Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To define the molecular basis of human chemoattractant receptor regulation, rat basophilic leukemia RBL-2H3 cells, which are thrombin-responsive, were transfected to stably express epitope-tagged receptors for C5a, interleukin-8 (IL-8), formylpeptides (e.g. N-formyl-methionyl-leucyl-phenylalanine (fMLP)), and platelet-activating factor (PAF). Here we demonstrate that both thrombin and a synthetic peptide ligand for the thrombin receptor (sequence SFLLRN) caused phosphorylation and heterologous desensitization of the receptors for C5a, IL-8, and PAF but not that for formylpeptides as measured by agonist-stimulated [35S]guanosine 5'-3-O-(thio)triphosphate binding to membranes. Consistent with the PAF receptor phosphorylation, both thrombin and thrombin receptor peptide inhibited phosphoinositide hydrolysis, Ca2+ mobilization, and degranulation stimulated by PAF. Unexpectedly, despite heterologous desensitization at the level of receptor/G protein activation, there was enhancement ("priming") by thrombin of subsequent activities stimulated by C5a and IL-8 as well as fMLP. The priming effect of thrombin was blocked by its inhibitor, hirudin. However, two other activators of the thrombin receptor, the peptide SFLLRN and trypsin, stimulated Ca2+ mobilization in RBL-2H3 cells but did not cause priming. In addition, SFLLRN and the thrombin receptor antagonist peptide FLLRN both inhibited thrombin-induced Ca2+ mobilization but not priming. Furthermore, the proteolytically active gamma-thrombin, which does not stimulate the tethered ligand thrombin receptor and caused little or no Ca2+ mobilization in RBL-2H3 cells, effectively primed the response to fMLP. These data demonstrate that heterologous receptor phosphorylation and attenuation of G protein activation are not, by themselves, sufficient for the inhibition of biological responses mediated by C5a and IL-8. Moreover, thrombin appears to utilize mechanism(s) independent of its tethered ligand receptor to selectively prime phospholipase C-mediated biological responses of the C5a, IL-8, and formylpeptide receptors but not PAF. Because C5a, IL-8, and formylpeptide activate phospholipase Cbeta2, whereas PAF stimulates a different phospholipase C, the striking selectivity of thrombin's priming may be mediated via its ability to enhance receptor-mediated activation of phospholipase Cbeta2.
 ...
PMID:Thrombin primes responsiveness of selective chemoattractant receptors at a site distal to G protein activation. 862 21

We undertake a quantitative investigation of changes in intracellular free Ca2+ concentration ([Ca2+]i) in antigen-stimulated rat basophilic leukemia (RBL-2H3) cells, which include contributions of both Ca2+ store release and Ca2+ influx from the medium. Following Keizer and De Young (J. Keizer and G. De Young. Biophys. J. 61: 649-660, 1992), we develop a highly constrained mathematical model for [Ca2+]i oscillations in RBL-2H3 cells, which includes activation of the inositol trisphosphate receptor (IP3R) by inositol 1,4,5-trisphospate, indirect Ca2+ activation of the IP3R via Ca2+ -dependent activity of phospholipase C-gamma, slow inhibition of the IP3R by cytosolic Ca2+, refilling of Ca2+ stores by a Ca2+ -ATPase (SERCA)-type pump, and a simple representation of the dependence of plasma membrane (PM) fluxes on experimental conditions. Using this full (open cell) model, we simulate [Ca2+]i responses for protocols in which antigen concentration and external Ca2+ are manipulated and compare out calculations with experimental data. In protocol A, cells are stimulated in the presence of external Ca2+, in protocols B and C, cells are stimulated in the absence of external Ca2+, with external Ca2+ later reapplied in protocol C. We are able to reproduce quantitatively the important features of all three protocols, including the dose response of protocol B, the [Ca2+]i response to thapsigargin, and lag time results, and we provide qualitative explanations for the responses derived from our calculations. We also develop a simplified (closed cell) version of the model in which PM fluxes are neglected and total free Ca2+ concentration ([Ca2+]T) is a slowly varying parameter. This permits us to explain in a simple graphical fashion how PM fluxes may influence [Ca2+]i responses in RBH-2H3 cells through modulation of [Ca2+]T.
 ...
PMID:Effect of Ca2+ influx on intracellular free Ca2+ responses in antigen-stimulated RBL-2H3 cells. 863 49

