scholarly journals Multimodular biosensors reveal a novel platform for activation of G proteins by growth factor receptors

2015 ◽  
Vol 112 (9) ◽  
pp. E937-E946 ◽  
Author(s):  
Krishna K. Midde ◽  
Nicolas Aznar ◽  
Melanie B. Laederich ◽  
Gary S. Ma ◽  
Maya T. Kunkel ◽  
...  
Keyword(s):  
Growth Factor ◽  
G Proteins ◽  
Tyrosine Kinases ◽  
Living Cells ◽  
Molecular Engineering ◽  
Fluorescent Biosensors ◽  
Exchange Factor ◽  
Cellular Processes ◽  
Single Living Cells ◽  
G Protein Coupled

Environmental cues are transmitted to the interior of the cell via a complex network of signaling hubs. Receptor tyrosine kinases (RTKs) and trimeric G proteins are two such major signaling hubs in eukaryotes. Conventionally, canonical signal transduction via trimeric G proteins is thought to be triggered exclusively by G protein-coupled receptors. Here we used molecular engineering to develop modular fluorescent biosensors that exploit the remarkable specificity of bimolecular recognition, i.e., of both G proteins and RTKs, and reveal the workings of a novel platform for activation of G proteins by RTKs in single living cells. Comprised of the unique modular makeup of guanidine exchange factor Gα-interacting vesicle-associated protein (GIV)/girdin, a guanidine exchange factor that links G proteins to a variety of RTKs, these biosensors provide direct evidence that RTK–GIV–Gαi ternary complexes are formed in living cells and that Gαi is transactivated within minutes after growth factor stimulation at the plasma membrane. Thus, GIV-derived biosensors provide a versatile strategy for visualizing, monitoring, and manipulating the dynamic association of Gαi with RTKs for noncanonical transactivation of G proteins in cells and illuminate a fundamental signaling event regulated by GIV during diverse cellular processes and pathophysiologic states.

scholarly journals Visualizing endogenous Rho activity with an improved localization-based, genetically encoded biosensor

2021 ◽  
Author(s):  
Eike K. Mahlandt ◽  
Janine J. G. Arts ◽  
Werner J. van der Meer ◽  
Franka H. van der Linden ◽  
Simon Tol ◽  
...  
Keyword(s):  
Rho Gtpases ◽  
Fluorescent Protein ◽  
Rho Gtpase ◽  
Living Cells ◽  
Regulatory Proteins ◽  
Fluorescent Biosensors ◽  
Cellular Processes ◽  
Binding Peptides ◽  
Subcellular Resolution ◽  
G Protein Coupled

Rho GTPases are regulatory proteins, which orchestrate cell features such as morphology, polarity and movement. Therefore, probing Rho GTPase activity is key to understanding processes such as development and cell migration. Localization-based reporters for active Rho GTPases are attractive probes to study Rho GTPase-mediated processes, in real time with subcellular resolution in living cells and tissue. Until now, relocation Rho biosensors seem to only be useful in certain organisms and have not been characterized well. In this paper, we systematically examined the contribution of the fluorescent protein and Rho binding peptides, on the performance of localization-based sensors. To test the performance, we compared relocation efficiency and specificity in cell-based assays. We identified several improved localization-based, genetically encoded, fluorescent biosensors for detecting endogenous Rho activity. This enables a broader application of Rho relocation biosensors, which was demonstrated by using the improved biosensor to visualize Rho activity during several cellular processes, such as cell division, migration and G protein-coupled receptor signaling. Due to the improved avidity of the new biosensors for Rho activity, cellular processes regulated by Rho can be better understood.

scholarly journals Structural basis for activation of trimeric Gi proteins by multiple growth factor receptors via GIV/Girdin

