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Results for “Signal Transduction”

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PubMed1992

Coupling of two endothelin receptor subtypes to differing signal transduction in transfected Chinese hamster ovary cells.

We examined the intracellular signal transduction of two endothelin receptor subtypes (ETA and ETB) by transfection and stable expression of individual receptor cDNAs in Chinese hamster ovary cells. Both receptors showed a rapid and marked stimulation of phosphatidylinositol hydrolysis and arachidonic acid release in response to agonist interaction. The two receptors, however, exhibited different responses in the cyclic AMP transduction cascades. ETA mediated the accumulation of cyclic AMP formation, whereas ETB displayed an inhibitory action on the forskolin-stimulated cyclic AMP accumulation. In both receptors, the responses of phosphatidylinositol hydrolysis, arachidonic acid release, and cyclic AMP formation were induced in complete agreement with the endothelin-binding selectivity of each receptor subtype. Endothelin, added together with GTP, activated the adenylate cyclase activity in membrane preparations of ETA-expressing cells, indicating the direct linkage of ETA to the adenylate cyclase system. Pertussis toxin treatment of ETA-expressing cells resulted in partial inhibition of the endothelin-induced cyclic AMP accumulation, whereas the same treatment of ETB-expressing cells completely abolished the endothelin-induced inhibition of cyclic AMP formation. Thus, the two endothelin receptor subtypes are coupled to multiple but distinct signal transduction cascades through different G proteins.

Adenylate Cyclase Toxin↗

PubMed1992

Amino acids conserved in interleukin-1 receptors (IL-1Rs) and the Drosophila toll protein are essential for IL-1R signal transduction.

The cytoplasmic domain of the human T cell-type interleukin-1 receptor (hIL-1R) is not involved in the binding, internalization, or nuclear localization of interleukin-1 (IL-1), but is essential for signal transduction. We have previously localized a 50-amino acid region (residues 477-527) critical for IL-1-mediated activation of the interleukin-2 promoter in T cells. This region displays a striking degree of amino acid conservation in human, murine, and chicken IL-1Rs. Here we report the results of a site-directed mutational analysis of the cytoplasmic domain of the hIL-1R. We have introduced single-amino acid substitutions at positions conserved in all three receptors and at nonconserved positions and identified key amino acids for IL-1R function in signal transduction. Three basic (Arg431, Lys515, and Arg518) and 3 aromatic (Phe513, Trp514, and Tyr519) amino acids that are conserved in human, murine, and chicken IL-1Rs could not be replaced without abolishing IL-1R-mediated signal transduction. A substitution at another conserved position (Pro521) reduces significantly the ability of the IL-1R to transmit the IL-1 signal. Nonconserved residues could be replaced without affecting signal transduction. The cytoplasmic domain of the IL-1R is related to that of the Drosophila Toll protein, with a 26% identity and a 43% similarity in amino acid sequence. The amino acids shown to be essential for IL-1R function are conserved in the Toll protein. Our experimental data indicate that the amino acid sequence similarity between the IL-1R and the Drosophila toll protein reflects a functional homology between the two proteins.

Amino Acid Sequence↗

PubMed1991

The carboxy-terminal catalytic domain of the GTPase-activating protein inhibits nuclear signal transduction and morphological transformation mediated by the CSF-1 receptor.

To determine whether ras p21 products are necessary for signal transduction mediated by the colony stimulating factor-1 receptor (CSF-1R, the c-fms proto-oncogene product), we determined whether CSF-1R and ras activate a common nuclear target and whether the interruption of ras action affects CSF-1R signal transduction. Expression of the NVL3 retrotransposon was activated to the same extent in NIH-3T3 cells by both ras and v-fms oncogenes, and the ras-responsive element located in the long terminal repeat of NVL3 was demonstrated to be a common target for oncogene action. Human recombinant CSF-1 stimulated expression of the NVL3 element 30-fold in NIH-3T3 cells that contained human CSF-1R. Expression of the carboxy-terminal 374 amino acid residues of the human ras GTPase-activating protein (GAP) in cells containing CSF-1R was able to inhibit CSF-1 induction of NVL3 expression by 90%. Expression of the catalytic domain of GAP was also able to suppress transformation by either v-fms or ligand-activated CSF-1R. Expression of the c-jun proto-oncogene was activated by CSF-1R but was insensitive to the action of the catalytic domain of GAP. These results provide genetic evidence that in NIH-3T3 cells, ras p21 is involved in signal transduction mediated by CSF-1R.