We addressed the question as to which subtypes of G protein subunits mediate the activation of phospholipase C-beta by the muscarinic m1 receptor. We used the rat basophilic leukemia cell line RBL-2H3-hm1 stably transfected with the human muscarinic m1 receptor cDNA. We microinjected antisense oligonucleotides into the nuclei of the cells to inhibit selectively the expression of G protein subunits; 48 hr later muscarinic receptors were activated by carbachol, and the increase in free cytosolic calcium concentration ([Ca2+]i) was measured. Antisense oligonucleotides directed against the mRNA coding for alpha(q) and alpha11 subunits both suppressed the carbachol-induced increase in [Ca2+]i. In cells injected with antisense oligonucleotides directed against alpha(o1) and alpha14 subunits, the carbachol effect was unchanged. A corresponding reduction of Galpha(q), and Galpha11 proteins by 70-80% compared to uninjected cells was immunochemically detected 2 days after injection of a mixture of alpha(q) and alpha11 antisense oligonucleotides. Expression of Galpha(q) and Galpha11 completely recovered after 4 days. Cells injected with antisense oligonucleotides directed against the mRNAs encoding for beta1, beta4, and gamma4 subunits showed a suppression of the carbachol-induced increase in [Ca2+]i compared to uninjected cells measured at the same time from the same coverslip, whereas in cells injected with antisense oligonucleotides directed against the beta2, beta3, gamma1, gamma2, gamma3, gamma5, and gamma7 subunits, no suppression of carbachol effect was observed. In summary, the results from RBL-2H3-hm1 cells indicate that the m1 receptor utilizes a G protein complex composed of the subunits alpha(q), alpha11, beta1, beta4, and gamma4 to activate phospholipase C.
 ...
PMID:A heterotrimeric G protein complex couples the muscarinic m1 receptor to phospholipase C-beta. 864 42

The effects of adenosine (ADO) analogs on cells of the human promyelocytic HL-60 line were examined. ADO A(3) receptor agonists, N(6)-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide (IB-MECA, 30-60 microM) and 2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide (CI-IB-MECA, 10-30 microM) induced apoptotic cell death. In contrast, neither an A(1)/A(2) antagonist (XAC) nor other selective ADO receptor agonists (CPA, NECA and CGS21680) induced apoptosis at concentrations of <30 microM. Both IB-MECA and CI-IB-MECA significantly induced Ca(2+) release from intracellular Ca(2+) pools followed by Ca(2+) influx, suggesting the presence of phospholipase C-coupled ADO A(3) receptors on HL-60 cells. This was further supported by the presence of mRNA of ADO A3 receptor in the cells. These results suggest that activation of ADO A(3) receptors is responsible for the ADO-induced apoptosis in HL-60 cells and could be of potential therapeutic value in the treatment of leukemia.
 ...
PMID:Induction of apoptosis in HL-60 human promyelocytic leukemia cells by adenosine A(3) receptor agonists. 864 77

CD28/B7 interactions have been demonstrated to provide a co-stimulatory signal for the generation of CD8+ cytotoxic T lymphocytes in the absence of CD4+ T helper cells. The CD28 signals required for induction of cytotoxicity have yet to be described. To investigate further the biochemical signaling pathways associated with CD28-dependent cytotoxicity, we have studied the human thymic leukemia cell line, YT. YT cells kill B7+ targets in a non-major histocompatibility complex (MHC)-restricted, CD28-dependent manner. CD28 ligation on the surface of YT cells caused a rapid increase in the tyrosine phosphorylation of four major cellular substrates with masses estimated to be 110, 95, 85, and 44 kDa. The 110 and 85 kDa substrates were identified as the catalytic and regulatory subunits, respectively, of phosphatidylinositol 3-kinase (PI3-K). Engagement of CD28 caused the rapid receptor association and activation of PI3-K but did not activate phospholipase C gamma. CD28-induced tyrosine phosphorylation and PI3-K activation was independent of p56lck protein tyrosine kinase (PTK) activity (previously reported to be associated with CD28) and was insensitive to inhibition by the PTK inhibitor herbimycin A. Two structurally and mechanistically dissimilar inhibitors of PI3-K, wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) also failed to block CD28-dependent tyrosine phosphorylation events or the association of PI3-K with the CD28 receptor. However, both drugs inhibited CD28-dependent cytotoxicity and CD28 receptor associated PI3-K activity with IC50 values similar to the reported IC50 values for PI3-K inhibition. Although herbimycin A did not significantly block the observed CD28-dependent tyrosine phosphorylation or PI3-K activation, herbimycin did block CD28-dependent cytotoxicity in a dose-dependent manner. These data support a role for PI3-K activation in the CD28-dependent initiation of cytotoxic effector function and suggest that a herbimycin sensitive step(s) is either CD28-independent, resides within a PI3-K-independent CD28 signaling pathway, or is downstream of CD28-dependent PI3-K activation.
 ...
PMID:CD28-dependent killing by human YT cells requires phosphatidylinositol 3-kinase activation. 864 5

