Signal transduction of the erythropoietin receptor

Several studies have been carried out on the transmission of Onchocerciasis by Simulium damnosum s.l. in the forest zone of C?te d'Ivoire. This study, carried out in 1979-1980 was devoted to determine the risk of onchocerciasis transmission inside and outside the rain forest of Ta? (5 degrees 50' N-7 degrees 25' W). We present the vectorial capacity of S. sanctipauli in the region of Ta? before massive flow of refugees from areas of Liberia without any control Programme. The results of micromorphological technics for determination of S. damnosum adults, showed that mainly females of S. sanctipauli were present. The studied populations had low parturity rates: 39.2% outside and 30.9% of parous flies inside the rain forest. The parasitic rates (0.4% of infectious females outside and 0.1% inside) and their parasitic loads (15 and 3 infective larvae per 1000 parous female respectively outside and inside the rain forest) were low, consequently their vectorial capacity with Onchocerca volvulus was almost non-existent in natural conditions. Before massive flow of refugees including persons carrying microfilariae, there were no problem of onchocerciasis within and outside the rain forest of Ta?. However, the massive flow of refugees and the deforestation for growing crops can create situations favourable to the installation of more efficient vectors, increase man/vector contact and contribute to more intense onchocerciasis transmission. The monitoring of onchocerciasis transmission is necessary.     

Signal transduction through the CD19 receptor during discrete developmental stages of human B-cell ontogeny

We present evidence that the CD19 receptor is functionally operative and transmits pleiotropic signals throughout the pro-B, pre-pre-B, pre-B, early B, and mature B cell stages of human B-cell ontogeny. The signaling ability of CD19 does not depend on the existence of a functional B-cell antigen receptor complex (ARC). In B-cell precursors (BCP) lacking a functional ARC, CD19 is physically and functionally associated with Src family protein tyrosine kinases (PTK). The engagement of the CD19 receptor on BCP with a high affinity anti-CD19 monoclonal antibody (mAb) or its homoconjugate rapidly activates the associated PTK and results in tyrosine phosphorylation of CD19. Moreover, this proximal PTK activation step triggers downstream stimulation of several different intracellular messenger systems. Remarkably, CD19 becomes rapidly phosphorylated on tyrosine residues upon engagement of several other surface receptors as well, suggesting that it may function as a common response element linked via tyrosine phosphorylation to multiple BCP/B-cell receptors and signaling pathways. Furthermore, in all B-lineage lymphoid cell populations, co-approximation of the receptors CD19 and CD72 (ligand for the CD5 T-cell receptor) generates a stronger signal than the engagement of either individual receptor. These convergent observations constitute a strong argument for an important regulatory function of CD19 in human BCP and prompt the hypothesis that the CD19 receptor may play an important role in cognate interactions between B- and T-lineage lymphoid compartments as well as the coordinate production of BCP at multiple stages of human B-cell ontogeny.     

Signal transduction

A familial short stature syndrome is described in two sisters. Clinical features include severe pre- and post-natal growth failure, stridor, feeding difficulties in the first 2 years requiring nasogastric feeding and facial dysmorphism reminiscent of Three M syndrome. Intellectual function is normal. Skeletal surveys show short long bones, small square iliac bones, short femoral necks and vertebral bodies which are short in the antero-posterior diameter with narrowing of the interpedicular distance inferiorly.     

Signal transduction through trimeric G proteins in megakaryoblastic cell lines

The biogenesis of trimeric G proteins was investigated by measurement of the expression of alpha-subunits in the megakaryoblastic cell lines MEG-01, DAMI, and CHRF-288-11, representing stages of increasing maturation, and compared with platelets. Megakaryoblasts and platelets contained approximately equal amounts of Gi alpha-1/2, Gi alpha-3, Gq alpha, and G12 alpha protein. Maturation was accompanied by (1) downregulation of mRNA for Gs alpha and disappearance of iloprost-induced Ca2+ mobilization, (2) upregulation of the long form of Gs alpha protein (Gs alpha-L) and an increase in iloprost-induced cAMP formation, and (3) upregulation of G16 alpha mRNA and G16 alpha protein and appearance of thromboxane A2-induced signaling (Ca2+ mobilization and stimulation of prostaglandin I2-induced cAMP formation). Gz alpha protein was absent in the megakaryoblasts despite weak expression of Gz alpha mRNA in DAMI and relatively high levels of Gz alpha mRNA and Gz alpha protein in platelets. These findings reveal major changes in G protein-mediated signal transduction during megakaryocytopoiesis and indicate that G16 alpha couples the thromboxane receptor to phospholipase C beta.     

