cGAS-STING, an important pathway in cancer immunotherapy

Cytosolic DNA sensing, the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, is an important novel role in the immune system. Multiple STING agonists were developed for cancer therapy study with great results achieved in pre-clinical work. Recent progress in the mechanical understanding of STING pathway in IFN production and T cell priming, indicates its promising role for cancer immunotherapy. STING agonists co-administrated with other cancer immunotherapies, including cancer vaccines, immune checkpoint inhibitors such as anti-programmed death 1 and cytotoxic T lymphocyte-associated antigen 4 antibodies, and adoptive T cell transfer therapies, would hold a promise of treating medium and advanced cancers. Despite the applications of STING agonists in cancer immunotherapy, lots of obstacles remain for further study. In this review, we mainly examine the biological characters, current applications, challenges, and future directions of cGAS-STING in cancer immunotherapy.

Heterogeneity of pulmonary endothelial cyclic nucleotide response to Pseudomonas aeruginosa ExoY infection

Here, we tested the hypothesis that a promiscuous bacterial cyclase synthesizes purine and pyrimidine cyclic nucleotides in the pulmonary endothelium. To test this hypothesis, pulmonary endothelial cells were infected with a strain of the Gram-negative bacterium Pseudomonas aeruginosa that introduces only exoenzyme Y (PA103 ΔexoUexoT::Tc pUCPexoY; ExoY(+)) via a type III secretion system. Purine and pyrimidine cyclic nucleotides were simultaneously detected using mass spectrometry. Pulmonary artery (PAECs) and pulmonary microvascular (PMVECs) endothelial cells both possess basal levels of four different cyclic nucleotides in the following rank order: cAMP > cUMP ≈ cGMP ≈ cCMP. Endothelial gap formation was induced in a time-dependent manner following ExoY(+) intoxication. In PAECs, intercellular gaps formed within 2 h and progressively increased in size up to 6 h, when the experiment was terminated. cGMP concentrations increased within 1 h postinfection, whereas cAMP and cUMP concentrations increased within 3 h, and cCMP concentrations increased within 4 h postinfection. In PMVECs, intercellular gaps did not form until 4 h postinfection. Only cGMP and cUMP concentrations increased at 3 and 6 h postinfection, respectively. PAECs generated higher cyclic nucleotide levels than PMVECs, and the cyclic nucleotide levels increased earlier in response to ExoY(+) intoxication. Heterogeneity of the cyclic nucleotide signature in response to P. aeruginosa infection exists between PAECs and PMVECs, suggesting the intracellular milieu in PAECs is more conducive to cNMP generation.

Novel signaling mechanisms in the ovary during oocyte maturation and ovulation

During the peri-ovulatory period, the gonadotropin LH triggers major changes in both the somatic and germ cell compartments of the ovarian follicle. The oocyte completes the meiotic cell cycle to become a fertilizable egg, and dramatic changes in gene expression and secretion take place in the somatic compartment of the follicle in preparation for follicular rupture and oocyte release. The concerted changes are regulated by activation of intracellular signaling pathways as well as paracrine and autocrine regulatory loops. This review will provide a summary of the current knowledge of the molecular events triggered by LH focusing mostly on the signaling pathways required for oocyte maturation.

Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle

Vascular smooth muscle tone is controlled by a balance between the cellular signaling pathways that mediate the generation of force (vasoconstriction) and release of force (vasodilation). The initiation of force is associated with increases in intracellular calcium concentrations, activation of myosin light-chain kinase, increases in the phosphorylation of the regulatory myosin light chains, and actin-myosin crossbridge cycling. There are, however, several signaling pathways modulating Ca(2+) mobilization and Ca(2+) sensitivity of the contractile machinery that secondarily regulate the contractile response of vascular smooth muscle to receptor agonists. Among these regulatory mechanisms involved in the physiological regulation of vascular tone are the cyclic nucleotides (cAMP and cGMP), which are considered the main messengers that mediate vasodilation under physiological conditions. At least four distinct mechanisms are currently thought to be involved in the vasodilator effect of cyclic nucleotides and their dependent protein kinases: (1) the decrease in cytosolic calcium concentration ([Ca(2+)]c), (2) the hyperpolarization of the smooth muscle cell membrane potential, (3) the reduction in the sensitivity of the contractile machinery by decreasing the [Ca(2+)]c sensitivity of myosin light-chain phosphorylation, and (4) the reduction in the sensitivity of the contractile machinery by uncoupling contraction from myosin light-chain phosphorylation. This review focuses on each of these mechanisms involved in cyclic nucleotide-dependent relaxation of vascular smooth muscle under physiological conditions.

