The epidermal growth factor receptor associates with and recruits phosphatidylinositol 3-kinase to the platelet-derived growth factor beta receptor

Mu-opioid receptor and receptor tyrosine kinase crosstalk: Implications in mechanisms of opioid tolerance, reduced analgesia to neuropathic pain, dependence, and reward

Despite the prevalence of opioid misuse, opioids remain the frontline treatment regimen for severe pain. However, opioid safety is hampered by side-effects such as analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, or reward. These side effects promote development of opioid use disorders and ultimately cause overdose deaths due to opioid-induced respiratory depression. The intertwined nature of signaling via μ-opioid receptors (MOR), the primary target of prescription opioids, with signaling pathways responsible for opioid side-effects presents important challenges. Therefore, a critical objective is to uncouple cellular and molecular mechanisms that selectively modulate analgesia from those that mediate side-effects. One such mechanism could be the transactivation of receptor tyrosine kinases (RTKs) via MOR. Notably, MOR-mediated side-effects can be uncoupled from analgesia signaling via targeting RTK family receptors, highlighting physiological relevance of MOR-RTKs crosstalk. This review focuses on the current state of knowledge surrounding the basic pharmacology of RTKs and bidirectional regulation of MOR signaling, as well as how MOR-RTK signaling may modulate undesirable effects of chronic opioid use, including opioid analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, and reward. Further research is needed to better understand RTK-MOR transactivation signaling pathways, and to determine if RTKs are a plausible therapeutic target for mitigating opioid side effects.

Comprehensive Biology and Genetics Compendium of Wilms Tumor Cell Lines with Different WT1 Mutations

Simple Summary

Wilms tumor is a childhood kidney tumor arising from embryonal cells. Wilms tumors are heterogeneous with several distinct subgroups that differ in their response to treatment. The genetic basis for these diverse forms of Wilms tumor is not fully understood. One subgroup of Wilms tumors is associated with mutations in the WT1 gene, encoding a transcription factor with a role in early kidney differentiation. Patients with WT1 mutant Wilms tumor may harbor germline mutations in this gene. Cell lines from Wilms tumors are notoriously difficult to establish and only few exist. We developed a method to cultivate cells from the WT1 mutant subtype of Wilms tumors and have established 11 cell lines with different mutations in WT1 to date. These cells will be instrumental to study the biology and genetics ultimately to develop precision treatments

Abstract

Purpose: WT1 mutant Wilms tumors represent a distinct subgroup, frequently associated with CTNNB1 mutations. The genetic basis for the development of this subtype is currently not fully understood. Methods: Live WT1 mutant Wilms tumors were collected during surgery of patients and cell cultures established in mesenchymal stem cell medium. They were studied for mutations in WT1 and CTNNB1, their differentiation capacity and protein activation status. Four cell lines were immortalized with a triple mutant ts SV40 largeT antigen and Telomerase. Results: 11 cell lines were established from Wilms tumors of nine patients, including a left and right tumor from the same patient and a primary and second tumor from another patient. Six patients had germ line and three were tumor specific mutations. All cell lines harbored only mutant or deleted WT1 genes. CTNNB1 was wild type in three, all others carried mutations affecting amino acid S45. They had variable and limited capacities for mesenchymal differentiation, a high migratory capacity and a low invasive potential. All cells showed an activation of multiple receptor tyrosine kinases and downstream signaling pathways. Conclusions: These cell lines represent an important new tool to study WT1 mutant Wilms tumors, potentially leading to new treatment approaches.

EGFR Signaling Causes Morphine Tolerance and Mechanical Sensitization in Rats

The safety and efficacy of opioids are compromised as analgesic tolerance develops. Opioids are also ineffective against neuropathic pain. Recent reports have suggested that inhibitors of the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase (RTK), may have analgesic effects in cancer patients suffering from neuropathic pain. It has been shown that the platelet-derived growth factor receptor-β (PDGFR-β), an RTK that has been shown to interact with the EGFR, mediates opioid tolerance but does not induce analgesia. Therefore, we sought to determine whether EGFR signaling was involved in opioid tolerance and whether EGFR and PDGFR signaling could induce pain in rats. We found that gefitinib, an EGFR antagonist, eliminated morphine tolerance. In addition, repeated EGF administration rendered animals unresponsive to subsequent analgesic doses of morphine, a phenomenon we call "pre-tolerance." Using a nerve injury model, we found that gefitinib alone was not analgesic. Rather, it reversed insensitivity to morphine analgesia (pre-tolerance) caused by the release of EGF by injured nerves. We also showed that repeated, but not acute EGF or PDGF-BB administration induced mechanical hypersensitivity in rats. EGFR and PDGFR-β signaling interacted to produce this sensitization. EGFR was widely expressed in primary sensory afferent cell bodies, demonstrating a neuroanatomical substrate for our findings. Taken together, our results suggest a direct mechanistic link between opioid tolerance and mechanical sensitization. EGFR antagonism could eventually play an important clinical role in the treatment of opioid tolerance and neuropathic pain that is refractory to opioid treatment.

The RTK Interactome: Overview and Perspective on RTK Heterointeractions

Receptor tyrosine kinases (RTKs) play important roles in cell growth, motility, differentiation, and survival. These single-pass membrane proteins are grouped into subfamilies based on the similarity of their extracellular domains. They are generally thought to be activated by ligand binding, which promotes homodimerization and then autophosphorylation in trans. However, RTK interactions are more complicated, as RTKs can interact in the absence of ligand and heterodimerize within and across subfamilies. Here, we review the known cross-subfamily RTK heterointeractions and their possible biological implications, as well as the methodologies which have been used to study them. Moreover, we demonstrate how thermodynamic models can be used to study RTKs and to explain many of the complicated biological effects which have been described in the literature. Finally, we discuss the concept of the RTK interactome: a putative, extensive network of interactions between the RTKs. This RTK interactome can produce unique signaling outputs; can amplify, inhibit, and modify signaling; and can allow for signaling backups. The existence of the RTK interactome could provide an explanation for the irreproducibility of experimental data from different studies and for the failure of some RTK inhibitors to produce the desired therapeutic effects. We argue that a deeper knowledge of RTK interactome thermodynamics can lead to a better understanding of fundamental RTK signaling processes in health and disease. We further argue that there is a need for quantitative, thermodynamic studies that probe the strengths of the interactions between RTKs and their ligands and between different RTKs.

