Acute activation of β2-adrenergic receptor regulates focal adhesions through βArrestin2- and p115RhoGEF protein-mediated activation of RhoA

GPCRs that Rhoar the Guanine nucleotide exchange factors

Cell migration, a crucial step in numerous biological processes, is tightly regulated in space and time. Cells employ Rho GTPases, primarily Rho, Rac, and Cdc42, to regulate their motility. Like other small G proteins, Rho GTPases function as biomolecular switches in regulating cell migration by operating between GDP bound 'OFF' and GTP bound 'ON' states. Guanine nucleotide exchange factors (GEFs) catalyse the shuttling of GTPases from OFF to ON state. G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors that are involved in many signalling phenomena including cell survival and cell migration events. In this review, we summarize signalling mechanisms, involving GPCRs, leading to the activation of RhoGEFs. GPCRs exhibit diverse GEF activation modes that include the interaction of heterotrimeric G protein subunits with different domains of GEFs, phosphorylation, protein-protein interaction, protein-lipid interaction, and/or a combination of these processes.

Catecholaminergic Vasopressors Reduce Toll-Like Receptor Agonist-Induced Microvascular Endothelial Cell Permeability But Not Cytokine Production

Supplemental Digital Content is available in the text.

OBJECTIVES:

Catecholaminergic vasopressors are the cornerstone of circulatory shock management. Nevertheless, catecholamines have problematic side effects, arousing a growing interest in noncatecholaminergic agents such as vasopressin or angiotensin-II. However, their respective effects on sepsis-associated microvascular endothelial dysfunction such as permeability or inflammation remain elusive. We investigated the role of catecholamines and other vasopressors on Toll-like receptor agonists-induced microvascular endothelial permeability and inflammation.

SETTING:

University research laboratory/cell research.

SUBJECTS:

Human pulmonary microvascular endothelial cells from multiple donors.

INTERVENTION:

Confluent monolayers of human pulmonary microvascular endothelial cells were treated with Toll-like receptor agonists (lipopolysaccharide, Poly[I:C], or tripalmitoyl-S-glyceryl cysteine) in the presence or absence of epinephrine, norepinephrine, vasopressin, and angiotensin-II. Permeability was inferred from transendothelial resistance, measured using electrical cell impedance sensing, where decreased transendothelial resistance is consistent with increased permeability. Cell-cell junction molecule expression was assessed via immunofluorescence microscopy and flow cytometry. We quantified cytokines in supernatants of Toll-like receptor agonist-treated human pulmonary microvascular endothelial cells.

MEASUREMENTS AND MAIN RESULTS:

Epinephrine and norepinephrine both ameliorate lipopolysaccharide, polyinosinic:polycytidylic acid, or tripalmitoyl-S-glyceryl cysteine–induced reductions in transendothelial resistance, a surrogate for endothelial permeability. In contrast, the noncatecholaminergic agents, vasopressin, and angiotensin-II did not affect Toll-like receptor agonists-induced reductions in transendothelial resistance. β1- and β2-adrenergic receptor antagonists reduced the effects of the catecholamines on transendothelial resistance, whereas α-adrenergic receptor antagonists did not. We observed that epinephrine and norepinephrine induced actin cytoskeletal rearrangement and normalized the membrane expression of proteins involved with adherens-junctions (vascular endothelial-cadherin) and tight-junctions (zona occludens-1). Despite having a substantial effect on endothelial permeability, epinephrine and norepinephrine did not affect human pulmonary microvascular endothelial cell survival or production of interleukin-8, interleukin-6, or monocyte chemoattractant protein-1 (CCL-2) induced by Toll-like receptor agonists, suggesting that these functions are regulated separately from permeability.

CONCLUSIONS:

Our findings demonstrate that treatment with epinephrine or norepinephrine strongly reduces endothelial permeability induced by agonists of multiple Toll-like receptors (Toll-like receptor-2, Toll-like receptor-3, Toll-like receptor-4) in vitro. Our studies suggest that both β1- and β2-adrenergic receptors mediate the stabilizing effects of epinephrine and norepinephrine on the endothelial barrier.

