Hydrogen peroxide impairs GRK2 translation via a calpain-dependent and cdk1-mediated pathway

Transcriptomic analysis reveals the potential biological mechanism of AIS and lung adenocarcinoma

Introduction

Acute ischemic stroke (AIS) and lung adenocarcinoma (LUAD) are associated with some of the highest morbidity and mortality rates worldwide. Despite reports on their strong correlation, the causal relationship is not fully understood. The study aimed to identify and annotate the biological functions of hub genes with clinical diagnostic efficacy in AIS and LUAD.

Methods

Transcriptome and single-cell datasets were obtained from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA). We identified the differentially expressed genes (DEGs) upregulated in AIS and LUAD and found 372 genes intersecting both datasets. Hub genes were identified using protein-protein interaction (PPI) networks, and the diagnostic and prognostic utility of these hub genes was then investigated using receiver operating characteristic (ROC) curves, survival analysis, and univariable Cox proportional hazard regression. Single-cell analysis was used to detect whether the hub genes were expressed in tumor epithelial cells. The immune microenvironment of AIS and LUAD was assessed using the CIBERSORT algorithm. The protein expression of these hub genes was tracked using the Human Protein Atlas (HPA). We calculated the number of positive cells using the digital pathology software QuPath. Finally, we performed molecular docking after using the Enrichr database to predict possible medicines.

Results

We identified the molecular mechanisms underlying hub genes in AIS and LUAD and found that CCNA2, CCNB1, CDKN2A, and CDK1 were highly expressed in AIS and LUAD tissue samples compared to controls. The hub genes were mainly involved in the following pathways: the cell cycle, cellular senescence, and the HIF-1 signaling pathway. Using immunohistochemical slices from the HPA database, we confirmed that these hub genes have a high diagnostic capability for AIS and LUAD. Further, their high expression is associated with poor prognosis. Finally, curcumin was tested as a potential medication using molecular docking modeling.

Discussion

Our findings suggest that the hub genes we found in this study contribute to the development and progression of AIS and LUAD by altering the cellular senescence pathway. Thus, they may be promising markers for diagnosis and prognosis.

G protein-coupled receptor kinase 2 (GRK2) as a multifunctional signaling hub

Accumulating evidence indicates that G protein-coupled receptor kinase 2 (GRK2) is a versatile protein that acts as a signaling hub by modulating G protein-coupled receptor (GPCR) signaling and also via phosphorylation or scaffolding interactions with an extensive number of non-GPCR cellular partners. GRK2 multifunctionality arises from its multidomain structure and from complex mechanisms of regulation of its expression levels, activity, and localization within the cell, what allows the precise spatio-temporal shaping of GRK2 targets. A better understanding of the GRK2 interactome and its modulation mechanisms is helping to identify the GRK2-interacting proteins and its substrates involved in the participation of this kinase in different cellular processes and pathophysiological contexts.

Chapter Three - Ubiquitination and Protein Turnover of G-Protein-Coupled Receptor Kinases in GPCR Signaling and Cellular Regulation

G-protein-coupled receptors (GPCRs) are responsible for regulating a wide variety of physiological processes, and distinct mechanisms for GPCR inactivation exist to guarantee correct receptor functionality. One of the widely used mechanisms is receptor phosphorylation by specific G-protein-coupled receptor kinases (GRKs), leading to uncoupling from G proteins (desensitization) and receptor internalization. GRKs and β-arrestins also participate in the assembly of receptor-associated multimolecular complexes, thus initiating alternative G-protein-independent signaling events. In addition, the abundant GRK2 kinase has diverse "effector" functions in cellular migration, proliferation, and metabolism homeostasis by means of the phosphorylation or interaction with non-GPCR partners. Altered expression of GRKs (particularly of GRK2 and GRK5) occurs during pathological conditions characterized by impaired GPCR signaling including inflammatory syndromes, cardiovascular disease, and tumor contexts. It is increasingly appreciated that different pathways governing GRK protein stability play a role in the modulation of kinase levels in normal and pathological conditions. Thus, enhanced GRK2 degradation by the proteasome pathway occurs upon GPCR stimulation, what allows cellular adaptation to chronic stimulation in a physiological setting. β-arrestins participate in this process by facilitating GRK2 phosphorylation by different kinases and by recruiting diverse E3 ubiquitin ligase to the receptor complex. Different proteolytic systems (ubiquitin-proteasome, calpains), chaperone activities and signaling pathways influence the stability of GRKs in different ways, thus endowing specificity to GPCR regulation as protein turnover of GRKs can be differentially affected. Therefore, modulation of protein stability of GRKs emerges as a versatile mechanism for feedback regulation of GPCR signaling and basic cellular processes.