Inhibition of EGFR attenuates fibrosis and stellate cell activation in diet-induced model of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. NAFLD begins with steatosis and advances to nonalcoholic steatohepatitis (NASH) and cirrhosis. The molecular mechanisms involved in NAFLD progression are not understood. Based on recent studies showing dysregulation of epidermal growth factor receptor (EGFR) in animal models of liver injury, we sought to determine if inhibition of EGFR mitigates liver fibrosis and HSC activation in NAFLD. We utilized the high fat diet (HFD)-induced murine model of liver injury to study the role of EGFR in NAFLD. The lipid accumulation, oxidative stress, hepatic stellate cell (HSC) activation and matrix deposition were examined in the liver tissues. We also evaluated the EGFR signaling pathway, ROS activation and pro-fibrogenic phenotype in oxidized low density lipoproteins (ox-LDL) challenged cultured HSCs. We demonstrate that EGFR was phosphorylated in liver tissues of HFD murine model of NAFLD. Inhibition of EGFR prevented diet-induced lipid accumulation, oxidative stress, and HSC activation and matrix deposition. In cultured HSCs, we show that ox-LDL caused rapid activation of the EGFR signaling pathway and induce the production of reactive oxygen species. EGFR also mediated HSC activation and promoted a pro-fibrogenic phenotype. In conclusion, our data demonstrate that EGFR plays an important role in NAFLD and is an attractive target for NAFLD therapy.

The Under-Appreciated Promiscuity of the Epidermal Growth Factor Receptor Family

Each member of the epidermal growth factor receptor (EGFR) family plays a key role in normal development, homeostasis, and a variety of pathophysiological conditions, most notably in cancer. According to the prevailing dogma, these four receptor tyrosine kinases (RTKs; EGFR, ERBB2, ERBB3, and ERBB4) function exclusively through the formation of homodimers and heterodimers within the EGFR family. These combinatorial receptor interactions are known to generate increased interactome diversity and therefore influence signaling output, subcellular localization and function of the heterodimer. This molecular plasticity is also thought to play a role in the development of resistance toward targeted cancer therapies aimed at these known oncogenes. Interestingly, many studies now challenge this dogma and suggest that the potential for EGFR family receptors to interact with more distantly related RTKs is much greater than currently appreciated. Here we discuss how the promiscuity of these oncogenic receptors may lead to the formation of many unexpected receptor pairings and the significant implications for the efficiency of many targeted cancer therapies.

EGFR Signaling in Liver Diseases

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase that is activated by several ligands leading to the activation of diverse signaling pathways controlling mainly proliferation, differentiation, and survival. The EGFR signaling axis has been shown to play a key role during liver regeneration following acute and chronic liver damage, as well as in cirrhosis and hepatocellular carcinoma (HCC) highlighting the importance of the EGFR in the development of liver diseases. Despite the frequent overexpression of EGFR in human HCC, clinical studies with EGFR inhibitors have so far shown only modest results. Interestingly, a recent study has shown that in human HCC and in mouse HCC models the EGFR is upregulated in liver macrophages where it plays a tumor-promoting function. Thus, the role of EGFR in liver diseases appears to be more complex than what anticipated. Further studies are needed to improve the molecular understanding of the cell-specific signaling pathways that control disease development and progression to be able to develop better therapies targeting major components of the EGFR signaling network in selected cell types. In this review, we compiled the current knowledge of EGFR signaling in different models of liver damage and diseases, mainly derived from the analysis of HCC cell lines and genetically engineered mouse models (GEMMs).

Macitentan inhibits the transforming growth factor-β profibrotic action, blocking the signaling mediated by the ETR/TβRI complex in systemic sclerosis dermal fibroblasts

INTRODUCTION

Systemic sclerosis (SSc) is a complex and not fully understood autoimmune disease associated with fibrosis of multiple organs. The main effector cells, the myofibroblasts, are collagen-producing cells derived from the activation of resting fibroblasts. This process is regulated by a complex repertoire of profibrotic cytokines, and among them transforming growth factor beta (TGF-β) and endothelin-1 (ET-1) play a major role. In this paper we show that TGF-β and ET-1 receptors co-operate in myofibroblast activation, and macitentan, an ET-1 receptor antagonist binding ET-1 receptors, might interfere with both TGF-β and ET-1 pathways, preventing myofibroblast differentiation.

METHODS

Fibroblasts isolated from healthy controls and SSc patients were treated with TGF-β and ET-1 and successively analyzed for alpha smooth muscle actin (α-SMA) and collagen (Col1A1) expression and for the Sma and Mad Related (SMAD) phosphorylation. We further tested the ability of macitentan to interfere with these process. Furthermore, we silenced ET-1 and endothelin-1 receptor A expression and evaluated the formation of an ET-1/TGF-β receptor complex by immunoprecitation assay.

RESULTS

We showed myofibroblast activation in SSc fibroblasts assessing the expression of α-SMA and Col1A1, after stimulation with TGF-β and ET-1. Macitentan interfered with both ET-1- and TGF-β-induced fibroblast activation. To explain this unexpected inhibitory effect of macitentan on TGF-β activity, we silenced ET-1 expression on SSc fibroblasts and co-immunoprecipitated these two receptors, showing the formation of an ET-1/TGF-β receptor complex.

CONCLUSIONS

During SSc, ET-1 produced by activated endothelia contributes to myofibroblast activation using TGF-β machinery via an ET-1/TGF-β receptor complex. Macitentan interferes with the profibrotic action of TGF-β, blocking the ET-1 receptor portion of the ET-1/TGF-β receptor complex.

Identification of a NFKBIA polymorphism associated with lower NFKBIA protein levels and poor survival outcomes in patients with glioblastoma multiforme

The aberrant constitutive activation of nuclear factor-κB (NF-κB) has been observed in glioblastomas, while NF-κB inhibitor alpha (NFKBIA) inhibits the NF-κB signaling pathway under several physiological processes. However, the contribution of NFKBIA to glioblastomas is poorly understood. In the present study, using gene sequencing, we identified rs1957106 as a novel single nucleotide polymorphism (SNP) in NFKBIA in glioblastoma and found that it was more frequently present in glioblastoma patients. In addition, we examined the association between different genotypes of the rs1957106 SNP of NFKBIA and the gene copy number, mRNA level and protein expression of NFKBIA. The SNP rs1957106 CT and TT genotypes were found to be associated with lower NFKBIA protein levels and a poor prognosis of pateints with glioblastoma. Hence, by identifying rs1957106 as a novel SNP in NFKBIA in glioblastoma patients, we provide a new platform for further investigating the function of NFKBIA in the pathobiology of glioblastoma.

