scholarly journals Regulation of platelet-activating-factor receptors and the desensitization response in polymorphonuclear neutrophils

1992 ◽  
Vol 288 (1) ◽  
pp. 241-248 ◽  
Author(s):  
J T O'Flaherty ◽  
D P Jacobson ◽  
J F Redman
Keyword(s):  
Actinomycin D ◽  
Platelet Activating Factor ◽  
Receptor Expression ◽  
Polymorphonuclear Neutrophils ◽  
Target Cells ◽  
Surface Compound ◽  
Down Regulation ◽  
High Affinity ◽  
Kinase C ◽  
Paf Receptor

Platelet-activating factor (PAF) desensitizes as well as stimulates its various target cells, We find that human polymorphonuclear neutrophils (PMN) exposed to PAF became maximally unresponsive to a second PAF challenge within 15-90 s in assays of Ca2+ mobilization and degranulation. The cells regained full PAF-sensitivity over the ensuing 20-40 min. These effects correlated with changes in PAF receptor availability. PMN treated with PAF, washed in regular buffer and assayed for PAF binding exhibited falls (maximal in 15 s), followed by rises (reaching control levels by 60 min), in the number of high-affinity PAF receptors. However, tracking studies showed that [3H]PAF accumulated on the cell surface for approximately 2 min before being internalized. Regular-buffer washes did not remove this superficial PAF, whereas a washing regimen using excess albumin to adsorb PAF removed 99% of the surface compound. PMN washed by the latter regimen after PAF exposure lost PAF receptors relatively slowly (maximal at approximately 5 min), but the ultimate extent of this loss and the rate at which receptor expression normalized were similar to those of cells washed in regular buffer. Neither cycloheximide nor actinomycin D influenced the course of the receptor changes, but two protein kinase C (PKC) blockers, staurosporine and 1-(5-isoquinolinesulphonyl)piperazine, inhibited the receptor-receptor-depleting actions of PAF. Indeed, a phorbol diester activator of PKC also caused PMN to decrease high-affinity PAF receptor numbers, and the two PKC blockers antagonized this action at concentrations that inhibited PAF-induced PAF receptor losses. We conclude that: (a) PAF induces PMN to down-regulate and then to re-express PAF receptors independently of protein synthesis; (b) these changes are likely to underlie the later stages and reversal of desensitization; (c) the onset (t < or = 2 min) of desensitization, however, precedes receptor down-regulation and must be due to receptor uncoupling from transductional elements; and (d) down-regulation of receptors for PAF appears to be mediated by PKC and/or elements inhibited by PKC blockers.

Oxidized low-density lipoprotein and peroxisome-proliferator-activated receptor α down-regulate platelet-activating-factor receptor expression in human macrophages

2001 ◽  
Vol 354 (1) ◽  
pp. 225-232 ◽  
Author(s):  
Delphine HOURTON ◽  
Philippe DELERIVE ◽  
Jana STANKOVA ◽  
Bart STAELS ◽  
M. John CHAPMAN ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Platelet Activating Factor ◽  
Density Lipoprotein ◽  
Receptor Expression ◽  
Peroxisome Proliferator ◽  
Low Density ◽  
Peroxisome Proliferator Activated Receptor ◽  
Receptor Mrna ◽  
Paf Receptor ◽  
Pparα Agonist

Regulation of the expression of platelet-activating factor (PAF) receptor by atherogenic lipoproteins might contribute to atherogenesis. We show that progressive oxidation of low-density lipoprotein (LDL) gradually inhibits PAF receptor expression on the macrophage cell surface. We tested the effect of oxidized LDL (oxLDL) on PAF receptor expression in human monocytes that do not contain peroxisome-proliferator-activated receptor γ (PPARγ), a nuclear receptor activated by oxLDL. OxLDL decreased by 50% (P ⩽0.001) and by 29% (P⩽0.05) the binding of PAF and the expression of PAF receptor mRNA respectively. Next we demonstrated that progressive oxidation of LDLs significantly activated PPARα-dependent transcription in transfected mouse aortic endothelial cells. Finally we demonstrated, in mature macrophages, that fenofibrate (20µM), a specific PPARα agonist, but not the specific PPARγ agonist BRL49653 (20nM), significantly decreased both PAF binding and PAF receptor mRNA expression, by 65% and 40% (P⩽0.001) respectively. Additionally, another PPARα agonist, Wy14,643, decreased PAF receptor promoter activity by 70% (P⩽0.05) in transfected THP-1 cells, suggesting the involvement of the proximal promoter region (-980 to -500) containing a series of four nuclear factor (NF)-κB motifs. Thus PPARα might be involved in the down-regulation of PAF receptor gene expression by oxLDLs in human monocytes/macrophages. The oxidation of one or more lipid components of LDLs might result in the formation of natural activators of PPARα. It is hypothesized that such activators might modulate inflammation and apoptosis upon atherogenesis by decreasing the expression of PAF receptor.

