Duration Of Signaling Research Articles

Structural motifs in the RGS RZ subfamily combine to attenuate interactions with Gα subunits

Regulators of G-protein Signaling (RGS) proteins inactivate heterotrimeric G proteins, thereby setting the duration of active signaling. In particular, the RGS RZ subfamily, which consists of RGS17, RGS19, and RGS20, mediates numerous physiological functions and human pathologies – mostly by functioning as GTPase Activating Proteins (GAPs) towards the Gαi subfamily. Yet, which RZ subfamily members mediate particular functions and how their GAP activity and specificity are governed at the amino acid level is not well understood. Here, we show that all RZ subfamily members have similar and relatively low GAP activity towards Gαo. We characterized four RZ-specific structural motifs that mediate this low activity, and suggest they perturb optimal interactions with the Gα subunit. Indeed, inserting these RZ-specific motifs into the representative high-activity RGS16 impaired GAP activity in a non-additive manner. Our results provide residue-level insights into the specificity determinants of the RZ subfamily, and enable to study their interactions in signaling cascades by using redesigned mutants such as those presented in this work.

STAT3 in Skeletal Muscle Function and Disorders

Signal transducer and activator of transcription 3 (STAT3) signaling plays critical roles in regulating skeletal muscle mass, repair, and diseases. In this review, we discuss the upstream activators of STAT3 in skeletal muscles, with a focus on interleukin 6 (IL6) and transforming growth factor beta 1 (TGF-β1). We will also discuss the double-edged effect of STAT3 activation in the muscles, including the role of STAT3 signaling in muscle hypertrophy induced by exercise training or muscle wasting in cachectic diseases and muscular dystrophies. STAT3 is a critical regulator of satellite cell self-renewal after muscle injury. STAT3 knock out affects satellite cell myogenic progression by impairing proliferation and inducing premature differentiation. Recent studies in STAT3 signaling demonstrated its direct role in controlling myogenic capacity of myoblasts and satellite cells, as well as the potential benefit in using STAT3 inhibitors to treat muscle diseases. However, prolonged STAT3 activation in muscles has been shown to be responsible for muscle wasting by activating protein degradation pathways. It is important to balance the extent of STAT3 activation and the duration and location (cell types) of the STAT3 signaling when developing therapeutic interventions. STAT3 signaling in other tissues and organs that can directly or indirectly affects skeletal muscle health are also discussed.

3021 - LGR5 Mediates Positive B-Cell Selection and is Critical for Survival of Normal and Transformed B Cells

Leucine-rich repeat containing G-protein coupled receptor 5 (Lgr5), through binding to its ligand R-spondin, increases strength and duration of Wnt signaling in multiple epithelial tissues, however a role of Lgr5 in hematopoietic cells was not explored. Successful completion of immunoglobulin V(D)J gene recombination and initial encounter of antigen in germinal centers represent key events in the life of developing B cells that promote survival and positive selection. Here, we found that both events result in strong upregulation of Lgr5 surface expression in B cell precursors in the bone marrow and germinal center B cells.

Abstract 102: RUNX3 inhibits invasiveness and stemness through downregulation of Gli-1 in colon cancer cells

Abstract Disabled tumor suppressor genes and hyperactive oncogenes contribute considerably to cell fates during cancer development via genetic alterations such as somatic mutations. To date, little is known about how tumor suppressor genes react to diverse oncogenes during tumor progress. Our previous report showed that RUNX3 inhibits metastasis by preventing vascular endothelial growth factor (VEGF) secretion and suppressed endothelial cell growth and tube formation in colorectal cancer. Hedgehog signaling is crucial for the physiological maintenance and self-renewal of stem cells, and its deregulation is responsible for their tumor development. The mechanisms that inhibit this pathway during the proliferation are poorly understood. Here, we show that the tumor suppressor RUNX3 modulates tumorigenesis in response to cancer cells induced by inhibition by oncogene Gli-1 ubiquitination. Moreover, we demonstrated that RUNX3 and Gli-1 expression had inverse correlation in colorectal cancer cells and tissues. We observed a direct interaction between RUNX3 and Gli-1, promoting ubiquitination of Gli-1 at the intracellular level. The increased ubiquitination of Gli-1 was induced through the E3 ligase β-TrCP. This novel RUNX3-dependent regulatory loop may limit the extent and duration of Hedgehog signaling during extension of tumor initiation capacity. Base on this research, a search for agents that can induce RUNX3 might result in new and effective therapies for colorectal cancer. Citation Format: Bo Ram Kim, Yoo Jin Na, Jung Lim Kim, Soyeon Jeong, Seong Hae Park, Min Jee Jo, YoonA Jeong, Dae-Hee Lee, Sang Cheul Oh. RUNX3 inhibits invasiveness and stemness through downregulation of Gli-1 in colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 102.

