Regulation of cAMP responses by the G12/13 pathway converges on adenylyl cyclase VII

Regulation of intracellular cyclic adenosine 3’, 5’-monophosphate (cAMP) by multiple pathways enables differential function of this ubiquitous second messenger in a context dependent manner. Modulation of Gs-stimulated intracellular cAMP has long been known to be modulated by the Gi and Gq/Ca2+ pathways. Recently, the G13 pathway was also shown to facilitate cAMP responses in murine macrophage cells. We report here that this synergistic regulation of cAMP synthesis by the Gs and G13 pathways is mediated by a specific isoform of adenylyl cyclase, AC7. Furthermore, this signaling paradigm exists in several hematopoietic lineages and can be recapitulated by exogenous expression of AC7 in HEK 293 cells. Mechanistic characterization of this synergistic interaction indicates that it occurs downstream of receptor activation and it can be mediated by the alpha subunit of either G12 or G13. Our results demonstrate that AC7 is a specific downstream effector of the G12/13 pathway

ADENYLYL CYCLASE TYPE 9: REGULATION AND CARDIAC FUNCTION

Abnormalities in cardiac stress signaling underlie a number of cardiovascular diseases (e.g. arrhythmias and heart failure). Cardiac stress signaling pathways normally integrate signals from the sympathetic nervous system to promote efficient contraction and relaxation under stress. Sympathetic control through β-adrenergic stimulation is propagated by adenylyl cyclase (AC). AC synthesizes cyclic AMP (cAMP), an important second messenger that initiates signaling pathways to modulate physiological and pathophysiological functions of the heart, including the activation of PKA and subsequent phosphorylation of ion channels, contractile machinery, and stress response proteins that enhance cardiac function. Alterations of cAMP signaling occur in the failing heart and contribute to impaired function. Of the AC isoforms present in adult cardiomyocytes (AC 4, 5, 6, and 9), AC9 is the most divergent in sequence and understudied. The work presented in this dissertation sought to evaluate the direct regulatory properties of AC9 and explores roles for AC9 in heart. To clarify conflicting reports for AC9 regulation, proposed regulators were systematically evaluated, including G-proteins, protein kinases, and forskolin utilizing in vitro and cell based assays. Overall, I conclude that most G-proteins or protein kinases do not directly regulate AC9, except Gαs, in vitro. Although AC9 is forskolin insensitive alone, weak activation by forskolin in the presence of Gαs is possible. AC9 shows significant homodimerization and modest heterodimerization with AC5/6, which may account for the conflicting reports surrounding the regulation of this AC isoform. viii To study the role of AC9 in heart, a mouse model of AC9 genetic deletion was utilized. Although deletion of AC9 reduces less than 3% of total AC activity in heart, Yotiao-associated AC activity is eliminated. AC9-/- mice exhibit no structural abnormalities but show a significant bradycardia and alterations in Doppler echocardiography indicative of grade 1 diastolic dysfunction with preserved ejection fraction. Identification of novel AC9 binding partners, including the small heat shock protein 20 (Hsp20) and Popeye domain containing (Popdc) proteins may contribute to the underlying mechanisms of AC9-/- phenotypes. Collectively, this work suggests that AC9 forms distinct macromolecular complexes that contribute to local cAMP pools important for driving physiological function of the heart

Overexpression of the type 1 adenylyl cyclase in the forebrain leads to deficits of behavioral inhibition

The type 1 adenylyl cyclase (AC1) is an activity-dependent, calcium-stimulated adenylyl cyclase expressed in the nervous system that is implicated in memory formation. We examined the locomotor activity, and impulsive and social behaviors of AC1+ mice, a transgenic mouse strain overexpressing AC1 in the forebrain. Here we report that AC1+ mice exhibit hyperactive behaviors and demonstrate increased impulsivity and reduced sociability. In contrast, AC1 and AC8 double knock-out mice are hypoactive, and exhibit increased sociability and reduced impulsivity. Interestingly, the hyperactivity of AC1+ mice can be corrected by valproate, a mood-stabilizing drug. These data indicate that increased expression of AC1 in the forebrain leads to deficits in behavioral inhibition

