The CXCL12/CXCR4/ACKR3 Axis in the Tumor Microenvironment: Signaling, Crosstalk, and Therapeutic Targeting.

Elevated expression of the chemokine receptors CXCR4 and ACKR3 and of their cognate ligand CXCL12 is detected in a wide range of tumors and the tumor microenvironment (TME). Yet, the molecular mechanisms by which the CXCL12/CXCR4/ACKR3 axis contributes to the pathogenesis are complex and not fully understood. To dissect the role of this axis in cancer, we discuss its ability to impinge on canonical and less conventional signaling networks in different cancer cell types; its bidirectional crosstalk, notably with receptor tyrosine kinase (RTK) and other factors present in the TME; and the infiltration of immune cells that supporttumor progression. We discuss current and emerging avenues that target the CXCL12/CXCR4/ACKR3 axis. Coordinately targeting both RTKs and CXCR4/ACKR3 and/or CXCL12 is an attractive approach to consider in multitargeted cancer therapies. In addition, inhibiting infiltrating immune cells or reactivating the immune system along with modulating the CXCL12/CXCR4/ACKR3 axis in the TME has therapeutic promise.

GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo.

BACKGROUND: Insulin secretion from the pancreatic ß-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed. RESULTS: Using GRK2 hemizygous mice, isolated pancreatic islets, and model ß-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/- mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/- mice. Using nanoBRET in ß-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent ß-arrestin recruitment. CONCLUSIONS: Overall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor ß-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.

Crosstalk between CXCR4/ACKR3 and EGFR Signaling in Breast Cancer Cells.

A better understanding of the complex crosstalk among key receptors and signaling pathways involved in cancer progression is needed to improve current therapies. We have investigated in cell models representative of the major subtypes of breast cancer (BC) the interplay between the chemokine CXCL12/CXCR4/ACKR3 and EGF receptor (EGFR) family signaling cascades. These cell lines display a high heterogeneity in expression profiles of CXCR4/ACKR3 chemokine receptors, with a predominant intracellular localization and different proportions of cell surface CXCR4+, ACKR3+ or double-positive cell subpopulations, and display an overall modest activation of oncogenic pathways in response to exogenous CXCL12 alone. Interestingly, we find that in MDA-MB-361 (luminal B subtype, Her2-overexpressing), but not in MCF7 (luminal A) or MDA-MB-231 (triple negative) cells, CXCR4/ACKR3 and EGFR receptor families share signaling components and crosstalk mechanisms to concurrently promote ERK1/2 activation, with a key involvement of the G protein-coupled receptor kinase 2 (GRK2) signaling hub and the cytosolic tyrosine kinase Src. Our findings suggest that in certain BC subtypes, a relevant cooperation between CXCR4/ACKR3 and growth factor receptors takes place to integrate concurrent signals emanating from the tumor microenvironment and foster cancer progression.

HDAC6 at Crossroads of Infection and Innate Immunity.

Histone deacetylase 6 (HDAC6) acts by enzyme-dependent and -independent mechanisms to regulate diverse cellular processes including autophagy, the ubiquitin proteasome system, and cell migration. HDAC6 also has emerging roles in innate immunity, including pathogen sensing and destruction, thus placing this enzyme at the crossroads of infection and innate immunity.

Autophagy mediates hepatic GRK2 degradation to facilitate glucagon-induced metabolic adaptation to fasting.