Expression levels and significance of nuclear factor-κB and epidermal growth factor receptor in hepatolithiasis associated with intrahepatic cholangiocarcinoma

BACKGROUND

An increasing incidence of cholangiocarcinoma (CCA) and CCA mortality rates has been observed around the world. Patients with intrahepatic biliary stones have a 10% risk of developing CCA, and up to 70% of patients with histologically confirmed CCA have hepatolithiasis. Few previous studies have addressed the associations between the expression of nuclear factor (NF)-κB and epidermal growth factor receptor (EGFR) and clinicopathological prognosis in patients with hepatolithiasis-associated intrahepatic CCA.

AIMS

This study was designed to investigate the clinicopathological and prognostic significance of NF-κB and EGFR expression in hepatolithiasis-associated intrahepatic CCA and hepatolithiasis.

METHODS

A total of 90 liver specimens were immunohistochemically stained for NF-κB and EGFR expression, and the characteristics of 90 individual patients were retrospectively reviewed.

RESULTS

Differences in the positive rates of NF-κB and EGFR expression between the hepatolithiasis-associated intrahepatic CCA group, intrahepatic lithiasis group, and control group were found to be statistically significant. EGFR expression was closely associated with the degree of differentiation and depth of invasion (p < 0.05). The 1-, 3-, and 5-year overall survival rates were respectively 42.8, 21.0, and 10.3% in intrahepatic CCA groups. The survival rate of the EGFR-negative group was higher than in the EGFR-positive group (p < 0.01). Lymph node metastasis (HR 1.24, 95% CI 1.02-1.51) and EGFR positivity (HR 1.74, 95% CI 1.30-2.23) were associated with decreases in the survival rate.

CONCLUSION

The expression of NF-κB may be an early step in intrahepatic cholangiocarcinogenesis. Overexpression of EGFR is associated with the degree of malignancy and with poor prognosis. NF-κB and EGFR may cooperate during intrahepatic cholangiocarcinogenesis and progression. Lymph node metastasis and EGFR positivity were associated with decreases in the survival rate.

Role and regulation of PDGFRα signaling in liver development and regeneration

Aberrant platelet-derived growth factor receptor-α (PDGFRα) signaling is evident in a subset of hepatocellular cancers (HCCs). However, its role and regulation in hepatic physiology remains elusive. In the current study, we examined PDGFRα signaling in liver development and regeneration. We identified notable PDGFRα activation in hepatic morphogenesis that, when interrupted by PDGFRα-blocking antibody, led to decreased hepatoblast proliferation and survival in embryonic liver cultures. We also identified temporal PDGFRα overexpression, which is regulated by epidermal growth factor (EGF) and tumor necrosis factor α, and its activation at 3 to 24 hours after partial hepatectomy. Through generation of hepatocyte-specific PDGFRA knockout (KO) mice that lack an overt phenotype, we show that absent PDGFRα compromises extracelluar signal-regulated kinases and AKT activation 3 hours after partial hepatectomy, which, however, is alleviated by temporal compensatory increases in the EGF receptor (EGFR) and the hepatocyte growth factor receptor (Met) expression and activation along with rebound activation of extracellular signal-regulated kinases and AKT at 24 hours. These untimely increases in EGFR and Met allow for normal hepatocyte proliferation at 48 hours in KO, which, however, are aberrantly prolonged up to 72 hours. Intriguingly, such compensation also was visible in primary KO hepatocyte cultures but not in HCC cells after siRNA-mediated PDGFRα knockdown. Thus, temporal activation of PDGFRα in liver development is important in hepatic morphogenesis. In liver regeneration, despite increased signaling, PDGFRα is dispensable owing to EGFR and Met compensation, which is unique to normal hepatocytes but not HCC cells.

EGFR and c-Met Cross Talk in Glioblastoma and Its Regulation by Human Cord Blood Stem Cells

Receptor tyrosine kinases (RTK) and their ligands control critical biologic processes, such as cell proliferation, migration, and differentiation. Aberrant expression of these receptor kinases in tumor cells alters multiple downstream signaling cascades that ultimately drive the malignant phenotype by enhancing tumor cell proliferation, invasion, metastasis, and angiogenesis. As observed in human glioblastoma (hGBM) and other cancers, this dysregulation of RTK networks correlates with poor patient survival. Epidermal growth factor receptor (EGFR) and c-Met, two well-known receptor kinases, are coexpressed in multiple cancers including hGBM, corroborating that their downstream signaling pathways enhance a malignant phenotype. The integration of c-Met and EGFR signaling in cancer cells indicates that treatment regimens designed to target both receptor pathways simultaneously could prove effective, though resistance to tyrosine kinase inhibitors continues to be a substantial obstacle. In the present study, we analyzed the antitumor efficacy of EGFR inhibitors erlotinib and gefitinib and c-Met inhibitor PHA-665752, along with their respective small hairpin RNAs (shRNAs) alone or in combination with human umbilical cord blood stem cells (hUCBSCs), in glioma cell lines and in animal xenograft models. We also measured the effect of dual inhibition of EGFR/c-Met pathways on invasion and wound healing. Combination treatments of hUCBSC with tyrosine kinase inhibitors significantly inhibited invasion and wound healing in U251 and 5310 cell lines, thereby indicating the role of hUCBSC in inhibition of RTK-driven cell behavior. Further, the EGFR and c-Met localization in glioma cells and hGBM clinical specimens indicated that a possible cross talk exists between EGFR and c-Met signaling pathway.

Epidermal Growth Factor Receptor (EGFR) Crosstalks in Liver Cancer

Hepatocarcinogenesis is a complex multistep process in which many different molecular pathways have been implicated. Hepatocellular carcinoma (HCC) is refractory to conventional chemotherapeutic agents, and the new targeted therapies are meeting with limited success. Interreceptor crosstalk and the positive feedback between different signaling systems are emerging as mechanisms of targeted therapy resistance. The identification of such interactions is therefore of particular relevance to improve therapeutic efficacy. Among the different signaling pathways activated in hepatocarcinogenesis the epidermal growth factor receptor (EGFR) system plays a prominent role, being recognized as a “signaling hub” where different extracellular growth and survival signals converge. EGFR can be transactivated in response to multiple heterologous ligands through the physical interaction with multiple receptors, the activity of intracellular kinases or the shedding of EGFR-ligands. In this article we review the crosstalk between the EGFR and other signaling pathways that could be relevant to liver cancer development and treatment.

