G-Proteins: implications for pathophysiology and disease

1994 ◽  
Vol 131 (6) ◽  
pp. 557-574 ◽  
Author(s):  
Jan O Gordeladze ◽  
Per W Johansen ◽  
Ruth H Paulssen ◽  
Eyvind J Paulssen ◽  
Kaare M Gautvik
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Protein Function ◽  
Tyrosine Kinases ◽  
Point Mutations ◽  
Pharmacological Intervention ◽  
Short Term ◽  
Hormonal Activation ◽  
University Of Oslo ◽  
Gtpase Cycle

Gordeladze JO, Johansen PW, Paulssen RH, Paulssen EJ, Gautvik KM. G-Proteins: implications for pathophysiology and disease. Eur J Endocrinol 1994;131:557–74. ISSN 0804–4643 This article focuses on the involvement of G-proteins in neuroendocrine secretion, cell growth and phenotype alterations. The current concept of hormonal activation of the GTPase cycle, as well as the molecular diversity of G-protein families and receptor * G-protein * effector coupling, are described. Also described are certain G-proteins as possible proto-oncogenes and how point mutations and frame shift mutations alter G-protein function and determine the characteristics of various endocrine diseases. The article outlines in detail how receptors and G-proteins interact in prolactin and growth-hormone-secreting pituicytes, how G-proteins are involved in the growth and differentiation of preadipocytes and osteoblasts. All in all, it seems that hormonal activation through G-proteins is modulated through direct intra- and inter-signalling system cross-talk at the plasma membrane level (short-term) and through interactions on the level of transcription (HREs) from tyrosine kinases, steroid-like hormones and metabolic pathways. Pharmacological intervention to treat diseases where G-proteins are involved should take both long and short-term regulatory phenomena into consideration. JO Gordeladze, Institute of Medical Biochemistry, University of Oslo, PO Box 1112, Blindern, 0317 Oslo, Norway

scholarly journals A predictive computational model reveals that GIV/girdin serves as a tunable valve for EGFR-stimulated cyclic AMP signals

2019 ◽  
Vol 30 (13) ◽  
pp. 1621-1633 ◽  
Author(s):  
Michael Getz ◽  
Lee Swanson ◽  
Debashish Sahoo ◽  
Pradipta Ghosh ◽  
Padmini Rangamani
Keyword(s):  
Growth Factor ◽  
G Protein ◽  
G Proteins ◽  
Cross Talk ◽  
Tyrosine Kinases ◽  
Control Valve ◽  
Camp Signaling ◽  
Nucleotide Exchange ◽  
Camp Concentration ◽  
Camp Levels

Cellular levels of the versatile second messenger cyclic (c)AMP are regulated by the antagonistic actions of the canonical G protein → adenylyl cyclase pathway that is initiated by G-protein–coupled receptors (GPCRs) and attenuated by phosphodiesterases (PDEs). Dysregulated cAMP signaling drives many diseases; for example, its low levels facilitate numerous sinister properties of cancer cells. Recently, an alternative paradigm for cAMP signaling has emerged in which growth factor–receptor tyrosine kinases (RTKs; e.g., EGFR) access and modulate G proteins via a cytosolic guanine-nucleotide exchange modulator (GEM), GIV/girdin; dysregulation of this pathway is frequently encountered in cancers. In this study, we present a network-based compartmental model for the paradigm of GEM-facilitated cross-talk between RTKs and G proteins and how that impacts cellular cAMP. Our model predicts that cross-talk between GIV, G αs, and G αi proteins dampens ligand-stimulated cAMP dynamics. This prediction was experimentally verified by measuring cAMP levels in cells under different conditions. We further predict that the direct proportionality of cAMP concentration as a function of receptor number and the inverse proportionality of cAMP concentration as a function of PDE concentration are both altered by GIV levels. Taking these results together, our model reveals that GIV acts as a tunable control valve that regulates cAMP flux after growth factor stimulation. For a given stimulus, when GIV levels are high, cAMP levels are low, and vice versa. In doing so, GIV modulates cAMP via mechanisms distinct from the two most often targeted classes of cAMP modulators, GPCRs and PDEs.

scholarly journals Receptor tyrosine kinases activate heterotrimeric G proteins via phosphorylation within the interdomain cleft of Gαi