The ubiquitin ligase Mdm2 controls oligodendrocyte maturation by intertwining mTOR with G protein-coupled receptor kinase 2 in the regulation of GPR17 receptor desensitization

During oligodendrocyte precursor cell (OPC) differentiation, defective control of the membrane receptor GPR17 has been suggested to block cell maturation and impair remyelination under demyelinating conditions. After the immature oligodendrocyte stage, to enable cells to complete maturation, GPR17 is physiologically down-regulated via phosphorylation/desensitization by G protein-coupled receptor kinases (GRKs); conversely, GRKs are regulated by the "mammalian target of rapamycin" mTOR. However, how GRKs and mTOR are connected to each other in modulating GPR17 function and oligodendrogenesis has remained elusive. Here we show, for the first time, a role for Murine double minute 2 (Mdm2), a ligase previously involved in ubiquitination/degradation of the onco-suppressor p53 protein. In maturing OPCs, both rapamycin and Nutlin-3, a small molecule inhibitor of Mdm2-p53 interactions, increased GRK2 sequestration by Mdm2, leading to impaired GPR17 down-regulation and OPC maturation block. Thus, Mdm2 intertwines mTOR with GRK2 in regulating GPR17 and oligodendrogenesis and represents a novel actor in myelination.

Role of G protein-coupled receptor kinase 2 in tumoral angiogenesis

Downregulation of G protein-coupled receptor kinase 2 (GRK2) in endothelial cells has recently been identified as a relevant event in the tumoral angiogenic switch. Based on the effects of altering GRK2 dosage in cell and animal models, this kinase appears to act as a hub in key signaling pathways involved in vascular stabilization and remodeling. Accordingly, decreased GRK2 expression in endothelial cells accelerates tumor growth in mice by impairing the pericytes ensheathing the vessels, thereby promoting hypoxia and macrophage infiltration. These results raise new questions regarding the mechanisms by which transformed cells trigger the decrease in GRK2 observed in human breast cancer vessels and how GRK2 modulates the interactions between different cell types that occur in the tumor microenvironment.

Targeting G protein coupled receptor-related pathways as emerging molecular therapies

G protein coupled receptors (GPCRs) represent the most important targets in modern pharmacology because of the different functions they mediate, especially within brain and peripheral nervous system, and also because of their functional and stereochemical properties. In this paper, we illustrate, via a variety of examples, novel advances about the GPCR-related molecules that have been shown to play diverse roles in GPCR pathways and in pathophysiological phenomena. We have exemplified how those GPCRs’ pathways are, or might constitute, potential targets for different drugs either to stimulate, modify, regulate or inhibit the cellular mechanisms that are hypothesized to govern some pathologic, physiologic, biologic and cellular or molecular aspects both in vivo and in vitro. Therefore, influencing such pathways will, undoubtedly, lead to different therapeutical applications based on the related pharmacological implications. Furthermore, such new properties can be applied in different fields. In addition to offering fruitful directions for future researches, we hope the reviewed data, together with the elements found within the cited references, will inspire clinicians and researchers devoted to the studies on GPCR’s properties.

Combined argatroban and anti-oxidative agents prevents increased vascular contractility to thrombin and other ligands after subarachnoid haemorrhage

BACKGROUND AND PURPOSE

Increased vascular contractility plays a fundamental role in cerebral vasospasm in subarachnoid haemorrhage (SAH). We investigated the role of thrombin and its receptor, proteinase-activated receptor 1 (PAR1), and other G protein-coupled receptors in the increased contractility, and examined the preventive effects of the thrombin inhibitor, argatroban, and anti-oxidative agents, vitamin C and tempol.

EXPERIMENTAL APPROACH

A rabbit model of SAH was utilized. Contractile responses of the isolated basilar artery and the level of oxidative stress of brain tissues were evaluated.

