scholarly journals Wortmannin alters the intracellular trafficking of the bradykinin B2 receptor: role of phosphoinositide 3-kinase and Rab5

2003 ◽  
Vol 375 (1) ◽  
pp. 151-158 ◽  
Author(s):  
Steeve HOULE ◽  
François MARCEAU
Keyword(s):  
Fluorescent Protein ◽  
Dominant Negative ◽  
Bafilomycin A1 ◽  
Hek 293 ◽  
Agonist Stimulation ◽  
293 Cells ◽  
Dominant Negative Form ◽  
Phosphoinositide 3 Kinase ◽  
Green Fluorescent ◽  
Negative Form

Wortmannin reportedly induces the formation of enlarged cytoplasmic endosomes. Such vesicles were observed in a definite time window after wortmannin treatment (250 nM) in HEK-293 cells stably expressing a B2R (B2 receptor)–green fluorescent protein conjugate and other cell types. The alternative PI3K (phosphoinositide 3-kinase) inhibitor LY 294002 (100 μM) and a dominant-negative form of the enzyme (p85α ΔiSH2) induce a more modest vesicle enlargement. PI3K inhibition by drugs did not affect agonist-induced [3H]arachidonate release. The wortmannin-induced formation of giant endosomes also involves Rab5 activity, since a dominant-negative form of this GTPase (Rab5 S34N) partially inhibits the wortmannin effect and a constitutively active form of Rab5 (Rab5 Q79L) induces the formation of enlarged endosomes. Moreover, agonist stimulation targeted B2R–green fluorescent protein towards the periphery of the giant vesicles and led to partial receptor degradation only in wortmannin-treated cells. Receptor degradation was decreased by protease inhibitors and by bafilomycin A1, a drug that inhibits lysosome function. Accumulation of fluorescent material inside the enlarged endosomes was observed in cells treated with bafilomycin A1, wortmannin and an agonist. [3H]Bradykinin binding was decreased in HEK-293 cells treated with both wortmannin and the agonist, but not with either separately. Furthermore, a wortmannin-induced functional down-regulation of B2R was observed in rabbit jugular veins after repeated agonist stimulation (contractility assay). This is the first report of a G-protein-coupled receptor down-regulation induced by an alteration of its usual routing in the cell. These results suggest that both PI3K and Rab5 influence B2R intracellular trafficking.

scholarly journals Parathyroid Hormone Receptor Recycling: Role of Receptor Dephosphorylation and β-Arrestin

2002 ◽  
Vol 16 (12) ◽  
pp. 2720-2732 ◽  
Author(s):  
Stephanie Chauvin ◽  
Margaret Bencsik ◽  
Tom Bambino ◽  
Robert A. Nissenson
Keyword(s):  
Plasma Membrane ◽  
Fluorescent Protein ◽  
Dominant Negative ◽  
Receptor Recycling ◽  
Binding Assays ◽  
Parathyroid Hormone Receptor ◽  
293 Cells ◽  
Dominant Negative Form ◽  
Green Fluorescent

Abstract The recovery of PTH receptor (PTHR) function after acute homologous receptor desensitization and down-regulation in bone and kidney cells has been attributed to receptor recycling. To determine the role of receptor dephosphorylation in PTHR recycling, we performed morphological and functional assays on human embryonic kidney 293 cells stably expressing wild-type (wt) or mutant PTHRs. Confocal microscopy and ligand binding assays revealed that the wt PTHR is rapidly recycled back to the plasma membrane after removal of the agonist. Receptors that were engineered to either lack the sites of phosphorylation or to resemble constitutively phosphorylated receptors were able to recycle back to the plasma membrane with the same kinetics as the wt PTHR. The PTHR was found to be dephosphorylated by an enzyme apparently distinct from protein phosphatases 1 or 2A. The PTHR and β-arrestin-2-green fluorescent protein (GFP) were found to stably colocalize during PTHR internalization, whereas after agonist removal and during receptor recycling, the colocalization slowly disappeared. Experiments using phosphorylation-deficient PTHRs and a dominant-negative form of β-arrestin showed that β-arrestin does not regulate the efficiency of PTHR recycling. These studies indicate that, unlike many G protein-coupled receptors, PTHR recycling does not require receptor dephosphorylation or its dissociation from β-arrestin.

scholarly journals Alteration of intracellular histamine H2 receptor cycling precedes antagonist-induced upregulation

