Showing papers on "Signal transduction published in 1993"

Programmed cell death induced by ceramide

Abstract: Sphingomyelin hydrolysis and ceramide generation have been implicated in a signal transduction pathway that mediates the effects of tumor necrosis factor-alpha (TNF-alpha) and other agents on cell growth and differentiation In many leukemic cells, TNF-alpha causes DNA fragmentation, which leads to programmed cell death (apoptosis) C2-ceramide (06 to 5 microM), a synthetic cell-permeable ceramide analog, induced internucleosomal DNA fragmentation, which was inhibited by zinc ion Other amphiphilic lipids failed to induce apoptosis The closely related C2-dihydroceramide was also ineffective, which suggests a critical role for the sphingolipid double bond The effects of C2-ceramide on DNA fragmentation were prevented by the protein kinase C activator phorbol 12-myristate 13-acetate, which suggests the existence of two opposing intracellular pathways in the regulation of apoptosis

Signal transduction from the extracellular matrix.

Abstract: Adhesive interactions between cells and the insoluble meshwork of extracellular matrix proteins play a vital role in embryonic morphogenesis (33, 36, 94, 109, 135, 145), and in the regulation of gene expression in cells of the adult organism (1, 6, 105, 124). While the overall phenomenology ofextracellular matrix (ECM) 1 effects on cell differentiation is well known, the biochemical and molecular bases for these effects have remained elusive. It is clear that many of the interactions between cells and the ECM are mediated by the integrin family of cell surface receptors (2, 3, 13, 72). However, the precise mechanism(s) whereby signals from ECM proteins are transduced via integfins to the intraceUular machinery that controls cell growth, behavior, and differentiation, remains poorly defined. There are many compelling examples of control of cell differentiation and gene expression through adhesive interactions with extracellular matrix. In fibroblasts, cell attachment has been reported to rapidly increase expression of c-los and pro al(I) collagen messages (26, 27). Adhesion to fibronectin fragments, or cross-linking of the integfin oe5/~l fibronectin receptor with antibody, induced the expression of metalloprotease genes in fibroblastic cells; interestingly, intact fibronectin did not provoke this response nor did fibronectin fragments in solution (137). In a somewhat similar vein, stimulation of the C~v//~3 integrin in melanoma cells induced the expression of type IV collagenase and increased the invasive ability of these cells (115). The capacity of breast epithelial cells to express milk proteins in response to hormonal stimuli is quite dependent on the presence of an appropriate ECM (124). Studies in this system have led to the preliminary identification of matrix-dependent elements in the promoter region of the ~ casein gene (111). In the immune system, activation of T-lymphocytes through the T-cell antigen receptor is markedly enhanced by integrin-mediated adhesion to fibronectin or laminin (85, 97, 119). This process is part of a complex dialogue involving adhesive receptors occurring between mature T-cells and antigen presenting cells, as well as during lymphocyte differentiation (40, 132, 133). There is extensive signaling \"cross talk\" between

Tumor Cell Interactions with the Extracellular Matrix During Invasion and Metastasis

Abstract: Recent findings have produced great strides in developing an understanding of the molecular events involved in processes necessary for tumor cell invasion and subsequent metastasis formation. This information has been useful in developing new targets for therapeutic intervention such as disruption of tumor cell attachment by peptide analogues of cell adhesion molecules and the use of protease inhibitors to limit extracellular matrix proteolysis required for tumor cell invasion. Future efforts must focus on how the events of cell attachment, matrix proteolysis, and cell migration are controlled and integrated. This requires a better understanding of the transcriptional controls and cell signaling mechanisms that are involved in these events. Preliminary findings suggest that cell-matrix interactions influence gene expression and that the protease inhibitor balance can greatly influence cell-matrix interactions. Therefore it appears that all three steps in the invasive process are linked and interdependent. While this complicates the study of these processes, it is our belief that understanding this interdependence is critical for further development of metastasis research.