The Short-Chain Fatty Acid Receptor GPR43 Modulates YAP/TAZ via RhoA

GPR43 (also known as FFAR2 or FFA2) is a G-protein-coupled receptor primarily expressed in immune cells, enteroendocrine cells and adipocytes that recognizes short-chain fatty acids, such as acetate, propionate, and butyrate, likely to be implicated in innate immunity and host energy homeostasis. Activated GPR43 suppresses the cAMP level and induces Ca2+ flux via coupling to Gαi and Gαq families, respectively. Additionally, GPR43 is reported to facilitate phosphorylation of ERK through G-protein-dependent pathways and interacts with β-arrestin 2 to inhibit NF-κB signaling. However, other G-protein-dependent and independent signaling pathways involving GPR43 remain to be established. Here, we have demonstrated that GPR43 augments Rho GTPase signaling. Acetate and a synthetic agonist effectively activated RhoA and stabilized YAP/TAZ transcriptional coactivators through interactions of GPR43 with Gαq/11 and Gα12/13. Acetate-induced nuclear accumulation of YAP was blocked by a GPR43-specific inverse agonist. The target genes induced by YAP/TAZ were further regulated by GPR43. Moreover, in THP-1-derived M1-like macrophage cells, the Rho-YAP/TAZ pathway was activated by acetate and a synthetic agonist. Our collective findings suggest that GPR43 acts as a mediator of the Rho-YAP/TAZ pathway.

RhoA Signaling in Immune Cell Response and Cardiac Disease

Chronic inflammation, the activation of immune cells and their cross-talk with cardiomyocytes in the pathogenesis and progression of heart diseases has long been overlooked. However, with the latest research developments, it is increasingly accepted that a vicious cycle exists where cardiomyocytes release cardiocrine signaling molecules that spiral down to immune cell activation and chronic state of low-level inflammation. For example, cardiocrine molecules released from injured or stressed cardiomyocytes can stimulate macrophages, dendritic cells, neutrophils and even T-cells, which then subsequently increase cardiac inflammation by co-stimulation and positive feedback loops. One of the key proteins involved in stress-mediated cardiomyocyte signal transduction is a small GTPase RhoA. Importantly, the regulation of RhoA activation is critical for effective immune cell response and is being considered as one of the potential therapeutic targets in many immune-cell-mediated inflammatory diseases. In this review we provide an update on the role of RhoA at the juncture of immune cell activation, inflammation and cardiac disease.

β-Adrenoceptor regulation of metabolism in U937 derived macrophages

Macrophages have important roles in the immune system including clearing pathogens and wound healing. Metabolic phenotypes in macrophages have been associated with functional phenotypes, where pro-inflammatory macrophages have an increased rate of glycolysis and anti-inflammatory macrophages primarily use oxidative phosphorylation. β-adrenoceptor (βAR) signalling in macrophages has been implicated in disease states such as cancer, atherosclerosis and rheumatoid arthritis. The impact of βAR signalling on macrophage metabolism has not been defined. Using metabolomics and proteomics, we describe the impact of βAR signalling on macrophages treated with isoprenaline. We found that βAR signalling alters proteins involved in cytoskeletal rearrangement and redox homeostasis of the cell. We showed that βAR signalling in macrophages shifts glucose metabolism from glycolysis towards the tricarboxylic acid cycle and pentose phosphate pathways. We also show that βAR signalling perturbs purine metabolism by accumulating adenylate and guanylate pools. Taken together, these results indicate that βAR signalling shifts metabolism to support redox processes and upregulates proteins involved in cytoskeletal changes, which may contribute to βAR effects on macrophage function.

Beta-arrestins operate an on/off control switch for focal adhesion kinase activity

Focal adhesion kinase (FAK) regulates key biological processes downstream of G protein-coupled receptors (GPCRs) in normal and cancer cells, but the modes of kinase activation by these receptors remain unclear. We report that after GPCR stimulation, FAK activation is controlled by a sequence of events depending on the scaffolding proteins β-arrestins and G proteins. Depletion of β-arrestins results in a marked increase in FAK autophosphorylation and focal adhesion number. We demonstrate that β-arrestins interact directly with FAK and inhibit its autophosphorylation in resting cells. Both FAK-β-arrestin interaction and FAK inhibition require the FERM domain of FAK. Following the stimulation of the angiotensin receptor AT1AR and subsequent translocation of the FAK-β-arrestin complex to the plasma membrane, β-arrestin interaction with the adaptor AP-2 releases inactive FAK from the inhibitory complex, allowing its activation by receptor-stimulated G proteins and activation of downstream FAK effectors. Release and activation of FAK in response to angiotensin are prevented by an AP-2-binding deficient β-arrestin and by a specific inhibitor of β-arrestin/AP-2 interaction; this inhibitor also prevents FAK activation in response to vasopressin. This previously unrecognized mechanism of FAK regulation involving a dual role of β-arrestins, which inhibit FAK in resting cells while driving its activation at the plasma membrane by GPCR-stimulated G proteins, opens new potential therapeutic perspectives in cancers with up-regulated FAK.

