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Y Yarden

Publications and source records attributed to Y Yarden.

At least 55 records · Page 3Linked to original sources
PubMed1998

The oncogenic ErbB-2/ErbB-3 heterodimer is a surrogate receptor of the epidermal growth factor and betacellulin.

The ErbB-1 receptor tyrosine kinase binds to six different growth factors, whose prototype is the epidermal growth factor (EGF). Two homologous epithelial receptors, ErbB-3 and ErbB-4, bind all isoforms of another family of growth factors, the Neu differentiation factors (NDFs/neuregulins). The fourth member of the ErbB family, ErbB-2, acts as the preferred heterodimeric partner of ligand-occupied complexes of the three other ErbB proteins. Here we report that at high concentrations, EGF can induce cell growth and differentiation in the absence of ErbB-1. This function is shared by betacellulin, but not by three other ligands, including the transforming growth factor alpha (TGFalpha). The functional receptor was identified as a heterodimer between ErbB-3 and ErbB-2, a previously identified oncogenic complex. When singly expressed, neither ErbB-3 nor ErbB-2 can mediate signaling by EGF. In addition, when co-expressed, blocking either receptor by using site-specific antibodies inhibited EGF and betacellulin activities, indicating strict cooperativity between ErbB-3 and ErbB-2. Through analysis of chimeras between EGF and TGFalpha, we identified the middle portion of EGF (loop B) as the site that enables activation of ErbB-2/ErbB-3. In conclusion, cooperative and promiscuous binding of stroma-derived growth factors by the epithelium-expressed ErbB-2/ErbB-3 heterodimer may be significant to cancer development. The mechanistic implications of our results for a model that attributes receptor dimerization to ligand bivalency, as well as to a recently proposed mechanism of secondary dimerization, are discussed.

Animals↗
PubMed1998

The ErbB-2/HER2 oncogenic receptor of adenocarcinomas: from orphanhood to multiple stromal ligands.

Extensive clinical and biochemical evidence implicates ErbB-2, a transmembrane tyrosine kinase related to growth factor receptors, in the development, metastasis, and resistance to therapy of multiple, common human carcinomas. Previous attempts to uncover an ErbB-2-specific ligand led to isolation of the neuregulin (NRG) family, but these ligands, like all other growth factors with an EGF-like motif, only indirectly active ErbB-2. On the other hand, biochemical and genetic evidence suggest a non-autonomous function of ErbB-2 in an interactive ErbB signaling network. Accordingly, the oncoprotein acts as a shared signaling subunit of primary growth factor receptors. By stabilizing heterodimers with other ErbB proteins, ErbB-2 prolongs and enhances signal transduction by a large group of stroma-derived growth factors. Furthermore, we have proposed a model in which all ErbB-2 ligands are bivalent and bind to ErbB-2 with low affinity, following high affinity binding to a primary receptor with which ErbB-2 is heterodimerized. Thus the presence of ErbB-2 in relevant ErbB heterodimeric structures on the surfaces of certain epithelial tumor cells can amplify signals arising from the binding of stromal ErbB ligands. This effect, in turn, may promote the growth of carcinoma cells.

Adenocarcinoma↗
PubMed1998

Activity-dependent regulation of Neu differentiation factor/neuregulin expression in rat brain.

Neu differentiation factor (NDF/neuregulin) is widely expressed in the central and peripheral nervous systems, where it functions as a mediator of the interactions between nerve cells and Schwann, glia, oligodendrocyte, and muscle cells, to control cellular proliferation, differentiation, and migration. NDF binds to two receptor tyrosine kinases, ErbB-3 and ErbB-4. Here we demonstrate that NDF and its ErbB-4 receptor are highly reactive to changes in ambient neuronal activity in the rodent brain in a region-selective manner. Generation of epileptic seizures by using kainic acid, a potent glutamate analog, elevated levels of NDF transcripts in limbic cortical areas, hippocampus, and amygdala. Concomitantly, ErbB-4 mRNA was increased with a similar spatial distribution, but transcription of the other NDF receptor, ErbB-3, did not change. A more moderate stimulation, forced locomotion, was accompanied by an increase in NDF transcripts and protein in the hippocampus and in the motor cortex. Similar changes were found with ErbB-4, but not ErbB-3. Last, a pathway-specific tetanic stimulation of the perforant path, which produced long-term potentiation, was followed by induction of NDF expression in the ipsilateral dentate gyrus and CA3 area of the hippocampus. Taken together, these results indicate that NDF is regulated by physiological activity and may play a role in neural plasticity.