3T3 Cells↗

PubMed1999

[The suppression of T cell functions and its relationship with the change of signal transduction after trauma].

OBJECTIVE: To study the relationship between the suppression of T cell functions and the change of signal transduction in traumatized mice. METHODS: 60 Balb/c mice were randomized into six groups: normal control, 1st, 2nd, 4th, 7th, 10th day posttrauma (n = 10). A murine closed trauma model was used, T cells were separated from splenocytes using nylon column. T cell functions were determined and their relationship with intracellular signal transduction was investigated. RESULTS: Interleukin 2 (IL-2) mRNA and IL-2 receptor alpha (IL-2R alpha) mRNA levels were decreased in activated T cells from traumatized mice, IL-2 production, IL-2R alpha expression and T lymphocytes transformation were suppressed. cAMP contents in activated T cells were increased after trauma while cGMP contents, free calcium (Ca2+) concentration and protein kinase C (PKC) activities were decreased. These changes were closely related to the suppression of T cell functions. In addition, adenylate cyclase (AC) and protein kinase A (PKA) activities were increased while cAMP-dependent phosphodiesterase (cAMP-PDE), calmodulin (CaM), CaM-dependent protein kinase (CaM-PK) activities were decreased. Levamisole (a stimulator of cGMP), H-8 (an inhibitor of PKA), A23187 (an ionophore of Ca2+) and TPA (an activator of PKC) could in vitro elevate activated T cell functions after trauma in various degrees. CONCLUSIONS: Alteration in the pathway of signal transduction following trauma related to cyclic nucleotide and phosphatidylinositol metabolism in activated T cells participate in mediating the suppressive progress of T cell functions.

Animals↗

PubMed1992

Regulatory effect of antiphospholipid antibodies on signal transduction: a possible model for autoantibody-induced reproductive failure.

OBJECTIVES: The broad range of reproductive processes apparently affected by antiphospholipid antibodies suggests that antiphospholipid antibodies have to exert their clinical effects at every basic cellular level. Because phospholipids constitute essential components of every cell membrane, and because signal transduction processes are dependent on second messengers with phospholipid epitopes, we investigated the hypothesis that interference with signal transduction processes by antiphospholipid antibodies could represent such a basic cellular process. STUDY DESIGN: To test this hypothesis we established an in vitro placental culture system in which the stimulation of explants by phospholipase A2 and phospholipase C in the presence of normal human serum resulted in a significant increase in human chorionic gonadotropin secretion. RESULTS: When normal human sera were replaced with antiphospholipid antibody-containing sera from two women with established histories of reproductive failure, this increase in human chorionic gonadotropin production was inhibited 42% to 44% under phospholipase A2 stimulation and by 34% to 39% under phospholipase C stimulation. The hypothesis that antiphospholipid antibodies can interfere with signal transduction processes was further strengthened by the observation that antiphospholipid antibody-positive sera contained significantly higher immunoglobulin A antibody reactivity toward the second messenger inositol 1,4,5-triphosphate than control sera (p less than 0.049). CONCLUSIONS: These observations suggest the possibility that if present at excessive levels antiphospholipid antibodies may exert their adverse effect on reproductive processes through the interception of signal transduction processes.

Antibodies↗

PubMed1999

HSP27 in signal transduction and association with contractile proteins in smooth muscle cells.