Functional mapping of receptor tyrosine kinases in myxoid liposarcoma

PURPOSE

The aim of this study was to analyze receptor tyrosine kinases (RTK) and their downstream signaling activation profile in myxoid liposarcomas (MLS) by investigating 14 molecularly profiled tumors: 7 naive and 7 treated with conventional chemotherapy/radiotherapy or the new drug trabectedin.

EXPERIMENTAL DESIGN

Frozen and matched formalin-fixed, paraffin-embedded material from surgical specimens were analyzed using biochemical, molecular, and molecular/cytogenetic approaches, complemented by immunohistochemistry and confocal microscopy.

RESULTS

In the absence of any RTK and downstream effector deregulation, the naive cases revealed epidermal growth factor receptor, platelet-derived growth factor receptor B, RET, and MET activation sustained by autocrine/paracrine loops, and RTK cross-talk as a result of heterodimerization. Interestingly, RET and MET activation seems to play a major role in the pathogenesis of MLS by involving different targets through different mechanisms. RET activation (which may activate MET) involves the tumoral vascular component by means of RET/MET cross-talk and VEGFA (vascular endothelial growth factor A)/GFRalpha3 (glial cell-derived neurotrophic factor family receptor alpha3)/artemin-mediated signaling as revealed by VEGF receptor 2/RET coimmunoprecipitation. MET activation involves the cellular tumor component by means of a direct ligand-dependent loop and indirect GFRalpha3 (RET coreceptor)/artemin-mediated signaling. About downstream signaling, the association of AKT activation with the round cell variant is interesting. No relevant changes in the original RTK activation profiles were observed in the posttreatment cases, a finding that is in keeping with the nontargeted treatments used.

CONCLUSIONS

These findings highlight the particular cell-specific activation profile of RET/GFRalpha3 and MET in MLS, and the close correlation between AKT activation and the round cell variant, thus opening up new therapeutic perspectives for MET/AKT inhibitors and antagonistic small molecules binding GFRalpha3.

The plasticity of oncogene addiction: implications for targeted therapies directed to receptor tyrosine kinases

A common mutation of the epidermal growth factor receptor (EGFR) in glioblastoma multiforme (GBM) is an extracellular truncation known as the de2-7 EGFR (or EGFRvIII). Hepatocyte growth factor (HGF) is the ligand for the receptor tyrosine kinase (RTK) c-Met, and this signaling axis is often active in GBM. The expression of the HGF/c-Met axis or de2-7 EGFR independently enhances GBM growth and invasiveness, particularly through the phosphatidylinositol-3 kinase/pAkt pathway. Using RTK arrays, we show that expression of de2-7 EGFR in U87MG GBM cells leads to the coactivation of several RTKs, including platelet-derived growth factor receptor beta and c-Met. A neutralizing antibody to HGF (AMG102) did not inhibit de2-7 EGFR-mediated activation of c-Met, demonstrating that it is ligand-independent. Therapy for parental U87MG xenografts with AMG 102 resulted in significant inhibition of tumor growth, whereas U87MG.Delta 2-7 xenografts were profoundly resistant. Treatment of U87MG.Delta 2-7 xenografts with panitumumab, an anti-EGFR antibody, only partially inhibited tumor growth as xenografts rapidly reverted to the HGF/c-Met signaling pathway. Cotreatment with panitumumab and AMG 102 prevented this escape leading to significant tumor inhibition through an apoptotic mechanism, consistent with the induction of oncogenic shock. This observation provides a rationale for using panitumumab and AMG 102 in combination for the treatment of GBM patients. These results illustrate that GBM cells can rapidly change the RTK driving their oncogene addiction if the alternate RTK signals through the same downstream pathway. Consequently, inhibition of a dominant oncogene by targeted therapy can alter the hierarchy of RTKs resulting in rapid therapeutic resistance.

Epidermal growth factor-induced proliferation of chicken primordial germ cells: involvement of calcium/protein kinase C and NFKB1

Epidermal growth factor (EGF) has been shown to stimulate survival in diverse cells in vitro. In the present study, the effects of EGF and the EGF-related signaling pathway on proliferation of chicken primordial germ cells (PGCs) were investigated. Results showed that EGF (10-100 ng/ml) increased the number and area of PGC colonies in a time- and dose-dependent manner. EGF also activated PKC, a process that was inhibited by AG1478 (an EGFR tyrosine kinase inhibitor) and ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA; an intracellular Ca(2+) chelator). In addition, the degradation of NFKBIA and NFKB1 (p65) translocation was observed after EGF treatment, which was significantly blocked by pretreatment with AG1478, EGTA, H(7), or SN50 (NFKB1-specific inhibitor). Furthermore, we found that EGF-induced cell proliferation was significantly attenuated by AG1478, EGTA, H(7), and SN50, respectively. On the other hand, inhibition of EGFR, Ca(2+)/PKC, or NFKB1 abolished the EGF-stimulated increase in the expression of cyclins CCND1 and CCNE1, cyclin-dependent kinase 6 (CDK6), CDK2, and BCL2, and restored the EGF-induced inhibition of BAX expression and caspase 3/9 activity, indicating that EGFR, PKC, and NFKB1 signaling cascades were involved in EGF-stimulated DNA synthesis and antiapoptosis action. In conclusion, EGF stimulated proliferation of chicken PGCs via activation of Ca(2+)/PKC involving NFKB1 signaling pathway. These observations suggest that EGF signaling is important in regulating germ cell proliferation in the chicken embryonic gonad.

Epidermal growth factor (EGF) activates nuclear factor-κB through IκBα kinase-independent but EGF receptor-kinase dependent tyrosine 42 phosphorylation of IκBα

Overexpression of epidermal growth factor (EGF) receptor and constitutive activation of nuclear factor-kappaB (NF-kappaB) are frequently encountered in tumor cells. Although EGF has been shown to induce NF-kappaB activation, the mechanism is poorly understood. EGF activated NF-kappaB DNA binding, induced NF-kappaB reporter activity and the expression of antiapoptotic and cell-proliferative gene products. Interestingly, non-small cell lung adenocarcinoma cell lines (HCC827 and H3255), which exhibit EGFR amplification, showed ligand-independent activation of NF-kappaB. Unlike tumor-necrosis factor (TNF), however, EGF failed to induce IkappaBalpha phosphorylation and ubiquitination and the activation of IkappaBalpha kinase (IKK). Although DN-IKKbeta inhibited TNF-induced NF-kappaB activity, DN-IKKbeta had no effect on EGF-induced NF-kappaB activation, suggesting that EGF-induced NF-kappaB activation is IKK independent. Using dominant-negative plasmids, we also demonstrated the role of TRADD, TRAF2, NIK and Ras in EGF-induced NF-kappaB activation. By using specific antibodies and IkappaBalpha plasmid, which is mutated at tyrosine 42 to phenylalanine, we show that EGF induced the tyrosine phosphorylation of IkappaBalpha at residue 42. Furthermore, EGF receptor kinase inhibitor blocked IkappaBalpha phosphorylation and consequent NF-kappaB activation. Overall, our results indicate that tyrosine phosphorylation of IkappaBalpha at residue 42 is critical for EGF-induced NF-kappaB activation pathway.