Abstract LB-111: Precise regulation of CAR signaling prevents and reverses CAR T cell exhaustion

Abstract In patients with chronic viral infection or cancer, continuous antigen exposure results in T cell exhaustion, which is characterized by sustained co-expression of multiple inhibitory receptors (ex. PD-1, TIM-3, LAG-3) and a hierarchical loss of effector function. Human T cells expressing a high-affinity anti-GD2 chimeric antigen receptor (CAR, HA.28z) develop phenotypic and functional hallmarks of exhaustion due to clustering of surface CAR and tonic signaling in the absence of antigen. In the present study, we exploited the HA.28z CAR as a model to characterize human T cell exhaustion and assess its potential for reversibility. CyTOF analyses of dysfunctional HA.28z CAR T cells demonstrated a distinct phenotype in which canonical exhaustion markers, T cell differentiation markers, and effector transcription factors were differentially expressed compared to CD19.28z CAR T cells that do not tonically signal. To interrogate the reversibility of T cell exhaustion, we engineered a regulatable HA.28z CAR by fusing a destabilization domain to the C-terminus of the CAR that rapidly induces CAR protein degradation. Addition of a small molecule stabilizes the protein and results in CAR surface expression. Using this model, we modulated the duration and intensity of tonic signaling by precisely modulating CAR surface expression. We hypothesized that transient cessation of tonic signaling would allow exhausted CAR T cells to recover and regain effector function. Following onset of exhaustion, elimination of CAR surface expression for 4 days resulted in a profound reversal of the exhausted phenotype. CyTOF analyses of reinvigorated cells indicated enhanced T cell memory formation, diminished surface marker expression of multiple exhaustion markers (ex. PD-1, TIM-3, LAG-3, CTLA-4, CD39) and reduced expression of transcription factors T-bet and Blimp-1. Furthermore, RNA sequencing of exhausted and reinvigorated HA.28z CAR T cells revealed a global molecular reprogramming upon removal of tonic CAR signaling, suggesting that CAR T cell exhaustion is functionally reversible. Upon CAR re-expression and co-culture with tumor antigen, reinvigorated HA.28z CAR T cells exhibited augmented killing and cytokine secretion compared to exhausted cells that continuously expressed surface CAR during expansion. In vivo studies assessing CAR T cell exhaustion reversibility using this model are currently being evaluated. In summary, tuning CAR surface expression offers a novel strategy to augment both the safety and efficacy of CAR T cell therapy. Moreover, these studies suggest that transient “rest” in T cells experiencing chronic antigen stimulation may be one mechanism by which exhaustion is prevented or reversed. Citation Format: Evan W. Weber, Rachel C. Lynn, Meena Malipatlolla, Elena Sotillo, Peng Xu, Crystal L. Mackall. Precise regulation of CAR signaling prevents and reverses CAR T cell exhaustion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-111.