Leukemia-Associated Rho Guanine Nucleotide Exchange Factor and Ras Homolog Family Member C Play a Role in Glioblastoma Cell Invasion and Resistance

Glioblastoma (GBM) is the most common primary malignant brain cancer in adults. A hallmark of GBM is aggressive invasion of tumor cells into the surrounding normal brain. Both the current standard of care and targeted therapies have largely failed to specifically address this issue. Therefore, identifying key regulators of GBM cell migration and invasion is important. The leukemia-associated Rho guanine nucleotide exchange factor (LARG) has previously been implicated in cell invasion in other tumor types; however, its role in GBM pathobiology remains undefined. Herein, we report that the expression levels of LARG and ras homolog family members C (RhoC), and A (RhoA) increase with glial tumor grade and are highest in GBM. LARG and RhoC protein expression is more prominent in invading cells, whereas RhoA expression is largely restricted to cells in the tumor core. Knockdown of LARG by siRNA inhibits GBM cell migration in vitro and invasion ex vivo in organotypic brain slices. Moreover, siRNA-mediated silencing of RhoC suppresses GBM cell migration in vitro and invasion ex vivo, whereas depletion of RhoA enhances GBM cell migration and invasion, supporting a role for LARG and RhoC in GBM cell migration and invasion. Depletion of LARG increases the sensitivity of GBM cells to temozolomide treatment. Collectively, these results suggest that LARG and RhoC may represent unappreciated targets to inhibit glioma invasion.

New Routes in GPCR/β-Arrestin-Driven Signaling in Cancer Progression and Metastasis

Tumor cells acquire invasive and metastatic behavior by sensing changes in the localization and activation of signaling pathways, which in turn determine changes in actin cytoskeleton. The core-scaffold machinery associated to β-arrestin (β-arr) is a key mechanism of G-protein coupled receptors (GPCR) to achieve spatiotemporal specificity of different signaling complexes driving cancer progression. Within different cellular contexts, the scaffold proteins β-arr1 or β-arr2 may now be considered organizers of protein interaction networks involved in tumor development and metastatic dissemination. Studies have uncovered the importance of the β-arr engagement with a growing number of receptors, signaling molecules, cytoskeleton regulators, epigenetic modifiers, and transcription factors in GPCR-driven tumor promoting pathways. In many of these molecular complexes, β-arrs might provide a physical link to active dynamic cytoskeleton, permitting cancer cells to adapt and modify the tumor microenvironment to promote the metastatic spread. Given the complexity and the multidirectional β-arr-driven signaling in cancer cells, therapeutic targeting of specific GPCR/β-arr molecular mechanisms is an important avenue to explore when considering future new therapeutic options. The focus of this review is to integrate the most recent developments and exciting findings of how highly connected components of β-arr-guided molecular connections to other pathways allow precise control over multiple signaling pathways in tumor progression, revealing ways of therapeutically targeting the convergent signals in patients.

Cytoskeleton actin-binding proteins in clinical behavior of pituitary tumors

Although generally benign, pituitary tumors are frequently locally invasive, with reduced success of neurosurgery and unresponsive to pharmacological treatment with somatostatin or dopamine analogues. The molecular basis of the different biological behavior of pituitary tumors are still poorly identified, but a body of work now suggests that the activity of specific cytoskeleton proteins is a key factor regulating both the invasiveness and drug resistance of these tumors. This review recapitulates the experimental evidence supporting a role for the actin-binding protein filamin A (FLNA) in the regulation of somatostatin and dopamine receptors expression and signaling in pituitary tumors, thus in determining the responsiveness to currently used drugs, somatostatin analogues and dopamine receptor type 2 agonists. Regarding the regulation of invasive behavior of pituitary tumoral cells, we bring evidence to the role of the actin-severing protein cofilin, whose activation status may be modulated by dopaminergic and somatostatinergic drugs, through FLNA involvement. Molecular mechanisms involved in the regulation of FLNA expression and function in pituitary tumors will also be discussed.

β-Arrestins: Multitask Scaffolds Orchestrating the Where and When in Cell Signalling

The β-arrestins (β-arrs) were initially appreciated for the roles they play in the desensitization and endocytosis of G protein-coupled receptors (GPCRs). They are now also known to act as multifunctional adaptor proteins binding many non-receptor protein partners to control multiple signalling pathways. β-arrs therefore act as key regulatory hubs at the crossroads of external cell inputs and functional outputs in cellular processes ranging from gene transcription to cell growth, survival, cytoskeletal regulation, polarity, and migration. An increasing number of studies have also highlighted the scaffolding roles β-arrs play in vivo in both physiological and pathological conditions, which opens up therapeutic avenues to explore. In this introductory review chapter, we discuss the functional roles that β-arrs exert to control GPCR function, their dynamic scaffolding roles and how this impacts signal transduction events, compartmentalization of β-arrs, how β-arrs are regulated themselves, and how the combination of these events culminates in cellular regulation.