KEY RESULTS

Contractile responses to thrombin and PAR1-activating peptide (PAR1-AP) were enhanced and prolonged after SAH. The thrombin-induced contraction persisted even after terminating thrombin stimulation. When sequentially stimulated with PAR1-AP, the second response was maintained in SAH, while it was substantially attenuated in the control. Only a combination of argatroban with vitamin C or tempol prevented both the enhancement and prolongation of the contractile response to PAR1-AP and restored the reversibility of the thrombin-induced contraction. The responses to angiotensin II, vasopressin and PGF(2α) were enhanced and prolonged after SAH to varying degrees, and responded differently to the treatment. The response to vasopressin exhibited a similar phenomenon to that seen with PAR1-AP. Oxidative stress was increased in SAH, and normalized by the treatment with argatroban, vitamin C or their combination.

CONCLUSIONS AND IMPLICATIONS

Increased vascular reactivity to agonists in SAH was attributable to the enhancement and prolongation of the contractile response. A combination of argatroban and anti-oxidative agents was required to prevent both the enhancement and prolongation of the contractile response.

Growth inhibition of human hepatocellular carcinoma cells by overexpression of G-protein-coupled receptor kinase 2

Hepatocellular carcinoma (HCC) is one of the deadliest forms of human liver cancer and does not respond well to conventional therapies. Novel effective treatments are urgently in need. G-protein-coupled kinase 2 (GRK2) is unique serine/threonine kinase that involves in many signaling pathways and regulates various essential cellular processes. Altered levels of GRK2 have been linked with several human diseases including cancer. In this study, we investigated a novel approach for HCC treatment by inducing overexpression of GRK2 in human HCC cells. We found that overexpression of GRK2 through recombinant adenovirus transduction inhibits the growth of human HCC cells. BrdU incorporation assay showed that the growth inhibition caused by elevated GRK2 level was due to reduced cell proliferation but not apoptosis. To examine the anti-proliferative function of increased GRK2 level, we performed cell cycle analysis using propidium iodide staining. We found that the proliferation suppression was associated with G2/M phase cell cycle arrest by the wild-type GRK2 but not its kinase-dead K220R mutant. Furthermore, increased levels of wild-type GRK2 induced upregulation of phosphor-Ser(15) p53 and cyclin B1 in a dose-dependent manner. Our data indicate that the anti-proliferative function of elevated GRK2 is associated with delayed cell cycle progression and is GRK2 kinase activity-dependent. Enforced expression of GRK2 in human HCC by molecular delivery may offer a potential therapeutic approach for the treatment of human liver cancer.

7β-Hydroxycholesterol-induced energy stress leads to sequential opposing signaling responses and to death of C6 glioblastoma cells

7β-Hydroxycholesterol cytotoxicity has been shown in vivo and in vitro to be dependent on the accumulation of its esters. We show in our study, using a detergent-free raft preparation and LC/MS lipid content analysis, that membrane microdomains isolated from 7β-hydroxycholesterol-treated C6 cells have a reduced cholesterol: cholesterol ester ratio and accumulate 7keto-hydroxycholesterol, 7β-hydroxycholesterol and 7β-hydroxycholesterol esters. These modifications in lipid content are accompanied by a redistribution of flotillin-1 in the lipid rafts. Transient increases of AMPK phosphorylation and mitochondrial activity during the first 12 h of 7β-hydroxycholesterol treatment indicate that C6 cells undergo energy stress and increase oxidative phosphorylation. Even so, ATP levels are maintained during 15 h until glucose uptake decreases. The cell's answers to raft modifications and energy stress are sequential activations of different signaling pathways such as ERK, AMPK and PI3K/Akt. These pathways, known to be activated under energy stress conditions, are transiently activated at 6 h (ERK, AMPK) and 12 h (Akt) of treatment respectively suggesting a shift from cell survival to cell proliferation. The persistence of 7β-hydroxycholesterol-induced stress led after 24 h to P38 activation, loss of GSK3β activation and to cell death. Finally we demonstrate that the observed signaling responses depend on 7β-hydroxycholesterol esterification, confirming that esterification of 7β-hydroxycholesterol is essential for cytotoxicity.