scholarly journals Platelet-activating factor (PAF) receptor expression is associated with histopathological stage and grade and patients’ survival in gastric adenocarcinoma

Neoplasma ◽  
2014 ◽  
Vol 61 (03) ◽  
pp. 309-317 ◽  
Author(s):  
C. GIAGINIS,E. KOUROU ◽  
A. GIAGINI ◽  
N. GOUTAS ◽  
E. PATSOURIS ◽  
G. KOURAKLIS ◽  
...  
Keyword(s):  
Gastric Adenocarcinoma ◽  
Platelet Activating Factor ◽  
Receptor Expression ◽  
Paf Receptor

scholarly journals Expression and modulation of specific, high affinity binding sites for erythropoietin on the human erythroleukemic cell line K562

Blood ◽  
1988 ◽  
Vol 71 (1) ◽  
pp. 104-109 ◽  
Author(s):  
JK Fraser ◽  
FK Lin ◽  
MV Berridge
Keyword(s):  
Cell Line ◽  
K562 Cell ◽  
K562 Cells ◽  
Erythroid Differentiation ◽  
Receptor Expression ◽  
Target Cells ◽  
Epo Receptor ◽  
High Affinity ◽  
Erythroleukemic Cell ◽  
Erythroleukemic Cell Line

Erythroid differentiation is mediated by several interacting factors which include the glycoprotein hormone erythropoietin (Epo), interleukin-3 (IL-3) in the mouse, and erythroid-potentiating activity (EPA) in humans. Each of these factors binds to specific cell surface receptors on responsive target cells, but the way in which these factors interact to modulate erythropoiesis is unknown. In the present study, we used the human erythroleukemic cell line K562 to examine expression and regulation of the receptor for Epo using 125I-labeled, bioactive recombinant human Epo. K562 cells expressed low numbers of a single class of high-affinity Epo receptors corresponding to 4 to 6 receptors per K562 cell (KD = 270 to 290 pmol/L). Treatment of K562 cell cultures with medium conditioned by the EPA-secreting cell line U937 (U937CM) increased receptor expression 2.6 to 3.5-fold to 13 to 17 receptors/cell (KD = 260 to 300 pmol/L). That all of the Epo receptor- potentiating activity in U937CM was accounted for by EPA was shown by a similar increase in Epo receptor expression on K562 cells with recombinant EPA. The effect of U937CM on Epo receptors was reversed by culturing cells in inducer-free medium for 3 days. Medium conditioned by the 5637 cell line had no effect on Epo receptors on K562 cells. In methylcellulose culture, U937CM and Epo acted synergistically to increase erythroid differentiation of K562. Similarly, U937CM stimulated human cord blood CFU-E growth under conditions in which Epo was limiting or in excess. Increases in Epo receptor expression on K562 cells and on CFU-E in response to EPA may mediate the effects of Epo on these cells.

scholarly journals Phospholipase Cβ3 Mediates LH-Induced Granulosa Cell Differentiation

Endocrinology ◽  
2011 ◽  
Vol 152 (7) ◽  
pp. 2857-2869 ◽  
Author(s):  
Francesc X. Donadeu ◽  
Cristina L. Esteves ◽  
Lynsey K. Doyle ◽  
Catherine A. Walker ◽  
Stephanie N. Schauer ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
Granulosa Cells ◽  
Inositol Phosphate ◽  
Ex Vivo ◽  
Receptor Expression ◽  
Target Cells ◽  
Down Regulation ◽  
Protein Levels ◽  
Prostaglandin Endoperoxide Synthase ◽  
In Cells

Previous studies showed that under certain conditions LH can stimulate not only adenylate cyclase (AC) but also phospholipase Cβ (PLCβ) signaling in target cells; however, the physiological involvement of PLCβ in LH-induced ovarian follicular cell differentiation has not been determined. To address this, ex vivo expression analyses and specific PLCβ targeting were performed in primary bovine granulosa cells. Expression analyses in cells from small (2.0–5.9 mm), medium (6.0–9.9 mm), and ovulatory-size (10.0–13.9 mm) follicles revealed an increase in mRNA and protein levels of heterotrimeric G protein subunits-αs, -αq, -α11, and -αi2 in ovulatory-size follicles, simultaneous with a substantial increase in LH receptor expression. Among the four known PLCβ isoforms, PLCβ3 (PLCB3) was specifically up-regulated in cells from ovulatory-size follicles, in association with a predominantly cytoplasmic location of PLCB3 in these cells and a significant inositol phosphate response to LH stimulation. Furthermore, RNA interference-mediated PLCB3 down-regulation reduced the ability of LH to induce hallmark differentiation responses of granulosa cells, namely transcriptional up-regulation of prostaglandin-endoperoxide synthase 2 and down-regulation of both aromatase expression and estradiol production. Responses to the AC agonist, forskolin, however, were not affected. In addition, PLCB3 down-regulation did not alter cAMP responses to LH in granulosa cells, ruling out a primary involvement of AC in mediating the effects of PLCB3. In summary, we provide evidence of a physiological involvement of PLCβ signaling in ovulatory-size follicles and specifically identify PLCB3 as a mediator of LH-induced differentiation responses of granulosa cells.