Uncoupling between epidermal growth factor receptor and downstream signals defines resistance to the antiproliferative effect of Gefitinib in bladder cancer cells

Activation of the epidermal growth factor receptor (EGFR) and downstream signaling pathways, such as phosphatidylinositol-3 kinase/Akt and Ras/mitogen-activated protein kinase (MAPK), have been implicated in causing resistance to EGFR-targeted therapy in solid tumors, including the urogenital tumors. To investigate the mechanism of resistance to EGFR inhibition in bladder cancer, we compared EGFR tyrosine kinase inhibitor (Gefitinib, Iressa, ZD1839) with respect to its inhibitory effects on three kinases situated downstream of EGFR: MAPK, Akt, and glycogen synthase kinase-3beta (GSK-3beta). We found that the resistance to the antiproliferative effects of gefitinib, in vitro as well as in vivo in nude mice models, was associated with uncoupling between EGFR and MAPK inhibition, and that GSK-3beta activation and degradation of its target cyclin D1 were indicators of a high cell sensitivity to gefitinib. Further analysis of one phenotypic sensitive (253J B-V) and resistant (UM-UC13) cell lines revealed that platelet-derived growth factor receptor-beta (PDGFRbeta) activation was responsible for short circuiting the EGFR/MAPK pathway for mitogenic stimuli. However, invasion as well as actin dynamics were efficiently reduced by EGFR inhibition in UM-UC13. Chemical disruption of signaling pathways or of PDGFR kinase activity significantly reduced the inactive pool of cellular GSK-3beta in UM-UC13 cells. In conclusion, our data show that the uncoupling of EGFR with mitogenic pathways can cause resistance to EGFR inhibition in bladder cancer. Although this uncoupling may arise through different mechanisms, we suggest that the resistance of bladder cancer cells to EGFR blockade can be predicted early in the course of treatment by measuring the activation of GSK-3beta and of nuclear cyclin D1.

Fish oil supplementation in the treatment of cachexia in pancreatic cancer patients

Patients with pancreatic cancer often experience a loss of weight and appetite, known as the anorexia-cachexia syndrome, which is associated with decreased quality of life and reduced survival. Research into the biological mechanisms of cachexia has demonstrated that an array of inflammatory mediators and tumor-derived factors cause appetite suppression, skeletal muscle proteolysis, and lipolysis,producing an overall hypercatabolic state that contributes to loss of fat and lean body mass. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been shown to modulate levels of proinflammatory cytokines, hepatic acute phase proteins, eicosanoids, and tumor-derived factors in animal models of cancer and may reverse some aspects of the process of cachexia. Results of clinical trials of n-3 PUFAs in the form of fish oils have been mixed, but should encourage further investigation into dietary fish oil supplementation, including the most effective route of administration and the proper dosage to promote optimal weight maintenance and to limit side effects. Concerns about standardization and quality control should also be considered. With the current available evidence, a recommendation for the use of omega 3 polyunsaturated fatty acids in pancreatic cancer cachexia is premature.

NF-kappaB in pancreatic cancer

Although the genetic profile of pancreatic cancer is emerging as a result of much research, the role of specific genetic alterations that initiate tumorigenesis and produce its cardinal clinical features of locally aggressive growth, metastasis, and chemotherapy resistance remains unresolved. Recently, a number of studies have shown that the inhibition of constitutive NF-kappaB activation, one of the frequent molecular alterations in pancreatic cancer, inhibits tumorigenesis and metastasis. It also sensitizes pancreatic cancer cell lines to anticancer agent-induced apoptosis. Therefore because of the crucial role of NF-kappaB in pancreatic cancer, it is a potential target for developing novel therapeutic strategies for the disease. In vivo and in vitro models that mimic the tumorigenic phenotypes in the appropriate histological and molecular concert would be very useful for confirming the suspected role of the pancreatic cancer signature genetic lesions and better understanding the molecular basis of this disease.

Selective abrogation of the proinvasive activity of the trefoil peptides pS2 and spasmolytic polypeptide by disruption of the EGF receptor signaling pathways in kidney and colonic cancer cells

Trefoil peptides (TFFs) are now considered as scatter factors, proinvasive and angiogenic agents acting through cyclooxygenase-2 (COX-2)- and thromboxane A2 receptor (TXA2-R)-dependent signaling pathways. As expression and activation levels of the epidermal growth factor receptor (EGFR) predict the metastatic potential of human colorectal cancers, the purpose of this study was to establish whether the EGF receptor tyrosine kinase (EGFR-TK) contributes to cellular invasion induced by TFFs in kidney and colonic cancer cells. Both the dominant negative form of the EGFR (HER-CD533) and the EGFR-TK inhibitor ZD1839 (Iressa) abrogated cellular invasion induced by pS2, spasmolytic polypeptide (SP) and the src oncogene, but not by ITF and the TXA2-R. Similarly, EGFR-TK inhibition by ZD1839 reversed the invasive phenotype promoted by the constitutively activated form of the EGFR (EGFRvIII) and the EGFR agonists transforming growth factor alpha (TGFalpha), amphiregulin and EGF. We also provide evidence that TFFs, EGFRvIII, and TGFalpha trigger common proinvasive pathways using the PI3'-kinase and Rho/Rho- kinase cascades. These findings identify the EGFR-TK as a key signaling element for pS2- and SP-mediated cellular invasion. It is concluded that although pS2, SP and ITF belong to the same family of inflammation- and cancer-associated regulatory peptides, they do not control identical signaling networks.

