominant in MAPK cascade activation by EGF receptors: a modeling inference

In cell signaling cascades, one stimulus often leads to various physiological functions by multiple pathways. Perturbation of one pathway by blocking or overexpressing one of its components will result in changes in multiple pathways and multiple cell functions. Thus, it is important to reveal the relative contribution of each pathway to each function in order to assess the consequence of perturbations (e.g. drug delivery). By exploring an established mathematical model, the Shc-dependent pathway is found to be both redundant and dominant during activation of the mitogen-activated protein kinase cascade by epidermal growth factor receptor (EGFR). Its dominance results from the majority consumption of the common precursor ((EGF-EGFR*)2-GAP) by this pathway. The key steps for the dominance are the binding and phosphorylation of Shc. In conclusion, cells may prefer the long Shc-dependent pathway to the short Shc-independent pathway.

Role of the different mitogen-activated protein kinase subfamilies in the stimulation of dog and human thyroid epithelial cell proliferation by cyclic adenosine 5'-monophosphate and growth factors

We have investigated the role of the different classes of MAPKs, i.e. ERKs, c-Jun N-terminal kinases (JNKs), and p38 MAPK in the proliferation of dog and human thyroid epithelial cells (thyrocytes) in primary cultures. In these cells, TSH, acting through cAMP, epidermal growth factor, hepatocyte growth factor (HGF), and phorbol 12-myristate 13-acetate induce DNA synthesis. With the exception of HGF, all of these factors require the presence of insulin for mitogenic effects to be expressed. We found that TSH and forskolin are without effect on the phosphorylation and activity of the different classes of MAPKs. In contrast, all the cAMP-independent growth factors, whereas without effect on the phosphorylation and activity of JNKs and p38 MAPK, stimulated the ERKs. This effect was strong and sustained in response to HGF, epidermal growth factor and 12-myristate 13-acetate but weak and transient in response to insulin. Moreover, whereas in stimulated cells DNA synthesis was inhibited by PD 098059, an inhibitor of MAPK kinase 1 and consequently of ERKs, it was not modified by SB 203580, an inhibitor of p38 MAPK. Taken together, these data 1) exclude a role of JNKs and p38 MAPK in the proliferation of dog and human thyrocytes; 2) suggest that the mitogenic action of the cAMP-independent agents requires a strong and sustained activation of both ERKs and phosphatidylinositol 3-kinase/protein kinase B as realized by HGF alone or by the other agents together with insulin; and 3) show that TSH and cAMP do not activate ERKs but that the weak activation of ERKs by insulin is nevertheless necessary for DNA synthesis to occur.

Evidence of functional modulation of the MEKK/JNK/cJun signaling cascade by the low density lipoprotein receptor-related protein (LRP)

Lipoprotein receptors, such as LRP, have been shown to assemble multiprotein complexes containing intracellular signaling molecules; however, in vivo, their signaling function is poorly understood. Using a novel LRP receptor fusion construct, a type I transmembrane protein chimera, termed sIgG-LRP (bearing the intracellular COOH-terminal tail of human LRP as recombinant fusion to a transmembrane region plus the extracellular IgG-F(c) domain), we here investigated LRP signal transduction specificity in intact cells. First and similar to activated alpha2-macroglobulin as agonist of endogenous LRP, expression of sIgG-LRP demonstrated significant apoptosis protection. Second and similar to alpha2-macroglobulin-induced endogenous LRP, sIgG-LRP is sufficient to negatively modulate mitogen-induced Elk-1 and cJun (but not NF-kappaB) transcriptional activity. Third, expression of sIgG-LRP also impaired cJun transactivation mediated by constitutive active mutants of Rac-1 and MEKK-1. Fourth and unexpectedly, sIgG-LRP expression was found to be associated with a marked enhancement of mitogen-induced cJun amino-terminal kinase (JNK) activation. Fifth, confocal microscopic examination and subcellular fractionation demonstrated that sIgG-LRP and JNK co-localize in transfected cells. Therefore, sIgG-LRP expression was found to significantly impair activation-induced translocation of JNK into the nucleus. Taken together, we here demonstrate that sIgG-LRP protein sequesters activated JNK into the plasma membrane compartment in intact cells, inhibiting nuclear activation of the JNK-dependent transcription factors Elk-1 and cJun.