scholarly journals PAF-acetylhydrolase expressed during megakaryocyte differentiation inactivates PAF-like lipids

Blood ◽  
2009 ◽  
Vol 113 (26) ◽  
pp. 6699-6706 ◽  
Author(s):  
Jason M. Foulks ◽  
Gopal K. Marathe ◽  
Noemi Michetti ◽  
Diana M. Stafforini ◽  
Guy A. Zimmerman ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Platelet Activating Factor ◽  
Lipid Mediators ◽  
Target Cells ◽  
Signaling System ◽  
Human Cd34 ◽  
Paf Acetylhydrolase ◽  
Cd34 Cells ◽  
Paf Receptor ◽  
And Function

Abstract Platelet activating factor (PAF) and PAF-like lipids induce inflammatory responses in target cells. These lipid mediators are inactivated by PAF-acetylhydrolase (PAF-AH). The PAF signaling system affects the growth of hematopoietic CD34+ cells, but roles for PAF-AH in this process are unknown. Here, we investigated PAF-AH function during megakaryopoiesis and found that human CD34+ cells accumulate this enzymatic activity as they differentiate toward megakaryocytes, consistent with the expression of mRNA and protein for the plasma PAF-AH isoform. Inhibition of endogenous PAF-AH activity in differentiated megakaryocytes increased formation of lipid mediators that signaled the PAF receptor (PAFR) in fully differentiated human cells such as neutrophils, as well as megakaryocytes themselves. PAF-AH also controlled megakaryocyte αIIbβ3-dependent adhesion, cell spreading, and mobility that relied on signaling through the PAFR. Together these data suggest that megakaryocytes generate PAF-AH to modulate the accumulation of intracellular phospholipid mediators that may detrimentally affect megakaryocyte development and function.

Eicosanoid production from porcine neutrophils and platelets: differential production with various agonists

1997 ◽  
Vol 272 (6) ◽  
pp. C1821-C1828 ◽  
Author(s):  
G. L. Stahl ◽  
D. S. Morse ◽  
S. L. Martin
Keyword(s):  
Human Disease ◽  
Cytochalasin B ◽  
Flow Cytometric Analysis ◽  
Platelet Activating Factor ◽  
Lipid Mediators ◽  
Polymorphonuclear Neutrophils ◽  
Lipoxin A4 ◽  
Flow Cytometric ◽  
A 23187 ◽  
Paf Receptor

Polymorphonuclear neutrophils (PMN) and platelets interact to produce both inflammatory and anti-inflammatory lipid mediators during human disease. Because swine models of human disease are used, it is important to understand the mechanisms involved in the formation of lipid mediators from porcine PMN-platelet interactions. In the present study, we investigated the mechanism of thromboxane (Tx) A2 and lipoxin A4 (LXA4) formation from porcine PMN and platelets, respectively. PMN (10(7)/ml) and platelet (30 x 10(7)/ml) suspensions stimulated with porcine C5a (pC5a), but not recombinant human C5a (rhC5a), significantly enhanced TxB2 formation. After cytochalasin B treatment, pC5a or rhC5a significantly and equally enhanced TxB2 formation from PMN-platelet suspensions. A-23187-induced TxB2 formation from platelets was not significantly augmented by the presence of PMN in these suspensions. A-23187 induced significant LXA4 production from porcine PMN that was not augmented by addition of platelets. Flow cytometric analysis of PMN-platelet suspensions revealed activated platelets adherent to PMN following pC5a stimulation. CV-6209, a platelet-activating factor (PAF) receptor antagonist, dose dependently prevented pC5a-induced platelet adherence to PMN and TxB2 formation. These data demonstrate that 1) porcine PMN alone can biosynthesize LXA4 without the assistance of platelets, which is in sharp contrast to human PMN-platelet interactions, and 2) in the absence of cytochalasin B, pC5a stimulates PAF biosynthesis from porcine PMN, resulting in TxB2 formation from platelets.