Sustained smooth muscle contraction is mediated by protein kinase C (PKC) through a signal transduction cascade leading to contraction. Heat-shock protein 27 (HSP27) appears to be the link between these two major events, i.e., signal transduction and sustained smooth muscle contraction. We have investigated the involvement of HSP27 in signal transduction and HSP27 association with contractile proteins (e.g., actin, myosin, tropomyosin, and caldesmon) resulting in sustained smooth muscle contraction. We have carried out confocal microscopy to investigate the cellular reorganization and colocalization of proteins and immunoprecipitation of HSP27 with actin, myosin, tropomyosin, and caldesmon as detected by sequential immunoblotting. Our results indicate that 1) translocation of Raf-1 to the membrane when stimulated with ceramide is inhibited by vasoactive intestinal peptide (VIP), a relaxant neuropeptide; 2) PKC-alpha and mitogen-activated protein kinase translocate and colocalize on the membrane in response to ceramide, and PKC-alpha translocation is inhibited by VIP; 3) HSP27 colocalizes with actin when contraction occurs; and 4) HSP27 immunoprecipitates with actin and with the contractile proteins myosin, tropomyosin, and caldesmon. We propose a model in which HSP27 is involved in sustained smooth muscle contraction and modulates the interaction of actin, myosin, tropomyosin, and caldesmon.

Actins↗

PubMed2002

Signal transduction and endocytosis: close encounters of many kinds.

Binding of hormones, growth factors and other cell modulators to cell-surface receptors triggers a complex array of signal-transduction events. The activation of many receptors also accelerates their endocytosis. Endocytic transport is important in regulating signal transduction and in mediating the formation of specialized signalling complexes. Conversely, signal-transduction events modulate specific components of the endocytic machinery. Recent studies of protein tyrosine kinases and G-protein-coupled receptors have shed new light on the mechanisms and functional consequences of this bidirectional interplay between signalling and membrane-transport networks.

Animals↗

PubMed1997

CSF-1 signal transduction.

Colony-stimulating factor-1 (CSF-1) or macrophage-CSF (M-CSF) is a growth factor involved in the proliferation, differentiation, and activation of cells of the monocyte/macrophage lineage. Its receptor is the homodimeric, tyrosine kinase product of the c-fms proto-oncogene, which contains a so-called kinase insert domain. This review focuses mainly on recent studies of signal transduction events that are initiated on interaction of CSF-1 and its receptor. A summary is given of the tyrosine autophosphorylation sites on c-Fms identified to date, including their interaction with various substrates and their possible significance for signal transduction and cellular function. In addition, the signal transduction pathways that have been identified to lie downstream of activated c-Fms are reviewed. Although it is apparent that there have been many recent significant developments in our understanding of CSF-1 signaling, a number of examples are mentioned of significant discrepancies in the literature, some possible reasons for which can sometimes be offered. It is also apparent that any particular biochemical response or signal transduction pathway, even though widespread in other ligand receptor/cellular systems, including those with similar receptor structures to c-Fms, may not be relevant to CSF-1 signaling. The relevance of any potentially important molecular signaling pathway activated by CSF-1 in cells in vitro will ultimately have to be related to the functions of monocytes/macrophages in vivo.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Steroid-induced oocyte maturation in Atlantic croaker (Micropogonias undulatus) is dependent on activation of the phosphatidylinositol 3-kinase/Akt signal transduction pathway.

