Phospholipase C-gamma 1 directly associates with the p70 trk oncogene product through its src homology domains

Human Tumorous Imaginal Disc 1 (TID1) Associates with Trk Receptor Tyrosine Kinases and Regulates Neurite Outgrowth in nnr5-TrkA Cells

The human tumorous imaginal disc 1 (TID1) proteins including TID1(L) and TID1(S), members of the DnaJ domain protein family, are involved in multiple intracellular signaling pathways such as apoptosis induction, cell proliferation, and survival. Here we report that TID1 associates with the Trk receptor tyrosine kinases and regulates nerve growth factor (NGF)-induced neurite outgrowth in PC12-derived nnr5 cells. Binding assays and transfection studies showed that the carboxyl-terminal end of TID1 (residues 224-429) bound to Trk at the activation loop (Tyr(P)(683)-Tyr(684)(P)(684) in rat TrkA) and that TID1 was tyrosine phosphorylated by Trk both in yeast and in transfected cells. Moreover endogenous TID1 was also tyrosine phosphorylated by and co-immunoprecipitated with Trk in neurotrophin-stimulated primary rat hippocampal neurons. Overexpression studies showed that both TID1(L) and TID1(S) significantly facilitated NGF-induced neurite outgrowth in TrkA-expressing nnr5 cells possibly through a mechanism involving increased activation of mitogen-activated protein kinase. Consistently knockdown of endogenous TID1, mediated with specific short hairpin RNA, significantly reduced NGF-induced neurite growth in nnr5-TrkA cells. These data provide the first evidence that TID1 is a novel intracellular adaptor that interacts with the Trk receptor tyrosine kinases in an activity-dependent manner to facilitate Trk-dependent intracellular signaling.

Brain-metastatic melanoma: a neurotrophic perspective

The brain is a unique microenvironment enclosed by the skull and maintaining a highly regulated vascular transport barrier. To metastasize to the brain, malignant tumor cells must attach to microvessel endothelial cells, invade the blood-brain barrier (BBB), and respond to brain survival and growth factors. Neurotrophins (NT) are important in brain invasion because they stimulate this process. In brain-metastatic melanoma cells, NT can promote invasion by enhancing the production of extracellular matrixdegradative enzymes such as heparanase, an enzyme capable of locally destroying both the extracellular matrix and the basement membrane of the BBB. We have examined human and murine melanoma cell lines exhibiting varying abilities to form brain metastases, and have found that they express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials. They do not, however, express trkA, the gene encoding the tyrosine kinase receptor TrkA, the high-affinity receptor for nerve growth factor (NGF), the prototypic NT. Presence of functional TrkC, the putative receptor for the invasion-promoting neurotrophin NT-3, was also expressed in these cells. Brain-metastatic melanoma cells can also produce autocrine factors and inhibitors that influence their growth, invasion, and survival in the brain. Synthesis of these factors may influence NT production by brain cells adjacent to the neoplastic invasion front, such as oligodendrocytes and astrocytes. In brain biopsies, we observed increased amounts of NGF and NT-3 in tumor-adjacent tissues at the invasion front of human melanoma tumors. Additionally, we found that astrocytes contribute to the brain-metastatic specificity of melanoma cells by producing NT-regulated heparanase. Trophic, autocrine, and paracrine growth factors may therefore determine whether metastatic cells can successfully invade, colonize, and grow in the central nervous system (CNS).

Inhibition of PLC-gamma1 activity converts nerve growth factor from an anti-mitogenic to a mitogenic signal in CHO cells