Role of phosphodiesterases in adult-onset pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by increased mean pulmonary artery pressure (mPAP) due to vasoconstriction and structural changes in the small pulmonary arteries (PAs); proliferation of pulmonary artery smooth muscle cells (PASMCs) contributes to the remodeling. The abnormal pathophysiology in the pulmonary vasculature relates to decreased cyclic nucleotide levels in PASMCs. Phosphodiesterases (PDEs) catalyze the hydrolysis of cAMP and cGMP, thereby PDE inhibitors are effective in vasodilating the PA and decreasing PASMC proliferation. Experimental studies support the use of PDE3, PDE5, and PDE1 inhibitors in PAH. PDE5 inhibitors such as sildenafil are clinically approved to treat different forms of PAH and lower mPAP, increase functional capacity, and decrease right ventricular hypertrophy, without decreasing systemic arterial pressure. New evidence suggests that the combination of PDE inhibitors with other therapies for PAH may be beneficial in treating the disease. Furthermore, inhibiting PDEs in the heart and the inflammatory cells that infiltrate the PA may offer new targets to reduce right ventricular hypertrophy and inhibit inflammation that is associated with and contributes to the development of PAH. This chapter summarizes the advances in the area and the future of PDEs in PAH.

Evidence for the potential influence of cyclic nucleotides on maintenance of or reactivation from latency of herpes simplex virus in trigeminal ganglionic neurons

Herpes simplex virus infections are epidemic throughout developed countries, and recurrent herpes simplex keratitis is the most common cause of corneal blindness in these countries, NIH (1973). No available antiviral agent is capable of eradicating the state of viral ganglionic latency, and hence no effective treatment currently exists for prevention of viral re-activation from latency, with resultant recurrent infectious viral clinical manifestations. Putative triggers of re-activation include stress, sunburn, menses, trauma, and fever. These 'triggers' seem to share at least one common characteristic: the potential ability to influence intracellular cyclic nucleotide levels through the action of such first order messengers as catacolamines (stress, trauma) and/or arachadonic acid metabolites (sunburn, fever, trauma, and menses). We exploited an in vitro model of HSV ganglionic latency, and developed a model of in vitro organ culture ganglionic viral reactivation from latency. We then examined the effect of a variety of agents on this model. We found that agents which have been shown to elevate cyclic AMP levels consistently produce increased viral shedding (compared to control, spontaneous reactivation rate) in our model of viral reactivation from latency. In contrast, agents which have been shown to depress c-AMP levels and/or to elevate c-GMP levels inhibit viral reactivation from latency in this in vitro model. We conclude that intracellular cyclic nucleotide levels may influence events which control herpes simplex genome transcription.

Cyclic nucleotide-regulated ion channels: spotlight on symmetry

In this issue of Structure, Chiu et al. (2007) report the 16 A EM structure of the prokaryotic cyclic nucleotide-regulated K(+) channel MloK1. This structure reveals that the channel is arranged as a four-fold symmetric tetramer.

Membrane currents and mechanisms of olfactory transduction

The term olfactory transduction refers to the mechanisms that transform chemical information into electrical signals. With the patch-clamp technique it is possible to record those signals and to infer something about the mechanism that produced them. The direct activation of a cation-permeable channel by cAMP is the final step in producing the odour-induced ionic current. Because it occupies a critical position in the transduction process, measurements of the ion channel's activity provide useful insights into the molecular processes underlying olfactory transduction. In addition to its activation by cAMP and cGMP, the channel is modulated by both extracellular and intracellular Ca2+ ions and by extracellular Mg2+ ions, all at physiological concentrations. These effects are probably important in promoting signal reliability. An unusual feature of this channel is its termination kinetics--it can remain active for hundreds of milliseconds after the agonist has been removed. This is likely to add to the integrating properties of the olfactory sensory neuron.