Pepducin-mediated cardioprotection via β-arrestin-biased β2-adrenergic receptor-specific signaling

Reperfusion as a therapeutic intervention for acute myocardial infarction-induced cardiac injury itself induces further cardiomyocyte death. β-arrestin (βarr)-biased β-adrenergic receptor (βAR) activation promotes survival signaling responses in vitro; thus, we hypothesize that this pathway can mitigate cardiomyocyte death at the time of reperfusion to better preserve function. However, a lack of efficacious βarr-biased orthosteric small molecules has prevented investigation into whether this pathway relays protection against ischemic injury in vivo. We recently demonstrated that the pepducin ICL1-9, a small lipidated peptide fragment designed from the first intracellular loop of β2AR, allosterically engaged pro-survival signaling cascades in a βarr-dependent manner in vitro. Thus, in this study we tested whether ICL1-9 relays cardioprotection against ischemia/reperfusion (I/R)-induced injury in vivo.

Methods: Wild-type (WT) C57BL/6, β2AR knockout (KO), βarr1KO and βarr2KO mice received intracardiac injections of either ICL1-9 or a scrambled control pepducin (Scr) at the time of ischemia (30 min) followed by reperfusion for either 24 h, to assess infarct size and cardiomyocyte death, or 4 weeks, to monitor the impact of ICL1-9 on long-term cardiac structure and function. Neonatal rat ventricular myocytes (NRVM) were used to assess the impact of ICL1-9 versus Scr pepducin on cardiomyocyte survival and mitochondrial superoxide formation in response to either serum deprivation or hypoxia/reoxygenation (H/R) in vitro and to investigate the associated mechanism(s).

Results: Intramyocardial injection of ICL1-9 at the time of I/R reduced infarct size, cardiomyocyte death and improved cardiac function in a β2AR- and βarr-dependent manner, which led to improved contractile function early and less fibrotic remodeling over time. Mechanistically, ICL1-9 attenuated mitochondrial superoxide production and promoted cardiomyocyte survival in a RhoA/ROCK-dependent manner. RhoA activation could be detected in cardiomyocytes and whole heart up to 24 h post-treatment, demonstrating the stability of ICL1-9 effects on βarr-dependent β2AR signaling.

Conclusion: Pepducin-based allosteric modulation of βarr-dependent β2AR signaling represents a novel therapeutic approach to reduce reperfusion-induced cardiac injury and relay long-term cardiac remodeling benefits.

Designer Approaches for G Protein-Coupled Receptor Modulation for Cardiovascular Disease

The new horizon for cardiac therapy may lie beneath the surface, with the downstream mediators of G protein–coupled receptor (GPCR) activity. Targeted approaches have shown that receptor activation may be biased toward signaling through G proteins or through GPCR kinases (GRKs) and β-arrestins, with divergent functional outcomes. In addition to these canonical roles, numerous noncanonical activities of GRKs and β-arrestins have been demonstrated to modulate GPCR signaling at all levels of receptor activation and regulation. Further, research continues to identify novel GRK/effector and β-arrestin/effector complexes with distinct impacts on cardiac function in the normal heart and the diseased heart. Coupled with the identification of once orphan receptors and endogenous ligands with beneficial cardiovascular effects, this expands the repertoire of GPCR targets. Together, this research highlights the potential for focused therapeutic activation of beneficial pathways, with simultaneous exclusion or inhibition of detrimental signaling, and represents a new wave of therapeutic development.

G Protein-Coupled Receptor Signaling Through β-Arrestin-Dependent Mechanisms

β-arrestin1 (or arrestin2) and β-arrestin2 (or arrestin3) are ubiquitously expressed cytosolic adaptor proteins that were originally discovered for their inhibitory role in G protein-coupled receptor (GPCR) signaling through heterotrimeric G proteins. However, further biochemical characterization revealed that β-arrestins do not just "block" the activated GPCRs, but trigger endocytosis and kinase activation leading to specific signaling pathways that can be localized on endosomes. The signaling pathways initiated by β-arrestins were also found to be independent of G protein activation by GPCRs. The discovery of ligands that blocked G protein activation but promoted β-arrestin binding, or vice-versa, suggested the exciting possibility of selectively activating intracellular signaling pathways. In addition, it is becoming increasingly evident that β-arrestin-dependent signaling is extremely diverse and provokes distinct cellular responses through different GPCRs even when the same effector kinase is involved. In this review, we summarize various signaling pathways mediated by β-arrestins and highlight the physiologic effects of β-arrestin-dependent signaling.

