scholarly journals Role of the Prenyl Group on the G Protein γ Subunit in Coupling Trimeric G Proteins to A1 Adenosine Receptors

1996 ◽  
Vol 271 (31) ◽  
pp. 18588-18595 ◽  
Author(s):  
Hiroshi Yasuda ◽  
Margaret A. Lindorfer ◽  
Karen A. Woodfork ◽  
Julia E. Fletcher ◽  
James C. Garrison
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Adenosine Receptors ◽  
Γ Subunit ◽  
A1 Adenosine Receptors

scholarly journals A2B Adenosine Receptor and Cancer

2019 ◽  
Author(s):  
Zhan-Guo Gao ◽  
Kenneth A. Jacobson
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Anticancer Agents ◽  
Immune Suppression ◽  
Adenosine Receptors ◽  
G Protein Coupled Receptors ◽  
Normal Tissues ◽  
Cancer Tissues ◽  
G Protein Coupled

There are four subtypes of adenosine receptors (ARs), named A1, A2A, A2B and A3, all of which are G protein-coupled receptors. The A2BAR, coupled to both Gαi and Gαq G proteins, is one of the several G-protein-coupled receptors that are expressed in a significantly higher level in some cancer tissues in comparison to adjacent normal tissues. There is growing evidence that the A2BAR plays an important role in tumor cell proliferation, angiogenesis, metastasis, and immune suppression. Thus, A2BAR antagonists are potentially novel attractive anticancer agents. Several antagonists targeting at the A2BAR are currently in clinical trials for various types of cancers. In this review, we first describe the signaling, agonists, and antagonists of the A2BAR. We further discuss the role of the A2BAR in the progression of various types cancers, and the rationale of using A2BAR antagonists in cancer therapy

scholarly journals Mutations in the ‘DRY’ motif of the CB1 cannabinoid receptor result in biased receptor variants

2014 ◽  
Vol 54 (1) ◽  
pp. 75-89 ◽  
Author(s):  
Pál Gyombolai ◽  
András D Tóth ◽  
Dániel Tímár ◽  
Gábor Turu ◽  
László Hunyady
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Double Mutant ◽  
Cannabinoid Receptor ◽  
Camp Accumulation ◽  
Protein Activation ◽  
Cb1 Cannabinoid Receptor ◽  
G Protein Activation ◽  
Dry Motif

The role of the highly conserved ‘DRY’ motif in the signaling of the CB1cannabinoid receptor (CB1R) was investigated by inducing single-, double-, and triple-alanine mutations into this site of the receptor. We found that the CB1R-R3.50A mutant displays a partial decrease in its ability to activate heterotrimeric Goproteins (∼80% of WT CB1R (CB1R-WT)). Moreover, this mutant showed an enhanced basal β-arrestin2 (β-arr2) recruitment. More strikingly, the double-mutant CB1R-D3.49A/R3.50A was biased toward β-arrs, as it gained a robustly increased β-arr1 and β-arr2 recruitment ability compared with the WT receptor, while its G-protein activation was decreased. In contrast, the double-mutant CB1R-R3.50A/Y3.51A proved to be G-protein-biased, as it was practically unable to recruit β-arrs in response to agonist stimulus, while still activating G-proteins, although at a reduced level (∼70% of CB1R-WT). Agonist-induced ERK1/2 activation of the CB1R mutants showed a good correlation with their β-arr recruitment ability but not with their G-protein activation or inhibition of cAMP accumulation. Our results suggest that G-protein activation and β-arr binding of the CB1R are mediated by distinct receptor conformations, and the conserved ‘DRY’ motif plays different roles in the stabilization of these conformations, thus mediating both G-protein- and β-arr-mediated functions of CB1R.

scholarly journals Heterotrimeric G-Proteins Are Indispensable for FLT3-ITD autophosphorylation and Oncogenic Function

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2712-2712
Author(s):  
Maike Rehage ◽  
Susanne Wingert ◽  
Nadine Haetscher ◽  
Sabrina Bothur ◽  
Hubert Serve ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
G Protein ◽  
G Proteins ◽  
B Cell Lymphoma ◽  
Physical Interaction ◽  
Heterotrimeric G Proteins ◽  
Leukemic Transformation ◽  
Hematopoietic Stem ◽  
Oncogenic Function