Signal decay through a reverse phosphorelay in the Arc two-component signal transduction system

Escherichia coli senses and signals anoxic or low redox conditions in its growth environment by the Arc two-component system. Under those conditions, the tripartite sensor kinase ArcB undergoes autophosphorylation at the expense of ATP and subsequently transphosphorylates its cognate response regulator ArcA through a His --> Asp --> His --> Asp phosphorelay pathway. In this study we used various combinations of wild-type and mutant ArcB domains to analyze in vitro the pathway for signal decay. The results indicate that ArcA-P dephosphorylation does not occur by direct hydrolysis but by transfer of the phosphoryl group to the secondary transmitter and subsequently to the receiver domain of ArcB. This reverse phosphorelay involves both the conserved His-717 of the secondary transmitter domain and the conserved Asp-576 of the receiver domain of ArcB but not the conserved His-292 of its primary transmitter domain. This novel pathway for signal decay may generally apply to signal transduction systems with tripartite sensor kinases.     

Signal transduction via Ras

Ras is a major regulator of cell growth. It is a GTP-binding protein that functions as a molecular switch, cycling between the GDP-bound OFF and GTP-bound ON states. In the GTP-bound state it interacts with effector proteins that mediate the biological function. It is found as an oncogene in about 30% of human tumors. Structural and mechanistic studies on Ras and its interaction with effectors and GAP will be discussed in the context of the biology and pathophysiology of this protein.     

Signal transduction by the PDGF receptors

The three isoforms of PDGF bind with different affinities to two related tyrosine kinase receptors, denoted the PDGF alpha- and beta-receptors. Ligand binding induces receptor dimerization, creating receptor homo- or heterodimers. Dimerization is accompanied by, and might be a prerequisite for, receptor autophosphorylation and kinase activation. Receptor autophosphorylation serves to regulate the kinase activity and to create binding sites on the receptor molecule for downstream signalling components. The activities of the signalling components are ultimately manifested as specific biological responses. All the currently described PDGF receptor-binding components, e.g. phospholipase C-gamma, members of the src family of cytoplasmic tyrosine kinases, the rasGT-Pase activating protein and p85, the regulatory subunit of phosphatidylinositol 3' kinase, contain a conserved src homology 2-domain, through which the association with the receptor takes place. The receptor-binding components appear to either possess an intrinsic enzymatic activity, or they function as adaptors, which may complex with catalytically active components. For most receptor-binding components, there is insufficient understanding of how binding to the receptor affects the catalytic function. Certain of these components become tyrosine-phosphorylated, i.e. they are substrates for the receptor tyrosine kinase. Moreover, the change in subcellular localization, which most of the receptor binding components undergo in conjunction with receptor binding, could play a critical role. The current efforts of many laboratories are aimed at delineating different PDGF receptor signal transduction pathways and what roles the different receptor-binding components play in the establishment of these pathways.     

Signal transduction by the IL-1 type I receptor: evidence for the involvement of a receptor-coupled protein kinase

A novel serine/threonine specific protein kinase was found to be associated with the type I IL-1 receptor in the murine T cell lines D10N and EL-4. This kinase was identified in immunoprecipitates from IL-1 stimulated T-cells by its ability to phosphorylate exogenous substrates in the presence of radiolabeled ATP. An endogenous protein, most likely a member of the IL-1 R1 complex, was also phosphorylated. The activation of the kinase is specific for IL-1, neither TNF nor phorbol esters were able to activate the IL-1 RI associated kinase activity. The IL-1 receptor antagonist had no intrinsic activity and inhibited the activation of the kinase. The activation of the kinase was rapid and detectable after 30 seconds of IL-1 stimulation. A minimal model of the IL-RI signal transduction complex is discussed, presenting this novel serine/threonine kinase as a constituent of the complex.     

