scholarly journals RGS4 and RGS2 Bind Coatomer and Inhibit COPI Association with Golgi Membranes and Intracellular Transport

2000 ◽  
Vol 11 (9) ◽  
pp. 3155-3168 ◽  
Author(s):  
Brandon M. Sullivan ◽  
Kimberly J. Harrison-Lavoie ◽  
Vladimir Marshansky ◽  
Herbert Y. Lin ◽  
John H. Kehrl ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Intracellular Transport ◽  
Gel Filtration ◽  
Inhibitory Effect ◽  
Small Gtpase ◽  
Rgs Proteins ◽  
Placental Alkaline Phosphatase ◽  
Protein Signaling ◽  
Golgi Membranes

COPI, a protein complex consisting of coatomer and the small GTPase ARF1, is an integral component of some intracellular transport carriers. The association of COPI with secretory membranes has been implicated in the maintenance of Golgi integrity and the normal functioning of intracellular transport in eukaryotes. The regulator of G protein signaling, RGS4, interacted with the COPI subunit β′-COP in a yeast two-hybrid screen. Both recombinant RGS4 and RGS2 bound purified recombinant β′-COP in vitro. Endogenous cytosolic RGS4 from NG108 cells and RGS2 from HEK293T cells cofractionated with the COPI complex by gel filtration. Binding of β′-COP to RGS4 occurred through two dilysine motifs in RGS4, similar to those contained in some aminoglycoside antibiotics that are known to bind coatomer. RGS4 inhibited COPI binding to Golgi membranes independently of its GTPase-accelerating activity on Giα. In RGS4-transfected LLC-PK1 cells, the amount of COPI in the Golgi region was considerably reduced compared with that in wild-type cells, but there was no detectable difference in the amount of either Golgi-associated ARF1 or the integral Golgi membrane protein giantin, indicating that Golgi integrity was preserved. In addition, RGS4 expression inhibited trafficking of aquaporin 1 to the plasma membrane in LLC-PK1 cells and impaired secretion of placental alkaline phosphatase from HEK293T cells. The inhibitory effect of RGS4 in these assays was independent of GTPase-accelerating activity but correlated with its ability to bind COPI. Thus, these data support the hypothesis that these RGS proteins sequester coatomer in the cytoplasm and inhibit its recruitment onto Golgi membranes, which may in turn modulate Golgi–plasma membrane or intra-Golgi transport.

Inhibition of Human Platelet Aggregation by the Proteolytic Effect of Streptokinase (SK). Role of the Factor VIII Related Antigen

1975 ◽  
Author(s):  
R. Castillo ◽  
S. Maragall ◽  
J. A. Guisasola ◽  
F. Casals ◽  
C. Ruiz ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Factor Viii ◽  
Platelet Rich Plasma ◽  
Gel Filtration ◽  
Inhibitory Effect ◽  
Factor Viii Related Antigen ◽  
Human Factor Viii ◽  
Induced Aggregation

Defective ADP-induced platelet aggregation has been observed in patients treated with streptokinase. This same effect appears “in vitro” when adding SK to platelet rich plasma (PRP). Classic hemophilia and normal platelet poor plasmas (PPP) treated with SK inhibit the aggregation of washed platelets; plasmin-treated normal human serum also shows an inhibitory effect on platelet aggregation. However, von Willebrand SK-treated plasmas do not inhibit the aggregation of washed platelets. The same results appear when plasmas are previously treated with a rabbit antibody to human factor VIII.This confirms that the antiaggregating effect is mainly linked to the digested factor VIII related antigen.The inhibition of ADP-induced platelet aggregation has been proved in gel filtration-isolated and washed platelets from SK-treated PRP.Defective ristocetin-induced platelet aggregation has also been observed- This action does not appear in washed platelets from SK-treated PRP in presence of normal PPP, but it does in presence of SK-treated PPP, which suggests that the inhibition of the ristocetin-induced aggregation is due to the lack of factor VIII and not to the factor VIII-related products.Heparin, either “in vivo” or “in vitro”, has corrected the antiaggregating effect of SK.

scholarly journals A Ral GAP complex links PI 3-kinase/Akt signaling to RalA activation in insulin action