Exposure of fully grown fish and amphibian oocytes to a maturation-inducing steroid (MIS) activates numerous signal transduction pathways to initiate the final stage of oocyte maturation. These events culminate in the activation of maturation-promoting factor and germinal vesicle breakdown (GVBD). In most species, exposure to MIS causes a transient decrease in oocyte cAMP levels. Whether this reduction in oocyte cAMP concentration is sufficient to induce GVBD is unclear. The current study tested the hypothesis that activation of cAMP-independent signal transduction pathways by the naturally occurring MIS, 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S), is necessary for GVBD in Atlantic croaker (Micropogonias undulatus) oocytes. Results indicate that although 20beta-S treatment of oocyte membranes significantly reduced cAMP production, incubation of follicles with the cell-permeable cAMP-dependent protein kinase (Prka) inhibitors Rp-cAMP or KT5720 did not promote GVBD in the absence of 20beta-S. Additionally, treatment of follicles with the phosphodiesterase (Pde) inhibitors Cilostamide (Pde3) or Rolipram (Pde4) significantly reduced GVBD, but they were not able to completely block it. In contrast, pharmacologic inhibition of the cAMP-independent phosphatidylinositol 3-kinase (Pik3)/Akt signal transduction pathway using the Pik3 inhibitors Wortmannin or LY294002, or the Akt inhibitor ML-9, blocked 20beta-S-induced GVBD. Finally, mitogen-activated protein kinase (Mapk1/3) activity increased after treatment with 20beta-S; however, inhibition of Mapk1/3 activity using PD98059 or U0126 had no effect on GVBD. These results demonstrate that activation of cAMP-independent signaling pathways, especially the Pik3/Akt pathway, is necessary for 20beta-S-induced GVBD in Atlantic croaker oocytes.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1998

Osteoblasts induce osteopontin expression in response to attachment on fibronectin: demonstration of a common role for integrin receptors in the signal transduction processes of cell attachment and mechanical stimulation.

Osteopontin is a predominant integrin binding protein of bone and its expression has been shown to be induced by mechanical stimuli within osteoblasts (Toma et al. [1997] J. Bone Miner. Res. 12:1626-1636). The present studies examined if the cell adhesion would mimic the mechano-transduction that stimulated opn mRNA expression and whether integrin receptors were involved in these processes. Osteopontin mRNA expression was induced three- to four-fold, 24 hours after embryonic chicken calvaria osteoblast attachment to fibronectin (FN), however no induction was observed if the cells were plated on tissue culture plastic alone. Osteopontin mRNA induction in response to cell attachment on FN was dependent on new protein synthesis and the activation of a tyrosine protein kinase(s) but unlike mechano-induction was independent of the maintenance of the cell's microfilament structure. Integrin receptor(s) were shown to be involved in mediating the signal transduction processes of both cell attachment and mechanical stimulation since incubation of osteoblasts with the integrin binding peptide RGDS partially blocked the induction of opn expression in response to both stimuli. Interestingly, incubation of the osteoblasts that were adherent on tissue culture plastic alone with the RGDS peptide lead to an induction in opn expression suggesting that integrin occupancy by itself was sufficient to initiate the signal transduction process that induced opn expression. In order to assess the role of integrin occupancy vs. focal adhesion complex formation that accompanies cell attachment, in the signal transduction process that induces opn expression, receptor clustering was stimulated pharmacologically with bombesin or lysophosphatidic acid in osteoblasts attached to tissue culture plastic. Neither compound in the absence of occupancy of the integrin receptors was capable of stimulating opn expression in attached cells, however if the cells were placed in suspension pharmacological mediation of receptor clustering and integrin occupancy were additive in their effect of inducing opn expression. These data demonstrate that induction of opn expression by mechanical stimuli and cell attachment are commonly mediated through integrin receptor(s). However, when cells are attached receptor clustering alone which accompanies focal adhesion formation was incapable of mediating signal transduction suggesting that receptor occupancy was a prerequisite to the signal transduction process that leads to the induction of opn mRNA expression.

Animals↗

PubMed2001

Selective pharmacological inhibitors reveal differences between Thy-1- and T cell receptor-mediated signal transduction in mouse T lymphocytes.