The mitochondrial protease HtrA2 restricts the NLRP3 and AIM2 inflammasomes

Activation of the inflammasome pathway is crucial for effective intracellular host defense. The mitochondrial network plays an important role in inflammasome regulation but the mechanisms linking mitochondrial homeostasis to attenuation of inflammasome activation are not fully understood. Here, we report that the Parkinson’s disease-associated mitochondrial serine protease HtrA2 restricts the activation of ASC-dependent NLRP3 and AIM2 inflammasomes, in a protease activity-dependent manner. Consistently, disruption of the protease activity of HtrA2 results in exacerbated NLRP3 and AIM2 inflammasome responses in macrophages ex vivo and systemically in vivo. Mechanistically, we show that the HtrA2 protease activity regulates autophagy and controls the magnitude and duration of inflammasome signaling by preventing prolonged accumulation of the inflammasome adaptor ASC. Our findings identify HtrA2 as a non-redundant mitochondrial quality control effector that keeps NLRP3 and AIM2 inflammasomes in check.

The adaptor molecule CD2AP in CD4 T cells modulates differentiation of follicular helper T cells during chronic LCMV infection.

CD4 T cell-mediated help to CD8 T cells and B cells is a critical arm of the adaptive immune system required for control of pathogen infection. CD4 T cells express cytokines and co-stimulatory molecules that support a sustained CD8 T cell response and also enhance generation of protective antibody by germinal center B cells. However, the molecular components that modulate CD4 T cell functions in response to viral infection or vaccine are incompletely understood. Here we demonstrate that inactivation of the signaling adaptor CD2-associated protein (CD2AP) promotes CD4 T cell differentiation towards the follicular helper lineage, leading to enhanced control of viral infection by augmented germinal center response in chronic lymphocytic choriomeningitis virus (LCMV) infection. The enhanced follicular helper differentiation is associated with extended duration of TCR signaling and enhanced cytokine production of CD2AP-deficient CD4 T cells specifically under TH1 conditions, while neither prolonged TCR signaling nor enhanced follicular helper differentiation was observed under conditions that induce other helper effector subsets. Despite the structural similarity between CD2AP and the closely related adaptor protein CIN85, we observed defective antibody-mediated control of chronic LCMV infection in mice lacking CIN85 in T cells, suggesting non-overlapping and potentially antagonistic roles for CD2AP and CIN85. These results suggest that tuning of TCR signaling by targeting CD2AP improves protective antibody responses in viral infection.

Peripheral PDGFRα+gp38+ mesenchymal cells support the differentiation of fetal liver-derived ILC2.

Group 2 innate lymphoid cells (ILC2s) are derived from common lymphoid progenitors (CLPs) via several specific precursors, and the transcription factors essential for ILC2 differentiation have been extensively studied. However, the external factors regulating commitment to the ILC lineage as well as the sites and stromal cells that constitute the optimal microenvironment for ILC2-specific differentiation are not fully defined. In this study, we demonstrate that three key external factors, the concentration of interleukin 7 (IL-7) and strength and duration of Notch signaling, coordinately determine the fate of CLP toward the T, B, or ILC lineage. Additionally, we identified three stages of ILC2 in the fetal mesentery that require STAT5 signals for maturation: ILC progenitors, CCR9+ ILC2 progenitors, and KLRG1- immature ILC2. We further demonstrate that ILC2 development is supported by mesenteric platelet-derived growth factor receptor α (PDGFRα)+ glycoprotein 38 (gp38)+ mesenchymal cells. Collectively, our results suggest that early differentiation of ILC2 occurs in the fetal liver via IL-7 and Notch signaling, whereas final differentiation occurs in the periphery with the aid of PDGFRα+gp38+ cells.

Regulation of TCR signaling by CD2AP in CD4 T cells modulates antibody responses to chronic LCMV infection

Abstract CD4 T cell-mediated help to CD8 T cells and B cells is a critical arm of the adaptive immune system required for control of pathogens. CD4 T cells express cytokines and co-stimulatory molecules that support a sustained CD8 T cell response and also enhance generation of protective antibody by germinal center B cells. However, the molecular components that regulate CD4 T cell functions in response to viral infection or vaccine is incompletely understood. Here we demonstrate that inactivation of the signaling adaptor CD2AP promotes CD4 T cell differentiation towards the follicular helper lineage, leading to enhanced control of viral infection by augmented germinal center response in chronic LCMV infection. The enhanced follicular helper differentiation is associated with extended duration of TCR signaling and enhanced cytokine production of CD2AP-deficient CD4 T cells specifically under TH1 conditions, while neither prolonged TCR signaling nor enhanced follicular helper differentiation was observed under conditions that induce other helper effector subsets. These results suggest that tuning of TCR signaling by targeting CD2AP improved protective antibody responses in viral infection.