Mice lacking the tumour necrosis factor receptor 1 are resistant to TNF-mediated toxicity but highly susceptible to infection by Listeria monocytogenes

Abstract: Tumour necrosis factor (TNF), jointly referring to TNF alpha and TNF beta, is a central mediator of immune and inflammatory responses; its activities are mediated by two distinct receptors, TNFR1 (p55) and TNFR2 (p75) (reviewed in refs 1-3). The cytoplasmic domains of the TNFRs are unrelated, suggesting that they link to different intracellular signalling pathways. Although most TNF responses have been assigned to one or the other of the TNF receptors (mostly TNFR1), there is no generally accepted model for the physiological role of the two receptor types. To investigate the role of TNFR1 in beneficial and detrimental activities of TNF, we generated TNFR1-deficient mice by gene targeting. We report here that mice homozygous for a disrupted Tnfr1 allele (Tnfr1(0)) are resistant to the lethal effect of low doses of lipopolysaccharide after sensitization with D-galactosamine, but remain sensitive to high doses of lipopolysaccharide. The increased susceptibility of Tnfr1(0)/Tnfr1(0) mutant mice to infection with the facultative intracellular bacterium Listeria monocytogenes indicates an essential role of TNF in nonspecific immunity.

Signal transduction via P2-purinergic receptors for extracellular ATP and other nucleotides

Abstract: Extracellular ATP, at micromolar concentrations, induces significant functional changes in a wide variety of cells and tissues. ATP can be released from the cytosol of damaged cells or from exocytotic vesicles and/or granules contained in many types of secretory cells. There are also efficient extracellular mechanisms for the rapid metabolism of released nucleotides by ecto-ATPases and 5'-nucleotidases. The diverse biological responses to ATP are mediated by a variety of cell surface receptors that are activated when ATP or other nucleotides are bound. The functionally identified nucleotide or P2-purinergic receptors include 1) ATP receptors that stimulate G protein-coupled effector enzymes and signaling cascades, including inositol phospholipid hydrolysis and the mobilization of intracellular Ca2+ stores; 2) ATP receptors that directly activate ligand-gated cation channels in the plasma membranes of many excitable cell types; 3) ATP receptors that, via the rapid induction of surface membrane channels and/or pores permeable to ions and endogenous metabolites, produce cytotoxic or activation responses in macrophages and other immune effector cells; and 4) ADP receptors that trigger rapid ion fluxes and aggregation responses in platelets. Current research in this area is directed toward the identification and structural characterization of these receptors by biochemical and molecular biological approaches.

Regulation of development and differentiation by the extracellular matrix

Abstract: Differentiation is a continuously regulated process and interactions between the cell and its environment play a major role in maintaining stable expression of differentiation specific genes (Blau and Baltimore, 1991). An important component of the cellular environment is the extracel-lular matrix (ECM), which is composed of glycoproteins, proteoglycans and glycosaminoglycans that are secreted and assembled locally into an organised network to which cells adhere (Hay, 1981). An ECM is present within mam-malian embryos from the two-cell stage and is a component of the environment of all cell types, although the composition of the ECM and the spatial relationships between cells and ECM differ between tissues. Cells may be completely surrounded by ECM, as is the case for chondrocytes, or may contact the ECM only at one surface, as exemplified by epithelial and endothelial cells. In some tissues only a proportion of the cells are exposed to ECM: for example , in stratified epithelia. The ECM offers structural support for cells, and can also act as a physical barrier or selective filter to soluble molecules. It has been clear for many years (Grobstein, 1954; Bis-sell et al., 1982) that the ECM plays a role in regulating the differentiated phenotype of cells (reviewed by Watt, 1986), but the mechanisms involved remained largely mysterious until recently, when cell-binding sites within individual ECM glycoproteins and specific ECM receptors were identified. The cell-binding sites were mapped by using pro-teolytic fragments and synthetic peptides to define the minimal sequences responsible for adhesive activity. In the case of fibronectin, the primary determinant of cell-binding activity for many cell types resides in the sequence GRGDSP, which occurs in one of the type III repeats that form the central domain of the molecule (Ruoslahti and Pierschbacher, 1987). Subsequently, RGD-containing sequences have been found in other matrix proteins, and additional short linear adhesive sequence motifs have been defined, although it is clear that the three-dimensional structure of matrix proteins is also an important determinant of adhesive activity (reviewed by Humphries, 1990). Affinity chromatography techniques, together with adhesion-perturbing antibodies that recognise specific plasma membrane glycoproteins, allowed the identification of ECM receptors, many of which belong to the integrin family of α/β het-erodimers (Ruoslahti and Pierschbacher, 1987; Hynes, 1987). In this review, we will summarise some of the evidence that ECM components regulate differentiation and development , describe the regulatory mechanisms involved and, finally, discuss the intracellular events that may transduce signals …

Protein kinase C isoenzymes: divergence in signal transduction?