2020 ◽  
Author(s):  
Nicholas A. Kalogriopoulos ◽  
Inmaculada Lopez-Sanchez ◽  
Changsheng Lin ◽  
Tony Ngo ◽  
Krishna Midde ◽  
...  
Keyword(s):  
Growth Factor ◽  
G Protein ◽  
G Proteins ◽  
Tyrosine Kinases ◽  
Molecular Mechanisms ◽  
Receptor Tyrosine Kinases ◽  
Second Messengers ◽  
Heterotrimeric G Proteins ◽  
Nucleotide Exchange ◽  
Key Steps

AbstractThe molecular mechanisms by which receptor tyrosine kinases (RTKs) and heterotrimeric G proteins, two major signaling hubs in eukaryotes, independently relay signals across the plasma membrane have been extensively characterized. How these hubs crosstalk has been a long-standing question, but answers remain elusive. Using linear-ion-trap mass spectrometry in combination with biochemical, cellular, and computational approaches, we unravel a mechanism of activation of heterotrimeric G proteins by RTKs and chart the key steps that mediate such activation. Upon growth factor stimulation, the guanine-nucleotide exchange modulator, GIV, dissociates Gαi•βγ trimers, scaffolds monomeric Gαi with RTKs, and facilitates the phosphorylation on two tyrosines located within the inter-domain cleft of Gαi. Phosphorylation triggers the activation of Gαi and inhibits second messengers (cAMP). Tumor-associated mutants reveal how constitutive activation of this pathway impacts cell’s decision to ‘go’ vs. ‘grow’. These insights define a tyrosine-based G protein signaling paradigm and reveal its importance in eukaryotes.Significance StatementGrowth factors and heterotrimeric G proteins are two of the most widely studied signaling pathways in eukaryotes; their crosstalk shapes some of the most fundamental cellular responses in both health and disease. Although mechanisms by which G protein pathways transactivate growth factor RTKs has been well-defined, how the reverse may happen is less understood. This study defines the key steps and cellular consequences of a fundamental mechanism of signal crosstalk that enables RTKs to transactivate heterotrimeric G protein, Gαi. Mutations found in tumors shed light on how derailing this mechanism impacts tumor cell behavior. Thus, findings not only show how cells integrate extracellular signals via pathway crosstalk, but also demonstrate the relevance of this pathway in cancers.

Phospholipase D in rat myometrium: occurrence of a membrane-bound ARF6 (ADP-ribosylation factor 6)-regulated activity controlled by βγ subunits of heterotrimeric G-proteins

2000 ◽  
Vol 352 (2) ◽  
pp. 491-499 ◽  
Author(s):  
Hervé LE STUNFF ◽  
Lien DOKHAC ◽  
Sylvain BOURGOIN ◽  
Marie-France BADER ◽  
Simone HARBON
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Ammonium Sulphate ◽  
Phospholipase D ◽  
Tyrosine Kinases ◽  
Glutathione S Transferase ◽  
Free System ◽  
Adp Ribosylation ◽  
A Cell ◽  
Membrane Bound

Both protein kinase C and protein tyrosine kinases have been shown to be involved in phospholipase D (PLD) activation in intact rat myometrium [Le Stunff, Dokhac and Harbon (2000) J. Pharmacol. Exp. Ther. 292, 629–637]. In this study we assessed the involvement of monomeric G-proteins in PLD activation in a cell-free system derived from myometrial tissue. Both the PLD1 and PLD2 isoforms were detected. Two forms of PLD activity, essentially membrane-bound, were found in myometrial preparations. One form was stimulated by oleate and insensitive to guanosine 5ƀ-[γ-thio] triphosphate (GTP[S]). The second required ammonium sulphate to be detected and was stimulated by GTP[S]. ADP-ribosylation factors (ARF1 and ARF6) and RhoA were immunodetected in myometrial preparations. ARF1 and RhoA were present in the membrane and cytosolic fractions whereas ARF6 was detected exclusively in the membrane fraction. A synthetic myristoylated peptide corresponding to the N-terminal domain of ARF6 [myrARF6(2–13)] totally abolished PLD activation in the presence of ammonium sulphate and GTP[S], whereas myrARF1(2–17) and the inhibitory GDP/GTP-exchange factor, Rho GDI, did not. These data are consistent with a membrane-bound ARF6-regulated PLD activity. Finally, the stimulation of PLD by ARF6 was inhibited by AlF-4 and this inhibition was counteracted by the fusion protein glutathione S-transferase-β-adrenergic receptor kinase 1 (495–689) and by the QEHA peptide (from adenylate cyclase ACII), which act as G-protein βγ-subunit scavengers. It is concluded that G-protein subunits βγ are involved in a pathway modulating PLD activation by ARF6, illustrating cross-talk between heterotrimeric and monomeric G-proteins.