The liver plays a key role during fasting to maintain energy homeostasis and euglycemia via metabolic processes mainly orchestrated by the insulin/glucagon ratio. We report here that fasting or calorie restriction protocols in C57BL6 mice promote a marked decrease in the hepatic protein levels of G protein-coupled receptor kinase 2 (GRK2), an important negative modulator of both G protein-coupled receptors (GPCRs) and insulin signaling. Such downregulation of GRK2 levels is liver-specific and can be rapidly reversed by refeeding. We find that autophagy, and not the proteasome, represents the main mechanism implicated in fasting-induced GRK2 degradation in the liver in vivo. Reducing GRK2 levels in murine primary hepatocytes facilitates glucagon-induced glucose production and enhances the expression of the key gluconeogenic enzyme Pck1. Conversely, preventing full downregulation of hepatic GRK2 during fasting using adenovirus-driven overexpression of this kinase in the liver leads to glycogen accumulation, decreased glycemia, and hampered glucagon-induced gluconeogenesis, thus preventing a proper and complete adaptation to nutrient deprivation. Overall, our data indicate that physiological fasting-induced downregulation of GRK2 in the liver is key for allowing complete glucagon-mediated responses and efficient metabolic adaptation to fasting in vivo.

GRK2 levels in myeloid cells modulate adipose-liver crosstalk in high fat diet-induced obesity.

Macrophages are key effector cells in obesity-associated inflammation. G protein-coupled receptor kinase 2 (GRK2) is highly expressed in different immune cell types. Using LysM-GRK2+/- mice, we uncover that a reduction of GRK2 levels in myeloid cells prevents the development of glucose intolerance and hyperglycemia after a high fat diet (HFD) through modulation of the macrophage pro-inflammatory profile. Low levels of myeloid GRK2 confer protection against hepatic insulin resistance, steatosis and inflammation. In adipose tissue, pro-inflammatory cytokines are reduced and insulin signaling is preserved. Macrophages from LysM-GRK2+/- mice secrete less pro-inflammatory cytokines when stimulated with lipopolysaccharide (LPS) and their conditioned media has a reduced pathological influence in cultured adipocytes or naïve bone marrow-derived macrophages. Our data indicate that reducing GRK2 levels in myeloid cells, by attenuating pro-inflammatory features of macrophages, has a relevant impact in adipose-liver crosstalk, thus preventing high fat diet-induced metabolic alterations.

G-protein-coupled receptor kinase 2 safeguards epithelial phenotype in head and neck squamous cell carcinomas.

Head and neck squamous cell carcinoma (HNSCC) arises from the mucosal lining of the upper aerodigestive tract and display few treatment options in advanced stages. Despite increased knowledge of HNSCC molecular biology, the identification of new players involved in triggering HNSCC recurrence and metastatic disease is needed. We uncover that G-protein-coupled receptor kinase-2 (GRK2) expression is reduced in undifferentiated, high-grade human HNSCC tumors, whereas its silencing in model human HNSCC cells is sufficient to trigger epithelial-to-mesenchymal transition (EMT) phenotypic features, an EMT-like transcriptional program and enhanced lymph node colonization from orthotopic tongue tumors in mice. Conversely, enhancing GRK2 expression counteracts mesenchymal cells traits by mechanisms involving phosphorylation and decreased functionality of the key EMT inducer Snail1. Our results suggest that GRK2 safeguards the epithelial phenotype, whereas its downregulation contributes to the activation of EMT programs in HNSCC.

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.

G protein-coupled receptor kinases (GRKs) in tumorigenesis and cancer progression: GPCR regulators and signaling hubs.

Increasing evidences point to G protein-coupled receptor kinases (GRKs), a subfamily of protein kinase A/G/C-like kinases, as relevant players in cancer progression, in a cell-type and tumor-specific way. Alterations in the expression and/or activity of particular GRKs have been identified in several types of tumors, and demonstrated to modulate the proliferation, survival or invasive properties of tumor cells by acting as integrating signaling nodes. GRKs are able to regulate the functionality of both G protein-coupled receptors (GPCR) and growth factor receptors and to directly control cytosolic, cytoskeletal or nuclear signaling components of pathways relevant for these processes. Furthermore, many chemokines as well as angiogenic and inflammatory factors present in the tumor microenvironment act through GPCR and other GRK-modulated signaling modules. Changes in the dosage of certain GRKs in the tumor stroma can alter tumor angiogenesis and the homing of immune cells, thus putting forward these kinases as potentially relevant modulators of the carcinoma-fibroblast-endothelial-immune cell network fostering tumor development and dissemination. A better understanding of the alterations in different GRK isoforms taking place during cancer development and metastasis in specific tumors and cell types and of its impact in signaling pathways would help to design novel therapeutic strategies.