Abstract: The development and life-time of multicellular eukaryotic organisms represents a complex interplay of numerous proliferation and differentiation events that proceed in a highly ordered manner. As a prerequisite for those events, cells must respond to extracellular signals with a specific set of mechanisms that regulate or modulate gene expression. Between the signal and the gene, a system of rather different cellular components is assembled to guarantee a specific and successful process of signal transduction. Pathways of signal transduction, though differing remarkably in their complexity and in the use of cellular components, seem to obey certain principles which are evolutionarily conserved and ubiquitously distributed amongst living organisms. Extracellular signals, so-called ligands, either penetrate the cellular membrane or bind to the extracellular domain of receptors. Activated receptors as such, or in association with socalled transducers, are capable of activating effectors-either directly or by means of changing the amount or intracellular distribution of so-called second messengers. These second

Signal transduction via the MAP kinases: proceed at your own RSK.

Abstract: An explosion of new information linking activation of cell surface signal initiators to changes in gene expression has recently emerged. The focus of much of this information has centered around the agonist-dependent activation of the mitogen-activated protein (MAP) kinases. Although this intracellular signal transduction pathway is extremely complex, conservation of many of its components has been observed in yeast, nematodes, Drosophila, and mammals. Thus, these signaling proteins may participate in the regulation of a variety of cellular processes.

Differential signal transduction by five splice variants of the PACAP receptor

Abstract: The two forms of pituitary adenylyl cyclase-activating polypeptide (PACAP-27 and -38) are neuropeptides of the secretin/glucagon/vasoactive intestinal polypeptide/growth-hormone-releasing hormone family and regulate hormone release from the pituitary and adrenal gland. They may also be involved in spermatogenesis, and PACAP-38 potently stimulates neuritogenesis and survival of cultured rat sympathetic neuroblast and promotes neurite outgrowth of PC-12 cells. The PACAP type-I receptor (found in hypothalamus, brain stem, pituitary, adrenal gland and testes), specific for PACAP, is positively coupled to adenylyl cyclase and phospholipase C. The recently cloned type II receptor does not discriminate between PACAP and vasoactive intestinal polypeptide and is coupled to only adenylyl cyclase. Here we have used a new expression cloning strategy, based on the induction of a reporter gene by cyclic AMP, to isolate a complementary DNA encoding the type-I PACAP receptor. On transfection of this cDNA, both PACAP-27 and -38 stimulate adenylyl cyclase with similar EC50 values (50% effective concentration, 0.1-0.4 nM), whereas only PACAP-38 stimulates phospholipase C with high potency (EC50 = 15 nM). Four other splice variants were isolated with insertions at the C-terminal end of the third intracellular loop. Expression of these cDNAs revealed altered patterns of adenylyl cyclase and phospholipase C stimulation, suggesting a novel mechanism for fine tuning of signal transduction.

Regulation of gene expression in hippocampal neurons by distinct calcium signaling pathways

Abstract: Calcium ions (Ca2+) act as an intracellular second messenger and can enter neurons through various ion channels. Influx of Ca2+ through distinct types of Ca2+ channels may differentially activate biochemical processes. N-Methyl-D-aspartate (NMDA) receptors and L-type Ca2+ channels, two major sites of Ca2+ entry into hippocampal neurons, were found to transmit signals to the nucleus and regulated gene transcription through two distinct Ca2+ signaling pathways. Activation of the multifunctional Ca(2+)-calmodulin-dependent protein kinase (CaM kinase) was evoked by stimulation of either NMDA receptors or L-type Ca2+ channels; however, activation of CaM kinase appeared to be critical only for propagating the L-type Ca2+ channel signal to the nucleus. Also, the NMDA receptor and L-type Ca2+ channel pathways activated transcription by means of different cis-acting regulatory elements in the c-fos promoter. These results indicate that Ca2+, depending on its mode of entry into neurons, can activate two distinct signaling pathways. Differential signal processing may provide a mechanism by which Ca2+ controls diverse cellular functions.