The sphingolipids, sphingosylphosphorylcholine (SPPC) and sphingosine-1-phosphate (SPP), induce a rapid and transient rise in intracellular free calcium concentration ([Ca2+]i) in a variety of cell lines via activation of pertussis toxin-sensitive G protein-coupled receptors. We investigated whether these sphingolipids act on different receptors by testing the effect of varying concentrations of SPPC on [Ca2+]i in human leukemia HL-60 cells, which have been found to be nonresponsive to SPP. SPPC potently (EC50 = 1.5 microM) and rapidly increased [Ca2+]i in HL-60 cells in a pertussis toxin-sensitive manner. Differentiation of HL-60 cells through treatment with dibutyryl cAMP into granulocyte-like cells did not change the magnitude or the pertussis toxin sensitivity of the SPPC-induced [Ca2+]i rise, indicating that the receptor for SPPC is constitutively expressed in HL-60 cells. SPPC did not activate phospholipase C or D in HL-60 cells. However, SPPC, but not SPP, stimulated the generation of superoxide anions in dibutyryl cAMP-differentiated HL-60 cells as well as in human neutrophils, suggesting that the SPPC receptor may play a role in the inflammatory defense against invading microorganisms. On the basis of these results, we conclude that there apparently is a heterogeneity of G protein-coupled receptors for sphingolipids in mammalian cells.
 ...
PMID:A distinct G(i) protein-coupled receptor for sphingosylphosphorylcholine in human leukemia HL-60 cells and human neutrophils. 864 55

Repetitive transient increases in cytosolic calcium concentration (calcium spikes or calcium oscillations) are a common mode of signal transduction in receptor-mediated cell activation. Repetitive calcium spikes are initiated by phospholipase C-mediated production of inositol 1,4,5-trisphosphate (InsP3) and are thought to be generated by a positive feedback mechanism in which calcium potentiates its own release, a negative feedback mechanism by which calcium release is terminated, and a slow recovery process that defines the time interval between calcium spikes. The molecular mechanisms that terminate each calcium spike and define the spike frequency are not yet known. Here we show, in intact rat basophilic leukemia cells, that calcium responses induced by InsP3 are diminished for a period of 30-60 s following an InsP3-induced calcium spike. The sensitivity of calcium release for InsP3 was probed by UV laser-mediated photorelease of InsP3, and calcium responses were monitored by fluorescence calcium imaging. A maximal loss in sensitivity (desensitization) was observed for InsP3 increases that resulted in a near maximal calcium spike and was expressed as an 80-100% reduction in the calcium response to an equal amount of InsP3, released 10 s after the first UV pulse. When the amount of released InsP3 in the second pulse was increased 2-3-fold, desensitization was overcome and a second calcium response of equal amplitude to the first was produced. A power dependence of 3.2 was measured between the amount of released InsP3 and the amplitude of the triggered calcium response, explaining how a small decrease in InsP3 sensitivity can lead to a nearly complete reduction in the calcium response. Desensitization was abolished by the addition of the calcium buffers BAPTA and EGTA and could be induced by microinjection of calcium, suggesting that it is a calcium-dependent process. Half-maximal desensitization was observed at a free calcium concentration of 290 nM and increased with a power of 3.7 with peak calcium concentration. These studies suggest that reversible desensitization of InsP3-induced calcium release serves as a "saw-tooth" parameter that controls the termination of each spike and the frequency of calcium spikes.
 ...
PMID:Reversible desensitization of inositol trisphosphate-induced calcium release provides a mechanism for repetitive calcium spikes. 866 16