2005 ◽  
Vol 289 (5) ◽  
pp. G880-G889 ◽  
Author(s):  
Satoshi Osawa ◽  
Masayoshi Kajimura ◽  
Seiji Yamamoto ◽  
Mutsuhiro Ikuma ◽  
Chihiro Mochizuki ◽  
...  
Keyword(s):  
Fluorescent Protein ◽  
Inverse Agonist ◽  
Recycling Endosome ◽  
Histamine H2 Receptor ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
293 Cells ◽  
Gfp Fluorescence ◽  
Term Administration ◽  
Green Fluorescent

Long-term administration of a histamine H2 receptor (H2R) antagonist (inverse agonist) induces upregulation of H2R in parietal cells, which may be relevant to the rebound hypersecretion of gastric acid that occurs after withdrawal of treatment. The mechanisms underlying this effect are unknown. We hypothesized that the H2R upregulation could be related to receptor trafficking and used H2R-green fluorescent protein (H2R-GFP) to test the hypothesis. Human H2R-GFP was generated and functionally expressed in HEK-293 cells. Binding of the H2R antagonist [3H]tiotidine was performed to quantify H2R expression, and H2R-GFP was imaged in living cells by confocal and evanescent wave microscopy. The binding affinity of [3H]tiotidine was not significantly different between H2R-GFP- and wild-type H2R-expressing HEK-293 cells, both of which had constitutive activity of adenylate cyclase. Visualization of H2R-GFP revealed that the agonist-induced H2R internalization and the antagonist-induced recycling of the internalized H2R from the recycling endosome within 2 h. Long exposure to the antagonist increased GFP fluorescence in the plasma membrane and also induced upregulation of H2R-GFP estimated by the binding assay, whereas long exposure to the agonist enhanced degradative trafficking of H2R-GFP. We examined whether the upregulation reflected an increase in receptor synthesis. Treatment with antagonist did not augment H2R mRNA, and subsequent inhibition of protein synthesis by cycloheximide had no effect on H2R upregulation. These findings suggested that upon exposure to an antagonist (inverse agonist), the equilibrium between receptor endocytosis and recycling is altered before H2R upregulation, probably via suppressing H2R degradation.

scholarly journals Differential PI 3-kinase dependence of early and late phases of recycling of the internalized AT1 angiotensin receptor

2002 ◽  
Vol 157 (7) ◽  
pp. 1211-1222 ◽  
Author(s):  
László Hunyady ◽  
Albert J. Baukal ◽  
Zsuzsanna Gáborik ◽  
Jesus A. Olivares-Reyes ◽  
Márta Bor ◽  
...  
Keyword(s):  
Cell Surface ◽  
Kinase Inhibitors ◽  
Fluorescent Protein ◽  
Slow Component ◽  
Ang Ii ◽  
Hek 293 ◽  
Recycling Endosomes ◽  
293 Cells ◽  
Early Endosomes ◽  
Green Fluorescent

Agonist-induced endocytosis and processing of the G protein–coupled AT1 angiotensin II (Ang II) receptor (AT1R) was studied in HEK 293 cells expressing green fluorescent protein (GFP)– or hemagglutinin epitope–tagged forms of the receptor. After stimulation with Ang II, the receptor and its ligand colocalized with Rab5–GFP and Rab4–GFP in early endosomes, and subsequently with Rab11–GFP in pericentriolar recycling endosomes. Inhibition of phosphatidylinositol (PI) 3-kinase by wortmannin (WT) or LY294002 caused the formation of large endosomal vesicles of heterogeneous Rab composition, containing the ligand–receptor complex in their limiting membranes and in small associated vesicular structures. In contrast to Alexa®–transferrin, which was mainly found in small vesicles associated with the outside of large vesicles in WT-treated cells, rhodamine–Ang II was also segregated into small internal vesicles. In cells labeled with 125I-Ang II, WT treatment did not impair the rate of receptor endocytosis, but significantly reduced the initial phase of receptor recycling without affecting its slow component. Similarly, WT inhibited the early, but not the slow, component of the recovery of AT1R at the cell surface after termination of Ang II stimulation. These data indicate that internalized AT1 receptors are processed via vesicles that resemble multivesicular bodies, and recycle to the cell surface by a rapid PI 3-kinase–dependent recycling route, as well as by a slower pathway that is less sensitive to PI 3-kinase inhibitors.

scholarly journals Determinants Present in the Receptor Carboxy Tail Are Responsible for Differences in Subtype-Specific Coupling ofβ-Adrenergic Receptors to Phosphoinositide 3-Kinase