The SH2 and SH3 domains of mammalian Grb2 couple the EGF receptor to the Ras activator mSos1

Abstract: Many tyrosine kinases, including the receptors for hormones such as epidermal growth factor (EGF), nerve growth factor and insulin, transmit intracellular signals through Ras proteins. Ligand binding to such receptors stimulates Ras guanine-nucleotide-exchange activity and increases the level of GTP-bound Ras, suggesting that these tyrosine kinases may activate a guanine-nucleotide releasing protein (GNRP). In Caenorhabditis elegans and Drosophila, genetic studies have shown that Ras activation by tyrosine kinases requires the protein Sem-5/drk, which contains a single Src-homology (SH) 2 domain and two flanking SH3 domains. Sem-5 is homologous to the mammalian protein Grb2, which binds the autophosphorylated EGF receptor and other phosphotyrosine-containing proteins such as Shc through its SH2 domain. Here we show that in rodent fibroblasts, the SH3 domains of Grb2 are bound to the proline-rich carboxy-terminal tail of mSos1, a protein homologous to Drosophila Sos. Sos is required for Ras signalling and contains a central domain related to known Ras-GNRPs. EGF stimulation induces binding of the Grb2-mSos1 complex to the autophosphorylated EGF receptor, and mSos1 phosphorylation. Grb2 therefore appears to link tyrosine kinases to a Ras-GNRP in mammalian cells.

Inhibition by cAMP of Ras-dependent activation of Raf

Abstract: Activation of the Raf and extracellular signal-regulated kinases (ERKs) (or mitogen-activated protein kinases) are key events in mitogenic signalling, but little is known about interactions with other signaling pathways. Agents that raise levels of intracellular cyclic adenosine 3',5'-monophosphate (cAMP) blocked DNA synthesis and signal transduction in Rat1 cells exposed to epidermal growth factor (EGF) or lysophosphatidic acid. In the case of EGF, receptor tyrosine kinase activity and association with the signaling molecules Grb2 and Shc were unaffected by cAMP. Likewise, EGF-dependent accumulation of the guanosine 5'-triphosphate-bound form of Ras was unaffected. In contrast, activation of Raf-1 and ERK kinases was inhibited. Thus, cAMP appears to inhibit signal transmission from Ras by preventing Ras-dependent activation of Raf-1.

Inhibition of the EGF-activated MAP kinase signaling pathway by adenosine 3',5'-monophosphate

Abstract: Mitogen-activated protein (MAP) kinases p42mapk and p44mapk are activated in cells stimulated with epidermal growth factor (EGF) and other agents. A principal pathway for MAP kinase (MAPK) activation by EGF consists of sequential activations of the guanine nucleotide exchange factor Sos, the guanosine triphosphate binding protein Ras, and the protein kinases Raf-1, MAPK kinase (MKK), and MAPK. Because adenosine 3',5'-monophosphate (cAMP) does not activate MAPK and has some opposing physiologic effects, the effect of increasing intracellular concentrations of cAMP with forskolin and 3-isobutyl-1-methylxanthine on the EGF-stimulated MAPK pathway was studied. Increased concentrations of cAMP blocked activation of Raf-1, MKK, and MAPK in Rat1hER fibroblasts, accompanied by a threefold increase in Raf-1 phosphorylation on serine 43 in the regulatory domain. Phosphorylation of Raf-1 in vitro and in vivo reduces the apparent affinity with which it binds to Ras and may contribute to the blockade by cAMP.

Sphingosine-1-phosphate as second messenger in cell proliferation induced by PDGF and FCS mitogens.

Abstract: GROWTH signalling networks that use glycerophospholipid metabolites as second messengers have been well characterized1,2, but less is known of the second messengers derived from sphingolipids3,4, another major class of membrane lipids. A tantalizing link between sphingolipids and cellular proliferation has emerged from the discovery that the sphingolipid metabolites sphingosine and sphingosine-1-phosphate stimulate growth of quiescent Swiss 3T3 fibroblasts by a pathway that is independent of protein kinase C5,6. Sphingosine-1-phosphate is rapidly produced from sphingosine and may mediate its biological effects6. Furthermore, sphingosine-1-phosphate triggers the dual signal transduction pathways of calcium mobilization6,7 and activation of phospholipase D8, prominent events in the control of cellular proliferation. Here we report that activation of sphingosine kinase and the formation of sphingosine-1-phosphate are important in the signal transduction pathways activated by the potent mitogens platelet-derived growth factor (PDGF) and fetal calf serum (FCS).