G protein-coupled receptor kinases: more than just kinases and not only for GPCRs

G protein-coupled receptor (GPCR) kinases (GRKs) are best known for their role in homologous desensitization of GPCRs. GRKs phosphorylate activated receptors and promote high affinity binding of arrestins, which precludes G protein coupling. GRKs have a multidomain structure, with the kinase domain inserted into a loop of a regulator of G protein signaling homology domain. Unlike many other kinases, GRKs do not need to be phosphorylated in their activation loop to achieve an activated state. Instead, they are directly activated by docking with active GPCRs. In this manner they are able to selectively phosphorylate Ser/Thr residues on only the activated form of the receptor, unlike related kinases such as protein kinase A. GRKs also phosphorylate a variety of non-GPCR substrates and regulate several signaling pathways via direct interactions with other proteins in a phosphorylation-independent manner. Multiple GRK subtypes are present in virtually every animal cell, with the highest expression levels found in neurons, with their extensive and complex signal regulation. Insufficient or excessive GRK activity was implicated in a variety of human disorders, ranging from heart failure to depression to Parkinson's disease. As key regulators of GPCR-dependent and -independent signaling pathways, GRKs are emerging drug targets and promising molecular tools for therapy. Targeted modulation of expression and/or of activity of several GRK isoforms for therapeutic purposes was recently validated in cardiac disorders and Parkinson's disease.

The contribution of reactive oxygen species and p38 mitogen-activated protein kinase to myofilament oxidation and progression of heart failure in rabbits

BACKGROUND AND PURPOSE

The formation of reactive oxygen species (ROS) is increased in heart failure (HF). However, the causal and mechanistic relationship of ROS formation with contractile dysfunction is not clear in detail. Therefore, ROS formation, myofibrillar protein oxidation and p38 MAP kinase activation were related to contractile function in failing rabbit hearts.

EXPERIMENTAL APPROACH AND KEY RESULTS

Three weeks of rapid left ventricular (LV) pacing reduced LV shortening fraction (SF, echocardiography) from 32 +/- 1% to 13 +/- 1%. ROS formation, as assessed by dihydroethidine staining, increased by 36 +/- 8% and was associated with increased tropomyosin oxidation, as reflected by dimer formation (dimer to monomer ratio increased 2.28 +/- 0.66-fold in HF vs. sham, P < 0.05). Apoptosis (TdT-mediated dUTP nick end labelling staining) increased more than 12-fold after 3 weeks of pacing when a significant increase in the phosphorylation of p38 MAP kinase and HSP27 was detected (Western blotting). Vitamins C and E abolished the increases in ROS formation and tropomyosin oxidation along with an improvement of LVSF (19 +/- 1%, P < 0.05 vs. untreated HF) and prevention of apoptosis, but without modifying p38 MAP kinase activation. Inhibition of p38 MAP kinase by SB281832 counteracted ROS formation, tropomyosin oxidation and contractile failure, without affecting apoptosis.

CONCLUSIONS AND IMPLICATIONS

Thus, p38 MAP kinase activation appears to be upstream rather than downstream of ROS, which impacts on LV function through myofibrillar oxidation. p38 MAP kinase inhibition is a potential target to prevent or treat HF.

The GRK2 Overexpression Is a Primary Hallmark of Mitochondrial Lesions during Early Alzheimer Disease

Increasing evidence points to vascular damage as an early contributor to the development of two leading causes of age-associated dementia, namely Alzheimer disease (AD) and AD-like pathology such as stroke. This review focuses on the role of G protein-coupled receptor kinases (GRKs) as they relate to dementia and how the cardio and cerebrovasculature is involved in AD pathogenesis. The exploration of GRKs in AD pathogenesis may help bridge gaps in our understanding of the heart-brain connection in relation to neurovisceral damage and vascular complications of AD. The a priori basis for this inquiry stems from the fact that kinases of this family regulate numerous receptor functions in the brain, myocardium and elsewhere. The aim of this review is to discuss the finding of GRK2 overexpression in the context of early AD pathogenesis. Also, we consider the consequences for this overexpression as a loss of G-protein coupled receptor (GPCR) regulation, as well as suggest a potential role for GPCRs and GRKs in a unifying theory of AD pathogenesis through the cerebrovasculature. Finally, we synthesize this newer information in an attempt to put it into context with GRKs as regulators of cellular function, which makes these proteins potential diagnostic and therapeutic targets for future pharmacological intervention.