Epidermal growth factor induces c-fos and c-jun mRNA via Raf-1/MEK1/ERK-dependent and -independent pathways in bovine luteal cells

Epidermal growth factor (EGF) modulates the actions of gonadotropins in the corpus luteum. The membrane-associated EGF receptors undergo rapid tyrosine phosphorylation and internalization upon ligand binding in ovarian cells, including luteal cells. However, little is known about the post-receptor signaling events induced by EGF that lead to the transcriptional regulation of EGF-responsive genes in the ovary. The present study was designed to examine in bovine luteal cells (1) activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling cascade (Raf/MEK/ERK) by EGF; (2) mRNA expression of AP-1 transcription factors, i.e. c-fos and c-jun, in response to EGF; and (3) the role of ERK in EGF-induced expression of c-fos and c-jun mRNA. Raf-1 and B-Raf, but not A-Raf, were activated by EGF (10 ng/ml) and the pharmacological protein kinase C (PKC) activator phorbol myristate acetate (PMA, 20 nM). Activation of Raf resulted in the phosphorylation and activation of MAPK kinase (MEK1) which subsequently activated ERKs. Treatment with EGF-induced the phosphorylation of both ERK2 and ERK1 in a time and concentration dependent manner. Additionally, activated ERK was found in the nucleus of the cells following treatment with EGF (10 ng/ml) and PMA (PMA, 20 nM) for 5 min. Depletion of PKC by chronic PMA treatment (2.5 microM, 24 h) only partially inhibited the stimulatory effects of EGF on Raf-1, ERK2 and ERK1. These data demonstrate that PKC-dependent and independent-mechanisms are involved in EGF activation of the Raf/MEK/ERK signaling cascade in bovine luteal cells. EGF rapidly and transiently stimulated the expression of c-fos and c-jun mRNA in bovine luteal cells. Maximal induction of c-fos and c-jun mRNA by EGF occurred within 30 min of treatment with 10 ng/ml EGF. Treatment with the MEK1 inhibitor PD098059 (50 microM) abolished EGF-induced ERK activation. However, blocking EGF-induced ERK activation by pretreatment with PD098059 only partially attenuated EGF-induced c-fos and c-jun mRNA expression. Thus, additional pathways are implicated in the regulation of c-fos and c-jun mRNA expression by EGF in bovine luteal cells.

Restoring apoptosis in pancreatic cancer cells by targeting the nuclear factor-kappaB signaling pathway with the anti-epidermal growth factor antibody IMC-C225

We have previously demonstrated that RelA is constitutively activated in the majority of human pancreatic cancers and plays an important role in tumorigenesis and metastasis. The antiapoptotic gene bcl-xl is a downstream target of RelA, and regulation of bcl-xl transcription is mediated directly by the nuclear factor kappaB (NF-kappaB) binding sites present in the upstream promoter element of the bcl-xl gene. In this study we investigated the effects of inhibition of epidermal growth factor receptor (EGFR) signaling pathway with the anti-EGFR monoclonal antibody IMC-C225 on constitutive NF-kappaB activation and regulation of apoptosis-related genes in human pancreatic cancer cells. We found that activation of EGFR can be blocked with the anti-EGFR antibody IMC-C225 in the human pancreatic cancer cell line MDA Panc-28, leading to a marked decrease in constitutive NF-kappaB DNA binding activity. Our data also suggest that downregulation of NF-kappaB DNA binding activity by IMC-C225 leads to a decrease in bcl-xl and bfl-1 expression. Therefore, targeting the NF-kappaB signaling pathway with an anti-EGFR antibody may be one strategy to restore apoptosis in human pancreatic cancer cells, thereby enhancing the effect of chemotherapy and radiation therapy.

The epidermal growth factor receptor engages receptor interacting protein and nuclear factor-kappa B (NF-kappa B)-inducing kinase to activate NF-kappa B. Identification of a novel receptor-tyrosine kinase signalosome

The transcription factor nuclear factor-kappaB (NF-kappaB) is activated by a diverse number of stimuli including tumor necrosis factor-alpha, interleukin-1, UV irradiation, viruses, as well as receptor tyrosine kinases such as the epidermal growth factor receptor (EGFR). NF-kappaB activation by the tumor necrosis factor receptor (TNFR) involves the formation of a multiprotein complex termed a signalosome. Although previous studies have shown that the activated EGFR can induce NF-kappaB, the mechanism of this activation remains unknown. In this study, we identify components of the signalosome formed by the activated EGFR required to activate NF-kappaB and show that, although the activated EGFR uses mechanisms similar to the TNFR, it recruits a distinct signalosome. We show the EGFR forms a complex with a TNFR-interacting protein (RIP), which plays a key role in TNFR-induced NF-kappaB activation, but not with TRADD, an adaptor protein which serves to recruit RIP to the TNFR. Furthermore, we show that the EGFR associates with NF-kappaB-inducing kinase (NIK) and provide evidence suggesting multiprotein complex formation between the EGFR, RIP, and NIK. Using a dominant negative NIK mutant, we show that NIK activation is required for EGFR-mediated NF-kappaB induction. We also show that a S32/36 IkappaBalpha mutant blocks EGFR-induced NF-kappaB activation. Our studies also suggest that a high level of EGFR expression, a frequent occurrence in human tumors, is optimal for epidermal growth factor-induced NF-kappaB activation. Finally, although protein kinase B/Akt has been implicated in tumor necrosis factor and PDGF-induced NF-kappaB activation, our studies do not support a role for this protein in EGFR-induced NF-kappaB activation.

Epidermal growth factor receptor induced apoptosis: potentiation by inhibition of Ras signaling

Previous studies have shown that certain tumor cell lines which naturally express high levels of the epidermal growth factor receptor (EGFR) undergo apoptosis when exposed to epidermal growth factor. Whether this phenomenon is a direct result of receptor overexpression or some other genetic alteration renders these cells sensitive to apoptosis is yet to be established. We show that experimentally increasing the level of EGFR expression predictably leads to apoptosis in a variety of cell types which requires an active tyrosine kinase but not EGFR autophosphorylation sites. Expression of a dominant negative Ras mutant in EGFR overexpressing cells results in a significant potentiation of EGFR induced apoptosis suggesting that Ras activation is a key survival signal generated by the EGFR. We propose that potentiation of EGFR induced apoptosis by dominant negative Ras results, at least in part, by a block of Akt activation.