2014 ◽  
Vol 25 (22) ◽  
pp. 3654-3671 ◽  
Author(s):  
Changsheng Lin ◽  
Jason Ear ◽  
Krishna Midde ◽  
Inmaculada Lopez-Sanchez ◽  
Nicolas Aznar ◽  
...  
Keyword(s):  
Growth Factor ◽  
G Proteins ◽  
Protein Interaction ◽  
Cross Talk ◽  
Tyrosine Kinases ◽  
Molecular Mechanisms ◽  
Growth Factor Receptors ◽  
Structural Basis ◽  
Nucleotide Exchange ◽  
Protein Protein Interaction

A long-standing issue in the field of signal transduction is to understand the cross-talk between receptor tyrosine kinases (RTKs) and heterotrimeric G proteins, two major and distinct signaling hubs that control eukaryotic cell behavior. Although stimulation of many RTKs leads to activation of trimeric G proteins, the molecular mechanisms behind this phenomenon remain elusive. We discovered a unifying mechanism that allows GIV/Girdin, a bona fide metastasis-related protein and a guanine-nucleotide exchange factor (GEF) for Gαi, to serve as a direct platform for multiple RTKs to activate Gαi proteins. Using a combination of homology modeling, protein–protein interaction, and kinase assays, we demonstrate that a stretch of ∼110 amino acids within GIV C-terminus displays structural plasticity that allows folding into a SH2-like domain in the presence of phosphotyrosine ligands. Using protein–protein interaction assays, we demonstrated that both SH2 and GEF domains of GIV are required for the formation of a ligand-activated ternary complex between GIV, Gαi, and growth factor receptors and for activation of Gαi after growth factor stimulation. Expression of a SH2-deficient GIV mutant (Arg 1745→Leu) that cannot bind RTKs impaired all previously demonstrated functions of GIV—Akt enhancement, actin remodeling, and cell migration. The mechanistic and structural insights gained here shed light on the long-standing questions surrounding RTK/G protein cross-talk, set a novel paradigm, and characterize a unique pharmacological target for uncoupling GIV-dependent signaling downstream of multiple oncogenic RTKs.

scholarly journals Cyclin-dependent kinase 5 activates guanine nucleotide exchange factor GIV/Girdin to orchestrate migration–proliferation dichotomy

2015 ◽  
Vol 112 (35) ◽  
pp. E4874-E4883 ◽  
Author(s):  
Deepali Bhandari ◽  
Inmaculada Lopez-Sanchez ◽  
Andrew To ◽  
I-Chung Lo ◽  
Nicolas Aznar ◽  
...  
Keyword(s):  
Wound Healing ◽  
Growth Factor ◽  
Transit Time ◽  
Tyrosine Kinases ◽  
Receptor Activation ◽  
Cyclin Dependent Kinase ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Early Endosomes ◽  
Cyclin Dependent Kinase 5

Signals propagated by receptor tyrosine kinases (RTKs) can drive cell migration and proliferation, two cellular processes that do not occur simultaneously—a phenomenon called “migration–proliferation dichotomy.” We previously showed that epidermal growth factor (EGF) signaling is skewed to favor migration over proliferation via noncanonical transactivation of Gαi proteins by the guanine exchange factor (GEF) GIV. However, what turns on GIV-GEF downstream of growth factor RTKs remained unknown. Here we reveal the molecular mechanism by which phosphorylation of GIV by cyclin-dependent kinase 5 (CDK5) triggers GIV's ability to bind and activate Gαi in response to growth factors and modulate downstream signals to establish a dichotomy between migration and proliferation. We show that CDK5 binds and phosphorylates GIV at Ser1674 near its GEF motif. When Ser1674 is phosphorylated, GIV activates Gαi and enhances promigratory Akt signals. Phosphorylated GIV also binds Gαs and enhances endosomal maturation, which shortens the transit time of EGFR through early endosomes, thereby limiting mitogenic MAPK signals. Consequently, this phosphoevent triggers cells to preferentially migrate during wound healing and transmigration of cancer cells. When Ser1674 cannot be phosphorylated, GIV cannot bind either Gαi or Gαs, Akt signaling is suppressed, mitogenic signals are enhanced due to delayed transit time of EGFR through early endosomes, and cells preferentially proliferate. These results illuminate how GIV-GEF is turned on upon receptor activation, adds GIV to the repertoire of CDK5 substrates, and defines a mechanism by which this unusual CDK orchestrates migration–proliferation dichotomy during cancer invasion, wound healing, and development.