The Role of ACKR3 in Breast, Lung, and Brain Cancer.

Recent reports regarding the significance of chemokine receptors in disease have put a spotlight on atypical chemokine receptor 3 (ACKR3). This atypical chemokine receptor is overexpressed in numerous cancer types and has been involved in the modulation of tumor cell proliferation and migration, tumor angiogenesis, or resistance to drugs, thus contributing to cancer progression and metastasis occurrence. Here, we focus on the clinical significance and potential mechanisms underlying the pathologic role of ACKR3 in breast, lung, and brain cancer and discuss its possible relevance as a prognostic factor and potential therapeutic target in these contexts.

CXCR4/ACKR3 Phosphorylation and Recruitment of Interacting Proteins: Key Mechanisms Regulating Their Functional Status.

The C-X-C motif chemokine receptor type 4 (CXCR4) and the atypical chemokine receptor 3 (ACKR3/CXCR7) are class A G protein-coupled receptors (GPCRs). Accumulating evidence indicates that GPCR subcellular localization, trafficking, transduction properties, and ultimately their pathophysiological functions are regulated by both interacting proteins and post-translational modifications. This has encouraged the development of novel techniques to characterize the GPCR interactome and to identify residues subjected to post-translational modifications, with a special focus on phosphorylation. This review first describes state-of-the-art methods for the identification of GPCR-interacting proteins and GPCR phosphorylated sites. In addition, we provide an overview of the current knowledge of CXCR4 and ACKR3 post-translational modifications and an exhaustive list of previously identified CXCR4- or ACKR3-interacting proteins. We then describe studies highlighting the importance of the reciprocal influence of CXCR4/ACKR3 interactomes and phosphorylation states. We also discuss their impact on the functional status of each receptor. These studies suggest that deeper knowledge of the CXCR4/ACKR3 interactomes along with their phosphorylation and ubiquitination status would shed new light on their regulation and pathophysiological functions.

Calpains mediate isoproterenol-induced hypertrophy through modulation of GRK2.

Inhibition of the Ca2+-dependent proteases calpains attenuates post-infarction remodeling and heart failure. Recent data suggest that calpain activity is elevated in non-ischemic cardiomyopathies and that upregulation of the key cardiac G-protein-coupled receptor kinase 2 (GRK2) signaling hub promotes cardiac hypertrophy. However, the functional interactions between calpains and GRK2 in this context have not been explored. We hypothesized that calpain modulates GRK2 levels in myocardial hypertrophy of non-ischemic cause, and analyzed the mechanisms involved and the potential therapeutic benefit of inhibiting calpain activity in this situation. The oral calpain inhibitor SNJ-1945 was administered daily to male Sprague-Dawley rats or wild-type and hemizygous GRK2 mice treated with 5 mg/Kg/day isoproterenol intraperitoneally for 1 week. In isoproterenol-treated animals, calpains 1 and 2 were overexpressed in myocardium and correlated with increased calpain activity and ventricular hypertrophy. Oral co-administration of SNJ-1945 attenuated calpain activation and reduced heart hypertrophy as assessed using morphological and biochemical markers. Calpain activation induced by isoproterenol increased GRK2 protein levels, while genetic downregulation of GRK2 expression prevented isoproterenol-mediated hypertrophy independently of calpain inhibition. GRK2 upregulation was associated to calpain-dependent degradation of the GRK2 ubiquitin ligase MDM2 and to enhanced NF-κB-dependent GRK2 gene expression in correlation with calpain-mediated IĸB proteolysis. These results demonstrate that calpain mediates isoproterenol-induced myocardial hypertrophy by modulating GRK2 protein content through mechanisms involving the control of GRK2 stability and expression. Sustained calpain inhibition attenuates isoproterenol-induced myocardial hypertrophy and could be an effective therapeutic strategy to limit ventricular remodeling of non-ischemic origin.