Animals↗
PubMed1998

Csk homologous kinase, a novel signaling molecule, directly associates with the activated ErbB-2 receptor in breast cancer cells and inhibits their proliferation.

Substantial evidence exists supporting direct roles for ErbB-2/neu and Src kinase activation in breast cancer. The Csk homologous kinase (CHK) is a recently identified tyrosine kinase which, like Csk, phosphorylates the C-terminal tyrosine of Src kinases, resulting in inactivation of these enzymes. Recently, we observed that CHK is associated with the ErbB-2/neu receptor upon heregulin stimulation of breast cancer cells. Here, we report that CHK expression was observed in 70 out of 80 primary breast cancer specimens but not in normal breast tissues (0/19). Confocal microscopy analysis revealed co-localization of CHK with ErbB-2 in these primary specimens (6/6). In addition, we observed that the cytoplasmic domain of the ErbB-2/neu receptor is sufficient for its interaction with the CHKSH2 domain. Phosphopeptide inhibition of the in vitro interaction of CHKSH2 or native CHK with ErbB-2/neu, as well as site-directed mutagenesis of ErbB-2/neu, indicated that CHKSH2 binds to Tyr1253 of ErbB-2/neu. Interestingly, autophosphorylation at this site confers oncogenicity to this receptor. Moreover, CHK was able to down-regulate ErbB-2/neu-activated Src kinases. Overexpression of CHK in MCF-7 breast cancer cells markedly inhibited cell growth and proliferative response to heregulin as well as decreased colony formation in soft agar. These studies indicate that CHK binds, via its SH2 domain, to Tyr1253 of the activated ErbB-2/neu and down-regulates the ErbB-2/neu-mediated activation of Src kinases, thereby inhibiting breast cancer cell growth. These data strongly suggest that CHK is a novel negative growth regulator in human breast cancer.

Breast Neoplasms↗
PubMed1998

Morphogenetic effects of neuregulin (neu differentiation factor) in cultured epithelial cells.

Neuregulin, or neu differentiation factor, induces cell proliferation or differentiation through interaction with members of the ErbB family of receptor tyrosine kinases. We report that neuregulin can also induce profound morphogenic responses in cultured epithelial cells of different origins. These effects include scattering of small epithelial islands and rearrangement of larger cell islands into ordered ring-shaped arrays with internal lumens. The ring-forming cells are interconnected by cadherin- and beta-catenin-containing adherens junctions. In confluent cultures, neuregulin treatment induces formation of circular lumenlike gaps in the monolayer. Both cell scattering and ring formation are accompanied by a marked increase in cell motility that is independent of hepatocyte growth factor/scatter factor and its receptor (c-Met). Affinity-labeling experiments implied that a combination of ErbB-2 with ErbB-3 mediates the morphogenic signal of neuregulin in gastric cells. Indeed, a similar morphogenic effect could be reconstituted in nonresponsive cells by coexpression of ErbB-2 and -3. We conclude that a heterodimer between the kinase-defective neuregulin receptor, ErbB-3, and the coreceptor, ErbB-2, mediates the morphogenetic action of neuregulin.

Cell Movement↗
PubMed1998

ErbB tyrosine kinases and the two neuregulin families constitute a ligand-receptor network.

The recently isolated second family of neuregulins, NRG2, shares its primary receptors, ErbB-3 and ErbB-4, and induction of mammary cell differentiation with NRG1 isoforms, suggesting functional redundancy of the two growth factor families. To address this possibility, we analyzed receptor specificity of NRGs by using an engineered cellular system. The activity of isoform-specific but partly overlapping patterns of specificities that collectively activate all eight ligand-stimulatable ErbB dimers was revealed. Specifically, NRG2-alpha [corrected], like NRG1-beta [corrected], emerges as a narrow-specificity ligand, whereas NRG2-beta [corrected] is a pan-ErbB ligand that binds with different affinities to all receptor combinations, including those containing ErbB-1, but excluding homodimers of ErbB-2. The latter protein, however, displayed cooperativity with the direct NRG receptors. Apparently, signaling by all NRGs is funneled through the mitogen-activated protein kinase (MAPK). However, the duration and potency of MAPK activation depend on the identity of the stimulatory ligand-receptor ternary complex. We conclude that the NRG-ErbB network represents a complex and nonredundant machinery developed for fine-tuning of signal transduction.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1997

Differential expression of NDF/neuregulin receptors ErbB-3 and ErbB-4 and involvement in inhibition of neuronal differentiation.