Nerve growth factor (NGF) treatment of Chinese hamster ovary fibroblast (CHO) cells exogenously expressing 2.5x105 TrkA receptors (CHO/TrkA) results in inhibition of serum and insulin-like growth factor-I (IGF-I) stimulated cell proliferation in a dose-dependent manner. Furthermore, NGF does not stimulate [3H]thymidine incorporation and inhibits IGF-I mediated DNA synthesis in CHO/TrkA cells. NGF and IGF-I induce extracellular-signal regulated kinase 1 (ERK1) and ERK2 activation, but NGF is able to stimulate a higher and more sustained activation of these enzymes compared with IGF-I. Cotreatment with NGF and IGF-I yields an ERK1/2 activity profile similar to that of NGF treatment alone. While pretreatment with mitogen activated protein kinase kinase (MKK) inhibitor PD98059 (30 microM) results in 100% inhibition of IGF-I stimulated MAPK phosphorylation (IC50<1 microM), NGF mediated MAPK phosphorylation is only decreased by 50% (IC50=3 microM). NGF, but not IGF-I, stimulates tyrosine phosphorylation and activation of PLC-gamma1 which can be inhibited in a dose-dependent manner by phosphoinositide-specific phospholipase C (PI-PLC) inhibitor U73122 (IC50=4 microM). Pretreatment with U73122 (IC50=7 microM) results in an 87% inhibition of NGF mediated MAPK phosphorylation, while cotreatment with PD98059 and U73122 results in 97% inhibition. U73122 pretreatment has no effect on NGF stimulated Akt activation. NGF, but not IGF-I, stimulates the tyrosine phosphorylation of Suc1-associated neurotrophic factor-induced tyrosine phosphorylation target (SNT-1)/fibroblast growth factor receptor substrate 2 (FRS2) which can be completely prevented by pretreatment with 10 microM U73122. Finally, inhibition of PI-PLC results in NGF's ability to stimulate DNA synthesis in the absence and presence of IGF-I.

Norepinephrine stimulates mitogen-activated protein kinase activity in GT1-1 gonadotropin-releasing hormone neuronal cell lines

The GT1-1 GnRH neuronal cell lines exhibit highly differentiated properties of GnRH neurons. We have used GT1-1 cells to study the roles of norepinephrine (NE), membrane depolarization, calcium influx, and phorbol esters in the regulation of mitogen-activated protein (MAP) kinase. NE, which is known to stimulate the release of GnRH, induced MAP kinase activity, the tyrosine phosphorylation of MAP kinase, and MAP kinase kinase activity. Forskolin led to activation of MAP kinase comparable with that induced by NE, and a selective inhibitor of cAMP-dependent protein kinase, H8, attenuated the NE-induced activation of MAP kinase. On the other hand, elimination of extracellular calcium by EGTA completely blocked NE-induced tyrosine phosphorylation of MAP kinase, and a selective inhibitor of calcium/calmodulin-dependent protein kinase, KN-62, attenuated the NE-induced activation of MAP kinase. Furthermore, depolarization of GT1-1 cells with 75 mM KCl, 10 microM BayK 8644, or 1 microM calcium ionophore (A23187) induced rapid tyrosine phosphorylation of MAP kinase. The omission of calcium from the extracellular medium completely abolished these effects of tyrosine phosphorylation of MAP kinase. Phorbol 12-myristate 13-acetate (PMA) also induced MAP kinase activity, but pretreatment of the cultured cells with PMA to down-regulate protein kinase C did not abolish the activation of MAP kinase by NE. In addition, although phosphorylation of Raf-1 kinase was stimulated by PMA, this phosphorylation was not induced by either NE or A23187. These results demonstrate that NE activates MAP kinase directly in GT1-1 cells, and that the effect of NE is mediated by increase in the cAMP level and by calcium influx, but not by PMA-sensitive protein kinase C or Raf-1 kinase.

Prolactin stimulates mitogen-activated protein kinase in human leiomyoma cells

The effects of prolactin (PRL) on proliferation of cultured human uterine leiomyoma-derived smooth muscle cells (SMC) and its mechanism of action were investigated. PRL stimulated DNA synthesis and the expression of PRL receptor was identified by ribonuclease protection assay. Moreover, the regulation of mitogen-activated protein (MAP) kinase by PRL in leiomyoma-derived SMC was investigated. PRL stimulated MAP kinase activity, as detected by 32P incorporation into MAP-2, in a dose-dependent manner. PRL also rapidly stimulated MAP kinase phosphorylation as detected by in vivo phosphorylation using 32P labeling and phosphotyrosine immunoblotting. These results suggest that PRL stimulates the proliferation of human leiomyoma cells via the MAP kinase cascade.