Depression promotes prostate cancer invasion and metastasis via a sympathetic-cAMP-FAK signaling pathway

Depression drives cancer progression and induces poor clinical outcome. However, the mechanisms underlying depression and cancer outcomes are unclear. In this work, we investigated 98 prostate cancer patients and found that patients with high score of psychological depression were correlated with tumor invasion and metastasis. We found focal adhesion kinase (FAK) was increased in cancer patients with metastatic features and high score of depression. FAK knockdown completely blocked depression-promoted tumor invasion in orthotopic transplantation tumors. In Hi-myc mice and a murine model of depression, sympathetic activation was detected in the prostate tissue. Further we showed that FAK activation was dependent on a cAMP-PKA signaling pathway. Our results demonstrated that the activation of a sympathetic-FAK signaling pathway in prostate cancer patients with high degrees of depression facilitates tumor invasion. We suggest that blocking β2AR with propranolol or inhibiting FAK activation with PF562 271 may be novel strategies for depressed patients with invasive prostate cancer.

Rho GTPase signaling complexes in cell migration and invasion

Cell migration is dependent on the dynamic formation and disassembly of actin filament-based structures, including lamellipodia, filopodia, invadopodia, and membrane blebs, as well as on cell-cell and cell-extracellular matrix adhesions. These processes all involve Rho family small guanosine triphosphatases (GTPases), which are regulated by the opposing actions of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Rho GTPase activity needs to be precisely tuned at distinct cellular locations to enable cells to move in response to different environments and stimuli. In this review, we focus on the ability of RhoGEFs and RhoGAPs to form complexes with diverse binding partners, and describe how this influences their ability to control localized GTPase activity in the context of migration and invasion.

Non-visual arrestins regulate the focal adhesion formation via small GTPases RhoA and Rac1 independently of GPCRs

Arrestins recruit a variety of signaling proteins to active phosphorylated G protein-coupled receptors in the plasma membrane and to the cytoskeleton. Loss of arrestins leads to decreased cell migration, altered cell shape, and an increase in focal adhesions. Small GTPases of the Rho family are molecular switches that regulate actin cytoskeleton and affect a variety of dynamic cellular functions including cell migration and cell morphology. Here we show that non-visual arrestins differentially regulate RhoA and Rac1 activity to promote cell spreading via actin reorganization, and focal adhesion formation via two distinct mechanisms. Arrestins regulate these small GTPases independently of G-protein-coupled receptor activation.

Corticotropin-releasing factor overexpression gives rise to sex differences in Alzheimer's disease-related signaling

Several neuropsychiatric and neurodegenerative disorders share stress as a risk factor and are more prevalent in women than in men. Corticotropin-releasing factor (CRF) orchestrates the stress response, and excessive CRF is thought to contribute to the pathophysiology of these diseases. We previously found that the CRF₁ receptor (CRF₁) is sex biased whereby coupling to its GTP-binding protein, Gs, is greater in females, whereas β-arrestin-2 coupling is greater in males. This study used a phosphoproteomic approach in CRF-overexpressing (CRF-OE) mice to test the proof of principle that when CRF is in excess, sex-biased CRF₁ coupling translates into divergent cell signaling that is expressed as different brain phosphoprotein profiles. Cortical phosphopeptides that distinguished female and male CRF-OE mice were overrepresented in unique pathways that were consistent with Gs-dependent signaling in females and β-arrestin-2 signaling in males. Notably, phosphopeptides that were more abundant in female CRF-OE mice were overrepresented in an Alzheimer's disease (AD) pathway. Phosphoproteomic results were validated by demonstrating that CRF overexpression in females was associated with increased tau phosphorylation and, in a mouse model of AD pathology, phosphorylation of β-secretase, the enzyme involved in the formation of amyloid β. These females exhibited increased formation of amyloid β plaques and cognitive impairments relative to males. Collectively, the findings are consistent with a mechanism whereby the excess CRF that characterizes stress-related diseases initiates distinct cellular processes in male and female brains, as a result of sex-biased CRF₁ signaling. Promotion of AD-related signaling pathways through this mechanism may contribute to female vulnerability to AD.

Dopamine receptor type 2 (DRD2) inhibits migration and invasion of human tumorous pituitary cells through ROCK-mediated cofilin inactivation