Normal and oncogenic p21ras proteins bind to the amino-terminal regulatory domain of c-Raf-1.

Abstract: In higher eukaryotes, the Ras and Raf-1 proto-oncoproteins transduce growth and differentiation signals initiated by tyrosine kinases. The Ras polypeptide and the amino-terminal regulatory domain of Raf-1(residues 1–257) are shown to interact, directly in vitro and in a yeast expression system. Raf-1(1-257) binds GTP-Ras in preference to GDP-Ras, and inhibits Ras-GAP activity. Mutations in and around the Ras effector domain impair Ras binding to Raf-1(1-257) and Ras transforming activity in parallel.

Controlling signal transduction with synthetic ligands

Abstract: Dimerization and oligomerization are general biological control mechanisms contributing to the activation of cell membrane receptors, transcription factors, vesicle fusion proteins, and other classes of intra- and extracellular proteins. Cell permeable, synthetic ligands were devised that can be used to control the intracellular oligomerization of specific proteins. To demonstrate their utility, these ligands were used to induce intracellular oligomerization of cell surface receptors that lacked their transmembrane and extracellular regions but contained intracellular signaling domains. Addition of these ligands to cells in culture resulted in signal transmission and specific target gene activation. Monomeric forms of the ligands blocked the pathway. This method of ligand-regulated activation and termination of signaling pathways has the potential to be applied wherever precise control of a signal transduction pathway is desired.

Intercellular signalling in Vibrio harveyi: sequence and function of genes regulating expression of luminescence

Abstract: Summary Density-dependent expression of luminescence in Vibrio harveyi is regulated by the concentration of an extracellular signal molecule (autoinducer) in the culture medium. A recombinant clone that restored function to one class of spontaneous dim mutants was found to encode functions necessary for the synthesis of, and response to, a signal molecule. Sequence analysis of the region encoding these functions revealed three open reading frames, two (luxL and luxM) that are required for production of an autoinducer substance and a third (luxN) that is required for response to this signal substance. The LuxL and LuxM proteins are not similar in amino acid sequence to other proteins in the database, but the LuxN protein contains regions of sequence resembling both the histidine protein kinase and the response regulator domains of the family of two–component, signal transduction proteins. The phenotypes of mutants with luxL, luxM and luxN defects indicated that an additional signal–response system controlling density-dependent expression of luminescence remains to be identified.

Sharing of the interleukin-2 (IL-2) receptor gamma chain between receptors for IL-2 and IL-4.

Abstract: The gamma chain of the interleukin-2 (IL-2) receptor is an indispensable subunit for IL-2 binding and intracellular signal transduction. A monoclonal antibody to the gamma chain, TUGm2, inhibited IL-2 binding to the functional IL-2 receptors and also inhibited IL-4-induced cell growth and the high-affinity binding of IL-4 to the CTLL-2 mouse T cell line. Another monoclonal antibody, TUGm3, which reacted with the gamma chain cross-linked with IL-2, also immunoprecipitated the gamma chain when cross-linked with IL-4. These results suggest that the IL-2 receptor gamma chain is functionally involved in the IL-4 receptor complex.

The protein tyrosine kinase JAK1 complements defects in interferon-α/β and -γ signal transduction

Abstract: We have produced a cell line which lacks the protein tyrosine kinase JAK1 and is completely defective in interferon response. Complementation of this mutant with JAK1 restored the response, establishing the requirement for JAK1 in both the interferon-α/β and -γ signal transduction pathways. The reciprocal interdependence between JAK1 and Tyk2 activities in the interferon-α pathway, and between JAK1 and JAK2 in the interferon-γ pathway, may reflect a requirement for these kinases in the correct assembly of interferon receptor complexes.

The Biochemistry and the Physiological and Molecular Actions of Jasmonates

Abstract: INTRODUCTION 569 BIOCHEMISTRY OF JASMONATES 570 Biosynthesis .. ....... 570 Metabolism 571 Occurrence 573 JASMONA TE ACTIONS AT PHYSIOLOGICAL LEVEL 575 JASMONATE ACTIONS AT CELLULAR AND MOLECULAR LEVELS ........ 577 Induction of Specific Proteins and mKNAs by Jasmonates .. .... 579 Gene Structures and Regulation of Gene Expression ......... ....... ... 582 Putative Position of Jasmonates in the Stress Signal Transduction Chain........ 584