Two receptor tyrosine kinases, ErB-3 and ErbB-4, mediate signaling by Neu differentiation factors (NDFs, also called neuregulins), while ErbB-1 and ErbB-2 serve as co-receptors. We show that the two NDF/neuregulin receptors differ in spatial and temporal expression patterns: The kinase-defective receptor, ErbB-3, is expressed primarily in epithelial layers of various organs, in the peripheral nervous system, and in adult brain, whereas ErbB-4 is restricted to the developing central nervous system and to the embryonic heart. An example of alternating expression of the two receptors is provided by the developing cerebellum: During postnatal cerebellar development, ErbB-4 expression slightly decreases along with a decline in NDF transcription, whereas ErbB-3 expression commences after the peak of neurogenesis. To study functional differences, we established primary brain cultures and found that ErbB-3 was expressed only in oligodendrocytes, whereas ErbB-4 expression was shared by oligodendrocytes, astrocytes and neurons. Blocking the action of endogenous NDF in vitro, by using a soluble form of ErbB-4, accelerated neurite outgrowth in both primary cultures and in neuronal-type cultures of the P19 teratocarcinoma, suggesting an inhibitory effect of NDF on neural differentiation. Apparently, ErbB-3 is associated with proliferation of P19 cells, whereas ErbB-4 correlates with a differentiated phenotype. We conclude that the two NDF receptors play distinct, rather than redundant, developmental and physiological roles.

Animals↗
PubMed1997

Bivalence of EGF-like ligands drives the ErbB signaling network.

Signaling by epidermal growth factor (EGF)-like ligands is mediated by an interactive network of four ErbB receptor tyrosine kinases, whose mechanism of ligand-induced dimerization is unknown. We contrasted two existing models: a conformation-driven activation of a receptor-intrinsic dimerization site and a ligand bivalence model. Analysis of a Neu differentiation factor (NDF)-induced heterodimer between ErbB-3 and ErbB-2 favors a bivalence model; the ligand simultaneously binds both ErbB-3 and ErbB-2, but, due to low-affinity of the second binding event, ligand bivalence drives dimerization only when the receptors are membrane anchored. Results obtained with a chimera and isoforms of NDF/neuregulin predict that each terminus of the ligand molecule contains a distinct binding site. The C-terminal low-affinity site has broad specificity, but it prefers interaction with ErbB-2, an oncogenic protein acting as a promiscuous low-affinity subunit of the three primary receptors. Thus, ligand bivalence enables signal diversification through selective recruitment of homo- and heterodimers of ErbB receptors, and it may explain oncogenicity of erbB-2/HER2.

Animals↗
PubMed1997

The ErbB signaling network in embryogenesis and oncogenesis: signal diversification through combinatorial ligand-receptor interactions.

Ligand-induced activation of receptor tyrosine kinases (RTK) results in the initiation of diverse cellular pathways, including proliferation, differentiation and cell migration. The ErbB family of RTKs represents a model for signal diversification through the formation of homo- and heterodimeric receptor complexes. Each dimeric receptor complex will initiate a distinct signaling pathway by recruiting a different set of Src homology 2- (SH2-) containing effector proteins. Further complexity is added due to the existence of an oncogenic receptor that enhances and stabilizes dimerization but has no ligand (ErbB-2), and a receptor that can recruit novel SH-2-containing proteins, but is itself devoid of kinase activity (ErbB-3). The resulting signaling network has important implications for embryonic development and malignant transformation.

Animals↗
PubMed1997

A subclass of tumor-inhibitory monoclonal antibodies to ErbB-2/HER2 blocks crosstalk with growth factor receptors.