Elevated JNK activation contributes to the pathogenesis of human brain tumors

The ERK pathway is typically associated with activation of the EGF receptor and has been shown to play a major role in promoting several tumor phenotypes. An analogous signaling module, the JNK pathway, has not been shown to be consistently activated by the EGF receptor but is instead more uniformly stimulated by cellular stresses and cytokines. The function of the JNK pathway in primary tumors is unclear as it has been implicated in both promoting apoptosis and cell growth in vitro, which may be a reflection of the cell lines chosen. Primary human brain tumors frequently show overexpression of the EGF receptor. To clarify the role of JNK in tumorigenesis, we have investigated the role of JNK in a large panel of primary human brain tumors and tumor derived cell lines. Here we present evidence that JNK has a major role in promoting tumorigenesis both in vivo and in vitro. Western blot analysis demonstrated that 86% (18 of 21) of primary brain tumors showed evidence of JNK activation but only 38% (8 of 21) showed evidence of ERK activation. Kinase assays revealed that 77% of brain tumor cell lines activated JNK in response to EGF (7 of 13) or had high levels of basal activity (3 of 13), whereas none of six normal cell lines analysed, including astrocytes, had these properties. Of several growth factors examined, EGF produced the highest level of JNK induction in tumor cell lines and the duration of activation was greater than that seen for ERK. Expression of a dominant-negative (dn) form of JNK potently inhibited EGF mediated anchorage independent growth and protection from cell death in two glial tumor cell lines. These findings demonstrate that enhanced JNK activation is frequently found in primary brain tumors and that this activation contributes to phenotypes related to transformation.

Discrimination between phosphotyrosine-mediated signaling properties of conventional and neuronal Shc adapter molecules

The phosphotyrosine (pTyr) adapter Shc/ShcA is a major connector in various tyrosine kinase signalings following a variety of stimulation such as growth factor/neurotrophin, as well as in those following calcium influx and integrin activation. As in other tissues, Shc has been implicated in neuronal signalings; however, recent evidence suggests that N-Shc/ShcC and Sck/ShcB would take over most of the roles of Shc in mature central neurons, and switching phenomena between Shc and N-Shc expression were observed in several neuronal paradigms. Little is, however, known as to the signal-output differences between Shc and N-Shc. Here we determined the efficacy of Shc and N-Shc toward Erk activation in NGF-treated PC12 cells, and found that N-Shc transduced Grb2/Sos/Ras-dependent Erk activation less efficiently than Shc. This was mainly because N-Shc has only one high-affinity Grb2-binding site, whereas Shc has two such sites. Phosphopeptide mapping revealed that N-Shc has novel tyrosine-phosphorylation sites at Y259/Y260 and Y286; in vivo-phosphorylation of these tyrosines was demonstrated by site-specific anti-pTyr antibodies. Phosphorylated Y286 bound to several proteins, of which one was Crk. The pY221/pY222 site, corresponding to one of the Grb2-binding sites of Shc, also preferentially bound to Crk. The phosphorylation-dependent interaction between N-Shc and Crk was demonstrated in vitro and in vivo. These results indicate that N-Shc has specific features of signal-output, and further suggest that the switching between Shc and N-Shc during neural development and regeneration would lead to differentiation of downstream signalings.

Involvement of JNK-mediated pathway in EGF-mediated protection against paclitaxel-induced apoptosis in SiHa human cervical cancer cells

We investigated the signalling pathways by which epidermal growth factor (EGF) modulates paclitaxel-induced apoptosis in SiHa human cervical cancer cells. SiHa cells exposed to paclitaxel underwent apoptosis, which was strongly inhibited by EGF. This inhibition of apoptosis by EGF was not altered by pharmacological blockade of phosphatidylinositol 3'-OH kinase (PI-3K) with the PI-3K specific inhibitor LY294002 or blockade of the mitogen-activated protein kinase (MAPK) kinase (MEK) with the MEK specific inhibitor PD98059, or by transfection of the cells with PI-3K or MEK dominant-negative expression vectors. EGF did not stimulate PI-3K/Akt, MEK/MAPK, or p38 MAPK activity in SiHa cells but did transiently activate the c-Jun NH2-terminal kinase (JNK). Co-exposure of SiHa cells to SB202190 at concentrations that inhibit JNK abolished the protective effect of EGF on SiHa cells against paclitaxel-induced apoptosis. Our findings indicate that the JNK signaling pathway plays an important role in EGF-mediated protection from paclitaxel-induced apoptosis in SiHa cells.