G Protein Regulation of Inwardly Rectifying K+ Channels

Physiology ◽  
1999 ◽  
Vol 14 (5) ◽  
pp. 215-220 ◽  
Author(s):  
Andreas Karschin
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Tyrosine Kinases ◽  
Cellular Responses ◽  
Signaling Cascades ◽  
Channel Activity ◽  
Protein Subunits ◽  
K Channels ◽  
Kir Channel ◽  
Inwardly Rectifying

Inwardly rectifying K+ (Kir) channels respond to receptor-stimulated signaling cascades that involve G proteins and other cytosolic messengers. Channel activity is controlled both by direct coupling of G protein subunits and by phosphorylation via protein serine/threonine and tyrosine kinases. The coincidence of both forms of Kir channel signaling may give rise to complex cellular responses.

Endotoxin tolerance is associated with altered GTP-binding protein function

1992 ◽  
Vol 73 (3) ◽  
pp. 1008-1013 ◽  
Author(s):  
K. A. Coffee ◽  
P. V. Halushka ◽  
S. H. Ashton ◽  
G. E. Tempel ◽  
W. C. Wise ◽  
...  
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Protein Function ◽  
Salmonella Enteritidis ◽  
Endotoxin Tolerance ◽  
Peritoneal Macrophages ◽  
Gtpase Activity ◽  
Guanosine Triphosphatase

Previous studies have suggested that guanine nucleotide regulatory (G) proteins modulate endotoxin-stimulated peritoneal macrophage arachidonic acid (AA) metabolism. Endotoxin-stimulated metabolism of AA by peritoneal macrophages is decreased in endotoxin tolerance (Rogers et al. Prostaglandins 31: 639–650, 1986). These observations led to a study of G protein function and AA metabolism by peritoneal macrophages in endotoxin tolerance. Endotoxin tolerance was induced by the administration of sublethal doses of endotoxin. AA metabolism was assessed by measurement of thromboxane B2 (TxB2), a cyclooxygenase metabolite. NaF (5 mM), an activator of G proteins, significantly stimulated TxB2 synthesis in control macrophages from 7.7 +/- 0.2 to 19.1 +/- 0.6 (SE) ng/ml (P less than 0.05) at 2 h and was partially inhibited by pertussis toxin, suggesting a G protein-dependent mechanism. Salmonella enteritidis endotoxin (50 micrograms/ml) stimulated a similar increase in TxB2 levels (23 +/- 0.4 ng/ml, P less than 0.05). In contrast to control macrophages, macrophages from endotoxin-tolerant rats stimulated with either NaF or S. enteritidis endotoxin had TxB2 levels that were only 30 and 2% of the respective stimulated control cells. Basal guanosine-triphosphatase (GTPase) activity (33 +/- 6 pmol.mg-1.min-1) in endotoxin-tolerant macrophage membranes was significantly lower (P less than 0.05) than control basal activity (158 +/- 5 pmol.mg-1.min-1). This suppression of macrophage GTPase activity was apparent 48 h after the first in vivo sublethal endotoxin injection (100 micrograms/kg ip). The reduced GTPase activity paralleled in vitro cellular hyporesponsiveness to endotoxin-stimulated TxB2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes.

1994 ◽  
Vol 104 (5) ◽  
pp. 941-959 ◽  
Author(s):  
Y Li ◽  
R Hanf ◽  
A S Otero ◽  
R Fischmeister ◽  
G Szabo
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Protein Function ◽  
Calcium Current ◽  
Potassium Current ◽  
Beta Agonist ◽  
Inwardly Rectifying ◽  
Alternate Possibilities ◽  
K Currents