Brain-regulated metabolic suppression during hibernation: a neuroprotective mechanism for perinatal hypoxia-ischemia

Hypoxic-ischemic brain injury in the perinatal period is a major cause of chronic disability and acute mortality in newborns. Despite numerous therapeutic strategies that reduce hypoxia-ischemia-induced damage in different experimental animal models, most of them have failed to translate to clinical therapies. This challenge calls for an urgent need to explore novel approaches to develop effective therapies for the clinical management of perinatal hypoxia-ischemia brain injury. This review focuses on studies that investigate neuroprotective related events during mammalian hibernation, characterized by dramatic reductions in several parameters including body temperature, oxygen consumption and heart rate, such that it is difficult to tell if the hibernating animal is dead or alive. The first part of this article reviews the mechanisms of metabolic suppression related events during hibernation. In the second part, hypoxic-ischemic events in the perinatal brain are discussed, and in turn, contrasted with brains experiencing metabolic suppression during mammalian hibernation. In the last part of this article, the diverse neuroprotective adaptations of hibernators and the mechanisms that might be involved in mammalian hibernation, and how they could in turn, contribute to neurprotection during perinatal hypoxia-ischemia related injuries are discussed. This article appraises the novel idea that knowledge of the central mechanisms involved in the regulatory metabolic suppression, during which; hibernators switch themselves off without dissolving their brains could represent brain neuroprotective strategy for the clinical management of perinatal hypoxia-ischemia brain injuries in newborns.

Low endogenous G-protein-coupled receptor kinase 2 sensitizes the immature brain to hypoxia-ischemia-induced gray and white matter damage

Hypoxic-ischemic brain injury is regulated in part by neurotransmitter and chemokine signaling via G-protein-coupled receptors (GPCRs). GPCR-kinase 2 (GRK2) protects these receptors against overstimulation by inducing desensitization. Neonatal hypoxic-ischemic brain damage is preceded by a reduction in cerebral GRK2 expression. We determined the functional importance of GRK2 in hypoxic-ischemic brain damage. Nine-day-old wild-type and GRK2(+/-) mice with a approximately 50% reduction in GRK2 protein were exposed to unilateral carotid artery occlusion and hypoxia. In GRK2(+/-) animals, gray and white matter damage was aggravated at 3 weeks after hypoxia-ischemia. In addition, cerebral neutrophil infiltration was increased in GRK2(+/-) animals. Neutrophil depletion reduced brain damage, but neuronal loss was still more pronounced in GRK2(+/-) animals. Onset of neuronal loss was advanced in GRK2(+/-) animals regardless of neutrophil depletion. White matter injury was advanced in GRK2(+/-) animals and was not affected by neutrophil depletion. Activation/infiltration of microglia/macrophages was stronger in GRK2(+/-) brains but only occurred 24 h after hypoxia-ischemia and is therefore not the primary cause of increased damage. During hypoxia, cerebral blood flow was reduced to the same extent in both genotypes. In vitro, GRK2(+/-) hippocampal slices and cerebellar granular neurons were more sensitive to glutamate-induced death. We propose the novel concept that the kinase GRK2 regulates onset and magnitude of hypoxic-ischemic brain damage. Increased gray and white matter damage in GRK2(+/-) animals was not dependent on infiltrating neutrophils and occurred before microglia/macrophage activation was detected. Collectively, our data suggest that cerebral GRK2 has an important endogenous neuroprotective role in ischemic cerebral damage.

Sustained Hydrogen Peroxide Induces Iron Uptake by Transferrin Receptor-1 Independent of the Iron Regulatory Protein/Iron-responsive Element Network

Local and systemic inflammatory conditions are characterized by the intracellular deposition of excess iron, which may promote tissue damage via Fenton chemistry. Because the Fenton reactant H(2)O(2) is continuously released by inflammatory cells, a tight regulation of iron homeostasis is required. Here, we show that exposure of cultured cells to sustained low levels of H(2)O(2) that mimic its release by inflammatory cells leads to up-regulation of transferrin receptor 1 (TfR1), the major iron uptake protein. The increase in TfR1 results in increased transferrin-mediated iron uptake and cellular accumulation of the metal. Although iron regulatory protein 1 is transiently activated by H(2)O(2), this response is not sufficient to stabilize TfR1 mRNA and to repress the synthesis of the iron storage protein ferritin. The induction of TfR1 is also independent of transcriptional activation via hypoxia-inducible factor 1alpha or significant protein stabilization. In contrast, pulse experiments with (35)S-labeled methionine/cysteine revealed an increased rate of TfR1 synthesis in cells exposed to sustained low H(2)O(2) levels. Our results suggest a novel mechanism of iron accumulation by sustained H(2)O(2), based on the translational activation of TfR1, which could provide an important (patho) physiological link between iron metabolism and inflammation.