Vascular wall regulator of G-protein signalling-1 (RGS-1) is required for angiotensin II–mediated blood pressure control

G-Protein coupled receptors (GPCRs) activate intracellular signalling pathways by coupling to heterotrimeric G-proteins that control many physiological processes including blood pressure homeostasis. The Regulator of G-Protein Signalling-1 (RGS1) controls the magnitude and duration of downstream GPCR signalling by acting as a GTPase-activating protein for specific Gα-proteins. RGS1 has contrasting roles in haematopoietic and non-haematopoietic cells. Rgs1−/−ApoE−/− mice are protected from Angiotensin II (Ang II)-induced aortic aneurysm rupture. Conversely, Ang II treatment increases systolic blood pressure to a greater extent in Rgs1−/−ApoE−/− mice than ApoE−/− mice, independent of its role in myeloid cells. However the precise role of RGS1 in hypertension and vascular-derived cells remains unknown. We determined the effects of Rgs1 deletion on vascular function in ApoE−/− mice. Rgs1 deletion led to enhanced vasoconstriction in aortas and mesenteric arteries from ApoE−/− mice in response to phenylephrine (PE) and U46619 respectively. Rgs1 was shown to have a role in the vasculature, with endothelium-dependent vasodilation being impaired, and endothelium-independent dilatation to SNP being enhanced in Rgs1−/−ApoE−/− mesenteric arteries. To address the downstream signalling pathways in vascular smooth muscle cells (VSMCs) in response to Ang II-stimulation, we assessed pErk1/2, pJNK and pp38 MAPK activation in VSMCs transiently transfected with Rgs1. pErk1/2 signalling but not pJNK and pp38 signalling was impaired in the presence of Rgs1. Furthermore, we demonstrated that the enhanced contractile response to PE in Rgs1−/−ApoE−/− aortas was reduced by a MAPK/Erk (MEK) inhibitor and an L-type voltage gated calcium channel antagonist, suggesting that Erk1/2 signalling and calcium influx are major effectors of Rgs1-mediated vascular contractile responses, respectively. These findings indicate RGS1 is a novel regulator of blood pressure homeostasis and highlight RGS1-controlled signalling pathways in the vasculature that may be new drug development targets for hypertension.

Regulator of G‐protein Signaling 6 (RGS6) Modulates Dopamine D2 Autoreceptor Function in Mice

The dopaminergic system plays a critical role in the regulation of movement, motivation and cognition and its dysfunction is linked to various neuropsychiatric disorders including Parkinson's Disease. Presynaptic dopamine D2 autoreceptors modulate dopamine signaling in the brain by attenuating its further synthesis and release following the initial synaptic release of dopamine. Consistent with this function, previous studies have demonstrated that pharmacological activation of D2 autoreceptors by quinpirole inhibits presynaptic dopamine release and suppresses locomotion, effects not observed in DAT‐Cre; D2Rfl/fl mice that lack the D2 autoreceptor. RGS6 is a member of the RGS protein family that functions as a GTPase‐activating protein for Gai/o subunits, thereby controlling the intensity and duration of signaling through Gai/o‐linked GPCRs like the D2R. Interestingly, RGS6 is exclusively expressed in dopaminergic neurons of the substantia nigra pars compacta (SNc) of mice and humans, whose loss causes Parkinson's disease, and RGS6 deficient mice exhibit an age‐dependent loss of SNc and striatal dopamine content as well as Parkinson‐like motor dysfunction. Therefore, we hypothesized that SNc dopamine neuron loss in RGS6 deficient mice might result from a lifetime of exaggerated pre‐synaptic D2 autoreceptor signaling culminating in the accumulation of cytotoxic dopamine. To test this hypothesis, we assessed D2 autoreceptor function both in vitro using mouse striatal slices and in vivo. First, we compared the ability of quinpirole to reduce forskolin‐stimulated PKA‐mediated phosphorylation of tyrosine hydroxylase (Ser40) in acute striatal slices derived from WT and RGS6−/− mice. RGS6 deficiency led to exaggerated quinpirole‐mediated inhibition of tyrosine hydroxylase phosphorylation compared to that observed in WT striatal slices. Consistent with these in vitro findings we also found that when 3 mo. WT and RGS6−/− mice, which do not yet display differences in dopamine content, were treated with quinpirole that RGS6−/− mice were more susceptible to quinpirole‐induced suppression of locomotion compared to WT animals despite the mild hyperactivity that has been reported in young RGS6−/− mice. Furthermore, quinpirole also suppressed unsupported rearing in RGS6−/− mice but not WT mice. Together these results demonstrate that RGS6 functions as a critical regulator of D2 autoreceptors in SNc dopamine neurons to modulate dopamine‐dependent motor behaviors. Therefore, loss of RGS6 would be expected to promote hyperactive D2 autoreceptor signaling in these neurons which may underlie their loss in both RGS6−/− mice and humans with Parkinson's.Support or Funding InformationNIH CA161882, MJ Fox 11551, Iowa Cardiovascular Interdisciplinary Research Fellowship T32HL007121.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