Critical role for Epac1 in inflammatory pain controlled by GRK2-mediated phosphorylation of Epac1.

cAMP signaling plays a key role in regulating pain sensitivity. Here, we uncover a previously unidentified molecular mechanism in which direct phosphorylation of the exchange protein directly activated by cAMP 1 (EPAC1) by G protein kinase 2 (GRK2) suppresses Epac1-to-Rap1 signaling, thereby inhibiting persistent inflammatory pain. Epac1(-/-) mice are protected against inflammatory hyperalgesia in the complete Freund's adjuvant (CFA) model. Moreover, the Epac-specific inhibitor ESI-09 inhibits established CFA-induced mechanical hyperalgesia without affecting normal mechanical sensitivity. At the mechanistic level, CFA increased activity of the Epac target Rap1 in dorsal root ganglia of WT, but not of Epac1(-/-), mice. Using sensory neuron-specific overexpression of GRK2 or its kinase-dead mutant in vivo, we demonstrate that GRK2 inhibits CFA-induced hyperalgesia in a kinase activity-dependent manner. In vitro, GRK2 inhibits Epac1-to-Rap1 signaling by phosphorylation of Epac1 at Ser-108 in the Disheveled/Egl-10/pleckstrin domain. This phosphorylation event inhibits agonist-induced translocation of Epac1 to the plasma membrane, thereby reducing Rap1 activation. Finally, we show that GRK2 inhibits Epac1-mediated sensitization of the mechanosensor Piezo2 and that Piezo2 contributes to inflammatory mechanical hyperalgesia. Collectively, these findings identify a key role of Epac1 in chronic inflammatory pain and a molecular mechanism for controlling Epac1 activity and chronic pain through phosphorylation of Epac1 at Ser-108. Importantly, using the Epac inhibitor ESI-09, we validate Epac1 as a potential therapeutic target for chronic pain.

ß-Arrestin-1 mediates the TCR-triggered re-routing of distal receptors to the immunological synapse by a PKC-mediated mechanism.

T-cell receptors (TCR) recognize their antigen ligand at the interface between T cells and antigen-presenting cells, known as the immunological synapse (IS). The IS provides a means of sustaining the TCR signal which requires the continual supply of new TCRs. These are endocytosed and redirected from distal membrane locations to the IS. In our search for novel cytoplasmic effectors, we have identified ß-arrestin-1 as a ligand of non-phosphorylated resting TCRs. Using dominant-negative and knockdown approaches we demonstrate that ß-arrestin-1 is required for the internalization and downregulation of non-engaged bystander TCRs. Furthermore, TCR triggering provokes the ß-arrestin-1-mediated downregulation of the G-protein coupled chemokine receptor CXCR4, but not of other control receptors. We demonstrate that ß-arrestin-1 recruitment to the TCR, and bystander TCR and CXCR4 downregulation, are mechanistically mediated by the TCR-triggered PKC-mediated phosphorylation of ß-arrestin-1 at Ser163. This mechanism allows the first triggered TCRs to deliver a stop migration signal, and to promote the internalization of distal TCRs and CXCR4 and their translocation to the IS. This receptor crosstalk mechanism is critical to sustain the TCR signal.

G-Protein-Coupled Receptor Kinase 2 as a Potential Modulator of the Hallmarks of Cancer.

Malignant features-such as sustained proliferation, refractoriness to growth suppressors, resistance to cell death or aberrant motility, and metastasis-can be triggered by a variety of mutations and signaling adaptations. Signaling nodes can act as cancer-associated factors by cooperating with oncogene-governed pathways or participating in compensatory transduction networks to strengthen tumor properties. G-protein-coupled receptor kinase 2 (GRK2) is arising as one of such nodes. Via its complex network of connections with other cellular proteins, GRK2 contributes to the modulation of basic cellular functions-such as cell proliferation, survival, or motility-and is involved in metabolic homeostasis, inflammation, or angiogenic processes. Moreover, altered GRK2 levels are starting to be reported in different tumoral contexts and shown to promote breast tumorigenesis or to trigger the tumoral angiogenic switch. The ability to modulate several of the hallmarks of cancer puts forward GRK2 as an oncomodifier, able to modulate carcinogenesis in a cell-type specific way.