A compelling body of evidence suggests a role for Thy-1 (CD90), a cell surface glycoprotein of mouse T lymphocytes, in signal transduction resulting in T cell activation. Despite more than 3 decades of investigation, intracellular biochemical events governing the Thy-1 signaling cascade are only vaguely understood. We have employed selective pharmacological inhibitors of signaling molecules to compare downstream elements participating in the Thy-1 signal transduction pathway with those involved in the T cell receptor (TCR)/CD3-associated signaling pathway. Mitogenic anti-Thy-1 or anti-CD3 monoclonal antibody (mAb) were used to cause T cells from C57BL/6 mice to proliferate in the presence or absence of different pharmacological inhibitors. Cyclosporine A, herbimycin A, LY294002, calphostin C and PD98059 all inhibited anti-Thy-1-induced T lymphocyte proliferation, indicating the involvement of calcineurin, protein tyrosine kinases, phosphatidylinositol 3-kinase, protein kinase C, and MEK1 (MAPK kinase 1), respectively, in Thy-1 signaling. Similar results were obtained when T cells were stimulated through the TCR with anti-CD3 monoclonal antibody in the presence or absence of the different inhibitors. Interestingly, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 augmented anti-Thy-1-induced T cell proliferation, whereas anti-CD3-induced proliferative response was partially suppressed by the same inhibitor. The Thy-1 signal transduction pathway, therefore, shares a requirement for calcineurin and several major kinase families with the TCR signaling pathway. However, Thy-1 and TCR-associated signaling pathways are differentially regulated by p38 MAPK.

Animals↗

PubMed2002

Arachidonic acid plays a role in rat vomeronasal signal transduction.

Sensory neurons of the vomeronasal organ (VNO) detect volatile chemicals that are released by conspecific animals and convey information about social and reproductive behavior. The signal transduction pathway in vomeronasal receptor neurons (VRNs) is not known in detail, but is believed to be distinct from that of the sensory neurons of the main olfactory system. Many of the identified olfactory transduction components are not expressed by VRNs. Using Ca2+ imaging and electrophysiological recordings, we investigated the signal transduction pathway of urine perception and the possible role of polyunsaturated fatty acids (PUFAs) as intracellular messengers in freshly dissociated rat VNO neurons. We found that application of urine induced a transient increase in intracellular Ca2+ that was dependent on the activity of phospholipase C and diacylglycerol (DAG) lipase. The Ca2+ transient was not dependent on depletion of intracellular Ca2+ stores but was dependent on the presence of extracellular Ca2+. Furthermore, the urine response was not sensitive to modulators of adenylate cyclase and inhibitors of inositol 1,4,5-trisphosphate receptors. Application of PUFAs (linolenic acid and arachidonic acid, synthesized in living cells from DAG) also elicited Ca2+ transients in fura 2 measurements and inward currents in whole-cell voltage-clamp recordings. Pharmacological inhibition of lipoxygenase and cyclooxygenase induced a transient increase in intracellular Ca2+, possibly by increasing the endogenous level of PUFAs, leading to activation of transduction channels. These data provide evidence for a role of PUFAs in rat vomeronasal signal transduction.

Adenylyl Cyclase Inhibitors↗

PubMed2004

The ColR-ColS two-component signal transduction system is involved in regulation of Tn4652 transposition in Pseudomonas putida under starvation conditions.

Bacteria use two-component signal transduction pathways to sense both extracellular and intracellular environment and to coordinate cellular events according to changing conditions. Adaptation can be either physiological or genetical. Here, we present evidence that a genome reorganization process such as transposition can be controlled by certain environmental cues sensed by a two-component signal transduction system. We demonstrate that transposition-dependent accumulation of phenol-utilizing mutants is severely decreased in Pseudomonas putida defective in a two-component system colRS. Translocation of Tn4652 is decreased both in colR- and colS-defective strains, indicating that signal transduction from a histidine kinase ColS to a response regulator ColR is necessary for the activation of Tn4652 in bacteria starving on phenol. However, overexpression of ColR in a colS-defective strain restores Tn4652 transposition, suggesting that absence of the signal from ColS can be compensated by an elevated amount of ColR. In vitro analysis of purified ColR and ColS proteins evidenced that they constitute a functional phosphorelay. Site-directed mutagenesis revealed that a conserved H221 can be the phosphoryl-accepting residue in ColS and that aspartate residues D8 and D51 of ColR are necessary for the phosphotransfer from ColS to ColR. To our knowledge, Tn4652 is the first bacterial transposon regulated by a two-component system. This finding indicates that transpositional activity can respond to signals sensed and processed by the host.