The ability of acetylcholine (ACh) to inhibit beta-agonist stimulated calcium current was compared to its ability to activate the inwardly rectifying potassium current IK(ACh) in frog atrial myocytes. As suggested by previous studies, ACh inhibited the calcium current at concentrations (EC50 = 8 nM) significantly lower than those required for the activation of IK(ACh) (EC50 = 101 nM). The pharmacological profiles of the two responses suggest that despite the differences in agonist sensitivity, both are mediated by the same (m2) type of muscarinic receptors. Intracellular application of GDP beta S, an inhibitor of G protein function, completely abolished both responses, implying that both actions of ACh are coupled to effectors by G proteins. In contrast, intracellular application of pertussis toxin (PTX) shifted to higher concentrations (EC50 = 170 nM) but did not abolish inhibition of the calcium current by ACh even though the block of the IK(ACh) response was complete. Increasingly large PTX concentrations and/or prolonged PTX treatments revealed a limiting, PTX-resistant inhibitory component that appears to be mediated by a PTX-insensitive G protein distinct from that mediating IK(ACh). For the PTX-sensitive components, the different agonist dependencies of IK(ACh) activation and calcium current inhibition may imply that different G proteins mediate each response although alternate possibilities involving the same G protein either functionally sequestered and/or differentially affected by interactions with effectors, can not be ruled out.

scholarly journals Convergence of Wnt, Growth Factor and Trimeric G protein signals on Daple

2017 ◽  
Author(s):  
Nicolas Aznar ◽  
Ying Dunkel ◽  
Nina Sun ◽  
Kendall Satterfield ◽  
Fang He ◽  
...  
Keyword(s):  
Growth Factor ◽  
G Protein ◽  
G Proteins ◽  
Cancer Progression ◽  
Tyrosine Kinases ◽  
Cancer Biology ◽  
Cellular Proliferation ◽  
Epithelial Mesenchymal Transition ◽  
Mesenchymal Transition ◽  
Canonical Wnt

AbstractCellular proliferation, differentiation, and morphogenesis are shaped by multiple signaling cascades; their concurrent dysregulation plays an integral role in cancer progression and is a common feature of many malignancies. Three such cascades that contribute to the oncogenic potential are the Wnt/Frizzled(FZD), growth factor-receptor tyrosine kinases (RTKs), and G-proteins/GPCRs. Here we identify Daple, a modulator of trimeric G-proteins and a Dishevelled (Dvl)-binding protein as an unexpected point of convergence for all three cascades. Daple-dependent activation of Gαi and enhancement of non-canonical Wnt signals is not just triggered by Wnt5a/FZD to suppress tumorigenesis, but also hijacked by growth factor-RTKs to stoke tumor progression. Phosphorylation of Daple by both RTKs and non-RTKs triggers Gαi activation and potentiates non-canonical Wnt signals that trigger epithelial-mesenchymal transition. In patients with colorectal cancers, concurrent upregulation of Daple and the prototype RTK, EGFR, carried poor prognosis. Thus, this work defines a novel growth factor↔G-protein↔Wnt crosstalk paradigm in cancer biology.

Coaction of Electrostatic and Hydrophobic Interactions: Dynamic Constraints on Disordered TrkA Juxtamembrane Domain

2019 ◽  
Author(s):  
Zichen Wang ◽  
Huaxun Fan ◽  
Xiao Hu ◽  
John Khamo ◽  
Jiajie Diao ◽  
...  
Keyword(s):  
Single Molecule ◽  
Protein Function ◽  
Hydrophobic Interactions ◽  
Transmembrane Helix ◽  
Point Mutations ◽  
Salt Bridge ◽  
Receptor Activation ◽  
Membrane Dynamics ◽  
Juxtamembrane Domain ◽  
Joint Work

<p>The receptor tyrosine kinase family transmits signals into cell via a single transmembrane helix and a flexible juxtamembrane domain (JMD). Membrane dynamics makes it challenging to study the structural mechanism of receptor activation experimentally. In this study, we employ all-atom molecular dynamics with Highly Mobile Membrane-Mimetic to capture membrane interactions with the JMD of tropomyosin receptor kinase A (TrkA). We find that PIP<sub>2 </sub>lipids engage in lasting binding to multiple basic residues and compete with salt bridge within the peptide. We discover three residues insertion into the membrane, and perturb it through computationally designed point mutations. Single-molecule experiments indicate the contribution from hydrophobic insertion is comparable to electrostatic binding, and in-cell experiments show that enhanced TrkA-JMD insertion promotes receptor ubiquitination. Our joint work points to a scenario where basic and hydrophobic residues on disordered domains interact with lipid headgroups and tails, respectively, to restrain flexibility and potentially modulate protein function.</p>

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