ErbB-2 is an orphan receptor that belongs to a family of tyrosine kinase receptors for either epidermal growth factor (EGF) or Neu differentiation factor (NDF/neuregulin). Because overexpression of the erbB-2 proto-oncogene is frequently associated with an aggressive clinical course of certain human adenocarcinomas, the encoded protein is an attractive target for immunotherapy. Indeed, certain monoclonal antibodies (mAbs) to ErbB-2 effectively inhibit tumor growth in animal models and in clinical trials, but the underlying mechanism is incompletely understood. To study this question, we generated a large battery of mAbs to ErbB-2, that were classified epitopically. Whereas most antibodies stimulated tyrosine phosphorylation of ErbB-2, their anti-tumor effect correlated with its accelerated endocytic degradation. One group of tumor-inhibitory mAbs (Class II mAbs) was elicited by the most antigenic site of ErbB-2, and inhibited in trans binding of NDF and EGF to their direct receptors. The inhibitory effect was due to acceleration of ligand dissociation, and it resulted in the reduction of the ability of ErbB-2 to transactivate the mitogenic signals of NDF and EGF. These results identify two potential mechanisms of antibody-induced therapy: acceleration of ErbB-2 endocytosis by homodimerization and blocking of heterodimerization between ErbB-2 and growth factor receptors.

Animals↗
PubMed1997

ErbB receptors and EGF-like ligands: cell lineage determination and oncogenesis through combinatorial signaling.

The ErbB/HER family of transmembrane receptor tyrosine kinases includes four members that bind more than two dozens ligands sharing an epidermal growth factor- (EGF)3 like motif. This family plays a pivotal role in cell lineage determination in a variety of tissues, including mesenchyme-epithelial inductive processes and the interactions between neurons and muscle, glia and Schwann cells. Certain ligands and receptors of the family, especially the ErbB-2 receptor tyrosine kinase, contribute to a relatively virulent phenotype of some human tumors; most notable are carcinomas of secretory epithelia. This large variety of biological signals is generated through a combinatorial network of signal transduction in which different ErbB ligands are apparently capable of stabilizing discrete homo- and heterodimeric receptor complexes, each coupled to a specific set of cytoplasmic signaling proteins. Because each receptor is unique in terms of catalytic activity, cellular routing and transmodulation, the resulting network allows not only an enormous potential for signal diversification but also fine tuning and stringent control of cellular functions. ErbB-2 emerges as a master coordinator of the network, prolonging and amplifying signaling by decelerating the dissociation rates of its heterologous ligands. Thus, the tumorigenic action of ErbB-2 may be attributed to its ability to act as a shared signaling subunit, rather than by functioning as a bone fide receptor.

Animals↗
PubMed1996

Differences between phosphotyrosine accumulation and Neu/ErbB-2 receptor expression in astrocytic proliferative processes. Implications for glial oncogenesis.

BACKGROUND: Previous work has shown that enhanced growth potential of malignant astrocytomas correlates with increased expression of growth factor receptor tyrosine kinases. The functional implications of increased receptor expression were addressed by analyzing possible accumulation of phosphotyrosyl proteins in neoplastic and nonneoplastic astrocytic proliferative processes. The results were compared with the expression of Neu receptor protein (also called ErbB-2 or HER-2). METHODS: Western immunoblots and immunocytochemistry were utilized to evaluate glioma and carcinoma cell lines, neonatal astrocytic cultures, and human brain biopsies of graded gliosis and astrocytomas. The effects of three tyrosine kinase inhibitors on 3H-thymidine uptake and cell proliferation and viability were examined in cultured glioma cells. RESULTS: Phosphotyrosine was conspicuously elevated in all three grades of astrocytoma, but remained at low levels in nonneoplastic astrocytic proliferations. Dose-dependent decreases in DNA synthesis and proliferation of cultured glioma cells occurred after inhibition of tyrosine kinase. Neu receptor protein showed increased expression in malignant astrocytomas (including glioblastomas) and severe reactive gliosis. CONCLUSIONS: Upregulation of tyrosyl protein phosphorylation enables differentiation of neoplastic from nonneoplastic astrocytic proliferative states. Inhibition of this phosphorylation impairs growth of cells. Increased Neu receptor protein expression can distinguish malignant from low grade astrocytomas. We speculate that genetic events leading to stably increased phosphotyrosine may be critical for neoplastic transformation of astrocytes, whereas increased receptor tyrosine kinase expression could be a factor in the aggressive growth associated with malignancy.