Cross-talk between epidermal growth factor receptor and c-Met signal pathways in transformed cells

In rat liver epithelial cells constitutively expressing transforming growth factor alpha (TGFalpha), c-Met is constitutively phosphorylated in the absence of its ligand, hepatocyte growth factor. We proposed that TGFalpha and the autocrine activation of its receptor, epidermal growth factor receptor (EGFR), leads to phosphorylation and activation of c-Met. We found that there is constitutive c-Met phosphorylation in human hepatoma cell lines and the human epidermoid carcinoma cell line, A431 which express TGFalpha, but not in normal human hepatocytes. Constitutive c-Met phosphorylation in A431, HepG2, AKN-1, and HuH6 cells was inhibited by neutralizing antibodies against TGFalpha and/or EGFR. Exposure to exogenous TGFalpha or EGF increased the phosphorylation of c-Met in the human epidermoid carcinoma cell line, A431. The increase of c-Met phosphorylation by TGFalpha in A431 cells was inhibited by neutralizing antibodies against TGFalpha and/or EGFR and by the EGFR-specific inhibitor tyrphostin AG1478. These results indicate that constitutive c-Met phosphorylation, and the increase of c-Met phosphorylation by TGFalpha or EGF, in tumor cell lines is the result of the activation via EGFR. We found that c-Met in tumor cells co-immunoprecipitates with EGFR regardless of the existence of their ligands in tumor cells, but not in normal human hepatocytes. We conclude that c-Met associates with EGFR in tumor cells, and this association facilitates the phosphorylation of c-Met in the absence of hepatocyte growth factor. This cross-talk between c-Met and EGFR may have significant implications for altered growth control in tumorigenesis.

Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor

We have studied whether activation of epidermal growth factor receptor (EGFR) is involved in stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and protein synthesis in cultured rat vascular smooth muscle cells (VSMC). Cyclic stretch (1 Hz) induced a rapid (within 5 min) phosphorylation of ERK1/2, an effect that was time and strength dependent and inhibited by an EGFR kinase inhibitor (AG-1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG-1296). The stretch rapidly (within 2 min) induced tyrosine phosphorylation of several proteins, among which 180-kDa protein was shown to be EGFR as revealed by blockade with AG-1478 as well as immunoprecipitation with anti-EGFR antibody coupled with immunoblotting with anti-phosphotyrosine antibody. The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione-S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies. Transfection of a dominant-negative mutant of H-Ras also inhibited stretch-induced ERK1/2 activation. Treatment with a stretch-activated ion channel blocker (Gd(3+)) and an intracellular Ca(2+) antagonist (TMB-8) inhibited stretch-induced phosphorylation of EGFR and ERK1/2. Treatment with AG-1478 and a mitogen-activated protein kinase kinase inhibitor (PD-98059), but not AG-1296, blocked [(3)H]leucine uptake stimulated by a high level of stretch. These data suggest that ERK1/2 activation by mechanical stretch requires Ca(2+)-sensitive EGFR activation mainly via stretch-activated ion channels, thereby leading to VSMC growth.

Platelet-derived growth factor-stimulated migration of murine fibroblasts is associated with epidermal growth factor receptor expression and tyrosine phosphorylation

Previous studies have shown that epidermal growth factor (EGF) synergizes with various extracellular matrix components in promoting the migration of B82L fibroblasts expressing wild-type EGF receptors and that functional EGF receptors are critical for the conversion of B82L fibroblasts to a migratory cell type (). In the present study, we examined the effects of platelet-derived growth factor (PDGF) on the motility of B82L fibroblasts using a microchemotaxis chamber. We found that PDGF can enhance fibronectin-induced migration of B82L fibroblasts expressing wild-type EGF receptors (B82L-clone B3). However, B82L cells that lack the EGF receptor (B82L-parental) or that express an EGF receptor that is kinase-inactive (B82L-K721M) or C-terminally truncated (B82L-c'973) exhibit little PDGF-stimulated migration. In addition, none of these three cell lines exhibit the capacity to migrate to fibronectin alone. These observations indicate that, similar to cell migration toward fibronectin, PDGF-induced cell migration of B82L fibroblasts is augmented by the expression of an intact EGF receptor kinase. The loss of PDGF-stimulated motility in B82L cells that do not express an intact EGF receptor does not appear to result from a gross dysfunction of PDGF receptors, because ligand-stimulated tyrosine phosphorylation of the PDGF-beta receptor and the activation of mitogen-activated protein kinases are readily detectable in these cells. Moreover, an interaction between EGF and PDGF receptor systems is supported by the observation that the EGF receptor exhibits an increase in phosphotyrosine content in a time-dependent fashion upon the addition of PDGF. Altogether, these studies demonstrate that the expression of EGF receptor is critical for PDGF-stimulated migration of murine B82L fibroblasts and suggest a role for the EGF receptor downstream of PDGF receptor activation in the signaling events that lead to PDGF-stimulated cell motility.

Tyrosine kinase signalling in breast cancer. Epidermal growth factor receptor: convergence point for signal integration and diversification

Cross-communication between different signalling systems is critical for the integration of multiple and changing environmental influences on individual cells. The epidermal growth factor receptor (EGFR) has been identified as a key element in the complex signalling network that is utilized by various classes of cell-surface receptors. This nonclassical mode of signalling system cross-talk, in distinction to receptor activation induced by cognate ligands, has been termed 'signal transactivation'. With the EGFR as the convergence point and distribution focus, this scenario may involve signals emitted by other members of the tyrosine kinase family, cytokine receptors, ion channels, G-protein-coupled receptors and integrins.

An epidermal growth factor receptor/Gab1 signaling pathway is required for activation of phosphoinositide 3-kinase by lysophosphatidic acid

Phosphoinositide 3-kinase (PI3K) has been shown to play an essential role in G protein-induced signaling even in non-myeloid cells where few agonists of G protein-coupled receptors are known to activate PI3K. We have identified adherent cell lines where lysophosphatidic acid (LPA) strongly and rapidly activates the accumulation of PI3K lipid products. The process is not modified by expression of a kinase-dead mutant of the Gbetagamma-responsive PI3K p110gamma. In contrast, it is inhibited by genistein or expression of a dominant negative mutant of p85 and potentiated by overexpressing wild-type p110alpha or -beta but not -gamma. By using a specific chemical inhibitor of the epidermal growth factor receptor (EGFR) and expression of a dominant negative mutant, we have observed that recruitment of p85/p110 PI3Ks occurs through transactivation of the EGFR by LPA and downstream mobilization of the docking protein Gab1 that associates with p85 upon LPA stimulation. Finally, we show that LPA cannot activate PI3K in cell lines lacking the EGFR/Gab1 pathway, including cells that transactivate the PDGF receptor. Altogether, these results demonstrate that activation of PI3K by LPA is conditioned by the ability of LPA to transactivate an EGFR/Gab1 signaling pathway.