Epidermal growth factor receptor transactivation by angiotensin II requires reactive oxygen species in vascular smooth muscle cells

Angiotensin II (Ang II) is a vasoactive hormone with critical roles in vascular smooth muscle cell growth, an important feature of hypertension and atherosclerosis. Many of these effects are dependent on the production of reactive oxygen species (ROS). Ang II induces phosphorylation of the epidermal growth factor (EGF) receptor (EGF-R), which serves as a scaffold for various signaling molecules. Here, we provide novel evidence that ROS are critical mediators of EGF-R transactivation by Ang II. Pretreatment of vascular smooth muscle cells with the antioxidants diphenylene iodonium, Tiron, N-acetylcysteine, and ebselen significantly inhibited ( approximately 80% to 90%) tyrosine phosphorylation of the EGF-R by Ang II but not by EGF. Of the 5 autophosphorylation sites on the EGF-R, Ang II mainly phosphorylated Tyr1068 and Tyr1173 in a redox-sensitive manner. The Src family kinase inhibitor PP1, overexpression of kinase-inactive c-Src, or chelation of intracellular Ca(2+) attenuated EGF-R transactivation. Although antioxidants had no effects on the Ca(2+) mobilization or phosphorylation of Ca(2+)-dependent tyrosine kinase Pyk2, they inhibited c-Src activation by Ang II, suggesting that c-Src is 1 signaling molecule that links ROS and EGF-R phosphorylation. Furthermore, Ang II-induced tyrosine phosphorylation of the autophosphorylation site and the SH2 domain of c-Src was redox sensitive. These findings emphasize the importance of ROS in specific Ang II-stimulated growth-related signaling pathways and suggest that redox-sensitive EGF-R transactivation may be a potential target for antioxidant therapy in vascular disease.

Phosphatidylinositol 3-kinase-dependent translocation of phospholipase Cgamma2 in mouse megakaryocytes is independent of Bruton tyrosine kinase translocation

Activation of the collagen receptor glycoprotein VI (GPVI) by a collagen-related peptide (CRP) induces stimulation of platelets and megakaryocytes through the phosphatidylinositol (PI) 3-kinase-dependent pathway leading to activation of Bruton tyrosine kinase (Btk) and phospholipase Cgamma2 (PLCgamma2). Here, we present evidence that both proteins undergo PI 3-kinase-dependent translocation to the plasma membrane on CRP stimulation that is markedly inhibited by wortmannin and LY294002. Translocation of PLCgamma2 but not Btk is also seen in megakaryocytes from X-linked immunodeficiency mice, which have a mutation that reduces the affinity of the pleckstrin homology (PH) domain of Btk for PI 3,4,5-trisphosphate (PI 3,4,5-P3). Activation of PC12 cells by epidermal growth factor (EGF) results in increased PI 3-kinase activity and high PI 3,4,5-P3 levels that trigger translocation of the green fluorescent protein (GFP)-labeled PH of Btk, but not the GFP-labeled PH and tandem Src homology 2 (SH2) domains of PLCgamma2. In contrast to the results with CRP, the G protein-coupled receptor agonist thrombin stimulates PI 3-kinase-independent translocation of Btk but not PLCgamma2. In conclusion, these results demonstrate that in mouse megakaryocytes, CRP leads to PI 3-kinase-dependent translocation of PLCgamma2 and Btk that are independent of one another, whereas thrombin only induces translocation of Btk through a pathway that is independent of PI 3-kinase activity.