Endocrinology and the brain: Corticotropin-Releasing Hormone signaling

Corticotropin-releasing hormone (CRH) is a key player of basal and stress activated responses in the hypothalamic-pituitary-adrenal axis (HPA) and in extrahypothalamic circuits, where it functions as a neuromodulator to orchestrate humoral and behavioral adaptive responses to stress. This review describes molecular components and cellular mechanisms involved in CRH signaling downstream of its G protein-coupled receptors (GPCRs) CRHR1 and CRHR2, and summarizes recent findings that challenge the classical view of GPCR signaling, and impact on our understanding of CRHRs function. Special emphasis is placed on recent studies of CRH signaling that revealed new mechanistic aspects of cAMP generation and ERK1/2 activation in physiologically relevant contexts of the neurohormone action. In addition, we present an overview of the pathophysiological role of the CRH system, which highlights the need for a precise definition of CRHRs signaling at molecular level to identify novel targets for pharmacological intervention in neuroendocrine tissues and specific brain areas involved in CRH-related disorders.Fil: Inda, María Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular; ArgentinaFil: Armando, Natalia Giannina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; ArgentinaFil: Dos Santos Claro, Paula Ayelen. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; ArgentinaFil: Silberstein Cuña, Susana Iris. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular; Argentin

Ca-Stimulated Type 8 Adenylyl Cyclase Is Required for Rapid Acquisition of Novel Spatial Information and for Working/Episodic-Like Memory

Ca-stimulated adenylyl cyclases (ACs) transduce neuronal stimulation-evoked increase in calcium to the production of cAMP, which impinges on the regulation of many aspects of neuronal function. Type 1 and type 8 AC (AC1 and AC8) are the only ACs that are directly stimulated by Ca. Although AC1 function was implicated in regulating reference spatial memory, the function of AC8 in memory formation is not known. Because of the different biochemical properties of AC1 and AC8, these two enzymes may have distinct functions. For example, AC1 activity is regulated by both Ca and G-proteins. In contrast, AC8 is a pure Ca sensor. It is neither stimulated by Gs nor inhibited by Gi. Recent studies also suggested that AC1 and AC8 were differentially concentrated at different subcellular domains, implicating that Ca-stimulated signaling might be compartmentalized. In this study, we used AC8 knock-out (KO) mice and found behavioral deficits in memory retention for temporal dissociative passive avoidance and object recognition memory. When examined by Morris water maze, AC8KOmice showed normal reference memory. However, the acquisition of newer spatial information was defective in AC8 KO mice. Furthermore, AC8 KO mice were severely impaired in hippocampus-dependent episodic-like memory when examined by the delayed matching-to-place task. Because AC8 is preferentially localized at the presynaptic active zone, our results suggest a novel role of presynaptic cAMP signaling in memory acquisition and retention, as well as distinct mechanisms underlying reference and working/episodic-like memory

Actin cytoskeleton-dependent regulation of corticotropin-releasing factor receptor heteromers

Stress responses are highly nuanced and variable, but how this diversity is achieved by modulating receptor function is largely unknown. Corticotropin-releasing factor receptors (CRFRs), class B G protein–coupled receptors, are pivotal in mediating stress responses. Here we show that the two known CRFRs interact to form heteromeric complexes in HEK293 cells coexpressing both CRFRs and in vivo in mouse pancreas. Coimmunoprecipitation and mass spectrometry confirmed the presence of both CRF1R and CRF2βR, along with actin in these heteromeric complexes. Inhibition of actin filament polymerization prevented the transport of CRF2βR to the cell surface but had no effect on CRF1R. Transport of CRF1R when coexpressed with CRF2βR became actin dependent. Simultaneous stimulation of cells coexpressing CRF1R+CRF2βR with their respective high-affinity agonists, CRF+urocortin2, resulted in approximately twofold increases in peak Ca2+responses, whereas stimulation with urocortin1 that binds both receptors with 10-fold higher affinity did not. The ability of CRFRs to form heteromeric complexes in association with regulatory proteins is one mechanism to achieve diverse and nuanced function