Non-functioning pituitary tumors (NFPTs) frequently present local invasiveness. Dopamine receptor 2 (DRD2) agonists are the only medical therapy that induces tumor shrinkage in some patients. Invasion requires cytoskeleton rearrangements that are tightly regulated by cofilin pathway, whose alterations correlate with invasion in different tumors. We investigated the effect of DR2D agonist on NFPT cells migration/invasion and the molecular mechanisms involved. We demonstrated that DRD2 agonist reduced migration (-44 ± 25%, p < 0.01) and invasion (-34 ± 6%, p < 0.001) and increased about 4-fold Ser3-phosphorylated inactive cofilin (P-cofilin) in NFPT cells. These effects were abolished by inhibiting ROCK, a kinase that phosphorylates cofilin. The overexpression of wild-type or phosphodeficient S3A-cofilin increased HP75 cells migration (+49 ± 6% and +57 ± 9% vs empty vector, respectively, p < 0.05), while phosphomimetic mutant had no effect. Interestingly, P-cofilin levels were lower in invasive vs non-invasive tumors by both western blot (mean P-cofilin/total cofilin ratio 0.77 and 1.93, respectively, p < 0.05) and immunohistochemistry (mean percentage of P-cofilin positive cells 17.6 and 45.7, respectively, p < 0.05). In conclusion, we showed that the invasiveness of pituitary tumors is promoted by the activation of cofilin, which can be regulated by DRD2 and might represent a novel biomarker for pituitary tumors' invasive behavior.

G protein-coupled receptors directly bind filamin A with high affinity and promote filamin phosphorylation

Although interaction of a few G protein-coupled receptors (GPCRs) with Filamin A, a key actin cross-linking and biomechanical signal transducer protein, has been observed, a comprehensive structure-function analysis of this interaction is lacking. Through a systematic sequence-based analysis, we found that a conserved filamin binding motif is present in the cytoplasmic domains of >20% of the 824 GPCRs encoded in the human genome. Direct high-affinity interaction of filamin binding motif peptides of select GPCRs with the Ig domain of Filamin A was confirmed by nuclear magnetic resonance spectroscopy and isothermal titration calorimetric experiments. Engagement of the filamin binding motif with the Filamin A Ig domain induced the phosphorylation of filamin by protein kinase A in vitro. In transfected cells, agonist activation as well as constitutive activation of representative GPCRs dramatically elicited recruitment and phosphorylation of cellular Filamin A, a phenomenon long known to be crucial for regulating the structure and dynamics of the cytoskeleton. Our data suggest a molecular mechanism for direct GPCR-cytoskeleton coupling via filamin. Until now, GPCR signaling to the cytoskeleton was predominantly thought to be indirect, through canonical G protein-mediated signaling cascades involving GTPases, adenylyl cyclases, phospholipases, ion channels, and protein kinases. We propose that the GPCR-induced filamin phosphorylation pathway is a conserved, novel biochemical signaling paradigm.

Endothelin A receptor drives invadopodia function and cell motility through the β-arrestin/PDZ-RhoGEF pathway in ovarian carcinoma

The endothelin-1 (ET-1)/ET A receptor (ETAR) signalling pathway is a well-established driver of epithelial ovarian cancer (EOC) progression. One key process promoted by ET-1 is tumor cell invasion, which requires the scaffolding functions of β-arrestin-1 (β-arr1) downstream of the receptor; however, the potential role of ET-1 in inducing invadopodia, which are crucial for cellular invasion and tumor metastasis, is completely unknown. We describe here that ET-1/ETAR, through β-arr1, activates RhoA and RhoC GTPase and downstream ROCK (Rho-associated coiled coil-forming kinase) kinase activity, promoting actin-based dynamic remodelling and enhanced cell invasion. This is accomplished by the direct interaction of β-arr1 with PDZ-RhoGEF (postsynaptic density protein 95/disc-large/zonula occludens-RhoGEF). Interestingly, ETAR-mediated invasive properties are related to the regulation of invadopodia, as evaluated by colocalization of actin with cortactin, as well as with TKS5 and MT1-MMP (membrane type 1-matrix metalloproteinase) with areas of matrix degradation, and activation of cofilin pathway, which is crucial for regulating invadopodia activity. Depletion of PDZ-RhoGEF, or β-arr1, or RhoC, as well as the treatment with the dual ET-1 receptor antagonist macitentan, significantly impairs invadopodia function, MMP activity and invasion, demonstrating that β-arr1/PDZ-RhoGEF interaction mediates ETAR-driven ROCK-LIMK-cofilin pathway through the control of RhoC activity. In vivo, macitentan is able to inhibit metastatic dissemination and cofilin phosphorylation. Collectively, our data unveil a noncanonical activation of the RhoC/ROCK pathway through the β-arr1/PDZ-RhoGEF complex as a regulator of ETAR-induced motility and metastasis, establishing ET-1 axis as a novel regulator of invadopodia protrusions through the RhoC/ROCK/LIMK/cofilin pathway during the initial steps of EOC invasion.