The mammalian ShcB and ShcC phosphotyrosine docking proteins function in the maturation of sensory and sympathetic neurons

Shc proteins possess SH2 and PTB domains and serve a scaffolding function in signaling by a variety of receptor tyrosine kinases. There are three known mammalian Shc genes, of which ShcB and ShcC are primarily expressed in the nervous system. We have generated null mutations in ShcB and ShcC and have obtained mice lacking either ShcB or ShcC or both gene products. ShcB-deficient animals exhibit a loss of peptidergic and nonpeptidergic nociceptive sensory neurons, which is not enhanced by additional loss of ShcC. Mice lacking both ShcB and ShcC exhibit a significant loss of neurons within the superior cervical ganglia, which is not observed in either mutant alone. The results indicate that these Shc family members possess both unique and overlapping functions in regulating neural development and suggest physiological roles for ShcB/ShcC in TrkA signaling.

Prolactin-induced cell proliferation in PC12 cells depends on JNK but not ERK activation

The effects of pituitary and extrapituitary prolactin include cellular proliferation and differentiation. PC12 cells was used as a model to delineate respective signaling of prolactin. Prolactin acted as a mitogen for undifferentiated PC12 cells, as measured by significant increases in bromodeoxyuridine incorporation and in cell numbers, with an efficacy equal to epidermal growth factor. Both the long and short form of the prolactin receptor was expressed, yet only the long isoform was tyrosine-phosphorylated upon agonist binding. Functional prolactin receptor signaling was further demonstrated in the activation of JAK2 and phosphorylation activation of the transcription factors Stat1, -3, and -5a. Surprisingly, prolactin stimulated a sustained activation of Raf-B, without activation of the MAP kinases ERK1 or -2. Instead, in solid phase kinase assays using a glutathione S-transferase-c-Jun fusion protein (amino acids 1-79) as the substrate, a significant activation of the mitogen-activated protein Janus kinase (c-Jun N-terminal kinase; JNK) was observed. The prolactin-induced activation of JNK was prolonged and accompanied by a significant increase in c-Jun mRNA abundance and c-Jun protein synthesis. Moreover, analysis of bromodeoxyuridine incorporation at the single cell level revealed that epidermal growth factor-dependent incorporation was inhibited by PD98059 and independent of SB203580, whereas prolactin-induced incorporation was ERK and mitogen-activated protein kinase p38 independent but was abolished with JNK inhibition by 30 microm SB203580. Our studies suggest that prolactin may have a role in the growth of PC12 cells, where it stimulates concurrent mitogenic and differentiation-promoting signaling pathways.

Role of the cyclic AMP response element binding complex and activation of mitogen-activated protein kinases in synergistic activation of the glycoprotein hormone alpha subunit gene by epidermal growth factor and forskolin

The aim of these studies was to elucidate a role for epidermal growth factor (EGF) signaling in the transcriptional regulation of the glycoprotein hormone alpha subunit gene, a subunit of chorionic gonadotropin. Studies examined the effects of EGF and the adenylate cyclase activator forskolin on the expression of a transfected alpha subunit reporter gene in a human choriocarcinoma cell line (JEG3). At maximal doses, administration of EGF resulted in a 50% increase in a subunit reporter activity; forskolin administration induced a fivefold activation; the combined actions of EGF and forskolin resulted in synergistic activation (greater than eightfold) of the alpha subunit reporter. Mutagenesis studies revealed that the cyclic AMP response elements (CRE) were required and sufficient to mediate EGF-forskolin-induced synergistic activation. The combined actions of EGF and forskolin resulted in potentiated activation of extracellular signal-regulated kinase (ERK) enzyme activity compared with EGF alone. Specific blockade of ERK activation was sufficient to block EGF-forskolin-induced synergistic activation of the alpha subunit reporter. Pretreatment of JEG3 cells with a p38 mitogen-activated protein kinase inhibitor did not influence activation of the alpha reporter. However, overexpression of c-Jun N-terminal kinase (JNK)-interacting protein 1 as a dominant interfering molecule abolished the synergistic effects of EGF and forskolin on the alpha subunit reporter. CRE binding studies suggested that the CRE complex consisted of CRE binding protein and EGF-ERK-dependent recruitment of c-Jun-c-Fos (AP-1) to the CRE. A dominant negative form of c-Fos (A-Fos) that specifically disrupts c-Jun-c-Fos DNA binding inhibited synergistic activation of the alpha subunit. Thus, synergistic activation of the alpha subunit gene induced by EGF-forskolin requires the ERK and JNK cascades and the recruitment of AP-1 to the CRE binding complex.