2009 ◽  
Vol 2009 ◽  
pp. 1-8
Author(s):  
Julie Simard ◽  
Matthieu Boucher ◽  
Rachel Massé ◽  
Terence E. Hébert ◽  
Guy Rousseau
Keyword(s):  
Pertussis Toxin ◽  
Transmembrane Domain ◽  
Dominant Negative ◽  
Akt Pathway ◽  
Hek 293 ◽  
Protein Receptor ◽  
293 Cells ◽  
Molecular Determinants ◽  
The Difference ◽  
Phosphoinositide 3 Kinase

An agonist-occupiedβ2-adrenergic receptor (β2-AR) recruits G protein receptor kinase-2 (GRK2) which is recruited to the membrane. Thus, the physical proximity of activatedβ2-AR and PI-3K allows the activation of the latter. In contrast, it has been observed that theβ1-AR is unable to activate the PI-3K/Akt pathway. We hypothesized that the difference might be due to molecular determinants present in the carboxy termini of the twoβ-AR subtypes. Using transiently transfected HEK 293 cells expressing eitherβ1- orβ2-AR, we also observed that in presence of an agonist,β2-AR, but notβ1-AR, is able to activate the PI-3K/Akt pathway. Switching the seventh transmembrane domain and the carboxy tail between the two receptors reverses this phenotype; that is,β1×β2-AR can activate the PI-3K/Akt pathway whereasβ2×β1-AR cannot. Pretreatment with pertussis toxin abolished the activation of PI-3K byβ2- orβ1×β2-AR stimulation. Ligand-mediated internalization of theβ2-AR induced by a 15-minute stimulation with agonist was abolished in the presence of a dominant negative of PI-3K or following pertussis toxin pretreatment. These results indicate that the subtype-specific differences in the coupling to PI-3K/Akt pathway are due to molecular determinants present in the carboxy tail of the receptor and further thatβ2-AR activates PI-3K via a pertussis toxin-sensitive mechanism.

PKC-δ sensitizes Kir3.1/3.2 channels to changes in membrane phospholipid levels after M3 receptor activation in HEK-293 cells

2005 ◽  
Vol 289 (3) ◽  
pp. C543-C556 ◽  
Author(s):  
Sean G. Brown ◽  
Alison Thomas ◽  
Lodewijk V. Dekker ◽  
Andrew Tinker ◽  
Joanne L. Leaney
Keyword(s):  
Fluorescent Protein ◽  
Receptor Activation ◽  
Dominant Negative ◽  
Membrane Phospholipid ◽  
Channel Activity ◽  
Receptor Stimulation ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
Channel Inhibition ◽  
293 Cells

G protein-gated inward rectifier (Kir3) channels are inhibited by activation of Gq/11-coupled receptors and this has been postulated to involve the signaling molecules protein kinase C (PKC) and/or phosphatidylinositol 4,5-bisphosphate (PIP2). Their precise roles in mediating the inhibition of this family of channels remain controversial. We examine here their relative roles in causing inhibition of Kir3.1/3.2 channels stably expressed in human embryonic kidney (HEK)-293 cells after muscarinic M3 receptor activation. In perforated patch mode, staurosporine prevented the Gq/11-mediated, M3 receptor, inhibition of channel activity. Recovery from M3-mediated inhibition was wortmannin sensitive. Whole cell currents, where the patch pipette was supplemented with PIP2, were still irreversibly inhibited by M3 receptor stimulation. When adenosine A1 receptors were co-expressed, inclusion of PIP2 rescued the A1-mediated response. Recordings from inside-out patches showed that catalytically active PKC applied directly to the intracellular membrane face inhibited the channels: a reversible effect modulated by okadaic acid. Generation of mutant heteromeric channel Kir3.1S185A/Kir3.2C-S178A, still left the channel susceptible to receptor, pharmacological, and direct kinase-mediated inhibition. Biochemically, labeled phosphate is incorporated into the channel. We suggest that PKC-δ mediates channel inhibition because recombinant PKC-δ inhibited channel activity, M3-mediated inhibition of the channel, was counteracted by overexpression of two types of dominant negative PKC-δ constructs, and, by using confocal microscopy, we have demonstrated translocation of green fluorescent protein-tagged PKC-δ to the plasma membrane on M3 receptor stimulation. Thus Kir3.1/3.2 channels are sensitive to changes in membrane phospholipid levels but this is contingent on the activity of PKC-δ after M3 receptor activation in HEK-293 cells.

scholarly journals Sequential Activities of Phosphoinositide 3-Kinase, PKB/Akt, and Rab7 during Macropinosome Formation inDictyostelium