Signal transduction for proliferation of glioma cells in vitro occurs predominantly through a protein kinase C-mediated pathway

Previous work has demonstrated that glioma cells have very high protein kinase C (PKC) enzyme activity when compared to non-malignant glia, and that their PKC activity correlates with their proliferation rate. The purpose of this study was to determine whether the elevated PKC activity in glioma is secondary to an autonomously active PKC isoform implying oncogenic transformation, or whether this activity is driven by upstream ligand-receptor tyrosine kinase interactions. We treated established human glioma cell lines A172, U563 or U251 with either the highly selective PKC inhibitor CGP 41 251, or with genistein, a tyrosine kinase inhibitor. The proliferation rate and PKC activity of all the glioma lines was reduced by CGP 41 251; the IC50 values for inhibiting cell proliferation corresponded to the IC50v values for inhibition of PKC activity. Genistein also inhibited cell proliferation, with IC50 proliferation values approximating those for inhibition of tyrosine kinase activity in cell free protein extracts. Importantly, in genistein-treated cells, downstream PKC enzyme activity was dose dependently reduced such that the correlation coefficient for effects of genistein on proliferation rate and PKC activity was 0.92. These findings suggest that upstream tyrosine kinase linked events, rather than an autonomously functioning PKC, result in the high PKC activity observed in glioma. Finally, fetal calf serum (FCS) evoked a strong mitogenic effect on glioma cell lines. This mitogenic activity was completely blocked by CGP 41 251, suggesting that although the many mitogens in FCS for glioma cells signal initially through genistein-inhibitable tyrosine kinases, they ultimately channel through a PKC-dependent pathway. We conclude that proliferative signal transduction in glioma cells occurs through a predominantly PKC-dependent pathway and that selectively targeting this enzyme provides an approach to glioma therapy.     

Rho prevents apoptosis through Bcl-2 expression: implications for interleukin-2 receptor signal transduction

Here we describe a Rho-mediated apoptosis suppression pathway driven by Bcl-2 expression in the interleukin (IL)-4- or IL-2-dependent murine T cell line TS1 alpha beta. IL-2, but not IL-4, induces Bcl-2 expression through RhoA activation which is inhibited by the specific Rho family inhibitor, Clostridium difficile Toxin B, as well as by a dominant negative RhoA mutant. Using transient transfections of RhoA mutants tagged with the vesicular stomatitis virus glycoprotein, we show that a constitutively active RhoA mutant induces Bcl-2 expression and prevents apoptosis upon IL-4 withdrawal. Finally, we have identified the signaling pathway involved together with RhoA in Bcl-2 induction and show compelling evidence for the implication of phosphatidylinositol 3 kinase and protein kinase C.     

Tissue distribution of erythropoietin and erythropoietin receptor in the developing human fetus

The purpose of this exploratory study was to describe a group of African American women who smoke crack. Using aggregate data from 208 interviews with women crack smokers, we randomly selected 25 women's interview data to create the 25 life-lines. These life-lines were developed in a similar manner to the time-line analysis described by Fullilove and her colleagues (1992); we focused on events that are either extraordinarily disturbing (e.g., rape, incest, death of a child, etc.), events that are usual but often stressful (e.g., birth of a child, death of a parent, etc.), and on periods of drug use. We chose this method of analysis so as to highlight the context in which many women come to use crack cocaine. The life-lines provided a retrospective (but time-ordered) perspective and in several ways provided preliminary support for a stress-diathesis perspective.     