Neurotrophins and their receptors in nerve injury and repair

Cytokines are a heterogenous group of polypeptide mediators that have been associated with activation of numerous functions, including the immune system and inflammatory responses. The cytokine families include, but are not limited to, interleukins (IL-I alpha, IL-I beta, ILIra and IL-2-IL-15), chemokines (IL-8/ NAP-I, NAP-2, MIP-I alpha and beta, MCAF/MCP-1, MGSA and RANTES), tumor necrosis factors (TNF-alpha and TNF-beta), interferons (INF-alpha, beta and gamma), colony stimulating factors (G-CSF, M-CSF, GM-CSF, IL-3 and some of the other ILs), growth factors (EGF, FGF, PDGF, TGF alpha, TGF beta and ECGF), neuropoietins (LIF, CNTF, OM and IL-6), and neurotrophins (BDNF, NGF, NT-3-NT-6 and GDNF). The neurotrophins represent a family of survival and differentiation factors that exert profound effects in the central and peripheral nervous system (PNS). The neurotrophins are currently under investigation as therapeutic agents for the treatment of neurodegenerative disorders and nerve injury either individually or in combination with other trophic factors such as ciliary neurotrophic factor (CNTF) or fibroblast growth factor (FGF). Responsiveness of neurons to a given neurotrophin is governed by the expression of two classes of cell surface receptor. For nerve growth factor (NGF), these are p75NTR (p75) and p140trk (referred to as trk or trkA), which binds both BDNF and neurotrophin (NT)-4/5, and trkC receptor, which binds only NT-3. After binding ligand, the neurotrophin-receptor complex is internalized and retrogradely transported in the axon to the soma. Both receptors undergo ligand-induced dimerization, which activates multiple signal transduction pathways. These include the ras-dependent pathway utilized by trk to mediate neurotrophin effects such as survival and differentiation. Indeed, cellular diversity in the nervous system evolves from the concerted processes of cell proliferation, differentiation, migration, survival, and synapse formation. Neural adhesion and extracellular matrix molecules have been shown to play crucial roles in axonal migration, guidance, and growth cone targeting. Proinflammatory cytokines, released by activated macrophages and monocytes during infection, can act on neural targets that control thermogenesis, behavior, and mood. In addition to induction of fever, cytokines induce other biological functions associated with the acute phase response, including hypophagia and sleep. Cytokine production has been detected within the central nervous system as a result of brain injury, following stab wound to the brain, during viral and bacterial infections (AIDS and meningitis), and in neurodegenerative processes (multiple sclerosis and Alzheimer's disease). Novel cytokine therapies, such as anticytokine antibodies or specific receptor antagonists acting on the cytokine network may provide an optimistic feature for treatment of multiple sclerosis and other diseases in which cytokines have been implicated.

Nerve growth factor stimulates the tyrosine phosphorylation of endogenous Crk-II and augments its association with p130Cas in PC-12 cells

The cellular homologs of the v-Crk oncogene product consist primarily of Src homology region 2 (SH2) and 3 (SH3) domains. v-Crk overexpression causes cell transformation and elevation of tyrosine phosphorylation in fibroblasts and accelerates differentiation of PC-12 cells in response to nerve growth factor (NGF). To further explore the role of Crk in NGF-induced PC-12 cell differentiation, we found that both NGF and epidermal growth factor stimulate the tyrosine phosphorylation of endogenous Crk II. Moreover, hormone stimulation enhanced the specific association of Crk proteins with the tyrosine-phosphorylated p130Cas, the major phosphotyrosine-containing protein in cells transformed with v-Crk. This interaction is mediated by the SH2 domain of Crk and can be inhibited with a phosphopeptide containing the Crk-SH2 binding motif. Furthermore, the Crk-SH2 domain binds tyrosine-phosphorylated paxillin, a cytoskeletal protein, following treatment of PC-12 cells with NGF or epidermal growth factor. These data suggest that Crk functions in a number of signaling processes in PC-12 cells.