CRISPR/Cas9‐mediated Knockout of G Proteins and β‐arrestins Determines Transducer Specific Contributions to Dopamine D1 Receptor Signaling

Dopamine D1 receptors (D1R), a subclass of G protein‐coupled receptors (GPCRs), regulate important neurobiological processes including movement, memory and responses to rewarding stimuli. D1Rs are also drug targets for treating motor deficits in Parkinson's disease and cognitive and motivational deficits in neuropsychiatric diseases. The D1R canonically activates heterotrimeric Gs and Golf G‐proteins which, in turn, activate adenylyl cyclase to increase cAMP/PKA signaling; however, the D1R also engages β‐arrestin proteins which may transduce an independent wave of intracellular signal transduction by scaffolding and activating kinases. The relative importance of G proteins versus arrestins for controlling the efficacy and duration of D1R signaling remains largely undefined. Here we delineate transducer‐specific contributions involved in D1R signaling using CRISPR/Cas9 genome editing to stably knockout (KO) Gs, Golf, multiple G‐proteins (Gs, Golf, Gq, G11 and G12) and β‐arrestin1/2 in HEK293 cells. Western blots confirmed a complete loss of the various G proteins or β‐arrestin1/2 proteins in KO cells versus wildtype cells. By measuring kinetic live‐cell cAMP production using the GloSensor and dose responses of selective agonists for the D1R (A‐77636, SKF‐81297), β2AR (isoproterenol) or Gs/olf (cholera toxin), we confirmed no cAMP was generated in the Gs/olf and multiple G protein KO cells. In contrast, β‐arrestin 1/2 KO greatly elevated and prolonged the duration of cAMP production after time course treatments with agonists for the D1R or the β2AR. Using antibody feeding followed by live‐cell confocal imaging of an HA tagged D1R, or a cell surface ELISA assay, we determined agonist‐mediated HA‐D1R endocytosis was entirely blocked in β‐arrestin 1/2 KO cells, but that Gs/olf KO had no effect on endocytosis. β‐arrestin1/2 KO also showed impaired agonist‐mediated D1R desensitization. Re‐expression of β‐arrestin 1 or 2 or both isoforms together in KO cells, restored receptor endocytosis and reduced the elevated D1R cAMP responses to that of wildtype cells. Lastly, knockout of Gs/olf or β‐arrestin1/2 differentially influenced the activation level and duration of ERK phosphorylation (p‐ERK). Western blotting indicated Gs/olf knockout completely blocked agonist‐induced p‐ERK induction by both D1R and β2AR agonists over a time course of 40 minutes. However, β‐arrestin1/2 knockout greatly increased and prolonged the duration of D1R and β2AR‐mediated p‐ERK. Taken together, this study provides fundamental insights into mechanisms of D1R signal transduction suggesting β‐arrestins are essential for D1R endocytosis and they primarily limit the intensity and duration of Gs/olf‐mediated D1R signaling. Gs/olf was essential for activating both cAMP signaling and ERK phosphorylation. Using this robust CRISPR/Cas9 KO model, future studies will examine downstream signaling events using proteomics and biased agonists to further define the role of both β‐arrestins and Gs/Golf for D1R pharmacology and signaling.Support or Funding InformationUTMB Center for Addiction Research and Dept. of Pharmacology and ToxicologyThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Dopaminergic Perturbations from Food Restriction and Exercise are Sex‐Dependently Amplified During Adolescence