How does alcohol impair neuronal migration?

Maternal alcohol consumption during pregnancy can cause serious birth defects, of which fetal alcohol syndrome (FAS) is the most devastating. Recognized by characteristic craniofacial abnormalities and growth deficiency, this condition produces severe alcohol-induced damage in the developing brain. FAS children experience ataxia; deficits in intellectual functioning; and difficulties in learning, memory, problem solving, and attention. Multiple aspects of central nervous system development can be affected by alcohol exposure, but the most striking abnormalities are neuronal and glial migration. Little is known about cellular mechanisms by which alcohol affects the migration of immature neurons. Recently, it has been found that Ca(2+) signaling and cyclic nucleotide signaling are the central targets of the action of alcohol in neuronal cell migration. Most importantly, the aberrant migration of immature neurons caused by alcohol exposure is significantly ameliorated by controlling the activity of these second-messenger pathways. In this Mini-Review, we first describe how alcohol exposure impairs the migration of cerebellar granule cells and then discuss the signaling mechanisms involved.

The role of cyclic nucleotides in axon guidance

During the formation of the nervous system, axonal growth cones navigate through the complex environment of the developing embryo to innervate their targets. Growth cones achieve this formidable feat by responding to attractive or repulsive guidance cues expressed at specific points along the trajectory of their growth, which impart the directional information required for accurate pathfinding. While much is known about guidance molecules and their receptors, many questions remain unanswered. Which signal transduction pathways are activated within the growth cone after encountering a guidance cue? How is this related to rearrangement of the growth cone cytoskeleton? Do different cues use different signal transduction pathways? This chapter will review some of the work that has addressed these fundamental questions, with a specific focus on the role of the cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), in axon guidance.

Sperm chemotaxis in marine invertebrates--molecules and mechanisms

Sperm are attracted by chemical substances which are released by the egg. This process is called chemotaxis. Several molecules that are involved in chemotactic signaling of sperm from marine invertebrates are described and a model of the signaling pathway is presented. We discuss the motor response during chemotaxis and propose a model of the navigation strategy of sperm.

CNG and HCN channels: two peas, one pod

Cyclic nucleotide-activated ion channels play a fundamental role in a variety of physiological processes. By opening in response to intracellular cyclic nucleotides, they translate changes in concentrations of signaling molecules to changes in membrane potential. These channels belong to two families: the cyclic nucleotide-gated (CNG) channels and the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels. The two families exhibit high sequence similarity and belong to the superfamily of voltage-gated potassium channels. Whereas HCN channels are activated by voltage and CNG channels are virtually voltage independent, both channels are activated by cyclic nucleotide binding. Furthermore, the channels are thought to have similar channel structures, leading to similar mechanisms of activation by cyclic nucleotides. However, although these channels are structurally and behaviorally similar, they have evolved to perform distinct physiological functions. This review describes the physiological roles and biophysical behavior of CNG and HCN channels. We focus on how similarities in structure and activation mechanisms result in common biophysical models, allowing CNG and HCN channels to be viewed as a single genre.

Compartmentation of cyclic nucleotide signaling in the heart: the role of A-kinase anchoring proteins

The activation of the cyclic nucleotide protein kinase A (PKA) and PKG by their respective second messengers is responsible for the modulation of many cellular functions in the heart including cardiac hypertrophy, strength of contraction, and ion flux. However, several studies have revealed that a general increase in cyclic nucleotide concentration in the cell is not sufficient for the specific regulation of target proteins. These studies found that PKA and PKG must be colocalized with their targets to ensure spatial-temporal control of substrate phosphorylation. This compartmentation of cyclic nucleotide signaling is accomplished by tethering the protein kinases with their respective substrates through the association with scaffolding proteins. For cAMP signaling, A-kinase anchoring proteins (AKAPs) provide a molecular mechanism for cAMP compartmentation, allowing for the precise control of PKA-mediated phosphorylation events. (cAMP, PKA, AKAP, PKG).