Chronophin coordinates cell leading edge dynamics by controlling active cofilin levels

Cofilin, a critical player of actin dynamics, is spatially and temporally regulated to control the direction and force of membrane extension required for cell locomotion. In carcinoma cells, although the signaling pathways regulating cofilin activity to control cell direction have been established, the molecular machinery required to generate the force of the protrusion remains unclear. We show that the cofilin phosphatase chronophin (CIN) spatiotemporally regulates cofilin activity at the cell edge to generate persistent membrane extension. We show that CIN translocates to the leading edge in a PI3-kinase-, Rac1-, and cofilin-dependent manner after EGF stimulation to activate cofilin, promotes actin free barbed end formation, accelerates actin turnover, and enhances membrane protrusion. In addition, we establish that CIN is crucial for the balance of protrusion/retraction events during cell migration. Thus, CIN coordinates the leading edge dynamics by controlling active cofilin levels to promote MTLn3 cell protrusion.

Phenotypic regulation of the sphingosine 1-phosphate receptor miles apart by G protein-coupled receptor kinase 2

The evolutionarily conserved DRY motif at the end of the third helix of rhodopsin-like, class-A G protein-coupled receptors (GPCRs) is a major regulator of receptor stability, signaling activity, and β-arrestin-mediated internalization. Substitution of the DRY arginine with histidine in the human vasopressin receptor results in a loss-of-function phenotype associated with diabetes insipidus. The analogous R150H substitution of the DRY motif in zebrafish sphingosine-1 phosphate receptor 2 (S1p2) produces a mutation, miles apart m⁹³ (mil^m93), that not only disrupts signaling but also impairs heart field migration. We hypothesized that constitutive S1p2 desensitization is the underlying cause of this strong zebrafish developmental defect. We observed in cell assays that the wild-type S1p2 receptor is at the cell surface whereas in distinct contrast the S1p2 R150H receptor is found in intracellular vesicles, blocking G protein but not arrestin signaling activity. Surface S1p2 R150H expression could be restored by inhibition of G protein-coupled receptor kinase 2 (GRK2). Moreover, we observed that β-arrestin 2 and GRK2 colocalize with S1p2 in developing zebrafish embryos and depletion of GRK2 in the S1p2 R150H miles apart zebrafish partially rescued cardia bifida. The ability of reduced GRK2 activity to reverse a developmental phenotype associated with constitutive desensitization supports efforts to genetically or pharmacologically target this kinase in diseases involving biased GPCR signaling.

Central and peripheral nervous systems: master controllers in cancer metastasis

Central and sympathetic nervous systems govern functional activities of many organs. Solid tumors like organs are also innervated by sympathetic nerve fibers. Neurotransmitters released from sympathetic nerve fibers can modulate biological behaviors of tumor cells. Multiple physiologic processes of tumor development may be dominated by central and sympathetic nervous systems as well. Recent studies suggest that dysfunction of central and sympathetic nervous systems and disorder of the hormone network induced by psychological stress may influence malignant progression of cancer by inhibiting the functions of immune system, regulating metabolic reprogramming of tumor cells, and inducing interactions between tumor and stromal cells. Over-release of inflammatory cytokines by tumors may aggravate emotional disorder, triggering the vicious cycles in tumor microenvironment and host macroenvironment. It is reasonable to hypothesize that cancer progression may be controlled by central and sympathetic nervous systems. In this review, we will focus on the recent information about the impacts of central and sympathetic nervous systems on tumor invasion and metastasis.

Development of inhibitors of heterotrimeric Gαi subunits

Heterotrimeric G-proteins are the immediate downstream effectors of G-protein coupled receptors (GPCRs). Endogenous protein guanine nucleotide dissociation inhibitors (GDIs) like AGS3/4 and RGS12/14 function through GPR/Goloco GDI domains. Extensive characterization of GPR domain peptides indicate they function as selective GDIs for Gαi by competing for the GPCR and Gβγ and preventing GDP release. We modified a GPR consensus peptide by testing FGF and TAT leader sequences to make the peptide cell permeable. FGF modification inhibited GDI activity while TAT preserved GDI activity. TAT-GPR suppresses G-protein coupling to the receptor and completely blocked α2-adrenoceptor (α2AR) mediated decreases in cAMP in HEK293 cells at 100nM. We then sought to discover selective small molecule inhibitors for Gαi. Molecular docking was used to identify potential molecules that bind to and stabilize the Gαi-GDP complex by directly interacting with both Gαi and GDP. Gαi-GTP and Gαq-GDP were used as a computational counter screen and Gαq-GDP was used as a biological counter screen. Thirty-seven molecules were tested using nucleotide exchange. STD NMR assays with compound 0990, a quinazoline derivative, showed direct interaction with Gαi. Several compounds showed Gαi specific inhibition and were able to block α2AR mediated regulation of cAMP. In addition to being a pharmacologic tool, GDI inhibition of Gα subunits has the advantage of circumventing the upstream component of GPCR-related signaling in cases of overstimulation by agonists, mutations, polymorphisms, and expression-related defects often seen in disease.