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 Phosphorylation of JAK2 at Serine 523: a Negative Regulator of JAK2 That Is Stimulated by GrowthHormone and Epidermal Growth Factor

2006 ◽  
Vol 26 (11) ◽  
pp. 4052-4062 ◽  
Author(s):  
Anna M. Mazurkiewicz-Munoz ◽  
Lawrence S. Argetsinger ◽  
Jean-Louis K. Kouadio ◽  
Allan Stensballe ◽  
Ole N. Jensen ◽  
...  
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Tyrosine Kinases ◽  
Kinase Activity ◽  
Negative Regulator ◽  
Affinity Enrichment ◽  
Extracellular Signal ◽  
Epidermal Growth ◽  
A Site ◽  
G Protein Coupled

ABSTRACT The tyrosine kinase JAK2 is a key signaling protein for at least 20 receptors in the cytokine/hematopoietin receptor superfamily and is a component of signaling for multiple receptor tyrosine kinases and several G-protein-coupled receptors. In this study, phosphopeptide affinity enrichment and mass spectrometry identified serine 523 (Ser523) in JAK2 as a site of phosphorylation. A phosphoserine 523 antibody revealed that Ser523 is rapidly but transiently phosphorylated in response to growth hormone (GH). MEK1 inhibitor UO126 suppresses GH-dependent phosphorylation of Ser523, suggesting that extracellular signal-regulated kinases (ERKs) 1 and/or 2 or another kinase downstream of MEK1 phosphorylate Ser523 in response to GH. Other ERK activators, phorbol 12-myristate 13-acetate and epidermal growth factor, also stimulate phosphorylation of Ser523. When Ser523 in JAK2 was mutated, JAK2 kinase activity as well as GH-dependent tyrosyl phosphorylation of JAK2 and Stat5 was enhanced, suggesting that phosphorylation of Ser523 inhibits JAK2 kinase activity. We hypothesize that phosphorylation of Ser523 in JAK2 by ERKs 1 and/or 2 or other as-yet-unidentified kinases acts in a negative feedback manner to dampen activation of JAK2 in response to GH and provides a mechanism by which prior exposure to environmental factors that regulate Ser523 phosphorylation might modulate the cell's response to GH.

scholarly journals Visualizing endogenous RhoA activity with an improved localization-based, genetically encoded biosensor

2021 ◽  
Author(s):  
Eike K. Mahlandt ◽  
Janine J. G. Arts ◽  
Werner J. van der Meer ◽  
Franka H. van der Linden ◽  
Simon Tol ◽  
...  
Keyword(s):  
Rho Gtpases ◽  
Fluorescent Protein ◽  
Rho Gtpase ◽  
Regulatory Proteins ◽  
Fluorescent Biosensors ◽  
Rhoa Activity ◽  
Cellular Processes ◽  
Binding Peptides ◽  
Subcellular Resolution ◽  
G Protein Coupled

AbstractRho GTPases are regulatory proteins, which orchestrate cell features such as morphology, polarity and movement. Therefore, probing Rho GTPase activity is key to understanding processes such as development, cell migration and wound healing. Localization-based reporters for active Rho GTPases are attractive probes to study Rho GTPase-mediated processes, in real time with subcellular resolution in living cells and tissue. Until now, relocation RhoA biosensors seem to only be useful in certain organisms and have not been characterized well. In this paper, we systematically examined the contribution of the fluorescent protein and RhoA binding peptides, on the performance of localization-based sensors. To test the performance, we compared relocation efficiency and specificity in cell-based assays. We identified several improved localization-based, genetically encoded, fluorescent biosensors for detecting endogenous RhoA activity. This enables a broader application of RhoA relocation biosensors, which was demonstrated by using the improved biosensor to visualize RhoA activity, during cell division, during random migration, at the Golgi membrane and induced by G protein-coupled receptor signaling. Due to the improved avidity of the new biosensors for RhoA activity, cellular processes regulated by RhoA can be better understood.Abstract Figure

scholarly journals Quantitative assessment of constitutive G protein-coupled receptor activity with BRET-based G protein biosensors