2011 ◽  
Vol 22 (1) ◽  
pp. 141-152 ◽  
Author(s):  
Xiao-Wei Chen ◽  
Dara Leto ◽  
Tingting Xiong ◽  
Genggeng Yu ◽  
Alan Cheng ◽  
...  
Keyword(s):  
Glucose Transporter ◽  
Critical Role ◽  
Inhibitory Effect ◽  
Small Gtpase ◽  
Regulatory Subunit ◽  
Hydrolysis Of ◽  
Identification And Characterization

Insulin stimulates glucose transport in muscle  and adipose tissue by translocation of glucose transporter 4 (GLUT4) to the plasma membrane. We previously reported that activation of the small GTPase RalA downstream of PI 3-kinase plays a critical role in this process by mobilizing the exocyst complex for GLUT4 vesicle targeting in adipocytes. Here we report the identification and characterization of a Ral GAP complex (RGC) that mediates the activation of RalA downstream of the PI 3-kinase/Akt pathway. The complex is composed of an RGC1 regulatory subunit and an RGC2 catalytic subunit (previously identified as AS250) that directly stimulates the guanosine triphosphate hydrolysis of RalA. Knockdown of RGC proteins leads to increased RalA activity and glucose uptake in adipocytes. Insulin inhibits the GAP complex through Akt2-catalyzed phosphorylation of RGC2 in vitro and in vivo, while activated Akt relieves the inhibitory effect of RGC proteins on RalA activity. The RGC complex thus connects PI 3-kinase/Akt activity to the transport machineries responsible for GLUT4 translocation.

scholarly journals Isolation Purification and Partial Characterization of Antisnake Venom Plant Peptide (BRS-P19) from Bauhinia rufescens (LAM FAM) Seed as Potential Alternative to Serum-Based Antivenin

2020 ◽  
pp. 18-26
Author(s):  
I. Sani ◽  
A.A. Umar ◽  
S.A. Jiga ◽  
F. Bello ◽  
A. Abdulhamid ◽  
...  
Keyword(s):  
Antioxidant Enzymes ◽  
Research Work ◽  
Gel Filtration ◽  
Inhibitory Effect ◽  
Untreated Group ◽  
Control Group ◽  
In Vivo Experiments ◽  
Potential Alternative

Several studies have been reported on active peptides isolated from some medicinal plants, which were effective inhibitors against snake venom induced toxicities. Hence, the aim of this research work was to isolate, purify and characterize an antisnake venom plant peptide from Bauhinia rufescens seed that can serve as potential alternative to serum-based antivenins. B. rufescens seed was collected, duly identified, authenticated and processed. The peptide was isolated from the seed and purified using gel filtration chromatography and SDS-PAGE and then named as BRS-P19. Venom Phospholipase A2 (VPLA2) was used for the study and was isolated from Naja nigricollis venom. Albino mice of both sexes were used for in vivo experiments. They were divided into seven (7) groups of three (3) mice each. Group 1 served as normal control, group 2 were injected with VPLA2 only, group 3 and 4 were injected with VPLA2 then treated with BRS-P19 at doses of 0.2 and 0.4 mg/kg b.w. respectively, while mice in group 5 were injected with VPLA2 then treated with standard antivenin, group 6 and 7 were injected with VPLA2 followed by administration of ascorbic acid and α-tocopherol respectively. In all the groups, hepatic and renal levels of reactive oxygen species (ROS), lipid peroxidation (MDA) and activities of antioxidant enzymes were determined. The results showed that, the BRS-P19 has molecular weight of ~19kD. Its percentage in vitro inhibitory effect against VPLA2 was 91.85 ± 0.32%. For the in vivo study, the animals treated with 0.4 mg/kg b.w. of the BRS-P19 showed a significant (P<0.05) decrease in the hepatic and renal ROS and MDA levels when compared with the VPLA2 untreated group. But, the activities of the antioxidant enzymes in all the treated groups were significantly (P<0.05) increased by the BRS-P19 at 0.4 mg/kg b.w. when compared to the VPLA2 untreated group. Based on these findings, it has been established that, BRS-P19 has antisnake venom effect through inhibition of VPLA2 and antioxidant activity as the possible mechanisms of action.

