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R Seger

Publications and source records attributed to R Seger.

At least 55 records · Page 3Linked to original sources
PubMed1999

Cutting edge: extracellular signal-regulated kinase activates syk: a new potential feedback regulation of Fc epsilon receptor signaling.

The protein tyrosine kinase Syk is an essential element in several cascades coupling Ag receptors to cell responses. Syk and the mitogen-activated protein kinase extracellular signal-regulated kinase 1 (ERK1) were found to form a tight complex in both resting and Ag-stimulated rat mucosal-type mast cells (rat basophilic leukemia 2H3 cell line RBL-2H3). A direct serine phosphorylation and activation of Syk by ERK was observed in in vitro experiments. Moreover the mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) kinase (MEK) inhibitors markedly decreased the Ag-induced phosphorylation of the tyrosyl residues of Syk and its activation as well as suppressed the degranulation of the cells. These results suggest a positive feedback regulation of Syk by ERK in the cascade coupling the type 1 Fc epsilon receptor to the secretory response of mast cells; hence, the existence of a novel type of cross-talk between protein serine/threonine kinases and protein tyrosine kinases is suggested.

Animals↗
PubMed1999

The C-terminus of the kinase-defective neuregulin receptor ErbB-3 confers mitogenic superiority and dictates endocytic routing.

Signaling by the epidermal growth factor (EGF) family and the neuregulin group of ligands is mediated by four ErbB receptor tyrosine kinases, that form homo- and heterodimeric complexes. Paradoxically, the neuregulin receptor ErbB-3 is devoid of catalytic activity, but its heterodimerization with other ErbBs, particularly the ligand-less ErbB-2 oncoprotein of carcinomas, reconstitutes superior mitogenic and transforming activities. To understand the underlying mechanism we constructed a chimeric EGF-receptor (ErbB-1) whose autophosphorylation C-terminal domain was replaced by the corresponding portion of ErbB-3. Consistent with the possibility that this domain recruits a relatively potent signaling pathway(s), the mitogenic signals generated by the recombinant fusion protein were superior to those generated by ErbB-1 homodimers and comparable to the proliferative activity of ErbB-2/ErbB-3 heterodimers. Upon ligand binding, the chimeric receptor recruited an ErbB-3-specific repertoire of signaling proteins, including Shc and the phosphatidylinositol 3-kinase, but excluding the ErbB-1-specific substrate, phospholipase Cgamma1. Unlike ErbB-1, which is destined to lysosomal degradation through a mechanism that includes recruitment of c-Cbl and receptor poly-ubiquitination, the C-terminal tail of ErbB-3 shunted the chimeric protein to the ErbB-3-characteristic recycling pathway. These observations attribute the mitogenic superiority of ErbB-3 to its C-terminal tail and imply that the flanking kinase domain has lost catalytic activity in order to restrain the relatively potent signaling capability of the C-terminus.

Adaptor Proteins, Signal Transducing↗
PubMed1999

CPG16, a novel protein serine/threonine kinase downstream of cAMP-dependent protein kinase.

Gene expression is necessary for the formation and consolidation of long term memory in both invertebrates and vertebrates. Here, we describe the expression and characterization of candidate plasticity gene 16 (cpg16), a protein serine/threonine kinase that was previously isolated from rat hippocampus as a plasticity-related gene. CPG16, when expressed in and purified from bacteria and COS7 cells, was only capable of autophosphorylation and phosphorylation of myelin basic protein but failed to phosphorylate many other peptides and proteins in in vitro phosphorylation assays. Recombinant CPG16, when overexpressed and purified from COS7 cells, had a relatively low level of autophosphorylation activity. This activity was significantly stimulated when cAMP-elevating agents (forskolin, 8-bromo-cAMP) were added to the cells but not by any other extracellular stimuli tested, e.g. serum, phorbol esters, and a calcium ionophore. Although the stimulation of CPG16 activity was inhibited by the cAMP-dependent protein kinase inhibitor H-89, it did not serve as a direct substrate for this kinase. This suggests that CPG16 may be activated by a cAMP-stimulated protein kinase cascade. Immunolocalization studies in COS7 and NIH-3T3 cells showed mostly cytoplasmic localization of CPG16 that turned partially nuclear upon stimulation with 8-bromo-cAMP. Moreover, overexpression of CPG16 seems to partially inhibit cAMP-stimulated activity of the transcription factor CREB (cAMP response element-binding protein), suggesting its involvement in the down-regulation of cAMP-induced transcription. Thus, CPG16 is a protein serine/threonine kinase that may be involved in a novel signaling pathway downstream of cAMP-dependent protein kinase.