Adolescent↗
PubMed1996

p91 STAT1 activation in interleukin-3-stimulated primary acute myeloid leukemia cells.

Interleukin-3 (IL-3) stimulates in vitro blast cell proliferation in a consistent proportion of acute myeloid leukemia (AML) cases, however the degree of response varies from case to case and it is not related to the FAB subtype or to other clinical parameters. IL-3-induced proliferation of myeloid cells is mediated by the interaction with an heterodimeric receptor (IL-3R) comprised of a ligand binding subunit denoted alpha and a common transducing subunit designated as beta (beta). Ligand binding to the receptor activates a number of signaling molecules including proteins of the STATs (signal transducing and activators of transcription) family. To elucidate the mechanisms responsible for the abnormal proliferative response of AML cells to IL-3, we evaluated, both in the IL-3-dependent M-07e cell line and in 20 AML cases, the activation of STAT1 p91 and its association with the beta c subunit. On the basis of the in vitro proliferation assay, 11 out of 20 cases were found to be responsive to IL-3 and eight out of 16 to GM-CSF. Our results demonstrated that in M-07e cells and in six AML cases (five IL-3 responsive and one unresponsive) p91 tyrosine phosphorylation was ligand dependent. Ligand independent p91 tyrosine phosphorylation was detected in 10 AML cases (five responsive and five unresponsive). p91 association with the beta c subunit was consistent with its ligand dependent activation and with the ability to form a DNA-binding complex containing p91. In the remaining four cases (three unresponsive and one responsive) no p91 tyrosine phosphorylation and/or association were detected. These findings, together with the observation that in five IL-3 responsive cases p91 was constitutively phosphorylated, suggest that IL-3-mediated AML proliferation is only partially sustained by p91 activation and that other post-receptor molecules are required to achieve maximal proliferative response. Moreover structural abnormalities of the receptor or of post-receptor signaling proteins may account for the constitutive p91 phosphorylation and growth factor independent proliferation observed in the unresponsive AML cases.

Cell Division↗
PubMed1996

Neu differentiation factor/neuregulin isoforms activate distinct receptor combinations.

The multiple isoforms of Neu differentiation factor (NDF/neuregulin) induce a pleiotropic cellular response that is isoform-specific and cell type-dependent. The molecular basis of this heterogeneity was addressed by comparing the two major groups of isoforms, alpha and beta. Both groups bind to the catalytically impaired receptor tyrosine kinase ErbB-3, whose mitogenic stimulation by NDF requires transactivation by other ErbB proteins, either ErbB-1 or ErbB-2. By expressing each pair of receptors in interleukin 3-dependent myeloid cells, we found that both isoforms induced mitogenic signals in cells co-expressing the combination of ErbB-3 with ErbB-2. However, only the beta isoform stimulated cells that expressed both ErbB-3 and ErbB-1, and neither isoform was active on cells expressing ErbB-3 alone. Both isoforms bind to all ErbB-3-expressing cells, albeit with different affinities, but the co-stimulatory mitogenic effect is correlated with the ability of each auxiliary receptor to transphosphorylate ErbB-3. These results imply that NDF isoforms differ in their ability to induce receptor heterodimers; whereas both types of isoforms signal through ErbB-3/ErbB-2 heterodimers, only beta isoforms are able to stabilize ErbB-3/ErbB-1 heterodimers.

Animals↗
PubMed1996

Neu differentiation factor (Heregulin) activates a p53-dependent pathway in cancer cells.