scholarly journals Neutrophil recruitment inhibitory factor: a possible candidate for a novel cytokine

1992 ◽  
Vol 1 (1) ◽  
pp. 49-54 ◽  
Author(s):  
W. M. S. C. Tamashiro ◽  
B. M. Tavares-Murta ◽  
F. Q. Cunha ◽  
M. C. Roque-Barreira ◽  
R. M. D. Nogueira ◽  
...  
Keyword(s):  
Inhibitory Activity ◽  
Inflammatory Responses ◽  
Neutrophil Migration ◽  
Gel Filtration ◽  
Inhibitory Effect ◽  
Neutrophil Recruitment ◽  
Tnf Α ◽  
Inflammatory Stimuli

Inhibitory effect upon neutrophil migration to the inflammatory focus was previously detected in the cell-free incubation fluid of lipopolysaccharide (LPS)-stimulated macrophage monolayers. In the present study we showed that the neutrophil recruitment inhibitory activity from this supernatant was mainly detected in a fraction (P2) obtained by gel filtration chromatography on Sephacryl S-300. P2 fraction was able to inhibit ‘in vivo’ neutrophil emigration induced by different inflammatory stimuli, but it did not affect ‘in vitro’ neutrophil chemotaxis induced by FMLP. When injected intravenously, P2 inhibited oedema induced by carrageenin or immunological stimulus but not the oedema induced by dextran, thus affecting cell-dependent inflammatory responses. It was observed that P2 also induced neutrophil migration when injected locally in peritoneal cavities. This activity was significantly reduced by pretreatment of the animals with dexamethasone. Cytokines, such as IL-8 and TNF-α that are known to exhibit inhibitory effect upon neutrophil migration, were not detected in P2 fraction by highly sensitive assays. Overall the results suggest the existence of a novel cytokine exhibiting ‘in vivo’ neutrophil inhibitory activity, referred as NRIF.

Regulation of Na+/glucose cotransporters.

1997 ◽  
Vol 200 (2) ◽  
pp. 287-293 ◽  
Author(s):  
E M Wright ◽  
J R Hirsch ◽  
D D Loo ◽  
G A Zampighi
Keyword(s):  
Plasma Membrane ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
Protein Kinases ◽  
Maximum Rate ◽  
Intracellular Transport ◽  
Xenopus Laevis Oocytes ◽  
Sugar Absorption ◽  
Vesicle Exocytosis

Na+/glucose cotransporters (SGLTs) are expressed in the small intestine and the proximal renal tubule, where they play a central role in the absorption of glucose and galactose from food and the reabsorption of glucose from the glomerular filtrate. The regulation of intestinal sugar absorption occurs over two distinct time scales, one over days and the other over minutes. This review focuses on the mechanisms involved in the shorter-term regulation. Recent studies of the mouse intestine in vitro demonstrated that Na+/glucose cotransport is increased two- to eightfold within minutes by the application of forskolin, an agent that increases intracellular cyclic AMP levels. Here we explore how cyclic AMP may upregulate Na+/glucose cotransport. Our strategy was to express cloned SGLT1s in Xenopus laevis oocytes and then use electrophysiological methods to measure (i) the kinetics of Na+/glucose cotransport, (ii) the number of cotransporters in the plasma membrane, and (iii) the net rate of exo- and endocytosis before and after activation of protein kinases. To evaluate the role of cotransporter phosphorylation, we have examined the effect of protein kinase activation on various SGLT1 isoforms and other cotransporters. In oocytes expressing rabbit SGLT1, the activation of protein kinase A (PKA) increased the maximum rate of Na+/glucose cotransport by 30%, and the activation of protein kinase C (PKC) decreased the maximum rate of transport by 60%. Changes in maximum transport rates were accompanied by proportional changes in the number of cotransporters in the plasma membrane and by changes in the area of the membrane. We conclude that PKA and PKC regulate rabbit SGLT1 activity by modulating the number of cotransporters in the plasma membrane and that this occurs through regulation of exocytosis and endocytosis. Given the size of intracellular transport vesicles containing SGLT1, 100-120 nm in diameter, and the density of cotransporters in these vesicles, 10-20 per vesicle, we estimate that the net rate of SGLT1 vesicle exocytosis is about 10,000 s-1 and that this rate increases 100-fold after activation of PKA. The effect of PKA is independent of the presence or absence of consensus sites for phosphorylation on SGLT1. Surprisingly, the effects of PKA or PKC depend critically on the sequence of the contransporter being expressed in the oocyte, e.g. activation of PKC inhibited rabbit and rat SGLT1, but stimulated human SGLT1. This dependency suggests that the regulation of vesicle trafficking by protein kinases depends upon the structure of the cotransporter expressed in the oocyte. Similar considerations apply to other classes of cotransporters, such as the neurotransmitter and dipeptide cotransporters. Our working hypothesis is that the regulation of cotransporter expression by protein kinases occurs largely by regulated exo- and endocytosis, and that the effect of the protein kinases is indirect and determined by critical domains in the cotransporter.