2001 ◽  
Vol 12 (9) ◽  
pp. 2813-2824 ◽  
Author(s):  
Adam Rupper ◽  
Kyung Lee ◽  
David Knecht ◽  
James Cardelli
Keyword(s):  
Dendritic Cells ◽  
Molecular Mechanisms ◽  
Fluorescent Protein ◽  
Microscopic Analysis ◽  
Dominant Negative ◽  
Actin Binding ◽  
Pleckstrin Homology Domain ◽  
Downstream Effector ◽  
Phosphoinositide 3 Kinase ◽  
Green Fluorescent

Macropinocytosis plays an important role in the internalization of antigens by dendritic cells and is the route of entry for many bacterial pathogens; however, little is known about the molecular mechanisms that regulate the formation or maturation of macropinosomes. Like dendritic cells, Dictyostelium amoebae are active in macropinocytosis, and various proteins have been identified that contribute to this process. As described here, microscopic analysis of null mutants have revealed that the class I phosphoinositide 3-kinases, PIK1 and PIK2, and the downstream effector protein kinase B (PKB/Akt) are important in regulating completion of macropinocytosis. Although actin-rich membrane protrusions form in these cell lines, they recede without forming macropinosomes. Imaging of cells expressing green fluorescent protein (GFP) fused to the pleckstrin homology domain (PH) of PKB (GFP-PHPKB) indicates that D3 phosphoinositides are enriched in the forming macropinocytic cup and remain associated with newly formed macropinosomes for <1 minute. A fusion protein, consisting of GFP fused to an F-actin binding domain, overlaps with GFP-PHPKB in the timing of association with forming macropinosomes. Although macropinocytosis is reduced in cells expressing dominant negative Rab7, microscopic imaging studies reveal that GFP-Rab7 associates only with formed macropinosomes at approximately the time that F-actin and D3 phosphoinositide levels decrease. These results support a model in which F-actin modulating proteins and vesicle trafficking proteins coordinately regulate the formation and maturation of macropinosomes.

scholarly journals Bnip3 mediates mitochondrial dysfunction and cell death through Bax and Bak

2007 ◽  
Vol 405 (3) ◽  
pp. 407-415 ◽  
Author(s):  
Dieter A. Kubli ◽  
John E. Ycaza ◽  
Åsa B. Gustafsson
Keyword(s):  
Cell Death ◽  
Mitochondrial Dysfunction ◽  
Fluorescent Protein ◽  
Mitochondrial Permeability Transition ◽  
Permeability Transition Pore ◽  
Permeability Transition ◽  
Dominant Negative ◽  
Dominant Negative Form ◽  
Wild Type Mefs ◽  
Green Fluorescent

Bnip3 is a pro-apoptotic member of the Bcl-2 family that is down-regulated in pancreatic cancers, which correlates with resistance to chemotherapy and a worsened prognosis. In contrast, Bnip3 is up-regulated in heart failure and contributes to loss of myocardial cells during I/R (ischaemia/reperfusion). Bnip3 exerts its action at the mitochondria, but the mechanism by which Bnip3 mediates mitochondrial dysfunction is not clear. In the present study, we have identified Bax and Bak as downstream effectors of Bnip3-mediated mitochondrial dysfunction. Bnip3 plays a role in hypoxia-mediated cell death, but MEFs (mouse embryonic fibroblasts) derived from mice deficient in Bax and Bak were completely resistant to hypoxia even with substantial up-regulation of Bnip3. These cells were also resistant to Bnip3 overexpression, but re-expression of Bax or Bak restored susceptibility to Bnip3, suggesting that Bnip3 can act via either Bax or Bak. In contrast, Bnip3 overexpression in wild-type MEFs induced mitochondrial dysfunction with loss of membrane potential and release of cytochrome c. Cell death by Bnip3 was reduced in the presence of mPTP (mitochondrial permeability transition pore) inhibitors, but did not prevent Bnip3-mediated activation of Bax or Bak. Moreover, overexpression of Bnip3ΔTM, a dominant-negative form of Bnip3, reduced translocation of GFP (green fluorescent protein)–Bax to mitochondria during sI/R (simulated I/R) in HL-1 myocytes. Similarly, down-regulation of Bnip3 using RNA interference decreased activation of Bax in response to sI/R in HL-1 myocytes. These results suggest that Bnip3 mediates mitochondrial dysfunction through activation of Bax or Bak which is independent of mPTP opening.

scholarly journals Leukemia inhibitory factor regulates trafficking of T-type Ca2+ channels