Loss of function effect of RET mutations causing Hirschsprung disease

We have introduced three Hirschsprung (HSCR) mutations localized in the tyrosine kinase domain of RET into the RET/PTC2 chimaeric oncogene which is capable of transforming NIH3T3 mouse fibroblasts and of differentiating pC12 rat pheochromocytoma cells. The three HSCR mutations abolished the biological activity of RET/PTC2 in both cell types and significantly decreased its tyrosine phosphorylation. By contrast, a rare polymorphism in exon 18 does not alter the transforming capability of RET/PTC2 or its tyrosine phosphorylation. These data suggest a loss of function effect of HSCR mutations which might act through a dominant negative mechanism. Our model system is therefore capable of discriminating between causative HSCR mutations and rare polymorphisms in the tyrosine kinase domain of RET.

The role of trophic factors and autocrine/paracrine growth factors in brain metastasis

The brain is a unique microenvironment enclosed by the skull, lacking lymphatic drainage and maintaining a highly regulated vascular transport barrier. To metastasize to the brain malignant tumor cells must attach to microvessel endothelial cells, respond to brain-derived invasion factors, invade the blood-brain barrier and respond to survival and growth factors. Trophic factors are important in brain invasion because they can act to stimulate this process. In responsive malignant cells trophic factors such as neurotrophins can promote invasion by enhancing the production of basement membrane-degradative enzymes (such as type IV collagenase/gelatinase and heparanase) capable of locally destroying the basement membrane and the blood-brain barrier. We examined human melanoma cell lines that exhibit varying abilities to form brain metastases. These melanoma lines express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials but the variants do not express trkA, the gene encoding a high affinity nerve growth factor (NGF) tyrosine kinase receptor p140trkA. Melanoma cells metastatic to brain also respond to paracrine factors made by brain cells. We have found that a paracrine form of transferrin is important in brain metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. Brain-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. We found that brain-metastatic melanoma cells synthesize transcripts for the following autocrine growth factors: TGF beta, bFGF, TGF alpha and IL-1 beta. Synthesis of these factors may influence the production of neurotrophins by adjacent brain cells, such as oligodendrocytes and astrocytes. Increased amounts of NGF were found in tumor-adjacent tissues at the invasion front of human melanoma tumors in brain biopsies. Trophic factors, autocrine growth factors, paracrine growth factors and other factors may determine whether metastatic cells can successfully invade, colonize and grow in the central nervous system.

Differentiation of peptide molecular recognition by phospholipase C gamma-1 Src homology-2 domain and a mutant Tyr phosphatase PTP1bC215S

Activated epidermal growth factor receptor (EGFR) undergoes autophosphorylation on several cytoplasmic tyrosine residues, which may then associate with the src homology-2 (SH2) domains of effector proteins such as phospholipase C gamma-1 (PLC gamma-1). Specific phosphotyrosine (pTyr)-modified EGFR fragment peptides can inhibit this intermolecular binding between activated EGFR and a tandem amino- and carboxy-terminal (N/C) SH2 protein construct derived from PLC gamma-1. In this study, we further explored the molecular recognition of phosphorylated EGFR988-998 (Asp-Ala-Asp-Glu-pTyr-Leu-Ile-Pro-Gln-Gln-Gly, I) by PLC gamma-1 N/C SH2 in terms of singular Ala substitutions for amino acid residues N- and C-terminal to the pTyr (P site) of phosphopeptide I. Comparison of the extent to which these phosphopeptides inhibited binding of PLC gamma-1 N/C SH2 to activated EGFR showed the critical importance of amino acid side chains at positions P+2 (Ile994), P+3 (Pro995), and P+4 (Gln996). Relative to phosphopeptide I, multiple Ala substitution throughout the N-terminal sequence, N-terminal sequence, N-terminal truncation, or dephosphorylation of pTyr each resulted in significantly decreased binding to PLC gamma-1 N/C SH2. These structure-activity results were analyzed by molecular modeling studies of the predicted binding of phosphopeptide I to each the N- and C-terminal SH2 domains of PLC gamma-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The low affinity NGF receptor, p75, can collaborate with each of the Trks to potentiate functional responses to the neurotrophins