3T3 Cells↗
PubMed1999

The cytoskeletal network controls c-Jun expression and glucocorticoid receptor transcriptional activity in an antagonistic and cell-type-specific manner.

The physical and functional link between adhesion molecules and the cytoskeletal network suggests that the cytoskeleton might mediate the transduction of cell-to-cell contact signals, which often regulate growth and differentiation in an antagonistic manner. Depolymerization of the cytoskeleton in confluent cell cultures is reportedly sufficient to initiate DNA synthesis. Here we show that depolymerization of the cytoskeleton is also sufficient to repress differentiation-specific gene expression. Glutamine synthetase is a glia-specific differentiation marker gene whose expression in the retinal tissue is regulated by glucocorticoids and is ultimately dependent on glia-neuron cell contacts. Depolymerization of the actin or microtubule network in cells of the intact retina mimics the effects of cell separation, repressing glutamine synthetase induction by a mechanism that involves induction of c-Jun and inhibition of glucocorticoid receptor transcriptional activity. Depolymerization of the cytoskeleton activates JNK and p38 mitogen-activated protein kinase and induces c-Jun expression by a signaling pathway that depends on tyrosine kinase activity. Induction of c-Jun expression is restricted to Müller glial cells, the only cells in the tissue that express glutamine synthetase and maintain the ability to proliferate upon cell separation. Our results suggest that the cytoskeletal network might play a part in the transduction of cell contact signals to the nucleus.

Animals↗
PubMed1999

Neu differentiation factor stimulates phosphorylation and activation of the Sp1 transcription factor.

Neu differentiation factors (NDFs), or neuregulins, are epidermal growth factor-like growth factors which bind to two tyrosine kinase receptors, ErbB-3 and ErbB-4. The transcription of several genes is regulated by neuregulins, including genes encoding specific subunits of the acetylcholine receptor at the neuromuscular junction. Here, we have examined the promoter of the acetylcholine receptor epsilon subunit and delineated a minimal CA-rich sequence which mediates transcriptional activation by NDF (NDF-response element [NRE]). Using gel mobility shift analysis with an NRE oligonucleotide, we detected two complexes that are induced by treatment with neuregulin and other growth factors and identified Sp1, a constitutively expressed zinc finger phosphoprotein, as a component of one of these complexes. Phosphatase treatment, two-dimensional gel electrophoresis, and an in-gel kinase assay indicated that Sp1 is phosphorylated by a 60-kDa kinase in response to NDF-induced signals. Moreover, Sp1 seems to act downstream of all members of the ErbB family and thus may funnel the signaling of the ErbB network into the nucleus.

Animals↗
PubMed1999

Fibroblast growth factor promotes recruitment of skeletal muscle satellite cells in young and old rats.

Although the role of satellite cells in muscle growth and repair is well recognized, understanding of the molecular events that accompany their activation and proliferation is limited. In this study, we used the single myofiber culture model for comparing the proliferative dynamics of satellite cells from growing (3-week-old), young adult (8- to 10-week-old), and old (9- to 11-month-old) rats. In these fiber cultures, the satellite cells are maintained in their in situ position underneath the fiber basement membrane. We first demonstrate that the cytoplasm of fiber-associated satellite cells can be monitored with an antibody against the extracellular signal regulated kinases 1 and 2 (ERK1 and ERK2), which belong to the mitogen-activated protein kinase (MAPK) superfamily. With this immunocytological marker, we show that the satellite cells from all three age groups first proliferate and express PCNA and MyoD, and subsequently, about 24 hr later, exit the PCNA+/MyoD+ state and become positive for myogenin. For all three age groups, fibroblast growth factor 2 (FGF2) enhances by about twofold the number of satellite cells that are capable of proliferation, as determined by monitoring the number of cells that transit from the MAPK+ phenotype to the PCNA+/MAPK+ or MyoD+/MAPK+ phenotype. Furthermore, contrary to the commonly accepted convention, we show that in the fiber cultures FGF2 does not suppress the subsequent transition of the proliferating cells into the myogenin+ compartment. Although myogenesis of satellite cells from growing, young adult, and old rats follows a similar program, two distinctive features were identified for satellite cells in fiber cultures from the old rats. First, a large number of MAPK+ cells do not appear to enter the MyoD-myogenin expression program. Second, the maximal number of proliferating satellite cells is attained a day later than in cultures from the young adults. This apparent "lag" in proliferation was not affected by hepatocyte growth factor (HGF), which has been implicated in accelerating the first round of satellite cell proliferation. HGF and FGF2 were equally efficient in promoting proliferation of satellite cells in fibers from old rats. Collectively, the investigation suggests that FGF plays a critical role in the recruitment of satellite cells into proliferation.