Erythrocyte Scaffolding Protein p55 Functions as An Essential Regulator of Neutrophil Polarity

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 318-318
Author(s):  
Brendan J. Quinn ◽  
Athar H. Chishti
Keyword(s):  
Plasma Membrane ◽  
Actin Polymerization ◽  
Leading Edge ◽  
Small Gtpase ◽  
Scaffolding Protein ◽  
Knockout Mouse Model ◽  
Surface Receptors ◽  
Lipid Product ◽  
Chemotactic Gradient

Abstract Erythrocyte p55 is a prototypical member of a family of scaffolding proteins known as Membrane Associated Guanylate Kinase Homologues (MAGUKs). MAGUKs are multi-domain proteins that couple signals from specialized sites at the plasma membrane to intracellular signal transduction pathways and the cytoskeleton. P55 was originally identified in the erythrocytes as part of a ternary complex with protein 4.1R and glycophorin C, providing a critical linkage between the actin cytoskeleton and the plasma membrane. Although p55 is expressed in a variety of tissues, especially hematopoietic cells, its biological function is unclear. Here, using a p55 knockout mouse model, we show that p55 plays a prominent role in the regulation of neutrophil polarization. Neutrophils are the first respondents during infection and injury, adopting a highly polarized morphology when stimulated with chemotactic factors. G proteincoupled surface receptors recognize the external chemotactic gradient and translate it into an internal gradient of signaling molecules. At the front of the cell, accumulation of the lipid product phosphatidylinositol-3,4,5-trisphosphate (PIP3), activation of the small GTPase Rac, and polymerization of F-actin stimulates a positive feedback loop promoting pseudopod formation. Here, we show that neutrophils lacking p55 form multiple transient pseudopods at the sides and back of the cell upon stimulation. P55 is required for limiting the pseudopod in the direction of chemoattractant. As a result, these neutrophils do not migrate efficiently up a chemotactic gradient in vitro. Biochemical analysis indicates that total F-actin polymerization and total Rac activation is similar between wild type and p55 knockout neutrophils. However, we found that phosphorylation of AKT, the major kinase downstream of the phosphatidylinositol 3-kinase (PI3K)-PIP3 pathway, is almost completely blocked in p55 knockout neutrophils. This finding suggests that p55 exerts its functional effect by regulating PIP3 accumulation or its localization at the membrane, which is responsible for amplification of the frontness signal and stability of the leading edge pseudopod. Consistent with this finding, the p55 null mice are significantly more susceptible to spontaneous and induced infections. Taken together, we have identified p55 as a novel mediator of the frontness signal in neutrophils that promotes polarization and efficient chemotaxis.

scholarly journals Arf1p Provides an Unexpected Link between COPI Vesicles and mRNA in Saccharomyces cerevisiae

2004 ◽  
Vol 15 (11) ◽  
pp. 5021-5037 ◽  
Author(s):  
Mark Trautwein ◽  
Jörn Dengjel ◽  
Markus Schirle ◽  
Anne Spang
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Short Range ◽  
Small Gtpase ◽  
Polya Tail ◽  
Cellular Processes ◽  
Golgi Membranes ◽  
The Stability ◽  
Ash1 Mrna