Eating disorders, which are 2.5‐fold more prevalent in females than males, typically emerge during adolescence. Afflicting at least 3 percent of teenagers, eating disorders such as anorexia nervosa, bulimia nervosa, and binge eating disorder entail severe health consequences in addition to their psychological toll. Yet no effective treatments for eating disorders exist. An established regulator of both eating behaviors and physical activity, the dopaminergic system undergoes a sensitive maturation period during adolescence. However, studies into the role of the dopaminergic system in ontogeny of eating disorders are lacking, as are investigations into dopaminergic system maturation in adolescent females. Here we measured function of the dopamine transporter (DAT), a critical regulator of dopaminergic signaling, using both in vivo high‐speed chronoamperometry and locomotor assays of acute cocaine response. Employing an activity‐based anorexia paradigm for 4–5 days, we investigated how food restriction, free exercise on a running wheel, or the combination thereof impacted DAT function in adult (postnatal day 90) and adolescent (postnatal day 30) Sprague‐Dawley rats of both sexes. Food restriction alone or with exercise in adolescent rats of both sexes produced leftward shifts in the dose‐response to the locomotor‐promoting effects of cocaine, though the maximal response to cocaine was blunted in females within these two groups. In adults, only food restricted females exhibited a significant increase in maximal cocaine‐induced locomotor response. Clearance of dopamine in dorsal striatum was not significantly altered by food restriction and/or exercise in adults. In contrast, food restriction plus exercise significantly attenuated dopamine clearance in adolescent males, and food restriction alone or combined with exercise elicited pronounced dopamine clearance reductions in adolescent females. Together, these findings suggest that adolescent plasticity of the dopaminergic system confers – particularly in females – vulnerability to eating disorders and persistence of associated unhealthy behaviors (e.g., compulsive exercise). Therefore, drugs that enhance dopamine uptake or otherwise reduce dopamine signaling duration may prove efficacious in the treatment of emerging adolescent eating disorders. Ongoing experiments are evaluating striatal DAT expression in these animals, and future experiments will focus on optimizing longer term food restriction and exercise conditions in adolescents to facilitate investigation of pharmacologic interventions.Support or Funding InformationThis research was supported by R21 DA038504 to LCD. TLG is supported by T32 DA031115 to Charles P. France.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cytochrome P4501-inhibiting chemicals amplify aryl hydrocarbon receptor activation and IL-22 production in T helper 17 cells

The aryl hydrocarbon receptor (AHR) controls interleukin 22 production by T helper 17 cells (Th17). IL-22 contributes to intestinal homeostasis but has also been implicated in chronic inflammatory disorders and colorectal cancer, highlighting the need for appropriate regulation of IL-22 production. Upon activation, the AHR induces expression of cytochrome P4501 (CYP1) enzymes which in turn play an important feedback role that curtails the duration of AHR signaling by metabolizing AHR ligands. Recently we described how agents that inhibit CYP1 function potentiate AHR signaling by disrupting metabolic clearance of the endogenous ligand 6-formylindolo[3,2-b]carbazole (FICZ). In the present study, we investigated the immune-modulating effects of environmental pollutants such as polycyclic aromatic hydrocarbons on Th17 differentiation and IL-22 production. Using Th17 cells deficient in CYP1 enzymes (Cyp1a1/1a2/1b1−/−) we show that these chemicals potentiate AHR activation through inhibition of CYP1 enzymes which leads to increases in intracellular AHR agonists. Our findings demonstrate that IL-22 production by Th17 cells is profoundly enhanced by impaired CYP1-function and strongly suggest that chemicals able to modify CYP1 function or expression may disrupt AHR-mediated immune regulation by altering the levels of endogenous AHR agonist(s).

