Inhibition of Gαi activity by Gβγ is mediated by PI 3-kinase-γ- and cSrc-dependent tyrosine phosphorylation of Gαi and recruitment of RGS12

The Nature of Noradrenergic Volume Transmission From Locus Coeruleus to Brainstem Mesencephalic Trigeminal Sensory Neurons

Noradrenergic neurons in the locus coeruleus (LC) release noradrenaline (NA) that acts via volume transmission to activate extrasynaptic G-protein coupled receptors (GPCRs) in target cells throughout the brain. As the closest projection, the dorsal LC laterally adjoins the mesencephalic trigeminal nucleus (MTN), in which proprioceptive primary sensory neurons innervating muscle spindles of jaw-closing muscles are exceptionally located. MTN neurons express α₂-adrenergic receptors (α₂-ARs) and display hyperpolarization-activated cyclic nucleotide-gated (HCN) currents (Ihs), which is downregulated by α₂-AR activation. To quantify the activity-dependent outcome of volume transmission of NA from LC to MTN, we investigated how direct LC activation inhibits Ih in MTN neurons by performing dual whole-cell recordings from LC and MTN neurons. Repetition of 20 Hz spike-train evoked with 1-s current-pulse in LC neurons every 30 s resulted in a gradual decrease in Ih evoked every 30 s, revealing a Hill-type relationship between the number of spike-trains in LC neurons and the degree of Ih inhibition in MTN neurons. On the other hand, when microstimulation was applied in LC every 30 s, an LC neuron repeatedly displayed a transient higher-frequency firing followed by a tonic firing at 5–10 Hz for 30 s. This subsequently caused a similar Hill-type inhibition of Ih in the simultaneously recorded MTN neuron, but with a smaller Hill coefficient, suggesting a lower signal transduction efficacy. In contrast, 20 Hz activity induced by a 1-s pulse applied every 5–10 s caused only a transient facilitation of Ih inhibition followed by a forced termination of Ih inhibition. Thus, the three modes of LC activities modulated the volume transmission to activate α₂-adrenergic GPCR to differentially inhibit Ih in MTN neurons.

Opioid receptors signaling network

Opioid receptors belong to the class A G-protein-coupled receptors and are activated by alkaloid opiates such as morphine, and endogenous ligands such as endorphins and enkephalins. Opioid receptors are widely distributed in the human body and are involved in numerous physiological processes through three major classical opioid receptor subtypes; the mu, delta and kappa along with a lesser characterized subtype, opioid receptor-like (ORL1). Opioids are the most potent analgesics and have been extensively used as a therapeutic drug for the treatment of pain and related disorders. Chronic administration of clinically used opioids is associated with adverse effects such as drug tolerance, addiction and constipation. Several investigations attempted to identify the molecular signaling networks associated with endogenous as well as synthetic opiates, however, there is a paucity of a cumulative depiction of these signaling events. Here, we report a systemic collection of downstream molecules pertaining to four subtypes of opioid receptors (MOR, KOR, DOR and ORL1) in the form of a signaling pathway map. We manually curated reactions induced by the activation of opioid receptors from the literature into five categories- molecular association, activation/inhibition, catalysis, transport, and gene regulation. This led to a dataset of 180 molecules, which is collectively represented in the opioid receptor signaling network following NetPath criteria. We believe that the public availability of an opioid receptor signaling pathway map can accelerate biomedical research in this area because of its high therapeutic significance. The opioid receptors signaling pathway map is uploaded to a freely available web resource, WikiPathways enabling ease of access ( https://www.wikipathways.org/index.php/Pathway:WP5093 ).

The protective effect of allicin on myocardial ischemia-reperfusion by inhibition of Ca2+ overload-induced cardiomyocyte apoptosis via the PI3K/GRK2/PLC-γ/IP3R signaling pathway

Purpose: To investigate the protective effect and mechanism of allicin on myocardial ischemia-reperfusion (MI/R) injury.