Abstract Heterotrimeric G-proteins transmit signals of G-protein coupled receptors and regulate many basic cellular functions. However, their role in normal and malignant hematopoietic stem cells remains obscure. Activating mutations in the heterotrimeric G-protein Gaq were found in various cancers and its expression is enhanced in diffuse large B-cell lymphoma and T-ALL. Our previous data suggested the involvement of heterotrimeric G-proteins in Flt3-ITD-mediated leukemic transformation. FMS-like tyrosine kinase 3 with internal tandem duplication (FLT3-ITD) is a frequent oncoprotein in acute myeloid leukemia causing constitutive active STAT5 signaling. Here, we investigated a novel role of Gaq in Flt3-ITD-induced leukemic transformation. We could show that Gaq is indispensable for aberrant FLT3-ITD activation and oncogenic function as Gaq activity is necessary to maintain the autophosphorylation of FLT3-ITD. Gaq abrogation resulted in diminished cell proliferation and colony formation as well as delayed leukemogenesis in vivo of Flt3-ITD leukemic cells. Importantly, the growth inhibition could be rescued by addition of IL3 and did not occur in the presence of FLT3 ligand-activated FLT3 wildtype receptor, demonstrating the specificity of Gaq requirement for FLT3-ITD oncogenic signaling. Interestingly, co-immunoprecipitations revealed a direct physical interaction between FLT3-ITD and Gaq which did not require phosphorylation of the receptor tyrosine kinase. Hence, FLT3-ITD hyperphosphorylation seems to be rather a consequence of the interaction than a prerequisite. Flt3-ITD-induced transformation of murine hematopoietic stem/progenitor cells (HSPCs) strictly depended on the presence of Gaq, and the ablation of Gaq/11 in transplanted Flt3-ITD-transduced HSPCs from conditional Gaq/11 double knock-out mice delayed leukemic burden. These findings of an unexpected, yet critical, role of Gaq place the molecule as an important target for antileukemic strategies. Disclosures No relevant conflicts of interest to declare.

scholarly journals A2B Adenosine Receptor and Cancer

2019 ◽  
Vol 20 (20) ◽  
pp. 5139 ◽  
Author(s):  
Zhan-Guo Gao ◽  
Kenneth A. Jacobson
Keyword(s):  
G Proteins ◽  
Anticancer Agents ◽  
Immune Suppression ◽  
Adenosine Receptors ◽  
Immune Surveillance ◽  
G Protein Coupled Receptors ◽  
Normal Tissues ◽  
Cancer Tissues ◽  
G Protein Coupled

There are four subtypes of adenosine receptors (ARs), named A1, A2A, A2B and A3, all of which are G protein-coupled receptors (GPCRs). Locally produced adenosine is a suppressant in anti-tumor immune surveillance. The A2BAR, coupled to both Gαs and Gαi G proteins, is one of the several GPCRs that are expressed in a significantly higher level in certain cancer tissues, in comparison to adjacent normal tissues. There is growing evidence that the A2BAR plays an important role in tumor cell proliferation, angiogenesis, metastasis, and immune suppression. Thus, A2BAR antagonists are novel, potentially attractive anticancer agents. Several antagonists targeting A2BAR are currently in clinical trials for various types of cancers. In this review, we first describe the signaling, agonists, and antagonists of the A2BAR. We further discuss the role of the A2BAR in the progression of various cancers, and the rationale of using A2BAR antagonists in cancer therapy.

G proteins activate ionic conductances at multiple sites in T84 cells

1997 ◽  
Vol 272 (4) ◽  
pp. C1222-C1231
Author(s):  
L. Izu ◽  
M. Li ◽  
R. DeMuro ◽  
M. E. Duffey
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Cell Voltage ◽  
Equilibrium Potential ◽  
T84 Cells ◽  
Ionic Conductances ◽  
Inward Currents ◽  
Cl Channels ◽  
K Current