Multiple Signaling Pathways for Platelet-Activating Factor Receptor

Physiology ◽  
1992 ◽  
Vol 7 (2) ◽  
pp. 72-75
Author(s):  
SD Shukla
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Signaling Pathways ◽  
G Protein ◽  
Platelet Activating Factor ◽  
G Protein Coupled Receptors ◽  
Kinase C ◽  
Paf Receptor ◽  
Multiple Signaling ◽  
G Protein Coupled

Platelet-activating factor (PAF) receptor is coupled to multiple signaling pathways, including phospholipid turnover via phospholipases C, D, A2;Ca2+ mobilization;and activation of protein kinase C and tyrosine kinase. The cloned receptor shows homology to G protein-coupled receptors. These developments highlight receptor functions of this novel phospholipid agonist.

scholarly journals Expression and modulation of specific, high affinity binding sites for erythropoietin on the human erythroleukemic cell line K562

Blood ◽  
1988 ◽  
Vol 71 (1) ◽  
pp. 104-109 ◽  
Author(s):  
JK Fraser ◽  
FK Lin ◽  
MV Berridge
Keyword(s):  
Cell Line ◽  
K562 Cell ◽  
K562 Cells ◽  
Erythroid Differentiation ◽  
Receptor Expression ◽  
Target Cells ◽  
Epo Receptor ◽  
High Affinity ◽  
Erythroleukemic Cell ◽  
Erythroleukemic Cell Line

Abstract Erythroid differentiation is mediated by several interacting factors which include the glycoprotein hormone erythropoietin (Epo), interleukin-3 (IL-3) in the mouse, and erythroid-potentiating activity (EPA) in humans. Each of these factors binds to specific cell surface receptors on responsive target cells, but the way in which these factors interact to modulate erythropoiesis is unknown. In the present study, we used the human erythroleukemic cell line K562 to examine expression and regulation of the receptor for Epo using 125I-labeled, bioactive recombinant human Epo. K562 cells expressed low numbers of a single class of high-affinity Epo receptors corresponding to 4 to 6 receptors per K562 cell (KD = 270 to 290 pmol/L). Treatment of K562 cell cultures with medium conditioned by the EPA-secreting cell line U937 (U937CM) increased receptor expression 2.6 to 3.5-fold to 13 to 17 receptors/cell (KD = 260 to 300 pmol/L). That all of the Epo receptor- potentiating activity in U937CM was accounted for by EPA was shown by a similar increase in Epo receptor expression on K562 cells with recombinant EPA. The effect of U937CM on Epo receptors was reversed by culturing cells in inducer-free medium for 3 days. Medium conditioned by the 5637 cell line had no effect on Epo receptors on K562 cells. In methylcellulose culture, U937CM and Epo acted synergistically to increase erythroid differentiation of K562. Similarly, U937CM stimulated human cord blood CFU-E growth under conditions in which Epo was limiting or in excess. Increases in Epo receptor expression on K562 cells and on CFU-E in response to EPA may mediate the effects of Epo on these cells.

scholarly journals Agonist-induced down-regulation of platelet-activating factor receptor gene expression in U937 cells

1994 ◽  
Vol 301 (3) ◽  
pp. 911-916 ◽  
Author(s):  
L Y Chau ◽  
K Peck ◽  
H H Yen ◽  
J Y Wang
Keyword(s):  
Prolonged Exposure ◽  
Radioligand Binding ◽  
Receptor Gene ◽  
Platelet Activating Factor ◽  
State Level ◽  
Transcriptional Level ◽  
U937 Cells ◽  
Down Regulation ◽  
Receptor Mrna ◽  
Paf Receptor

Prolonged exposure (8-24 h) of human promonocytic U937 cells to 100 nM 1-O-hexadecyl-2-N-methylcarbamyl-sn-glycero-3-phosphocholine (carbarmyl-PAF), a non-metabolizable analogue of platelet-activating factor (PAF), reduced the numbers of PAF receptors by 50-75%, as determined by the radioligand-binding assay. To clarify whether the down-regulation of receptor numbers is due to decreased expression level of the PAF-receptor gene, the effect of carbamyl-PAF on the steady-state level of PAF-receptor mRNA was examined by a highly sensitive reverse-transcriptase PCR method. A 50% decline in the level of PAF-receptor mRNA was observed in U937 cells pretreated with 100 nM carbamyl-PAF for 24 h. The effect of carbamyl-PAF was dose-dependent, with an EC50 value around 10 nM. PAF-receptor antagonist, SRI-63675, was able to attenuate the effect of carbamyl-PAF. Furthermore lysoPAF, at 1 uM, was unable to induce a significant decrease in PAF-receptor mRNA after incubation for 24 h, indicating that the effect of carbamyl-PAF was specific. The half-life of the PAF-receptor mRNA measured in the presence of actinomycin D was unaffected by carbamyl-PAF treatment. In contrast, nuclear run-off experiments demonstrated that the transcription rate of the PAF-receptor gene in carbamyl-PAF-treated cells was about 65% of that in control cells. These results suggest that the PAF receptor in U937 cells is subject to down-regulation by agonist, at least partly, at the transcriptional level.

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