Down-regulation of GRK2 after oxygen and glucose deprivation in rat hippocampal slices: role of the PI3-kinase pathway

G protein-coupled receptor kinase 2 (GRK2) modulates G protein-coupled receptor desensitization and signaling. We previously described down-regulation of GRK2 expression in vivo in rat neonatal brain following hypoxia-ischemia. In this study, we investigated the molecular mechanisms involved in GRK2 down-regulation, using organotypic cultures of neonatal rat hippocampal slices exposed to oxygen and glucose deprivation (OGD). We observed a 40% decrease in GRK2 expression 4 h post-OGD. No changes in GRK2 protein occurred after exposure of hippocampal slices to glucose deprivation only. No significant alterations in GRK2 mRNA expression were detected, suggesting a post-transcriptional effect of OGD on GRK2 expression. Blockade of the proteasome pathway by MG132 prevented OGD-induced decrease of GRK2. It has been shown that extracellular signal-regulated kinase-dependent phosphorylation of GRK2 at Ser670 triggers its turnover via the proteasome pathway. However, despite a significant increase of pSer670-GRK2 after OGD, inhibition of the extracellular signal-regulated kinase pathway by PD98059 did neither prevent the hypoxia-ischemia-induced increase in pSer670-GRK2 nor the down-regulation of GRK2 protein. Interestingly, inhibition of phosphoinositide-3-kinase with wortmannin inhibits both OGD-induced phosphorylation of GRK2 on Ser670 and the GRK2 decrease. In conclusion, OGD-induced phosphoinositide-3-kinase-dependent phosphorylation of GRK2 on Ser670 is a novel mechanism leading to down-regulation of GRK2 protein via a proteasome-dependent pathway.

A role for G protein-coupled receptor kinase 2 in mechanical allodynia

Inflammation and nerve injury can both induce mechanical allodynia via mechanisms involving the production of pro-inflammatory cytokines and increased neuronal activity. Many neurotransmitters involved in pain signal via G protein-coupled receptors (GPCRs). GPCR kinase (GRK)2 is a member of the GRK family that regulates agonist-induced desensitization and signalling of GPCRs. Low intracellular GRK2 levels are associated with increased receptor signalling. The aim of this study was to investigate whether mechanical allodynia is associated with decreased spinal cord GRK2 expression and whether reduced GRK2 increases inflammation-induced mechanical allodynia. Mechanical allodynia was induced in rats by chronic constriction injury of the sciatic nerve. After 2 weeks, neuronal GRK2 expression was decreased bilaterally in the superficial layers of the lumbar spinal cord dorsal horn. Moreover, interleukin-1beta significantly reduced GRK2 expression ex vivo in spinal cord slices. To investigate whether reduced GRK2 potentiates inflammation-induced mechanical allodynia, we used GRK2(+/-) animals expressing decreased GRK2. At baseline, the threshold for mechanical stimulation did not differ between GRK2(+/-) and wild-type mice. However, GRK2(+/-) animals were more sensitive to mechanical stimulation than wild-type animals after intraplantar lambda-carrageenan injection. We propose cytokine-induced down-regulation of spinal cord neuronal GRK2 expression as a novel mechanism that contributes to increased neuronal signalling in mechanical allodynia.

Receptor regulation in neuroendocrine-immune communication: current knowledge and future perspectives

Immune cells express receptors for every hormone or neurotransmitter we know so far. The neuroendocrine system signals to the immune system via the release of hormones and neurotransmitters that regulate cellular activity via these receptors. Much attention has been focused on the effect of glucocorticoids and catecholamines on the immune system. Glucocorticoids communicate with immune cells via glucocorticoid receptors of which the activity itself changes during immune activation. Many neuroendocrine mediators are ligands for G-protein coupled receptors on immune cells. Cytokines, oxygen-radicals, and catecholamines can influence the responsiveness of G-protein coupled receptors via decreasing the intracellular level of so-called G-protein coupled receptor kinases, of which the subtype GRK2 is highly expressed in immune cells. Therefore, changes in only one kinase can modulate the sensitivity of many receptors. We describe here that sensitivity of neuroendocrine receptors on immune cells is constantly regulated by inflammatory processes or chronic stress, which implies that not only the activity of the neuroendocrine system determines communication but that the sensitivity of receptors is a major factor in determining the final immune response. Finally, consequences of alterations in GRK2 during (neuro)-inflammatory diseases are discussed.