Signaling and regulation of G protein-coupled receptors in airway smooth muscle

Signaling through G protein-coupled receptors (GPCRs) mediates numerous airway smooth muscle (ASM) functions including contraction, growth, and "synthetic" functions that orchestrate airway inflammation and promote remodeling of airway architecture. In this review we provide a comprehensive overview of the GPCRs that have been identified in ASM cells, and discuss the extent to which signaling via these GPCRs has been characterized and linked to distinct ASM functions. In addition, we examine the role of GPCR signaling and its regulation in asthma and asthma treatment, and suggest an integrative model whereby an imbalance of GPCR-derived signals in ASM cells contributes to the asthmatic state

Ca2+ Dynamics and Ca2+ Sensitization in the Regulation of Airway Smooth Muscle Tone

Airway smooth muscle tone is ultimately generated by phosphorylation of myosin light chain, which is regulated by the balance between concentrations of Ca2+ and sensitivity to Ca2+ in the cytosolic side. The former is due to the Ca2+ influx passing through ion channels (Ca2+ dynamics), leading to activation of myosin light chain kinase, and the latter is due to Rho-kinase (Ca2+ sensitization), leading to the inactivation of myosin phosphatase. Alterations to contractility and to the proliferative phenotype, which are influenced by Ca2+ dynamics and Ca2+ sensitization, are involved in the pathophysiology of asthma and chronic obstructive pulmonary disease (COPD). Ca2+ dynamics are mainly due to store-operated capacitative Ca2+ influx and receptor-operated Ca2+ influx, and partly due to L-type voltage-dependent Ca2+ (VDC) channels. Large-conductance Ca2+-activated K+ (KCa, BKCa, Maxi-K+) channels are activated by Gs connected to β2-adrenoceptors, whereas these channels are inhibited by Gi connected to M2 muscarinic receptors. VDC channel activity regulated by KCa channels contributes to not only functional antagonism between β2-adrenoceptors and muscarinic receptors but also to synergistic effects between β2-adrenoceptor agonists and muscarinic receptor antagonists. Moreover, an increase in Ca2+ influx via the KCa/VDC channel linkage causes airflow limitation and β2-adrenergic desensitization. In contrast, an increase in sensitivity to Ca2+ via Rho-kinase causes airflow limitation, airway hyperresponsiveness, β2-adrenergic desensitization, and airway remodeling. These airway disorders are characteristic features of asthma and COPD. KCa channels are regulated by trimeric G proteins (Gs, Gi), and Rho-kinase is regulated by a monomeric G protein (RhoA). Therefore, Ca2+ dynamics due to G proteins/KCa/VDC channel linkage and Ca2+ sensitization due to RhoA/Rho-kinase processes are therapeutic targets for these diseases

G-Protein coupled receptor signalling in pluripotent stem cell-derived cardiovascular cells: Implications for disease modelling

Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies

Non-Raft AC2 Defines a cAMP Signaling Compartment That Selectively Regulates IL-6 Expression in Airway Smooth Muscle Cells

Adenylyl cyclase (AC) isoforms differ in their tissue distribution, cellular localization, regulation, and protein interactions. Most cell types express multiple AC isoforms. We hypothesized that cAMP produced by different AC isoforms regulates unique cellular responses in human bronchial smooth muscle cells (BSMC). Overexpression of AC2, AC3, or AC6 had distinct effects on forskolin (Fsk)-induced expression of a number of known cAMP-responsive genes. These data show that different AC isoforms can differentially regulate gene expression. Most notable, overexpression and activation of AC2 enhanced interleukin 6 (IL-6) expression, but overexpression of AC3 or AC6 had no effect. IL-6 production by BSMC was induced by Fsk and select G protein-coupled receptor (GPCR) agonists, though IL-6 levels did not directly correlate with global cAMP levels. Treatment with PKA selective 6-Bnz-cAMP or Epac selective 8-CPT-2Me-cAMP cAMP analogs revealed a predominant role for PKA in cAMP-mediated induction of IL-6. IL-6 promoter mutations demonstrated that AP-1 and CRE transcription sites were required for Fsk to stimulate IL-6 expression. Our present study defines an AC2 cAMP signaling compartment that specifically regulates IL-6 expression in BSMC via Epac and PKA and demonstrates that other AC isoforms are excluded from this pool