2021 ◽  
Author(s):  
Hannes Schihada ◽  
Rawan Shekhani ◽  
Gunnar Schulte
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Mammalian Cells ◽  
Living Cells ◽  
Optical Biosensors ◽  
Heterotrimeric G Proteins ◽  
G Protein Coupled Receptor ◽  
Cellular Expression ◽  
G Protein Coupled ◽  
Constitutively Active

AbstractHeterotrimeric G proteins constitute the primary transducers of G protein-coupled receptor (GPCR) signaling. Besides mediating ligand-induced GPCR activation, G proteins transduce basal levels of activity in various physiological and pathophysiological settings evoked by constitutively active, native GPCRs or disease-related receptor mutants. Several generations of optical biosensors were developed and optimized to monitor GPCR ligand-induced G protein activation, however, quantitative approaches to detect constitutively active GPCRs are not available. Here, we designed and validated a set of eight bioluminescence-resonance-energy-transfer (BRET)-based G protein sensors, covering all four major families of G proteins, and established a protocol to identify constitutive GPCR/G protein signaling in living cells. These sensors rely on the encoding of all three G protein subunits on a single plasmid, enabling their cellular expression at desired relative levels and resulting in reduced signal variability in mammalian cells. Based on this sensor platform, we further present here an experimental protocol to quantify constitutive signaling of native and mutated GPCRs through these heterotrimeric transducers. This approach will aid in the characterization of constitutively active GPCRs and the exploration of their role in health and disease.One Sentence SummaryThis Resource article describes the validation of a biophysical approach to directly assess the constitutive signaling activity of G protein-coupled receptors through heterotrimeric G proteins in living cells using optical biosensors.

scholarly journals PKC regulates the production of fibroblast growth factor 23 (FGF23)

2019 ◽  
Author(s):  
Ludmilla Bär ◽  
Philipp Hase ◽  
Michael Föller
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Tyrosine Kinases ◽  
Membrane Lipids ◽  
Fibroblast Growth Factor 23 ◽  
Fibroblast Growth ◽  
Pkc Isoforms ◽  
Proliferation And Differentiation ◽  
The Impact ◽  
G Protein Coupled

AbstractSerine/threonine protein kinase C (PKC) is activated by diacylglycerol that is released from membrane lipids by phospholipase C in response to activation of G protein-coupled receptors or receptor tyrosine kinases. PKC isoforms are particularly relevant for proliferation and differentiation of cells including osteoblasts. Osteoblasts/osteocytes produce fibroblast growth factor 23 (FGF23), a hormone regulating renal phosphate and vitamin D handling. PKC activates NFκB, a transcription factor complex controlling FGF23 expression. Here, we analyzed the impact of PKC on FGF23 synthesis. Fgf23 expression was analyzed by qRT-PCR in UMR106 osteoblastlike cells and in IDG-SW3 osteocytes. Phorbol ester 12-O-tetradecanoylphorbol-13-acetate (PMA), a PKC activator, up-regulated Fgf23 expression. In contrast, PKC inhibitors calphostin C, Gö6976, sotrastaurin and ruboxistaurin supressed Fgf23 gene expression. NFκB inhibitor withaferin A abolished the stimulatory effect of PMA on Fgf23. PKC is a powerful regulator of FGF23 synthesis, an effect which is at least partly mediated by NFκB.

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.

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