Protein Kinase C ζ Interacts with a Novel Binding Region of Gαq to Act as a Functional Effector.

Heterotrimeric G proteins play an essential role in the initiation of G protein-coupled receptor (GPCR) signaling through specific interactions with a variety of cellular effectors. We have recently reported that GPCR activation promotes a direct interaction between Gαq and protein kinase C ζ (PKCζ), leading to the stimulation of the ERK5 pathway independent of the canonical effector PLCß. We report herein that the activation-dependent Gαq/PKCζ complex involves the basic PB1-type II domain of PKCζ and a novel interaction module in Gαq different from the classical effector-binding site. Point mutations in this Gαq region completely abrogate ERK5 phosphorylation, indicating that Gαq/PKCζ association is required for the activation of the pathway. Indeed, PKCζ was demonstrated to directly bind ERK5 thus acting as a scaffold between Gαq and ERK5 upon GPCR activation. The inhibition of these protein complexes by G protein-coupled receptor kinase 2, a known Gαq modulator, led to a complete abrogation of ERK5 stimulation. Finally, we reveal that Gαq/PKCζ complexes link Gαq to apoptotic cell death pathways. Our data suggest that the interaction between this novel region in Gαq and the effector PKCζ is a key event in Gαq signaling.

A novel GRK2/HDAC6 interaction modulates cell spreading and motility.

Cell motility and adhesion involves dynamic microtubule (MT) acetylation/deacetylation, a process regulated by enzymes as HDAC6, a major cytoplasmic α-tubulin deacetylase. We identify G protein-coupled receptor kinase 2 (GRK2) as a key novel stimulator of HDAC6. GRK2, which levels inversely correlate with the extent of α-tubulin acetylation in epithelial cells and fibroblasts, directly associates with and phosphorylates HDAC6 to stimulate α-tubulin deacetylase activity. Remarkably, phosphorylation of GRK2 itself at S670 specifically potentiates its ability to regulate HDAC6. GRK2 and HDAC6 colocalize in the lamellipodia of migrating cells, leading to local tubulin deacetylation and enhanced motility. Consistently, cells expressing GRK2-K220R or GRK2-S670A mutants, unable to phosphorylate HDAC6, exhibit highly acetylated cortical MTs and display impaired migration and protrusive activity. Finally, we find that a balanced, GRK2/HDAC6-mediated regulation of tubulin acetylation differentially modulates the early and late stages of cellular spreading. This novel GRK2/HDAC6 functional interaction may have important implications in pathological contexts.

Obesity-induced cardiac lipid accumulation in adult mice is modulated by G protein-coupled receptor kinase 2 levels.

BACKGROUND: The leading cause of death among the obese population is heart failure and stroke prompted by structural and functional changes in the heart. The molecular mechanisms that underlie obesity-related cardiac remodeling are complex, and include hemodynamic and metabolic alterations that ultimately affect the functionality of the myocardium. G protein-coupled receptor kinase 2 (GRK2) is an ubiquitous kinase able to desensitize the active form of several G protein-coupled receptors (GPCR) and is known to play an important role in cardiac GPCR modulation. GRK2 has also been recently identified as a negative modulator of insulin signaling and systemic insulin resistance. METHODS: We investigated the effects elicited by GRK2 downregulation in obesity-related cardiac remodeling. For this aim, we used  9 month-old wild type (WT) and GRK2+/- mice, which display circa 50% lower levels of this kinase, fed with either a standard or a high fat diet (HFD) for 30 weeks. In these mice we studied different parameters related to cardiac growth and lipid accumulation. RESULTS: We find that GRK2+/- mice are protected from obesity-promoted cardiac and cardiomyocyte hypertrophy and fibrosis. Moreover, the marked intracellular lipid accumulation caused by a HFD in the heart is not observed in these mice. Interestingly, HFD significantly increases cardiac GRK2 levels in WT but not in GRK2+/- mice, suggesting that the beneficial phenotype observed in hemizygous animals correlates with the maintenance of GRK2 levels below a pathological threshold. Low GRK2 protein levels are able to keep the PKA/CREB pathway active and to prevent HFD-induced downregulation of key fatty acid metabolism modulators such as Peroxisome proliferator-activated receptor gamma co-activators (PGC1), thus preserving the expression of cardioprotective proteins such as mitochondrial fusion markers mitofusin MFN1 and OPA1. CONCLUSIONS: Our data further define the cellular processes and molecular mechanisms by which GRK2 down-regulation is cardioprotective during diet-induced obesity, reinforcing the protective effect of maintaining low levels of GRK2 under nutritional stress, and showing a role for this kinase in obesity-induced cardiac remodeling and steatosis.