Aging↗
PubMed1999

Gi-mediated activation of mitogen-activated protein kinase (MAPK) pathway by receptor mimetic basic secretagogues of connective tissue-type mast cells: bifurcation of arachidonic acid-induced release upstream of MAPK.

The family of basic secretagogues of connective tissue mast cells act as receptor mimetic agents, which trigger exocytosis by directly activating G proteins. We now demonstrate that pertussis toxin (Ptx)-sensitive Gi proteins, activated by compound 48/80 (c48/80), a potent member of this family, also activate the p42/p44 MAP kinases (MAPKs). This activation was potentiated by the protein tyrosine phosphatase inhibitor vanadate, whereas the tyrphostin AG-18, a competitive inhibitor of protein tyrosine kinases (PTKs); the protein kinase C inhibitors K252a and GF109203X; the phosphatidylinositol-3-kinase (PI-3K) inhibitors wortmannin and LY294002; and EGTA have abolished this activation. These results suggest that c48/80 activated the p42/p44 MAPKs via a mechanism that involves PTKs, protein kinase C, phosphatidylinositol-3-kinase and Ca2+ as mediators. Protein tyrosine phosphorylation and activation of the p42/p44 MAPKs were closely correlated with stimulation of arachidonic acid (AA) release by c48/80 but not with histamine secretion. However, whereas PD98059, the inhibitor of the MAPK kinase has abrogated MAPK activation, this inhibitor failed to effect release of AA. We therefore conclude that by activating Ptx-sensitive Gi protein(s), the basic secretagogues of mast cells stimulate multiple signaling pathways, which diverge to regulate the production and release of the different inflammatory mediators. Whereas the signaling pathway responsible for triggering histamine release is PTK independent, the pathway responsible for the stimulation of AA release bifurcates downstream to PTKs but upstream to the activation of MAPKs.

Androstadienes↗
PubMed1999

Mechanism of GnRH receptor signaling: from the membrane to the nucleus.

The purpose of this review is to update the information concerning the intracellular effect of GnRH. Binding of GnRH to a G-protein coupled receptor leads to stimulation of Gq and/or G11 protein and to activation of phospholipase C beta. Inositol 1-4-5-triphosphate and early diacylylycerol are the second messengers required for conventional protein kinase C activation. Activation of phospholipase A2 and phospholipase D are also involved, as demonstrated by the liberation of Arachidonic Acid and Phosphatidic Acid. Pituitary cells also express atypical protein kinase C isoforms which mode of activation is not known. Hypothesis concerning transcriptional regulation are presented.

Animals↗
PubMed1998

Specific and differential activation of mitogen-activated protein kinase cascades by unfamiliar taste in the insular cortex of the behaving rat.

Rats were given to drink an unfamiliar taste solution under conditions that result in long-term memory of that taste. The insular cortex, which contains the taste cortex, was then removed and assayed for activation of mitogen-activated protein kinase (MAPK) cascades by using antibodies to the activated forms of various MAPKs. Extracellular responsive kinase 1-2 (ERK1-2) in the cortical homogenate was significantly activated within <30 min of drinking the taste solution, without alteration in the total level of the ERK1-2 proteins. The activity subsided to basal levels within <60 min. In contrast, ERK1-2 was not activated when the taste was made familiar. The effect of the unfamiliar taste was specific to the insular cortex. Jun N-terminal kinase 1-2 (JNK1-2) was activated by drinking the taste but with a delayed time course, whereas the activity of Akt kinase and p38MAPK remained unchanged. Elk-1, a member of the ternary complex factor and an ERK/JNK downstream substrate, was activated with a time course similar to that of ERK1-2. Microinjection of a reversible inhibitor of MAPK/ERK kinase into the insular cortex shortly before exposure to the novel taste in a conditioned taste aversion training paradigm attenuated long-term taste aversion memory without significantly affecting short-term memory or the sensory, motor, and motivational faculties required to express long-term taste aversion memory. It was concluded that ERK and JNK are specifically and differentially activated in the insular cortex after exposure to a novel taste, and that this activation is required for consolidation of long-term taste memory.