Roles of A-Kinase Anchoring Proteins and Phosphodiesterases in the Cardiovascular System.

A-kinase anchoring proteins (AKAPs) and cyclic nucleotide phosphodiesterases (PDEs) are essential enzymes in the cyclic adenosine 3′-5′ monophosphate (cAMP) signaling cascade. They establish local cAMP pools by controlling the intensity, duration and compartmentalization of cyclic nucleotide-dependent signaling. Various members of the AKAP and PDE families are expressed in the cardiovascular system and direct important processes maintaining homeostatic functioning of the heart and vasculature, e.g., the endothelial barrier function and excitation-contraction coupling. Dysregulation of AKAP and PDE function is associated with pathophysiological conditions in the cardiovascular system including heart failure, hypertension and atherosclerosis. A number of diseases, including autosomal dominant hypertension with brachydactyly (HTNB) and type I long-QT syndrome (LQT1), result from mutations in genes encoding for distinct members of the two classes of enzymes. This review provides an overview over the AKAPs and PDEs relevant for cAMP compartmentalization in the heart and vasculature and discusses their pathophysiological role as well as highlights the potential benefits of targeting these proteins and their protein-protein interactions for the treatment of cardiovascular diseases.

Intensity and duration of TCR signaling is limited by p38 phosphorylation of ZAP-70T293 and destabilization of the signalosome

ZAP-70 is a tyrosine kinase that is essential for initiation of T cell antigen receptor (TCR) signaling. We have found that T cell p38 MAP kinase (MAPK), which is directly phosphorylated and activated by ZAP-70 downstream of the TCR, in turn phosphorylates Thr-293 in the interdomain B region of ZAP-70. Mutant T cells expressing ZAP-70 with an alanine substitution at this residue (ZAP-70T293A) had enhanced TCR proximal signaling and increased effector responses. Lack of ZAP-70T293 phosphorylation increased association of ZAP-70 with the TCR and prolonged the existence of TCR signaling microclusters. These results identify a tight negative feedback loop in which ZAP-70-activated p38 reciprocally phosphorylates ZAP-70 and destabilizes the signaling complex.

Ubiquitinated CD36 sustains insulin-stimulated Akt activation by stabilizing insulin receptor substrate 1 in myotubes

Both the magnitude and duration of insulin signaling are important in executing its cellular functions. Insulin-induced degradation of insulin receptor substrate 1 (IRS1) represents a key negative feedback loop that restricts insulin signaling. Moreover, high concentrations of fatty acids (FAs) and glucose involved in the etiology of obesity-associated insulin resistance also contribute to the regulation of IRS1 degradation. The scavenger receptor CD36 binds many lipid ligands, and its contribution to insulin resistance has been extensively studied, but the exact regulation of insulin sensitivity by CD36 is highly controversial. Herein, we found that CD36 knockdown in C2C12 myotubes accelerated insulin-stimulated Akt activation, but the activated signaling was sustained for a much shorter period of time as compared with WT cells, leading to exacerbated insulin-induced insulin resistance. This was likely due to enhanced insulin-induced IRS1 degradation after CD36 knockdown. Overexpression of WT CD36, but not a ubiquitination-defective CD36 mutant, delayed IRS1 degradation. We also found that CD36 functioned through ubiquitination-dependent binding to IRS1 and inhibiting its interaction with cullin 7, a key component of the multisubunit cullin-RING E3 ubiquitin ligase complex. Moreover, dissociation of the Src family kinase Fyn from CD36 by free FAs or Fyn knockdown/inhibition accelerated insulin-induced IRS1 degradation, likely due to disrupted IRS1 interaction with CD36 and thus enhanced binding to cullin 7. In summary, we identified a CD36-dependent FA-sensing pathway that plays an important role in negative feedback regulation of insulin activation and may open up strategies for preventing or managing type 2 diabetes mellitus.