2011 ◽  
Vol 300 (3) ◽  
pp. C576-C587 ◽  
Author(s):  
Deblina Dey ◽  
Andrew Shepherd ◽  
Judith Pachuau ◽  
Miguel Martin-Caraballo
Keyword(s):  
Membrane Trafficking ◽  
Leukemia Inhibitory Factor ◽  
Fluorescent Protein ◽  
Expression System ◽  
Functional Expression ◽  
Dominant Negative ◽  
Inhibitory Factor ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
293 Cells

Neuropoietic cytokines such as ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) stimulate the functional expression of T-type Ca2+ channels in developing sensory neurons. However, the molecular and cellular mechanisms involved in the cytokine-evoked membrane expression of T-type Ca2+ channels are not fully understood. In this study we investigated the role of LIF in promoting the trafficking of T-type Ca2+ channels in a heterologous expression system. Our results demonstrate that transfection of HEK-293 cells with the rat green fluorescent protein (GFP)-tagged T-type Ca2+ channel α1H-subunit resulted in the generation of transient Ca2+ currents. Overnight treatment of α1H-GFP-transfected cells with LIF caused a significant increase in the functional expression of T-type Ca2+ channels as indicated by changes in current density. LIF also evoked a significant increase in membrane fluorescence compared with untreated cells. Disruption of the Golgi apparatus with brefeldin A inhibited the stimulatory effect of LIF, indicating that protein trafficking regulates the functional expression of T-type Ca2+ channels. Trafficking of α1H-GFP was also disrupted by cotransfection of HEK-293 cells with the dominant-negative form of ADP-ribosylation factor (ARF)1 but not ARF6, suggesting that ARF1 regulates the LIF-evoked membrane trafficking of α1H-GFP subunits. Trafficking of T-type Ca2+ channels required transient activation of the JAK and ERK signaling pathways since stimulation of HEK-293 cells with LIF evoked a considerable increase in the phosphorylation of the downstream JAK targets STAT3 and ERK. Pretreatment of HEK-293 cells with the JAK inhibitor P6 or the ERK inhibitor U0126 blocked ERK phosphorylation. Both P6 and U0126 also inhibited the stimulatory effect of LIF on T-type Ca2+ channel expression. These findings demonstrate that cytokines like LIF promote the trafficking of T-type Ca2+ channels.

Effect of mibefradil on sodium and calcium currents

2005 ◽  
Vol 289 (2) ◽  
pp. G249-G253 ◽  
Author(s):  
Peter R. Strege ◽  
Cheryl E. Bernard ◽  
Yijun Ou ◽  
Simon J. Gibbons ◽  
Gianrico Farrugia
Keyword(s):  
Slow Wave ◽  
Interstitial Cells Of Cajal ◽  
Fluorescent Protein ◽  
Calcium Currents ◽  
Hek 293 ◽  
293 Cells ◽  
Ionic Conductances ◽  
Mouse Intestine ◽  
Green Fluorescent ◽  
Cells Of Cajal

Interstitial cells of Cajal (ICC) generate the electrical slow wave. The ionic conductances that contribute to the slow wave appear to vary among species. In humans, a tetrodotoxin-resistant Na+ current (NaV1.5) encoded by SCN5A contributes to the rising phase of the slow wave, whereas T-type Ca2+ currents have been reported from cultured mouse intestine ICC and also from canine colonic ICC. Mibefradil has a higher affinity for T-type over L-type Ca2+ channels, and the drug has been used in the gastrointestinal tract to identify T-type currents. However, the selectivity of mibefradil for T-type Ca2+ channels over ICC and smooth muscle Na+ channels has not been clearly demonstrated. The aim of this study was to determine the effect of mibefradil on T-type and L-type Ca2+ and Na+ currents. Whole cell currents were recorded from HEK-293 cells coexpressing green fluorescent protein with either the rat brain T-type Ca2+ channel α13.3b + β2, the human intestinal L-type Ca2+ channel subunits α1C + β2, or NaV1.5. Mibefradil significantly reduced expressed T-type Ca2+ current at concentrations ≥ 0.1 μM (IC50 = 0.29 μM), L-type Ca2+ current at > 1 μM (IC50 = 2.7 μM), and Na+ current at ≥ 0.3 μM (IC50 = 0.98 μM). In conclusion, mibefradil inhibits the human intestinal tetrodotoxin-resistant Na+ channel at submicromolar concentrations. Caution must be used in the interpretation of the effects of mibefradil when several ion channel classes are coexpressed.

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