NGF and the other neurotrophins all bind to the low affinity NGF receptor (LNGFR). Although early studies suggested that the LNGFR was absolutely required for the formation of a functional neurotrophin receptor, current evidence indicates that the Trk family of receptor tyrosine kinases, in the absence of the LNGFR, can directly bind to and mediate responses to the neurotrophins. Here we describe a functional approach, in fibroblasts, designed to assay for the ability of the LNGFR to potentiate Trk-mediated responses to the neurotrophins. We report that although collaboration between the LNGFR and the Trks could be detected in this system, a truncated form of the LNGFR displayed a much more dramatic ability to interact functionally with each of the Trks, potentiating masked autocrine loops as well as responses to limiting amounts of exogenously provided neurotrophins.

The tyrosine kinase inhibitor tyrphostin blocks the cellular actions of nerve growth factor

A series of the synthetic protein kinase inhibitors known as tyrphostins were examined for their effects on the tyrosine autophosphorylation of the pp140c-trk, nerve growth factor (NGF) receptor. One of the tyrphostins, AG879, inhibited NGF-dependent pp140c-trk tyrosine phosphorylation, but did not affect tyrosine phosphorylation of epidermal growth factor or platelet-derived growth factor receptors. In addition, the tyrosine phosphorylation of the receptor-associated protein pp38 was also attenuated by the tyrphostin. This effect was time- and dose-dependent, although inhibition of pp38 phosphorylation occurred earlier and at lower concentrations of the compound. AG879 also inhibited NGF-induced PLC-gamma 1 phosphorylation, phosphatidylinositol-3 (PI3) kinase activation, the association of the tyrosine-phosphorylated proteins pp100 and pp110 with the p85 subunit of PI-3 kinase, mitogen activated protein and raf-1 kinases, and c-fos induction. In addition, AG879 inhibited NGF-induced neurite outgrowth in PC12 cells. These data indicate that tyrosine kinase activity of the pp140c-trk NGF receptor is essential for the cellular actions of this growth factor.

Epidermal growth factor and transforming growth factor-alpha can induce neuronal differentiation of rat pheochromocytoma PC12 cells under particular culture conditions

In rat pheochromocytoma PC12 cells, NGF induces neuronal differentiation. Upon stimulation with NGF, Ras is activated to a GTP-bound form, and the activated Ras can induce neuronal differentiation. Recently, we and others observed that epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) can also activate Ras in PC12 cells. This is puzzling since previous reports indicated that EGF stimulates proliferation rather than differentiation in PC12 cells. In this paper, we re-examined the biological effect of EGF and TGF-alpha, and found that these factors can also induce neuronal differentiation under particular culture conditions. Not only the outgrowth of long neurites, but the induction of neurofilament proteins and the metalloprotease transin was also observed in the EGF- and TGF-alpha-stimulated cells. These data clearly indicate that in addition to NGF, EGF and TGF-alpha can also induce the differentiation of PC12 cells under particular conditions.

Phosphoinositide metabolism in a polyoma-BK-virus-transformed pancreatic islet cell line: evidence for constitutively activated phospholipase C

We have characterized the phosphoinositide metabolism in a polyoma-BK-virus-transformed rat pancreatic islet cell line which has highly malignant characteristics, expresses viral T-antigen and has lost insulin-secreting capacity. After incorporation with [3H]inositol to isotopic equilibrium, all inositol metabolites were analyzed. When compared with normal pancreatic islets, increased levels of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3), inositol 1,3,4-trisphosphates and inositol tetrakisphosphate (Ins-P4), and decreased levels of phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP2) were found. The Ins-1,4,5-P3/PIP2 ratio increased, whereas the PIP2/PIP ratio was not altered after the transformation. In the pancreatic islet cell line there was a stable accumulation of inositol phosphates at 3.3 mM glucose. Glucose, KCl, cholecystokinin (CCK) and carbachol with and without LiCl were all without effect on the accumulation of inositol phosphates. Somatostatin inhibited the accumulation of inositol phosphates but a Ca(2+)-free/EDTA solution did not. Preincubation with cholera toxin or pertussis toxin inhibited the accumulation of inositol phosphates at 3.3 mM glucose except for Ins-P4, whereas no effect was observed on the phosphoinositides. NaF stimulated the accumulation of inositol phosphates, with a concomitant decrease in the phosphoinositides, whereas neomycin was without effect on the inositol phosphates. In normal pancreatic islets, pertussis toxin inhibited the CCK-induced increase in Ins-1,4,5-P3, whereas no effect was seen at 3.3 mM glucose. Finally, pertussis toxin inhibited the CCK-induced increase in the Ins-1,4,5-P3/PIP2 ratio in normal pancreatic islets. The same inhibition was also found in the pancreatic islet cell line at 3.3 mM glucose. We conclude that in the transformed pancreatic islet cell line the phosphoinositide hydrolysis is constitutively activated at the level of phospholipase C, with a substantial loss of regulatory control.