Previously we reported that neu differentiation factor (NDF)/heregulin (HRG) elevates tyrosine phosphorylation of its receptors erbB-3, erbB-4, and erbB-2 (through heterodimer formation). We also showed that both NDF/HRG and antibodies to erbB-2 can arrest growth and induce differentiation in breast cancer cells. In this study, we report on the mechanism of NDF/HRG-induced cellular effects. We show that NDF/HRG and antibodies to erbB-2 receptors up-regulate expression of p53 by stabilizing the protein. This is accompanied by up-regulation of the p53 inducible gene, p21CIP1/WAF1, in a variety of cell lines: MCF7 and their derivatives (MCF7/HER2, MN1 and MCF-7-puro), ZR75T and LnCap cells. The induction of p21 is further enhanced when cells are treated with both NDF/HRG and DNA-damaging chemotherapeutic agents (i.e. doxorubicin). The NDF/HRG mediated induction of p21 is dependent on wildtype p53, as it fails to occur in cells expressing dominant negative p53 (MDD2). Furthermore, p21 induction is capable of inactivating cdk2 complexes as measured by Histone H1 phosphorylation assays. Finally, we show that in primary cultures of breast and other cancers, p21 is significantly induced in response to NDF/HRG treatment. Collectively, these observations suggest that the mechanism of breast cancer cell growth inhibition and differentiation via erbB receptors activation is through a p53-mediated pathway.

Antibodies, Monoclonal↗
PubMed1996

Diversification of Neu differentiation factor and epidermal growth factor signaling by combinatorial receptor interactions.

The ErbB family includes two receptors, ErbB-1 and ErbB-3, that respectively bind to epidermal growth factor and Neu differentiation factor, and an orphan receptor, ErbB-2. Unlike ErbB-1 and ErbB-2, the intrinsic tyrosine kinase of ErbB-3 is catalytically impaired. By using interleukin-3-dependent cells that ectopically express the three ErbB proteins or their combinations, we found that ErbB-3 is devoid of any biological activity but both ErbB-1 and ErbB-2 can reconstitute its extremely potent mitogenic activity. Transactivation of ErbB-3 correlates with heterodimer formation and is reflected in receptor phosphorylation and the transregulation of ligand affinity. Inter-receptor interactions enable graded proliferative and survival signals: heterodimers are more potent than homodimers, and ErbB-3-containing complexes, especially the ErbB-2/ErbB-3 heterodimer, are more active than ErbB-1 complexes. Nevertheless, ErbB-1 signaling displays dominance over ErbB-3 when the two receptors are coexpressed. Although all receptor combinations activate the mitogen-activated protein kinases ERK and c-Jun kinase, they differ in their rate of endocytosis and in coupling to intervening signaling proteins. It is conceivable that combinatorial receptor interactions diversify signal transduction and confer double regulation, in cis and in trans, of the superior mitogenic activity of the kinase-defective ErbB-3.

Animals↗
PubMed1996

An immunological approach reveals biological differences between the two NDF/heregulin receptors, ErbB-3 and ErbB-4.

The group of subtype I transmembrane tyrosine kinases includes the epidermal growth factor (EGF) receptor (ErbB-1), an orphan receptor (ErbB-2), and two receptors for the Neu differentiation factor (NDF/heregulin), namely: ErbB-3 and ErbB-4. Here we addressed the distinct functions of the two NDF receptors by using an immunological approach. Two sets of monoclonal antibodies (mAbs) to ErbB-3 and ErbB-4 were generated through immunization with recombinant ectodomains of the corresponding receptors that were fused to immunoglobulin. We found that the shared ligand binds to highly immunogenic, but immunologically distinct sites of ErbB-3 and ErbB-4. NDF receptors differed also in their kinase activities; whereas the catalytic activity of ErbB-4 was activable by mAbs, ErbB-3 underwent no activation by mAbs in living cells. Likewise, down-regulation of ErbB-4, but not ErbB-3, was induced by certain mAbs. By using the generated mAbs, we found that the major NDF receptor on mammary epithelial cells is a heterodimer of ErbB-3 with ErbB-2, whereas an ErbB-1/ErbB-2 heterodimer, or an ErbB-1 homodimer, is the predominant species that binds EGF. Consistent with ErbB-2 being a shared receptor subunit, its tyrosine phosphorylation was increased by both heterologous ligands and it mediated a trans-inhibitory effect of NDF on EGF binding. Last, we show that the effect of NDF on differentiation of breast tumor cells can be mimicked by anti-ErbB-4 antibodies, but not by mAbs to ErbB-3. Nevertheless, an ErbB-3-specific mAb partially inhibited the effect of NDF on cellular differentiation. These results suggest that homodimers of ErbB-4 are biologically active, but heterodimerization of the kinase-defective ErbB-3, probably with ErbB-2, is essential for transmission of NDF signals through ErbB-3.

Animals↗