Animals↗
PubMed1998

[10 years Swiss bone marrow donor registry].

The Swiss Bone Marrow Donor Registry was established 1988 as a project of Swiss Transplant. Up to the end of 1997, 13,500 unrelated volunteer donors have been added to the central registry in Bern in cooperation with the regional transfusion centers of Switzerland. During this period, the registry responded to over 15,000 international search requests. 67 matching Swiss donors were found for patients all over the world. On the other hand, 77 Swiss patients received unrelated bone marrow transplantation from international donors. In 1997, 24 donors were selected from the Swiss registry and 21 bone marrow transplantations were performed, which is more than in any year before. The most recent developments are peripheral blood stem cell donation and the creation of cord blood banks.

Bone Marrow Transplantation↗
PubMed1998

Correction of respiratory burst activity in X-linked chronic granulomatous cells to therapeutically relevant levels after gene transfer into bone marrow CD34+ cells.

Chronic granulomatous disease (CGD) is a disorder of the lymphohematopoietic system, whereby phagocytes of affected patients are unable to kill microorganisms. CGD is caused by a functional defect in the phagocytic nicotinamide adenine dinucleotide phosphatase (NADPH) oxidase (phox) enzyme complex, leading to a lack of microbicidal metabolites. As a therapeutic approach toward the predominant X-linked form of CGD, we have developed a bicistronic retroviral vector containing the coding sequences of gp91-phox and a cytoplasmically truncated version of the human low-affinity receptor for nerve growth factor (deltaLNGFR). Full reconstitution of superoxide-generating activity was achieved with this vector in a gp91-phox-deficient cell line. Using an optimized gene transfer protocol, up to 85% of the CD34+ cells obtained from the bone marrow of X-CGD patients were transduced. CD15+ cells differentiated in vitro from transduced X-CGD CD34+ cells showed correction of NADPH oxidase activity to 45-52% of normal levels whereas deltaLNGFR expression was found in 40-67% of the CD15+ cells. Moreover, immunoblots prepared from extracts of transduced CD15+ cells revealed gp91-phox protein levels similar to those found in neutrophils derived from normal CD34+ cells. Taking into consideration that superoxide production in only 5 to 10% of wild-type neutrophils is sufficient to protect X-CGD heterozygotes from serious infections, the results achieved in this study shows that for X-CGD patients a curative approach based on the genetic modification of hematopoietic stem/progenitor cells is feasible.

Antigens, CD34↗
PubMed1998

Repeated pulses of serotonin required for long-term facilitation activate mitogen-activated protein kinase in sensory neurons of Aplysia.

Long-term facilitation of the connections between the sensory and motor neurons of the gill-withdrawal reflex in Aplysia requires five repeated pulses of serotonin (5-HT). The repeated pulses of 5-HT initiate a cascade of gene activation that leads ultimately to the growth of new synaptic connections. Several genes in this process have been identified, including the transcriptional regulators apCREB-1, apCREB-2, apC/EBP, and the cell adhesion molecule apCAM, which is thought to be involved in the formation of new synaptic connections. Here we report that the transcriptional regulators apCREB-2 and apC/EBP, as well as a peptide derived from the cytoplasmic domain of apCAM, are phosphorylated in vitro by Aplysia mitogen-activated protein kinase (apMAPK). We have cloned the cDNA encoding apMAPK and show that apMAPK activity is increased in sensory neurons treated with repeated pulses of 5-HT and by the cAMP pathway. These results suggest that apMAPK may participate with cAMP-dependent protein kinase during long-term facilitation in sensory cells by modifying some of the key elements involved in the consolidation of short- to long-lasting changes in synaptic strength.

Animals↗
PubMed1998

Co-stimulation-dependent activation of a JNK-kinase in T lymphocytes.

Previously we implicated c-Jun N-terminal kinase (JNK) as an element that is involved in signal integration during co-stimulation of T lymphocytes. This pathway has now been traced to an upper level, comprising MAPKK SEK1/MKK4/JNKK1 which, similarly to JNK, must receive input both from the TCR and CD28. A large portion of this input is probably integrated at the level of the Rho-family protein CDC42 which, here, activates SEK1 and JNK to the level reached by TCR and CD28 stimulation. We have identified another putative SEK/ JNK pathway regulator, PKCtheta, which in contrast to CDC42, activates SEK and JNK maximally only in conjunction with a calcium signal delivered through calcineurin. Signals originating at the TCR and CD28 may travel down the JNK pathway via PKCtheta, calcineurin, CDC42, MEKK1 and SEK1.