The chemokines interleukin-8 (IL-8) and GRO alpha bind in neutrophils to the interleukin-8 receptor alpha and beta (IL-8R alpha and beta) triggering reorganization of the actin cytoskeleton and activation of phospholipase C (PLC). Reconstitution of chemokine-induced activation of PLC indicated coupling of IL-8R alpha and beta to pertussis toxin-insensitive G alpha 16-proteins as well as to pertussis toxin-sensitive G alpha i2- or G alpha i3-proteins. To identify the signal transduction mechanisms of chemokine-induced actin response, undifferentiated human leukemia cells (HL-60 cells) constitutively expressing G alpha 16-, G alpha i2- and G alpha i3-proteins were chosen for reconstitution studies. Expression of recombinant receptors after transfection of the cells with the cDNA of IL-8R alpha and beta was confirmed by binding studies with radiolabeled ligands. IL-8R alpha bound IL-8 with high affinity (Kd approximately 1 nM) and GRO alpha with low affinity (Kd approximately 1 microM), whereas IL-8R beta bound both IL-8 and GRO alpha with high affinity (Kd approximately 1nM). Flow cytometric actin measurements indicated that high affinity ligand-receptor interactions in both receptor transfectants displayed inducible responses. Pretreatment of transfectants with pertussis toxin caused ADP-ribosylation of G-proteins and blocked chemokine-induced polymerization, indicating involvement of G alpha i2- or G alpha i3-proteins, but not G alpha 16-proteins in this response.
 ...
PMID:Reconstitution of chemokine-induced actin polymerization in undifferentiated human leukemia cells (HL-60) by heterologous expression of interleukin-8 receptors. 868 91

In human neutrophils, histamine H2-receptors mediate activation of adenylyl cyclase (AC) and inhibition of N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-induced superoxide anion (O2-) formation, and in HL-60 promyelocytes, H2-receptors mediate parallel activation of AC, phospholipase C (PLC) and non-selective cation (NSC) channels. As all-trans-retinoic acid (RA) is successfully used in the differentiation therapy of acute promyelocytic leukaemia, we studied signal transduction in RA-differentiated HL-60 cells. Histamine and the H2-receptor agonist, impromidine, induced both rises in cAMP levels and cytosolic Ca2+ ([Ca2+]i). Substances acting at post-receptor sites to increase cAMP did not increase [Ca2+]i. H2- but not H1-receptor antagonists inhibited histamine-induced cAMP accumulation and rises in [Ca2+]i were more effectively inhibited by H2- than by H1-receptor antagonists. Histamine-induced rises in [Ca2+]i were completely dependent on the presence of extracellular Ca2+ and were abolished by the blocker of NSC channels, Gd3+, but were resistant to inhibition by pertussis toxin. Unlike FMLP, histamine did not activate PLC. The effects of FMLP on [Ca2+]i were less sensitive to blockade by Gd3+ than those of histamine, and there was no cross-desensitization between the two stimuli. FMLP, but not histamine, inhibited transiently thapsigargin-induced rises in [Ca2+]. Taken together, our results show that histamine activates AC-mediated cAMP accumulation in RA-differentiated HL-60 cells via H2-receptors and NSC channel-mediated Ca2+ influx via H2- (and H1)-receptors. Histamine-induced NSC channel activation is not the consequence of AC- or PLC stimulation and occurs, directly or indirectly, via pertussis toxin-insensitive guanine nucleotide-binding proteins. FMLP and histamine activate Ca2+ influx by different mechanisms. There are similarities in H2-receptor-mediated signal transduction between RA-differentiated HL-60 cells and HL-60 promyelocytes and differences between the former cells and neutrophils, indicating that RA-differentiated HL-60 cells must be considered as partially immature.
 ...
PMID:Stimulation of histamine H2- (and H1)-receptors activates Ca2+ influx in all-trans-retinoic acid-differentiated HL-60 cells independently of phospholipase C or adenylyl cyclase. 871 51

Precursors from the neuroepithelium of the developing cortex and the adult subventricular zone can be cloned in vitro after stimulation with fibroblast growth factor 2 (FGF-2), and they have the potential to give rise to both neurons and glia. The generation of neurons from these clones can be stimulated by either a factor derived from an astrocyte precursor line, Ast-1, or FGF-1. We have shown that neuronal differentiation stimulated by FGF-1 can be inhibited by diacylglycerol lipase inhibitor and mimicked by arachidonic acid, suggesting that the neuronal differentiation is signalled through the phospholipase C gamma pathway. The sequential expression of FGF-2, followed by FGF within the developing forebrain neuroepithelium, fits with the different functions that the two FGFs play in precursor regulation. We have shown that the precursor response to FGF-1 is regulated by a heparan sulphate proteoglycan expressed within the developing neuroepithelium. Precursors restricted to the astrocyte cell lineage can be stimulated by epidermal growth factor or FGF-2F however, the differentiation into glial fibrillary acidic protein-positive astrocytes appears to require a cytokine acting through the leukaemia inhibitory factor-beta receptor.
 ...
PMID:Factors regulating the differentiation of neural precursors in the forebrain. 872 88


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>