Methods: We investigated the mechanisms by which allicin attenuated the MI/R injury by focusing on phosphoinositide 3-kinase, G protein coupled receptor kinases 2, phospholipase Cγ and cardiomyocyte apoptosis. Sixty male mice were randomly assigned into three groups: repeated MI/R (model), sham-operated (control), and MI/R+ allicin group (allicin). Ultrasound examination was used to examine the cardiac function. Masson staining was used to evaluate the myocardial infarct area. TUNEL assay was performed to examine the anti-apoptotic effect of allicin. Differentially expressed genes (DEGs) and pathways were analyzed by mRNA microarray analysis. Immunofluorescence staining and western blot were carried out to detect the effect of allicin on the PI3K. A pan-PLC activator, m-3M3FBS, was applied to investigate whether allicin induced cardiomyocyte apoptosis was via the GRK2/PLC/IP3R signaling pathway.

Results: Masson staining and the TUNEL assay revealed that allicin reduced infarct size and played an anti-apoptotic role in M/IR. Ultrasound examination revealed that allicin improved cardiac function after M/IR injury. Gene ontology analysis indicated that the calcium signaling pathway and PI3KCA(PI3K) were selected. Immunofluorescence staining and western blot exposed that PI3K was activated by allicin during MI/R injury. Fura-2AM staining revealed that the PI3K -mediated GRK2/PLC-γ/IP3R pathway may be involved in the protective effect of allicin on MI/R injury.

Conclusions: Allicin has a protective effect on MI/R injury. This effect might be associated with the inhibition of Ca²⁺ overload-induced apoptosis and the inhibition of the PI3K -mediated GRK2/PLC-γ/IP3R signaling pathway.

Macrophage regulator of G-protein signaling 12 contributes to inflammatory pain hypersensitivity

Background

Pain is a predominant symptom in rheumatoid arthritis (RA) patients that results from joint inflammation and is augmented by central sensitization. Regulator of G-protein signaling 12 (RGS12) is the largest protein in the RGS protein family and plays a key role in the development of inflammation. This study investigated the regulation of RGS12 in inflammatory pain and explored the underlying mechanisms and potential RA pain targets.

Methods

Macrophage-specific RGS12-deficient (LysM-Cre⁺;RGS12^fl/fl) mice were generated by mating RGS12^fl/fl mice with LysM-Cre⁺ transgenic mice. Collagen antibody-induced arthritis (CAIA) models were induced in LysM-Cre⁺;RGS12^fl/fl mice by the administration of a cocktail of five monoclonal antibodies and LPS. Mouse nociception was examined using the von Frey and heat plate tests. Primary macrophages and RAW264.7 cells were used to analyze the regulatory function and mechanism of RGS12 in vitro. The expression and function of RGS12 and COX2 (cyclooxygenase 2) were determined by real-time PCR, ELISA, and luciferase assays.

Results

Ablation of RGS12 in macrophages decreased pain-related phenotypes, such as paw swelling, the clinical score, and the inflammatory score, in the CAIA model. LysM-Cre⁺;RGS12^fl/fl mice displayed increased resistance to thermal and mechanical stimulation from day 3 to day 9 during CAIA, indicating the inhibition of inflammatory pain. Overexpression of COX2 and PGE2 in macrophages enhanced RGS12 expression, and PGE2 regulated RGS12 expression through the G-protein-coupled receptors EP2 and EP4. Furthermore, RGS12 or the RGS12 PTB domain strengthened the transcriptional regulation of COX2 by NF-κB, whereas inhibiting NF-κB suppressed RGS12-mediated regulation of COX2 in macrophages.

Conclusions

Our results demonstrate that the deletion of RGS12 in macrophages attenuates inflammatory pain, which is likely due to impaired regulation of the COX2/PGE2 signaling pathway.