Animals↗
PubMed1998

Hippocampal plasticity involves extensive gene induction and multiple cellular mechanisms.

Long-term plasticity of the central nervous system (CNS) involves induction of a set of genes whose identity is incompletely characterized. To identify candidate plasticity-related genes (CPGs), we conducted an exhaustive screen for genes that undergo induction or downregulation in the hippocampus dentate gyrus (DG) following animal treatment with the potent glutamate analog, kainate. The screen yielded 362 upregulated CPGs and 41 downregulated transcripts (dCPGs). Of these, 66 CPGs and 5 dCPGs are known genes that encode for a variety of signal transduction proteins, transcription factors, and structural proteins. Seven novel CPGs predict the following putative functions: cpg2--a dystrophin-like cytoskeletal protein; cpg4--a heat-shock protein: cpg16--a protein kinase; cpg20--a transcription factor; cpg21--a dual-specificity MAP-kinase phosphatase; and cpg30 and cpg38--two new seven-transmembrane domain receptors. Experiments performed in vitro and with cultured hippocampal cells confirmed the ability of the cpg-21 product to inactivate the MAP-kinase. To test relevance to neural plasticity, 66 CPGs were tested for induction by stimuli producing long-term potentiation (LTP). Approximately one-fourth of the genes examined were upregulated by LTP. These results indicate that an extensive genetic response is induced in mammalian brain after glutamate receptor activation, and imply that a significant proportion of this activity is coinduced by LTP. Based on the identified CPGs, it is conceivable that multiple cellular mechanisms underlie long-term plasticity of the nervous system.

Amino Acid Sequence↗
PubMed1998

Ras-signaling pathways: positive and negative regulation of tau expression in PC12 cells.

Tau is a microtubule-associated protein whose promoter is activated during the first phase of nerve growth factor-induced PC12 cell differentiation, whereas levels of its mRNA are accumulating throughout differentiation. In this study, we have followed the signal transduction cascades regulating tau induction. Using dominant negative Ras-expressing PC12 cells, we show that ras regulates tau expression during the first phase of PC12 cell differentiation. The ERK and JNK cascades, which are downstream of Ras, have opposing effects on tau promoter activity: ERK induces tau promoter activity, JNK inhibits it. Tau promoter activity in PC12 cells is correlated with a short-term activation of ERK, which declines after a few hours and is followed by an activation of the inhibitory JNK cascade 76 h later. These observations suggest that the induction and inhibition of tau promoter are mediated by alternate ERK and JNK activities, which may underlie a mechanism to turn on and off genes during PC12 cell differentiation.

Animals↗
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↗
PubMed1998

Stimulation of Jun N-terminal kinase (JNK) by gonadotropin-releasing hormone in pituitary alpha T3-1 cell line is mediated by protein kinase C, c-Src, and CDC42.

The signaling of ligands operating via heterotrimeric G proteins is mediated by a complex network that involves sequential phosphorylation events. Signaling by the G protein-coupled receptor GnRH was shown to include elevation of Ca2+ and activation of phospholipases, protein kinase C (PKC) and extra-cellular signal-regulated kinase (ERK). In this study, GnRH was shown to activate Jun N-Terminal Kinase (JNK)/SAPK in alpha T3-1 cells in a PKC- and tyrosine kinase-dependent manner. GnRH as well as tumor-promoting agent (TPA) also increased c-Src activity, which peaked at 2 min after GnRH stimulation and was sensitive both to PKC and to tyrosine kinase inhibitors. Coexpression of Csk, which serves as a Src-dominant interfering kinase, and constitutively active forms of Src, together with JNK, confirmed the involvement of c-Src downstream of PKC in the GnRH-JNK pathway. Coexpression of dominant negative and constitutively active forms of CDC42, Rac1, Ras, MEKK1, and MEK1 with JNK indicated that JNK activation by GnRH and TPA is mediated by CDC42 and MEKK1. Ras and MEK1, which are involved in a related mitogen-activated protein kinase (MAPK) pathway, did not affect JNK activation in alpha T3-1 cells. Taken together, our results suggest that GnRH stimulation of JNK activity is mediated by a unique pathway that includes sequential activation of PKC, c-Src, CDC42, and probably also MEKK1.

Animals↗