[Pathophysiologic significance of growth factors and new therapeutic concepts in cardiovascular disease]

Peptide growth factors such as PDGF, FGF, VEGF, and TGF-beta play a critical role in the pathogenesis of cardiovascular diseases. In addition to their pathophysiological role in atherosclerosis and myocardial remodeling, growth factors also promote beneficial effects such as stimulation of angiogenesis and formation of collateral vessels in ischemic tissue. This review focuses on the mechanisms of action and signal relay cascades of peptide growth factors, and summarizes novel therapeutic approaches in cardiovascular medicine. These approaches include both inhibition of growth factors in order to suppress pathogenic processes, and stimulation of growth factors to promote their beneficial effects.

Spatial organization of EGF receptor transmodulation by PDGF

Even though the modulation of EGF receptors by PDGF is well documented, it is not known where on the cell surface cross-talk between the two receptor systems takes place. The recent finding that both populations of receptors are concentrated in cell surface caveolae suggestes that the confinement of the two receptors to this space might facilitate their interaction. Here we show that stimulation of PDGF receptors in caveolae with PDGF causes a subpopulation of EGF receptors in the same membrane fraction to become phosphorylated on tyrosine. Coincident with tyrosine phosphorylation, the binding of EGF to its receptor markedly declines. Loss of EGF binding is partially blocked by tyrosine kinase inhibitors. Despite the close proximity of the two receptors in caveolae, we saw no evidence that EGF could stimulated PDGFR tyrosine phosphorylation. These results suggest that these two receptor systems are highly organized in caveolae.

Interactions between mitogenic stimuli, or, a thousand and one connections

Signals from G-protein-coupled receptors, tyrosine kinase receptors and integrins cooperate to determine cell growth. Work over the past two years has shown that this cooperation is based on crosstalk involving both receptors and their downstream signaling pathways. These interactions enable cells to integrate information from multiple stimuli that regulate cell cycle progression.

Epidermal growth factor receptors: critical mediators of multiple receptor pathways

Recently, the receptor for epidermal growth factor (EGF) was identified as a downstream element in different signaling pathways. This expanded its classical function as a receptor for EGF-like ligands to a role as mediator of diverse signaling systems and as a switch point of a cellular communication network. In addition, several downstream targets, (e.g. Smad proteins and STATs) into which signals from synergistic and antagonistic signaling pathways converge, were identified.

Multiple positive and negative regulators of signaling by the EGF-receptor

Signaling via the epidermal growth factor (EGF)-receptor family is subject to regulation and modulation by multiple ligands, effectors and negative regulators, as well as regulation by heterodimerization between family members and crosstalk between heterologous signaling pathways. Besides serving as a paradigm for receptor tyrosine kinases in general, this family is crucial for development and is often mutated or amplified in human tumors.

Cripto-1 indirectly stimulates the tyrosine phosphorylation of erb B-4 through a novel receptor

Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that fails to directly bind to any of the four known erb B type 1 receptor tyrosine kinases. The present study demonstrates that CR-1 indirectly induces tyrosine phosphorylation of erb B-4 but not of the epidermal growth factor-related receptors erb B-2 and erb B-3 in different mouse and human mammary epithelial cell lines. In addition, down-regulation of erb B-4 in NMuMG mouse mammary epithelial cells and in T47D human breast cancer cells, using an anti-erb B-4 blocking antibody or a hammerhead ribozyme vector targeted to erb B-4 mRNA, impairs the ability of CR-1 to fully activate mitogen-activated protein kinase. Finally, chemical cross-linking of 125I-CR-1 to mouse and human mammary epithelial cell membranes results in the labeling of two specific bands with a molecular weight of 130 and 60 kDa, suggesting that the CR-1 receptor represents a novel receptor structurally unrelated to any of the known type I receptor tyrosine kinases. In conclusion, these data demonstrate that CR-1, upon binding to an unknown receptor, can enhance the tyrosine kinase activity of erb B-4 and that a functional erb B-4 receptor is required for CR-1-induced MAPK activation.

Related adhesion focal tyrosine kinase and the epidermal growth factor receptor mediate the stimulation of mitogen-activated protein kinase by the G-protein-coupled P2Y2 receptor. Phorbol ester or [Ca2+]i elevation can substitute for receptor activation

The activation of growth factor receptors and receptors coupled to heterotrimeric guanine nucleotide-binding proteins (G-proteins) can increase mitogen-activated protein (MAP) kinase activity in many cells. Previously, we demonstrated that the activation of G-protein-coupled P2Y2 receptors by extracellular ATP and UTP stimulated MAP (p42 ERK2) kinase by a mechanism that was dependent on the elevation of [Ca2+]i and the activation of related adhesion focal tyrosine kinase (RAFTK) (also called PYK2, CAKbeta, and CADTK) and protein kinase C (PKC). Here, we examine further the signaling cascade between the P2Y2 receptor and MAP kinase. MAP kinase was transiently activated by exposure of PC12 cells to UTP. UTP, ionomycin, and phorbol ester (phorbol 12-myristate 13-acetate) increased MAP kinase activity and also promoted the tyrosine phosphorylation of RAFTK, the epidermal growth factor (EGF) receptor, SHC, and p120(cbl). Down-regulation of PKC and inhibition of the elevation of [Ca2+]i, conditions that block the activation of MAP kinase, also blocked the increases in the tyrosine phosphorylation of RAFTK and the EGF receptor. AG1478, a tyrphostin selective for the EGF receptor, reduced the activation of MAP kinase, the tyrosine phosphorylation of SHC, the association of Grb2 with SHC, and the tyrosine phosphorylation of the EGF receptor and p120(cbl) but did not block the tyrosine phosphorylation of RAFTK. The similar effects of UTP, ionomycin, and phorbol 12-myristate 13-acetate (PMA) on these signaling proteins demonstrate that the two signaling molecules from phosphatidylinositol 4,5-bisphosphate hydrolysis ([Ca2+]i, from inositol 1,4,5-trisphosphate production, and diacylglycerol) can individually initiate the activation of MAP kinase in an EGF receptor-dependent manner. These results demonstrate that the P2Y2 receptor-mediated transactivation of the EGF receptor occurs at a point downstream of RAFTK and indicate that the EGF receptor is required for P2Y2 receptor-mediated MAP kinase activation. Although P2Y2 and EGF receptors may both activate a similar multiprotein signaling cascade immediately upstream of MAP kinase, the P2Y2 receptor appears to uniquely utilize [Ca2+]i, PKC, and, subsequently, RAFTK.