Signal transduction in gastrointestinal smooth muscle

Signal transduction in gastric and intestinal smooth muscle is mediated by receptors coupled via distinct G proteins to various effector enzymes, including PI-specific PLC-beta 1 and PLC-beta 3, and phosphatidylcholine (PC)-specific PLC, PLD and PLA2. Activation of these enzymes is different in circular and longitudinal muscle cells, generating Ca(2+)-mobilizing (IP3, AA, cADPR) and other (DAG) messengers responsible for the initial and sustained phases of contraction, respectively. IP3-dependent Ca2+ release occurs only in circular muscle. Ca2+ mobilization in longitudinal muscle involves a cascade initiated by agonist-induced transient activation of PLA2 and formation of AA, AA-dependent depolarization of the plasma membrane and opening of voltage-sensitive Ca2+ channels. The influx of Ca2+ induces Ca2+ release by activating sarcoplasmic ryanodine receptor/Ca2+ channel and stimulates cADPR formation which enhances Ca(2+)-induced Ca2+ release. The initial [Ca2+]i transient in both muscle cell types results in Ca2+/calmodulin-dependent activation of MLC kinase, phosphorylation of MLC20 and interaction of actin and myosin. The sustained phase is mediated by a Ca(2+)-independent isoform of PKC, PKC-epsilon DAG for this process is generated by PLC- and PLD-mediated hydrolysis of PC. Relaxation is mediated by cAMP-and/or cGMP-dependent protein kinase which inhibit the initial [Ca2+]i transient and reduce the sensitivity of MLC kinase to [Ca2+]i. Relaxation induced by the main neurotransmitters, VIP and PACAP, involves two cascades, one of which reflects activation of adenylyl cyclase. A distinct cascade involves G-protein-dependent stimulation of Ca2+ influx leading to Ca2+/calmodulin-dependent activation of a constitutive eNOS in muscle cells; the generation of NO activates soluble guanylyl cyclase. The resultant activation of PKA and PKG is jointly responsible for muscle relaxation.     

Signal transduction in the wound response of tomato plants

The wound response of tomato plants has been extensively studied, and provides a useful model to understand signal transduction events leading from injury to marker gene expression. The principal markers that have been used in these studies are genes encoding proteinase inhibitor (pin) proteins. Activation of pin genes occurs in the wounded leaf and in distant unwounded leaves of the plant. This paper reviews current understanding of signalling pathways in the wounded leaf, and in the systemically responding unwounded leaves. First, the nature of known elicitors and their potential roles in planta are discussed, in particular, oligogalacturonides, jasmonates and the peptide signal, systemin. Inhibitors of wound-induced proteinase inhibitor (pin) expression are also reviewed, with particular reference to phenolics, sulphydryl reagents and fusicoccin. In each section, results obtained from the bioassay are considered within the wider context of data from mutants and from transgenic plants with altered levels of putative signalling components. Following this introduction, current models for pin gene regulation are described and discussed, together with a summary for the involvement of phosphorylation-dephosphorylation in wound signalling. Finally, a new model for wound-induced pin gene expression is presented, arising from recent data from the author's laboratory.     

Signal transduction pathways in guinea pig sperm

Trifluoperazine (TFP), the antagonist of calmodulin (CaM), significantly stimulated the capacitation and acrosome reaction of guinea pig spermatozoa at the concentration of 10-100 mumol/L, independent of the external Ca2+. Forskolin, dbcAMP and caffeine evidently promoted the occurrence of acrosome reaction of spermatozoa at early capacitation stage (5 h) in nonsynchronous system but not in synchronous system. If the spermatozoa were capacitated for 15 h in synchronous system, the above three drugs significantly stimulated acrosome reaction in a Ca(2+)-independent manner. Protein kinase C activators, i.e. phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDB) did not influence the occurrence of acrosome reaction of spermatozoa at early capacitation stage, but significantly increased the acrosome reaction rate in capacitated spermatozoa in a Ca(2+)-independent manner. In contrast, PKC inhibitor staurosporine significantly inhibited the occurrence of acrosome reaction.     