Adaptation, Physiological↗

PubMed2001

Sugar coordinately and differentially regulates growth- and stress-related gene expression via a complex signal transduction network and multiple control mechanisms.

In plants, sugars are required to sustain growth and regulate gene expression. A large set of genes are either up- or down-regulated by sugars; however, whether there is a common mechanism and signal transduction pathway for differential and coordinated sugar regulation remain unclear. In the present study, the rice (Oryza sativa cv Tainan 5) cell culture was used as a model system to address this question. Sucrose and glucose both played dual functions in gene regulation as exemplified by the up-regulation of growth-related genes and down-regulation of stress-related genes. Sugar coordinately but differentially activated or repressed gene expression, and nuclear run-on transcription and mRNA half-life analyses revealed regulation of both the transcription rate and mRNA stability. Although coordinately regulated by sugars, these growth- and stress-related genes were up-regulated or down-regulated through hexokinase-dependent and/or hexokinase-independent pathways. We also found that the sugar signal transduction pathway may overlap the glycolytic pathway for gene repression. alpha-Amylase and the stress-related genes identified in this study were coordinately expressed under sugar starvation, suggesting a convergence of the nutritional and environmental stress signal transduction pathways. Together, our studies provide a new insight into the complex signal transduction network and mechanisms of sugar regulation of growth and stress-related genes in plants.

DNA, Complementary↗

PubMed2005

Role of signal transduction and actin in G1 phase progression.

Progression through the cell cycle of mammalian cells is dependent upon external factors such as growth- and ECM factors. These factors exert their effect predominantly during the G1 phase of the cell cycle. When cells are cultured in suspension or when growth factors are withdrawn from the medium, cells will stop cell cycle progression and enter a quiescent state. Cells will remain in this quiescent state until extracellular conditions change and cells are stimulated to re-enter the cell cycle. This stimulation is mediated by various signal transduction cascades such as the mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol 3-kinase (PI3-kinase) pathway. In Chinese hamster ovary cells at least two serum-dependent points exist during G1 phase that lead to diffent cellular responses. The first point is located immediately after mitosis and is suggested to link with apoptosis. The second point is located in late G1 phase and probably corresponds with cellular differentiation. Signal transduction is mutually related to the cytoskeleton, especially the actin microfilament system. The actin microfilament system influences signal transduction and several signal transduction pathways influence the actin structure. Here we describe the role of the MAPK and PI3-kinase activities and of actin microfilaments in progression through the cell cycle and their role in the two G1 checkpoints.

Actins↗

PubMed1999

Signal transduction pathways associated with alpha1-adrenoceptor subtypes in cells and tissues including human prostate.

The complexity of the signal transduction pathways linked to alpha1A-adrenoceptors are becoming clearer. At one time it was thought that the alpha1A-subtype was linked to the influx of extracellular Ca2+ while the alpha1B-subtype was linked via inositol phosphate formation to the release of intracellular Ca2. However the coupling of the alpha1-adrenoceptors to G-proteins leads to the activation of a number of different effector enzymes which produce intracellular second messengers and alterations in biological activity. One area of diversity is in the many forms of the Galpha, beta, gamma heterotrimeric G-proteins which confer specificity towards certain effectors. All alpha1-adrenoceptor subtypes have been shown to couple to phospholipase C in many cells and tissues leading to the breakdown of PiP2 to give IP3, which releases intracellular Ca2+, and diacylglycerol, which stimulates protein kinase C. Additional effectors which can couple to alpha1-adrenoceptors include phospholipase D, adenylate cyclase and the mitogen-activated protein kinase pathway. The latter involves a longer term response and causes increased cell growth and may be important in, for example, the prostate as well as in vascular smooth muscle and the heart. In human prostate alpha1-adrenoceptor activation leads to the release of intracellular Ca2+ from ryanodine-sensitive store followed by an influx of extracellular Ca2+, a mechanism different from that linked to the same receptor subtype in several other smooth muscles. Therefore a given alpha1-subtype may be coupled to a variety of different signal transduction mechanisms in different systems. Further, there may be different effector mechanisms linked to alpha1-subtypes in a given cell or tissue e.g. phospholipase C and mitogen-activated protein kinase. An increased understanding of the complexity of signal transduction mechanisms and the elucidation of the details in a particular tissue will open up new possibilities for therapeutic interventions.