The small GTPase Arf1p is involved in different cellular processes that require its accumulation at specific cellular locations. The recruitment of Arf1p to distinct points of action might be achieved by association of Arf1p with different proteins. To identify new interactors of Arf1p, we performed an affinity chromatography with GTP- or GDP-bound Arf1p proteins. A new interactor of Arf1p-GTP was identified as Pab1p, which binds to the polyA-tail of mRNAs. Pab1p was found to associate with purified COPI-coated vesicles generated from Golgi membranes in vitro. The stability of the Pab1p–Arf1p complex depends on the presence of mRNA. Both symmetrically distributed mRNAs as well as the asymmetrically localized ASH1 mRNA are found in association with Arf1p. Remarkably, Arf1p and Pab1p are both required to restrict ASH1 mRNA to the bud tip. Arf1p and coatomer play an unexpected role in localizing mRNA independent and downstream of the SHE machinery. Hereby acts the SHE machinery in long-range mRNA transport, whereas COPI vesicles could act as short-range and localization vehicles. The endoplasmic reticulum (ER)–Golgi shuttle might be involved in concentrating mRNA at the ER.

scholarly journals The Response of Leukemic Lymphocytes to Cortisol: A Suggested Role of Transcortin

Blood ◽  
1971 ◽  
Vol 37 (4) ◽  
pp. 463-472 ◽  
Author(s):  
SEYMOUR WERTHAMER ◽  
LEONARD AMARAL
Keyword(s):  
Protein A ◽  
Gel Filtration ◽  
Inhibitory Effect ◽  
Lymphocytic Leukemia ◽  
Leukemic Cells ◽  
Absolute Requirement ◽  
Plasma Factor

Abstract Lymphocytes obtained from patients with chronic lymphocytic leukemia (CLL) respond to the in vitro presence of cortisol by depressed incorporation of precursors into RNA and protein. The decreased incorporation of uridine into RNA is the sum of (1) an inhibition in the synthesis of RNA and (2) an enhanced destruction of newly synthesized RNA. Whereas cortisol was not dependent upon plasma for the manifestation of the above effects, the presence of plasma was an absolute requirement in order for cortisol to have an inhibitory effect on the synthesis of protein. A comparison of leukemic and normal lymphocytes demonstrated that the magnitude of inhibition of precursors into RNA and protein was greater in leukemic cells. Because it is believed that the plasma factor required is transcortin, determination of transcortin levels by cortisolbinding gel filtration technics were performed. These indicated that transcortin levels of CLL plasma were about 50 per cent lower than that of the normal. Consequently, further experiments involving type-specific plasma substitutions were performed. The results obtained from these experiments indicated that the magnitude of the effect of cortisol on the synthesis of lymphocyte protein was directly related to the transcortin level of the plasma employed.

scholarly journals Multiple RGS proteins alter neural G protein signaling to allow C. elegans to rapidly change behavior when fed

2000 ◽  
Vol 14 (16) ◽  
pp. 2003-2014 ◽  
Author(s):  
Meng-Qiu Dong ◽  
Daniel Chase ◽  
Georgia A. Patikoglou ◽  
Michael R. Koelle
Keyword(s):  
G Protein ◽  
Egg Laying ◽  
G Protein Signaling ◽  
Rgs Proteins ◽  
Protein Signaling ◽  
C Elegans ◽  
Change Behavior ◽  
Rgs Protein ◽  
Heterotrimeric G Protein Signaling

Regulators of G protein signaling (RGS proteins) inhibit heterotrimeric G protein signaling by activating G protein GTPase activity. Many mammalian RGS proteins are expressed in the brain and can act in vitro on the neural G protein Go, but the biological purpose of this multiplicity of regulators is not clear. We have analyzed all 13 RGS genes in Caenorhabditis elegans and found that three of them influence the aspect of egg-laying behavior controlled by Go signaling. A previously studied RGS protein, EGL-10, affects egg laying under all conditions tested. The other two RGS proteins, RGS-1 and RGS-2, act as Go GTPase activators in vitro but, unlike EGL-10, they do not strongly affect egg laying when worms are allowed to feed constantly. However, rgs-1; rgs-2double mutants fail to rapidly induce egg-laying behavior when refed after starvation. Thus EGL-10 sets baseline levels of signaling, while RGS-1 and RGS-2 appear to redundantly alter signaling to cause appropriate behavioral responses to food.

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