We examined the role of G proteins in activation of ionic conductances in isolated T84 cells during cholinergic stimulation. When cells were whole cell voltage clamped to the K+ equilibrium potential (E(K)) or Cl- equilibrium potential (E(Cl)) under standard conditions, the cholinergic agonist, carbachol, induced a large oscillating K+ current but only a small inward current. Addition of the GDP analogue, guanosine 5'-O-(2-thiodiphosphate), to pipettes blocked the ability of carbachol to activate the K+ current. Addition of the nonhydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS), to pipettes stimulated large oscillating K+ and inward currents. This occurred even when Ca2+ was absent from the bath but not when the Ca2+ chelator, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, was added to pipettes. When all pipette and bath K+ was replaced with Na+ and cells were voltage clamped between E(Na) and E(Cl), GTPgammaS activated oscillating Na+ and Cl- currents. Finally, addition of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] to pipettes activated large oscillating K+ currents but only small inward currents. These results suggest that a carbachol-induced release of Ca2+ from intracellular stores is activated by a G protein through the phospholipase C-Ins(1,4,5)P3 signaling pathway. In addition, this or another G protein activates Cl- current by directly gating Cl- channels to increase their sensitivity to Ca2+.

Stimulation by G Protein βγ Subunits of Phospholipase C β Isoforms in Human Platelets

1998 ◽  
Vol 79 (05) ◽  
pp. 1008-1013 ◽  
Author(s):  
Yoshiko Banno ◽  
Tomiko Asano ◽  
Yoshinori Nozawa
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Human Platelet ◽  
Minor Component ◽  
Similar Efficacy ◽  
Human Platelets ◽  
Bovine Brain ◽  
Γ Subunit ◽  
A Minor

SummaryDifferent phospholipase C (PLC) isoforms were located in human platelet cytosol and membranes. PLCγ2 and PLCβ3b were mainly located in the cytosol and PLCβ2 and PLCβ3a were in both cytosol and membranes by using specific antibodies against PLC isozymes (Banno Y, Nakashima S, Ohzawa M, Nozawa Y. J Biol Chem 1996; 271: 14989-94). Three PLC fractions activated by G protein βγ subunits were purified from human platelet cytosol and membrane fractions. Two PLC fractions from membranes were identified as PLCβ2 and PLCβ3a, and one from cytosol was PLCβ3b. These PLCβ isoforms were activated by the purified βγ subunits of brain G proteins in the order PLCβ3b > PLCβ3a > PLCβ2. Western blot analysis of γ subunits of the purified platelet G proteins with antibodies against various standard γ subunits revealed that the major component of the γ subunit of Gi2 and Gq was γ5, and that γ7 was a minor component. Studies using various subtypes of βγ subunits, βγ2, βγ3, and βγ7 purified from bovine brain, βγ5 from bovine lung, or βγ12 from bovine spleen, failed to show differences in their ability to stimulate the isolated platelet PLCβ isoforms. These results suggest that the βγ subunits of Gi2 and Gq have similar efficacy in regulation of effectors in human platelets.

Role of A1 adenosine receptors in regulation of vascular tone

2005 ◽  
Vol 288 (3) ◽  
pp. H1411-H1416 ◽  
Author(s):  
Huda E. Tawfik ◽  
J. Schnermann ◽  
Peter J. Oldenburg ◽  
S. Jamal Mustafa
Keyword(s):  
Adenosine Receptors ◽  
Vascular Tone ◽  
Receptor Subtypes ◽  
Vascular Relaxation ◽  
Response Curves ◽  
Cgs 21680 ◽  
A1 Adenosine Receptors ◽  
The Impact ◽  
Regulation Of Vascular Tone

The vascular response to adenosine and its analogs is mediated by four adenosine receptors (ARs), namely, A1, A2A, A2B, and A3. A2AARs and/or A2BARs are involved in adenosine-mediated vascular relaxation of coronary and aortic beds. However, the role of A1ARs in the regulation of vascular tone is less well substantiated. The aim of this study was to determine the role of A1ARs in adenosine-mediated regulation of vascular tone. A1AR-knockout [A1AR(−/−)] mice and available pharmacological tools were used to elucidate the function of A1ARs and the impact of these receptors on the regulation of vascular tone. Isolated aortic rings from A1AR(−/−) and wild-type [A1AR(+/+)] mice were precontracted with phenylephrine, and concentration-response curves for adenosine and its analogs, 5′- N-ethyl-carboxamidoadenosine (NECA, nonselective), 2-chloro- N6-cyclopentyladenosine (CCPA, A1AR selective), 2-(2-carboxyethyl)phenethyl amino-5′- N-ethylcarboxamido-adenosine (CGS-21680, A2A selective), and 2-chloro- N6-3-iodobenzyladenosine-5′- N-methyluronamide (Cl-IBMECA, A3 selective) were obtained to determine relaxation. Adenosine and NECA (0.1 μM) caused small contractions of 13.9 ± 3.0 and 16.4 ± 6.4%, respectively, and CCPA at 0.1 and 1.0 μM caused contractions of 30.8 ± 4.3 and 28.1 ± 3.9%, respectively, in A1AR(+/+) rings. NECA- and CCPA-induced contractions were eliminated by 100 nM of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, selective A1AR antagonist). Adenosine, NECA, and CGS-21680 produced an increase in maximal relaxation in A1AR(−/−) compared with A1AR(+/+) rings, whereas Cl-IBMECA did not produce contraction in either A1AR(+/+) or A1AR(−/−) rings. CCPA-induced contraction at 1.0 μM was eliminated by the PLC inhibitor U-73122. These data suggest that activation of A1ARs causes contraction of vascular smooth muscle through PLC pathways and negatively modulates the vascular relaxation mediated by other adenosine receptor subtypes.