Crosstalk between beta-2-adrenoceptor and muscarinic acetylcholine receptors in the airway

The M3 and M2 muscarinic acetylcholine receptors (mAChRs) and beta-2-adrenoceptors (β2ARs) are important regulators of airway cell function, and drugs targeting these receptors are among the first line drugs in the treatment of the obstructive lung diseases asthma and chronic obstructive lung disease (COPD). Cross-regulation or crosstalk between mAChRs and β2ARs in airway smooth muscle (ASM) helps determine the contractile state of the muscle, thus airway diameter and resistance to airflow. In this review we will detail mAChR and β2AR-signaling and crosstalk, focusing on events in the ASM cell but also addressing the function of these receptors in other cell types that impact airway physiology. We conclude by discussing how recent advances in GPCR pharmacology offer a unique opportunity to fine tune mAChR and β2AR signaling and their crosstalk, and thereby produce superior therapeutics for obstructive lung and other diseases.

βArrestin1 regulates the guanine nucleotide exchange factor RasGRF2 expression and the small GTPase Rac-mediated formation of membrane protrusion and cell motility

βArrestin proteins shuttle between the cytosol and nucleus and have been shown to regulate G protein-coupled receptor signaling, actin remodeling, and gene expression. Here, we tested the hypothesis that βarrestin1 regulates actin remodeling and cell migration through the small GTPase Rac. Depletion of βarrestin1 promotes Rac activation, leading to the formation of multipolar protrusions and increased cell circularity, and overexpression of a dominant negative form of Rac reverses these morphological changes. Small interfering RNA library screen identifies RasGRF2 as a target of βarrestin1. RasGRF2 gene and protein expression levels are elevated following depletion of βarrestin1, and the consequent activation of Rac results in dephosphorylation of cofilin that can promote actin polymerization and formation of multipolar protrusions, thereby retarding cell migration and invasion. Together, these results suggest that βarrestin1 regulates rasgrf2 gene expression and Rac activation to affect membrane protrusion and cell migration and invasion.

Computational study on the different ligands induced conformation change of β2 adrenergic receptor-Gs protein complex

β₂ adrenergic receptor (β₂AR) regulated many key physiological processes by activation of a heterotrimeric GTP binding protein (Gs protein). This process could be modulated by different types of ligands. But the details about this modulation process were still not depicted. Here, we performed molecular dynamics (MD) simulations on the structures of β₂AR-Gs protein in complex with different types of ligands. The simulation results demonstrated that the agonist BI-167107 could form hydrogen bonds with Ser203^5.42, Ser207^5.46 and Asn293^6.55 more than the inverse agonist ICI 118,551. The different binding modes of ligands further affected the conformation of β₂AR. The energy landscape profiled the energy contour map of the stable and dissociated conformation of Gαs and Gβγ when different types of ligands bound to β₂AR. It also showed the minimum energy pathway about the conformational change of Gαs and Gβγ along the reaction coordinates. By using interactive essential dynamics analysis, we found that Gαs and Gβγ domain of Gs protein had the tendency to separate when the inverse agonist ICI 118,551 bound to β₂AR. The α5-helix had a relatively quick movement with respect to transmembrane segments of β₂AR when the inverse agonist ICI 118,551 bound to β₂AR. Besides, the analysis of the centroid distance of Gαs and Gβγ showed that the Gαs was separated from Gβγ during the MD simulations. Our results not only could provide details about the different types of ligands that induced conformational change of β₂AR and Gs protein, but also supplied more information for different efficacies of drug design of β₂AR.

A network-based approach for predicting Hsp27 knock-out targets in mouse skeletal muscles

Thanks to genomics, we have previously identified markers of beef tenderness, and computed a bioinformatic analysis that enabled us to build an interactome in which we found Hsp27 at a crucial node. Here, we have used a network-based approach for understanding the contribution of Hsp27 to tenderness through the prediction of its interactors related to tenderness. We have revealed the direct interactors of Hsp27. The predicted partners of Hsp27 included proteins involved in different functions, e.g. members of Hsp families (Hsp20, Cryab, Hsp70a1a, and Hsp90aa1), regulators of apoptosis (Fas, Chuk, and caspase-3), translation factors (Eif4E, and Eif4G1), cytoskeletal proteins (Desmin) and antioxidants (Sod1). The abundances of 15 proteins were quantified by Western blotting in two muscles of HspB1-null mice and their controls. We observed changes in the amount of most of the Hsp27 predicted targets in mice devoid of Hsp27 mainly in the most oxidative muscle. Our study demonstrates the functional links between Hsp27 and its predicted targets. It suggests that Hsp status, apoptotic processes and protection against oxidative stress are crucial for post-mortem muscle metabolism, subsequent proteolysis, and therefore for beef tenderness.