A role for cyclic nucleotide monophosphates in synaptic modulation by a crayfish neuropeptide

DF2 (DRNFLRFamide), a FMRFamide-like peptide, has been shown to increase the amount of transmitter released at crayfish neuromuscular junctions. Here, we examined a possible role for the cyclic nucleotide monophosphates, cAMP and cGMP, in DF2's effects on synaptic transmission. The effects of DF2 on synaptic transmission were monitored by recording excitatory postsynaptic potentials (EPSPs) in the deep abdominal extensor muscles of the crayfish, Procambarus clarkii. A number of activators and inhibitors were used to determine whether or not cAMP, cGMP, protein kinase A (PKA) and protein kinase G (PKG) mediate the effect of this neuropeptide. Phosphodiesterase inhibitors, known to inhibit the breakdown of cAMP (IBMX) and/or cGMP (mdBAMQ), potentiate the effect of DF2 on synaptic transmission. Activators of PKA (Sp-cAMPS) and PKG (8-pCPT-cGMP) increase EPSP amplitude, mimicking the effects of DF2. Inhibitors of PKA (Rp-cAMPS) and PKG (Rp-8-pCPT-cGMPS) each block a portion of the response to the peptide, and when applied together these two inhibitors completely block the response. Taken together, these results indicate that cyclic nucleotides and cyclic nucleotide-dependent protein kinases are necessary components of the pathway underlying modulation by this neuropeptide.

Cyclic nucleotides induce long-term augmentation of glutamate-activated chloride current in molluscan neurons

1. Literature data indicate that serotonin induces the long-term potentiation of glutamate (Glu) response in molluscan neurons. The aim of present work was to elucidate whether cyclic nucleotides can cause the same effect. 2. Experiments were carried out on isolated neurons of the edible snail (Helix pomatia) using a two-microelectrode voltage-clamp method. 3. In the majority of the cells examined, the application of Glu elicited a Cl- -current. The reversal potential (Er) of this current lied between -35 and -55 mV in different cells. 4. Picrotoxin, a blocker of Cl- -channels, suppressed this current equally on both sides of Er. Furosemide, an antagonist of both Cl- -channels and the Na+/K+/Cl- -cotransporter, had a dual effect on Glu-response: decrease in conductance, and shift of Er to negative potentials. 5. A short-term (2 min) cell treatment with 8-Br-cAMP or 8-Br-cGMP caused long-term (up to 30 min) change in Glu-response. At a holding potential of -60 mV, which was close to the resting level, an increase in Glu-activated inward current was observed. This potentiation seems to be related to the right shift of Er of Glu-activated Cl- -current rather than to the increase in conductance of Cl- -channels. The blocking effect of picrotoxin rested after 8-Br-cAMP treatment. 6. The change in the Cl- -homeostasis as a possible mechanism for the observed effect of cyclic nucleotides is discussed.

Cyclic nucleotide signaling in cavernous smooth muscle

INTRODUCTION

Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. AIMS. To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed.

METHODS

Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation.

RESULTS

More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG).

CONCLUSIONS

The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

Hyperpolarization-activated cyclic nucleotide-gated cation channels regulate auditory coincidence detection in nucleus laminaris of the chick

Coincidence detection of bilateral acoustic signals in nucleus laminaris (NL) is the first step in azimuthal sound source localization in birds. Here, we demonstrate graded expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels along the tonotopic axis of NL and its role in the regulation of coincidence detection. Expression of HCN1 and HCN2, but not HCN3 or HCN4, was detected in NL. Based on measurement of both subtype mRNA and protein, HCN1 varied along the tonotopic axis and was minimal in high-characteristic frequency (CF) neurons. In contrast, HCN2 was evenly distributed. The resting conductance was larger and the steady-state activation curve of Ih was more positive in neurons of middle to low CF than those of high CF, consistent with the predominance of HCN1 channels in these neurons. Application of 8-Br-cAMP or noradrenaline generated a depolarizing shift of the Ih voltage activation curve. This shift was larger in neurons of high CF than in those of middle CF. The shift in the activation voltage of Ih depolarized the resting membrane, accelerated the EPSP time course, and significantly improved the coincidence detection in neurons of high CF, suggesting that Ih may improve the localization of sound sources.