A role for Regulator of G protein Signaling-12 (RGS12) in the balance between myoblast proliferation and differentiation

Regulators of G Protein Signaling (RGS proteins) inhibit G protein-coupled receptor (GPCR) signaling by accelerating the GTP hydrolysis rate of activated Gα subunits. Some RGS proteins exert additional signal modulatory functions, and RGS12 is one such protein, with five additional, functional domains: a PDZ domain, a phosphotyrosine-binding domain, two Ras-binding domains, and a Gα·GDP-binding GoLoco motif. RGS12 expression is temporospatially regulated in developing mouse embryos, with notable expression in somites and developing skeletal muscle. We therefore examined whether RGS12 is involved in the skeletal muscle myogenic program. In the adult mouse, RGS12 is expressed in the tibialis anterior (TA) muscle, and its expression is increased early after cardiotoxin-induced injury, suggesting a role in muscle regeneration. Consistent with a potential role in coordinating myogenic signals, RGS12 is also expressed in primary myoblasts; as these cells undergo differentiation and fusion into myotubes, RGS12 protein abundance is reduced. Myoblasts isolated from mice lacking Rgs12 expression have an impaired ability to differentiate into myotubes ex vivo, suggesting that RGS12 may play a role as a modulator/switch for differentiation. We also assessed the muscle regenerative capacity of mice conditionally deficient in skeletal muscle Rgs12 expression (via Pax7-driven Cre recombinase expression), following cardiotoxin-induced damage to the TA muscle. Eight days post-damage, mice lacking RGS12 in skeletal muscle had attenuated repair of muscle fibers. However, when mice lacking skeletal muscle expression of Rgs12 were cross-bred with mdx mice (a model of human Duchenne muscular dystrophy), no increase in muscle degeneration was observed over time. These data support the hypothesis that RGS12 plays a role in coordinating signals during the myogenic program in select circumstances, but loss of the protein may be compensated for within model syndromes of prolonged bouts of muscle damage and repair.

Muscarinic m2 receptor-mediated actin polymerization via PI3 kinase γ and integrin-linked kinase in gastric smooth muscle

BACKGROUND

Actin polymerization plays an important role in smooth muscle contraction. Integrin-linked kinase (ILK) was shown to mediate actin polymerization in airway smooth muscle. The role of ILK in actin polymerization in response to m2 receptor activation was not in gastric smooth muscle.

METHODS

Phosphorylation of paxillin, neuronal Wiskott-Aldrich syndrome protein (N-WASp), and association of paxillin with GEF proteins (Cool2/αPix [Cool2/PAK-interacting exchange factor alpha], Cool1/βPix [Cool1/PAK-interacting exchange factor beta], and DOCK 180 [Dedicator of cytokinesis]) and N-WASp with Arp2/3 complex were measured by western blot. Activation of Cdc42 was determined using an antibody for activated Cdc42. Actin polymerization was measured as an increase in F-actin/G-actin ratio.

RESULTS

Phosphorylation of paxillin, an association of paxillin with GEF proteins, Cdc42 activity, and actin polymerization were increased in response to m2 receptor activation in gastric smooth muscle cells. The increases in paxillin phosphorylation, Cdc42 activity, and actin polymerization were inhibited by a PI3Kγ inhibitor (AS-605240), ILK siRNA, and ILK dominant negative mutant (ILK [R211]). Increase in actin polymerization was also inhibited by Cdc42 dominant negative mutant (Cdc42 [T17N]). Increases in the association of paxillin with GEF proteins, phosphorylation of N-WASp and its association with Arp2/3 complex were inhibited by ILK (R211).

CONCLUSION

In gastric smooth muscle cells, activation of PI3Kγ by muscarinic m2 receptors causes ILK-dependent phosphorylation of paxillin, an association of paxillin with Cdc42 GEF proteins and activation of Cdc42, which, in turn, causes phosphorylation of N-WASp and its association with Arp2/3 complex leading to actin polymerization.