Animals↗

PubMed1990

Human monocytes CD36 and CD16 are signaling molecules. Evidence from studies using antibody-induced chemiluminescence as a tool to probe signal transduction.

A panel of monoclonal antibodies (mAb) directed against human monocyte surface antigens was tested for their capacity to mediate signal transduction by measuring luminol-enhanced chemiluminescence (CL). The response patterns fell into three categories. The mAb Mo4, OKM3, OKM6 and antibodies specific for Fc receptor (FcR) type I and II did not mediate signal transduction directly or were weak triggers, but upon second-order cross-linking by goat anti-mouse immunoglobulin (Ig) F(ab')2 or rabbit anti-mouse Ig, a strong CL response was induced. The mAb recognizing different epitopes on CD11b (complement receptor type III alpha chain) were unique in their ability to induce a CL response either by direct stimulation or by second-order cross-linking. The mAb 3G8 recognizing FcR type III (FcRIII; CD16) on a monocyte subpopulation and CD36-specific monoclonals directly elicited a CL response. A response of similar magnitude was obtained with 3G8 F(ab')2 or with intact 3G8. Furthermore, elutriation-centrifugation-purified monocytes were stimulated by 3G8 to a similar extent as unseparated mononuclear cells, whereas lymphocytes did not respond. This suggests that a FcRIII-expressing monocyte subpopulation may mediate effector functions, including the generation of reactive oxygen species, via FcRIII triggering. Our finding that anti-CD36 F(ab')2 directly induces an oxidative burst is the first evidence that CD36 itself is a trigger molecule. CD36, which is thought to interact with erythrocytes infected with Plasmodium falciparum and with thrombospondin, may constitute a signal-transducing element and thus may have functions extending beyond mediation of adherence. The present CL system constitutes a simple assay for detecting mAb directed against monocyte surface signalling elements. Probing mAb for signal transduction requires suspended cells and antibodies in the fluid phase in order to avoid inadvertent FcR triggering, which may occur when cells are stimulated by surface-adherent whole antibodies.

Antibodies, Monoclonal↗

PubMed1994

Growth factor-induced binding of dynamin to signal transduction proteins involves sorting to distinct and separate proline-rich dynamin sequences.

Dynamin, a 100 kDa GTPase, is critical for endocytosis, synaptic transmission and neurogenesis. Endocytosis accompanies receptor processing and plays an essential role in attenuating receptor tyrosine kinase signal transduction. Dynamin has been demonstrated to be involved in the endocytic processing at the cell surface and may play a general role in coupling receptor activation to endocytosis. Src homology (SH) domain dependent protein-protein interactions are important to tyrosine kinase receptor signal transduction. The C-terminus of dynamin contains two clusters of SH3 domain binding proline motifs; these motifs may interact with known SH3 domain proteins during tyrosine kinase receptor activation. We demonstrate here that SH3 domain-containing signal transduction proteins, such as phospholipase C gamma-1 (PLC gamma-1), do indeed bind to dynamin in a growth factor inducible manner. The induction of PLC gamma-1 binding to dynamin occurs within minutes of the addition of platelet derived growth factor (PDGF) to cells. Binding of these signal transduction proteins to dynamin involves specific sorting to individual proline motif clusters and appears to be responsible for co-immunoprecipitation of tyrosine phosphorylated PDGF receptors with dynamin following PDGF stimulation of mammalian cells. The binding of dynamin to SH3 domain-containing proteins may therefore be important for formation of the protein complex required for the endocytic processing of activated tyrosine kinase receptors.

3T3 Cells↗