Activation of phosphatidylinositol-3 kinase by nerve growth factor involves indirect coupling of the trk proto-oncogene with src homology 2 domains

Growth factor receptor tyrosine kinases can form stable associations with intracellular proteins that contain src homology (SH) 2 domains, including the p85 regulatory subunit of phosphatidylinositol (PI)-3 kinase. The activation of this enzyme by growth factors is evaluated in PC12 pheochromocytoma cells and NIH 3T3 fibroblasts expressing the pp140c-trk nerve growth factor (NGF) receptor (3T3-c-trk). NGF causes the rapid stimulation of PI-3 kinase activity detected in anti-phosphotyrosine, but not in anti-trk, immunoprecipitates. This effect coincides with the tyrosine phosphorylation of two proteins, with molecular masses of of 100 kd and 110 kd, that coimmunoprecipitate with p85. Similar phosphorylation patterns are induced when an immobilized fusion protein containing the amino-terminal SH2 domain of p85 is used to precipitate tyrosine-phosphorylated proteins. Thus, although NGF produces the rapid activation of PI-3 kinase through a mechanism that involves tyrosine phosphorylation, there is no evidence for tyrosine phosphorylation of p85, or for its ligand-dependent association with the NGF receptor. Perhaps another phosphoprotein may link the NGF receptor to this enzyme.

Diversity in cellular signaling for nerve growth factor and insulin: variations on a common theme

Numerous similarities exist in the cellular signaling events observed for insulin and nerve growth factor. Because the two hormones share many functional properties, and exhibit similar effects on neurons, the possibility of common early signaling events has been explored. Many studies have focused on the important role of protein phosphorylation. Two distinct but related mechanisms are discussed that may mediate, in part, the ability of these two hormones to regulate the activities of protein kinases and phosphatases.

Inhibition of the cellular actions of nerve growth factor by staurosporine and K252A results from the attenuation of the activity of the trk tyrosine kinase

The protein kinase inhibitors staurosporine and K252A inhibit some of the cellular actions of nerve growth factor (NGF). To explore the molecular mechanisms involved, we test the ability of these agents to block one of the earliest cellular responses to NGF, protein tyrosine phosphorylation. Concentrations of 10-100 nM staurosporine and K252A inhibit NGF-dependent tyrosine phosphorylation in PC12 cells and inhibit trk oncogene-dependent tyrosine phosphorylation in trk-transformed NIH3T3 (trk-3T3 cells). In contrast, these compounds are without effect on epidermal growth factor (EGF)-stimulated tyrosine phosphorylation in PC12 cells. NGF-stimulated tyrosine phosphorylation of the pp140c-trk NGF receptor and tyrosine phosphorylation of pp70trk are also inhibited by similar concentrations of staurosporine and K252A, whereas tyrosine phosphorylation of the EGF receptor, insulin receptor, and v-src is not affected. Both staurosporine and K252A inhibit the autophosphorylation of pp70trk on tyrosine residues in an in vitro immune complex kinase reaction. Incubation of trk-3T3 cells with 10 nM staurosporine causes rounded transformed cells to revert to a normal flattened phenotype, whereas src-transformed cells are unaffected by this agent. These data suggest that staurosporine and K252A specifically inhibit the trk tyrosine kinase activity through a direct mechanism, probably accounting for the attenuation by these agents of the cellular actions of NGF.