Acetylcholine-dependent upregulation of TASK-1 channels in thalamic interneurons by a smooth muscle-like signalling pathway

KEY POINTS

The ascending brainstem transmitter acetylcholine depolarizes thalamocortical relay neurons while it induces hyperpolarization in local circuit inhibitory interneurons. Sustained K⁺ currents are modulated in thalamic neurons to control their activity modes; for the interneurons the molecular nature of the underlying ion channels is as yet unknown. Activation of TASK-1 K⁺ channels results in hyperpolarization of interneurons and suppression of their action potential firing. The modulation cascade involves a non-receptor tyrosine kinase, c-Src. The present study identifies a novel pathway for the activation of TASK-1 channels in CNS neurons that resembles cholinergic signalling and TASK-1 current modulation during hypoxia in smooth muscle cells.

ABSTRACT

The dorsal part of the lateral geniculate nucleus (dLGN) is the main thalamic site for state-dependent transmission of visual information. Non-retinal inputs from the ascending arousal system and inhibition provided by γ-aminobutyric acid (GABA)ergic local circuit interneurons (INs) control neuronal activity within the dLGN. In particular, acetylcholine (ACh) depolarizes thalamocortical relay neurons by inhibiting two-pore domain potassium (K_2P ) channels. Conversely, ACh also hyperpolarizes INs via an as-yet-unknown mechanism. By using whole cell patch-clamp recordings in brain slices and appropriate pharmacological tools we here report that stimulation of type 2 muscarinic ACh receptors induces IN hyperpolarization by recruiting the G-protein βγ subunit (Gβγ), class-1A phosphatidylinositol-4,5-bisphosphate 3-kinase, and cellular and sarcoma (c-Src) tyrosine kinase, leading to activation of two-pore domain weakly inwardly rectifying K⁺ channel (TWIK)-related acid-sensitive K⁺ (TASK)-1 channels. The latter was confirmed by the use of TASK-1-deficient mice. Furthermore inhibition of phospholipase Cβ as well as an increase in the intracellular level of phosphatidylinositol-3,4,5-trisphosphate facilitated the muscarinic effect. Our results have uncovered a previously unknown role of c-Src tyrosine kinase in regulating IN function in the brain and identified a novel mechanism by which TASK-1 channels are activated in neurons.

RGS12 Is a Novel Tumor-Suppressor Gene in African American Prostate Cancer That Represses AKT and MNX1 Expression

African American (AA) men exhibit a relatively high incidence and mortality due to prostate cancer even after adjustment for socioeconomic factors, but the biological basis for this disparity is unclear. Here, we identify a novel region on chromosome 4p16.3 that is lost selectively in AA prostate cancer. The negative regulator of G-protein signaling RGS12 was defined as the target of 4p16.3 deletions, although it has not been implicated previously as a tumor-suppressor gene. RGS12 transcript levels were relatively reduced in AA prostate cancer, and prostate cancer cell lines showed decreased RGS12 expression relative to benign prostate epithelial cells. Notably, RGS12 exhibited potent tumor-suppressor activity in prostate cancer and prostate epithelial cell lines in vitro and in vivo We found that RGS12 expression correlated negatively with the oncogene MNX1 and regulated its expression in vitro and in vivo Further, MNX1 was regulated by AKT activity, and RGS12 expression decreased total and activated AKT levels. Our findings identify RGS12 as a candidate tumor-suppressor gene in AA prostate cancer, which acts by decreasing expression of AKT and MNX1, establishing a novel oncogenic axis in this disparate disease setting. Cancer Res; 77(16); 4247-57. ©2017 AACR.