Downregulation of G protein-coupled receptor kinase 2 levels enhances cardiac insulin sensitivity and switches on cardioprotective gene expression patterns.

G protein-coupled receptor kinase 2 (GRK2) has recently emerged as a negative modulator of insulin signaling. GRK2 downregulation improves insulin sensitivity and prevents systemic insulin resistance. Cardiac GRK2 levels are increased in human heart failure, while genetically inhibiting GRK2 leads to cardioprotection in mice. However, the molecular basis underlying the deleterious effects of GRK2 up-regulation and the beneficial effects of its inhibition in the heart are not fully understood. Therefore, we have explored the interconnections among a systemic insulin resistant status, GRK2 dosage and cardiac insulin sensitivity in adult (9 month-old) animals. GRK2(+/-) mice display enhanced cardiac insulin sensitivity and mild heart hypertrophy with preserved systolic function. Cardiac gene expression is reprogrammed in these animals, with increased expression of genes related to physiological hypertrophy, while the expression of genes related to pathological hypertrophy or to diabetes/obesity co-morbidities is repressed. Notably, we find that cardiac GRK2 levels increase in situations where insulin resistance develops, such as in ob/ob mice or after high fat diet feeding. Our data suggest that GRK2 downregulation/inhibition can help maintain cardiac function in the face of co-morbidities such as insulin resistance, diabetes or obesity by sustaining insulin sensitivity and promoting a gene expression reprogramming that confers cardioprotection.

A novel p38 MAPK docking-groove-targeted compound is a potent inhibitor of inflammatory hyperalgesia.

The MAPK (mitogen-activated protein kinase) p38 is an important mediator of inflammation and of inflammatory and neuropathic pain. We have described recently that docking-groove-dependent interactions are important for p38 MAPK-mediated signal transduction. Thus virtual screening was performed to identify putative docking-groove-targeted p38 MAPK inhibitors. Several compounds of the benzo-oxadiazol family were identified with low micromolar inhibitory activity both in a p38 MAPK activity assay, and in THP-1 human monocytes acting as inhibitors of LPS (lipopolysaccharide)-induced TNFα (tumour necrosis factor α) secretion. Positions 2 and 5 in the phenyl ring are essential for the described inhibitory activity with a chloride in position 5 and a methyl group in position 2 yielding the best results, giving an IC50 value of 1.8 µM (FGA-19 compound). Notably, FGA-19 exerted a potent and long-lasting analgesic effect in vivo when tested in a mouse model of inflammatory hyperalgesia. A single intrathecal injection of FGA-19 completely resolved hyperalgesia, being 10-fold as potent and displaying longer lasting effects than the established p38 MAPK inhibitor SB239063. FGA-19 also reversed persistent pain in a model of post-inflammatory hyperalgesia in LysM (lysozyme M)-GRK2 (G-protein-coupled-receptor kinase)(+/-) mice. These potent in vivo effects suggested p38 MAPK docking-site-targeted inhibitors as a potential novel strategy for the treatment of inflammatory pain.