New thoughts on the role of the βγ subunit in G protein signal transduction

2000 ◽  
Vol 78 (5) ◽  
pp. 537-550 ◽  
Author(s):  
Barbara Vanderbeld ◽  
Gregory M Kelly
Keyword(s):  
Signal Transduction ◽  
G Protein ◽  
G Proteins ◽  
G Protein Coupled Receptors ◽  
Limited Information ◽  
Α Subunit ◽  
Downstream Effectors ◽  
Receptor Signal ◽  
G Protein Coupled

Heterotrimeric G proteins are involved in numerous biological processes, where they mediate signal transduction from agonist-bound G-protein-coupled receptors to a variety of intracellular effector molecules and ion channels. G proteins consist of two signaling moieties: a GTP-bound α subunit and a βγ heterodimer. The βγ dimer, recently credited as a significant modulator of G-protein-mediated cellular responses, is postulated to be a major determinant of signaling fidelity between G-protein-coupled receptors and downstream effectors. In this review we have focused on the role of βγ signaling and have included examples to demonstrate the heterogeneity in the heterodimer composition and its implications in signaling fidelity. We also present an overview of some of the effectors regulated by βγ and draw attention to the fact that, although G proteins and their associated receptors play an instrumental role in development, there is rather limited information on βγ signaling in embryogenesis.Key words: G protein, βγ subunit, G-protein-coupled receptor, signal transduction, adenylyl cyclase.

Role of G proteins in stimulation of Na-H exchange by cell shrinkage

1992 ◽  
Vol 262 (2) ◽  
pp. C533-C536 ◽  
Author(s):  
B. A. Davis ◽  
E. M. Hogan ◽  
W. F. Boron
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Transport Processes ◽  
Cell Shrinkage ◽  
Protein Activation ◽  
Kinase C ◽  
G Protein Activation ◽  
Barnacle Muscle Fibers ◽  
Stimulation Of

Many cells respond to shrinkage by stimulating specific ion transport processes (e.g., Na-H exchange). However, it is not known how the cell senses this volume change, nor how this signal is transduced to an ion transporter. We have studied the activation of Na-H exchange in internally dialyzed barnacle muscle fibers, measuring intracellular pH (pHi) with glass microelectrodes. When cells are dialyzed to a pHi of approximately 7.2, Na-H exchange is active only in shrunken cells. We found that the shrinkage-induced stimulation of Na-H exchange, elicited by increasing medium osmolality from 975 to 1,600 mosmol/kgH2O, is inhibited approximately 72% by including in the dialysis fluid 1 mM guanosine 5'-O-(2-thiodiphosphate). The latter is an antagonist of G protein activation. Even in unshrunken cells, Na-H exchange is activated by dialyzing the cell with 1 mM guanosine 5'-O-(3-thiotriphosphate), which causes the prolonged activation of G proteins. Activation of Na-H exchange is also elicited in unshrunken cells by injecting cholera toxin, which activates certain G proteins. Neither exposing cells to 100 nM phorbol 12-myristate 13-acetate nor dialyzing them with a solution containing 20 microM adenosine 3',5'-cyclic monophosphate (cAMP) (or 50 microM dibutyryl cAMP) plus 0.5 mM 3-isobutyl-1-methylxanthine substantially stimulates the exchanger. Thus our data suggest that a G protein plays a key role in the transduction of the shrinkage signal to the Na-H exchanger via a pathway that involves neither protein kinase C nor cAMP.

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