Molecular Pharmacology of δ-Opioid Receptors

Opioids are among the most effective analgesics available and are the first choice in the treatment of acute severe pain. However, partial efficacy, a tendency to produce tolerance, and a host of ill-tolerated side effects make clinically available opioids less effective in the management of chronic pain syndromes. Given that most therapeutic opioids produce their actions via µ-opioid receptors (MOPrs), other targets are constantly being explored, among which δ-opioid receptors (DOPrs) are being increasingly considered as promising alternatives. This review addresses DOPrs from the perspective of cellular and molecular determinants of their pharmacological diversity. Thus, DOPr ligands are examined in terms of structural and functional variety, DOPrs' capacity to engage a multiplicity of canonical and noncanonical G protein-dependent responses is surveyed, and evidence supporting ligand-specific signaling and regulation is analyzed. Pharmacological DOPr subtypes are examined in light of the ability of DOPr to organize into multimeric arrays and to adopt multiple active conformations as well as differences in ligand kinetics. Current knowledge on DOPr targeting to the membrane is examined as a means of understanding how these receptors are especially active in chronic pain management. Insight into cellular and molecular mechanisms of pharmacological diversity should guide the rational design of more effective, longer-lasting, and better-tolerated opioid analgesics for chronic pain management.

Pivotal Role of Regulator of G-protein Signaling 12 in Pathological Cardiac Hypertrophy

Cardiac hypertrophy is a major predictor of heart failure and is regulated by diverse signaling pathways. As a typical multi-domain member of the regulator of G-protein signaling (RGS) family, RGS12 plays a regulatory role in various signaling pathways. However, the precise effect of RGS12 on cardiac hypertrophy remains largely unknown. In this study, we observed increased expression of RGS12 in the development of pathological cardiac hypertrophy and heart failure. We then generated genetically engineered mice and neonatal rat cardiomyocytes to investigate the effects of RGS12 during this pathological process. Four weeks after aortic banding, RGS12-deficient hearts showed decreased cardiomyocyte cross area (374.7±43.2 μm(2) versus 487.1±47.9 μm(2) in controls; P<0.05) with preserved fractional shortening (43.0±3.4% versus 28.4±2.2% in controls; P<0.05), whereas RGS12-overexpressing hearts exhibited increased cardiomyocyte cross area (582.4±46.7 μm(2) versus 474.8±40.0 μm(2) in controls; P<0.05) and reduced fractional shortening (20.8±4.1% versus 28.6±3.2% in controls; P<0.05). RGS12 also contributed to angiotensin II-induced hypertrophy in isolated cardiomyocytes. Mechanistically, our data indicated that the activation of MEK1/2-ERK1/2 signaling may be responsible for the prohypertrophic action of RGS12. In addition, the requirement of the MEK1/2-ERK1/2 signaling for RGS12-mediated cardiac hypertrophy was confirmed in rescue experiments using the MEK1/2-specific inhibitor U0126. In conclusion, our findings provide a novel diagnostic and therapeutic target for pathological cardiac hypertrophy and heart failure.

The impact of RGS and other G-protein regulatory proteins on Gαi-mediated signaling in immunity

Leukocyte chemoattractant receptors are members of the G-protein coupled receptor (GPCR) family. Signaling downstream of these receptors directs the localization, positioning and homeostatic trafficking of leukocytes; as well as their recruitment to, and their retention at, inflammatory sites. Ligand induced changes in the molecular conformation of chemoattractant receptors results in the engagement of heterotrimeric G-proteins, which promotes α subunits to undergo GTP/GDP exchange. This results in the functional release of βγ subunits from the heterotrimers, thereby activating downstream effector molecules, which initiate leukocyte polarization, gradient sensing, and directional migration. Pertussis toxin ADP ribosylates Gαi subunits and prevents chemoattractant receptors from triggering Gαi nucleotide exchange. The use of pertussis toxin revealed the essential importance of Gαi subunit nucleotide exchange for chemoattractant receptor signaling. More recent studies have identified a range of regulatory mechanisms that target these receptors and their associated heterotrimeric G-proteins, thereby helping to control the magnitude, kinetics, and duration of signaling. A failure in these regulatory pathways can lead to impaired receptor signaling and immunopathology. The analysis of mice with targeted deletions of Gαi isoforms as well as some of these G-protein regulatory proteins is providing insights into their roles in chemoattractant receptor signaling.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.