Signal transduction via platelet-derived growth factor receptors

Platelet-derived growth factor (PDGF) exerts its stimulatory effects on cell growth and motility by binding to two related protein tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation, allowing binding and activation of cytoplasmic SH2-domain containing signal transduction molecules. Thereby, a number of different signaling pathways are initiated leading to cell growth, actin reorganization migration and differentiation. Recent observations suggest that extensive cross-talk occurs between different signaling pathways, and that stimulatory signals are modulated by inhibitory signals arising in parallel.     

Signal transduction in human hematopoietic cells by vascular endothelial growth factor related protein, a novel ligand for the FLT4 receptor

We have recently identified a novel ligand of the vascular endothelial growth factor (VEGF) family termed VEGF-related protein (VRP), which specifically binds to the FLT4 receptor. To characterize the signaling events after VRP engagement of its cognate receptor in hematopoietic cells, a population of human erythroleukemia (HEL) cells, termed HEL-JW, expressing high levels of FLT4 receptor was isolated. Stimulation of HEL-JW cells with VRP alone and in combination with the c-kit ligand/stem cell factor increased cell growth. VRP induced tyrosine phosphorylation of various proteins, including the FLT4 receptor. Further characterization of these tyrosine phosphorylated molecules revealed that Shc, Grb2, and SOS form a complex with the activated FLT4 receptor. HEL-JW cells also expressed RAFTK, a recently identified member of the focal adhesion kinase family. RAFTK was phosphorylated and activated upon VRP treatment, and there was an enhanced association of this kinase with the adaptor protein Grb2. Furthermore, the c-Jun NH2-terminal kinase (JNK), involved in growth activation and shown to mediate RAFTK signaling in other cell types, was activated by VRP stimulation. We also observed that VRP treatment of HEL-JW cells resulted in the phosphorylation of the cytoskeletal protein paxillin. This treatment resulted in an increased association of paxillin with RAFTK, which was mediated by the C-terminal region of RAFTK. These studies indicate that VRP stimulation induced the formation of a signaling complex at its activated receptor as well as activation of RAFTK. VRP-mediated activation of RAFTK may facilitate signal transduction to the cytoskeleton and downstream to the JNK pathway in FLT4-expressing blood cells.     

Signal transduction from the extracellular matrix--a role for the focal adhesion protein-tyrosine kinase FAK

The therapy concept of topical factor XIII application was developed on the basis of clinical and experimental investigations on improvement of wound healing, as well as on the morphological and pathophysiological topical site of venous ulcers. Topical treatment with factor XIII is special with regard to mode of application as well as efficacy, since a lot of other medications used for local wound treatment contain a fibrinolytic component. In the last 32 months, 23 inpatients (17 female, 6 male) averaging 62.9 +/- 14.1 years and suffering ulcerative leg disease were treated with topically applied factor XIII. The average period of distal venous ulcer in these patients was 3.3 +/- 2.04 years. The extent of the ulcer surface ranged between 2.5 x 3.0 cm (minimum) and 18.5 x 8.0 cm (maximum). All patients had been in medical consultation for several years. The venous ulcers were based upon a "postthrombotic syndrome" in 15 patients. Six patients were suffering from ulcerations due to arterial and venous mixed disease, and there were 2 patients with ulcerations of unknown etiology. In 5 patients, 2 with unknown etiology and 3 with arterial and venous mixed disease, local treatment with factor XIII was discontinued after 4 weeks because there was definitely no improvement in wound healing. Additionally, 3 patients with ulcerations due to arterial and venous mixed disease were treated for a maximum of 6 weeks with only moderate improvement in healing. Twelve of the 15 patients (79.3%) with extended, chronic ulceration on the basis of a postthrombotic syndrome showed such a distinct improvement of topical site after an average of only 3.15 +/- 1.14 weeks that they were released for further ambulatory treatment. Three patients had to be treated for a maximum period of 6 weeks, also with distinct improvement in wound healing. Apart from a wound surface reduction and a clinically documentable improvement of granulation tendency, there was a marked reduction of secretion and bleeding tendency within the ulcer area observed in all patients. None of the patients showed any systemic or local allergic reactions.