Regulation of vascular signalling by nuclear Sprouty2 in fetal lung epithelial cells: Implications for co-ordinated airway and vascular branching in lung development.

Sprouty2 (Spry2) acts as a central regulator of tubular growth and branch patterning in the developing mammalian lung by controlling both magnitude and duration of growth factor signalling. To determine if this protein coordinates airway and vascular growth factor signalling, we tested the hypothesis that Spry2 links the primary cue for airway outgrowth, fibroblast growth factor-10 (FGF-10), to genomic events underpinning the expression and release of vascular endothelial growth factor-A (VEGF-A). Using primary fetal distal lung epithelial cells (FDLE) from rat, and immortalised human bronchial epithelial cells (16HBE14o-), we identified a nuclear sub-population of Spry2 which interacted with regions of the rat and human VEGF-A promoter spanning the hypoxia response element (HRE) and adjacent 3′ sites. In FDLE cultured at the PO2 of the fetal lung, FGF-10 relieved the Spry2 interaction at the HRE region by promoting clearance of a 39 kDa form and this was accompanied by histone-3 S10K14 phosphoacetylation, promoter de-methylation, hypoxia inducible factor-1α activation and VEGF-A expression. This repressive characteristic of nuclear Spry2 was relieved in 16HBE14o- by shRNA knockdown, and stable expression of mutants (C218A; C221A) that do not interact with the VEGF-A promoter HRE region. We conclude that nuclear Spry2 acts as a molecular link which co-ordinates airway and vascular growth of the cardiopulmonary system. This identifies Spry2 as a contributing determinant of design optimality in the mammalian lung.

Aryl hydrocarbon receptor signaling modulates antiviral immune responses: ligand metabolism rather than chemical source is the stronger predictor of outcome

The aryl hydrocarbon receptor (AHR) offers a compelling target to modulate the immune system. AHR agonists alter adaptive immune responses, but the consequences differ across studies. We report here the comparison of four agents representing different sources of AHR ligands in mice infected with influenza A virus (IAV): TCDD, prototype exogenous AHR agonist; PCB126, pollutant with documented human exposure; ITE, novel pharmaceutical; and FICZ, degradation product of tryptophan. All four compounds diminished virus-specific IgM levels and increased the proportion of regulatory T cells. TCDD, PCB126 and ITE, but not FICZ, reduced virus-specific IgG levels and CD8+ T cell responses. Similarly, ITE, PCB126, and TCDD reduced Th1 and Tfh cells, whereas FICZ increased their frequency. In Cyp1a1-deficient mice, all compounds, including FICZ, reduced the response to IAV. Conditional Ahr knockout mice revealed that all four compounds require AHR within hematopoietic cells. Thus, differences in the immune response to IAV likely reflect variances in quality, magnitude, and duration of AHR signaling. This indicates that binding affinity and metabolism may be stronger predictors of immune effects than a compound’s source of origin, and that harnessing AHR will require finding a balance between dampening immune-mediated pathologies and maintaining sufficient host defenses against infection.

EGFR Trafficking in Physiology and Cancer.

Signaling from the epidermal growth factor receptor (EGFR) elicits multiple biological responses, including cell proliferation, migration, and survival. Receptor endocytosis and trafficking are critical physiological processes that control the strength, duration, diversification, and spatial restriction of EGFR signaling through multiple mechanisms, which we review in this chapter. These mechanisms include: (i) regulation of receptor density and activation at the cell surface; (ii) concentration of receptors into distinct nascent endocytic structures; (iii) commitment of the receptor to different endocytic routes; (iv) endosomal sorting and postendocytic trafficking of the receptor through distinct pathways, and (v) recycling to restricted regions of the cell surface. We also highlight how communication between organelles controls EGFR activity along the endocytic route. Finally, we illustrate how abnormal trafficking of EGFR oncogenic mutants, as well as alterations of the endocytic machinery, contributes to aberrant EGFR signaling in cancer.