Model of calcium oscillations due to negative feedback in olfactory cilia

We present a mathematical model for calcium oscillations in the cilia of olfactory sensory neurons. The underlying mechanism is based on direct negative regulation of cyclic nucleotide-gated channels by calcium/calmodulin and does not require any autocatalysis such as calcium-induced calcium release. The model is in quantitative agreement with available experimental data, both with respect to oscillations and to fast adaptation. We give predictions for the ranges of parameters in which oscillations should be observable. Relevance of the model to calcium oscillations in other systems is discussed.

[Signal transduction, pillar of the neurobiological integration of memory. An alternative view to the cholinergic hypothesis]

Neurophysiological, biochemical and molecular processes described in the integration of memory are closely related with neurotransmitters such as glutamate and serotonin (SHT) and with the function of calcium and potassium ion channels more than with cholinergic activity. Infact, glutamate and 5-HT receptors are closely related with Long-Term potentiation (L TP) processes, the mechanism by which memory is preserved throughout time. That is, the activation of the 5-HTI receptor triggers a transduction signal that after influencing nuclear cell activity, provokes several presynaptic changes, which leads to the displacement of magnesium from the postsynaptic area depolarizing the neuron and leading to the activation of N-methyl-D-aspartate receptors (NMDA). As a whole, this process contributes to the support and perpetuation of LTP, which consists of the following processes: LTPI that depends on protein kinase activity; LTP2 linked to translation of genes; and LTP3 closely related to genes transcription. On the opposite side but in perfect balance, we find the mechanism of Long-Term depression (LTD), which is triggered instead when the Ca+ +flow decreases in the presynaptic neuron activating the inhibitor-1 enzyme that promotes the dephosphorylation of a calmodulin-dependent protein kinasell and as a result, the inhibition of autophosphorylation and consequently of LTP too. Despite the widespread dissemination of the cholinergic hypothesis in Alzheimer's disease, memory build up rather than involving acetylcholine essentially depends on the participation of other neurotransmitters such as 5-HT and glutamate, which have not been adequately considered in the treatment of this disease. However, beyond neurotransmission, it is the cellular mechanism of autophosphorylation of several protein kinases, the process susceptible of being activated or controlled by the action of distinct substances. In such a case, it would be possible to exert some influence on gene expression improving perhaps, some of the physiopathological deficits that characterize memory disruption.

Phosphodiesterase inhibitors in female sexual dysfunction

Based on the increasing knowledge on both the physiology of penile erection and the pathophysiology of erectile dysfunction, selective phosphodiesterase (PDE) inhibitors have been successfully introduced in the oral treatment of male erectile dysfunction. Because of their central role in smooth muscle tone regulation, PDEs remain an attractive target for drug development in urology. Since the distribution and functional significance of PDE isoenzymes vary in different tissues, selective inhibitors of the isoenzymes have the potential to exert at least partially specific effects on the target tissue. Currently, PDE inhibitors are under investigation with potential uses in urinary stone disease, overactive bladder and the so-called benign prostatic syndrome. The convincing clinical data on the use of the orally active PDE5 inhibitors sildenafil (VIAGRA), vardenafil (LEVITRA) and tadalafil (CIALIS) in the treatment of erectile dysfunction are accompanied by boosting research activities on intracellular signal transduction and PDE characterisation in female genital tissues with the aid of immunohistochemistry and immunocytochemistry and molecular biology. The expression of various PDE isoforms in the human clitoris, vagina and labia minora was shown by means of immunohistochemistry and RT-PCR analyses and it was concluded from functional studies that an increase in cGMP or cAMP might be involved in the regulation of female genital blood flow and the control of genital non-vascular smooth muscle. As a consequence, the efficacy and safety of the PDE5 inhibitor sildenafil in the treatment of symptoms of female sexual dysfunction (FSD), including female sexual arousal disorders (FSAD), have been evaluated. Although the experiences from these early clinical studies have so far not been conclusive, they suggest that, after appropriate evaluation of patients, inhibition of PDE5 might be of benefit for selected individuals with FSAD. Such research efforts will possibly allow the identification of efficacious and diagnostic tools for erectile dysfunction and of even more selective drugs in its therapy.