The ShcA phosphotyrosine docking protein sensitizes cardiovascular signaling in the mouse embryo

The ShcA gene products have served as a model for the analysis of phosphotyrosine-recognition domains, and for the functions of docking proteins during tyrosine kinase signaling. Here we show that ShcA is primarily expressed in the cardiovascular system during early mouse embryogenesis and regulates both heart development and establishment of mature blood vessels. Targeted mutation suggests that the ShcA adaptor is a pivotal target of tyrosine kinases that selectively potentiates activation of the MAP kinase pathway in the remodeling vasculature. Biochemical analysis of mutant cells shows that ShcA sensitizes cells to growth factor-induced MAP kinase activation, and also organizes cytoskeletal rearrangement in response to the extracellular matrix. ShcA may therefore orchestrate complex interactions within the vascular compartment by rendering cells permissive to respond to soluble and adhesive external cues.

Involvement of Shc and Cbl-PI 3-kinase in Lyn-dependent proliferative signaling pathways for G-CSF

Granulocyte colony-stimulating factor (G-CSF) is the major hematopoietic factor which controls the production and differentiation of granulocytes. The G-CSF receptor (G-CSFR) belongs to the superfamily of the cytokine receptors, which transduce signals via the activation of cytosolic protein tyrosine kinases (PTK). To determine the role of specific PTK in G-CSF signaling we expressed the human G-CSFR in cell lines derived from DT40 B cells, which lack either the Src-related Lyn or Syk. Wild-type (wt) and syk-deficient cells underwent increased DNA synthesis in response to G-CSF; lyn-deficient cells did not. The purpose of these studies is to identify Lyn's downstream effectors in mediating DNA synthesis. While G-CSF stimulated Ras activity in all cell lines, G-CSF failed to induce the tyrosine phosphorylation of Shc in lyn-deficient cells. G-CSF induced a statistically significant activation of Erk1/Erk2 Kinase or p90Rsk only in the wt cells. G-CSF induced the tyrosine phosphorylation of Cbl and increased activity of PI 3-kinase in wild-type and syk-deficient, but non in lyn-deficient, cells. Inhibition of Shc by over-expression of its SH2 or PTB domains or PI 3-kinase by either treatment with wortmannin or expression of the CblY731F mutant decreased G-CSF-induced DNA synthesis. Thus, the Lyn, Cbl-PI 3-kinase, and Shc/non-Ras-dependent pathways correlate with the ability of cells to respond to G-CSF with increased DNA synthesis.

Accelerated mammary tumor development in mutant polyomavirus middle T transgenic mice expressing elevated levels of either the Shc or Grb2 adapter protein

The Grb2 and Shc adapter proteins play critical roles in coupling activated growth factor receptors to several cellular signaling pathways. To assess the role of these molecules in mammary epithelial development and tumorigenesis, we have generated transgenic mice which individually express the Grb2 and Shc proteins in the mammary epithelium. Although mammary epithelial cell-specific expression of Grb2 or Shc accelerated ductal morphogenesis, mammary tumors were rarely observed in these strains. To explore the potential role of these adapter proteins in mammary tumorigenesis, mice coexpressing either Shc or Grb2 and a mutant form of polyomavirus middle T (PyV mT) antigen in the mammary epithelium were generated. Coexpression of either Shc or Grb2 with the mutant PyV mT antigen resulted in a dramatic acceleration of mammary tumorigenesis compared to parental mutant PyV mT strain. The increased rate of tumor formation observed in these mice was correlated with activation of the epidermal growth factor receptor family and mitogen-activated protein kinase pathway. These observations suggest that elevated levels of the Grb2 or Shc adapter protein can accelerate mammary tumor progression by sensitizing the mammary epithelial cell to growth factor receptor signaling.