Differential regulation of chemotaxis: Role of Gβγ in chemokine receptor-induced cell migration

Biasing Gβγ Downstream Signaling with Gallein Inhibits Development of Morphine Tolerance and Potentiates Morphine-Induced Nociception in a Tolerant State

Opioid analgesics are widely used as a treatment option for pain management and relief. However, the misuse of opioid analgesics has contributed to the current opioid epidemic in the United States. Prescribed opioids such as morphine, codeine, oxycodone, and fentanyl are mu-opioid receptor (MOR) agonists primarily used in the clinic to treat pain or during medical procedures, but development of tolerance limits their utility for treatment of chronic pain. Here we explored the effects of biasing Gβγ signaling on tolerance development after chronic morphine treatment in vivo. We hypothesized that biasing Gβγ signaling with gallein could prevent activation of regulatory signaling pathways that result in tolerance to antinociceptive effects of MOR agonists. Gallein has been shown to bind to Gβγ and inhibit interactions of Gβγ with phospholipase-Cβ3 (PLCβ3) or G-protein-coupled receptor kinase 2 (GRK2) but not G-protein inwardly rectifying potassium (GIRK) channels. In mice, morphine-induced antinociception was evaluated in the 55°C warm water tail withdrawal assay. We used two paradigms for gallein treatment: administration during and after three times-daily morphine administration. Our results show that gallein cotreatment during repeated administration of morphine decreased opioid tolerance development and that gallein treatment in an opioid-tolerant state enhanced the potency of morphine. Mechanistically, our data suggest that PLCβ3 is necessary for potentiating effects of gallein in an opioid-tolerant state but not in preventing the development of tolerance. These studies demonstrate that small molecules that target Gβγ signaling could reduce the need for large doses of opioid analgesics to treat pain by producing an opioid-sparing effect. SIGNIFICANCE STATEMENT: Biasing Gβγ signaling prevents tolerance to repeated morphine administration in vivo and potentiates the antinociceptive effects of morphine in an opioid-tolerant state. Mechanistically, phospholipase-Cβ is necessary for potentiating effects of gallein in an opioid-tolerant state but not in preventing the development of tolerance. This study identifies a novel treatment strategy to decrease the development of tolerance to the analgesic effects of mu-opioid receptor agonists, which are necessary to improve pain treatment and decrease the incidence of opioid use disorder.

Biological characterization of ligands targeting the human CC chemokine receptor 8 (CCR8) reveals the biased signaling properties of small molecule agonists

The human CC chemokine receptor 8 (CCR8) is a promising drug target for cancer immunotherapy and autoimmune disease. Besides human and viral chemokines, previous studies revealed diverse classes of CCR8-targeting small molecules. We characterized a selection of these CCR8 ligands (hCCL1, vCCL1, ZK756326, AZ6; CCR8 agonists and a naphthalene-sulfonamide-based CCR8 antagonist), in in vitro cell-based assays (hCCL1^AF647 binding, calcium mobilization, cellular impedance, cell migration, β-arrestin 1/2 recruitment), and used pharmacological tools to determine G protein-dependent and -independent signaling pathways elicited by these ligands. Our data reveal differences in CCR8-mediated signaling induced by chemokines versus small molecules, which was most pronounced in cell migration studies. Human CCL1 most efficiently induced cell migration whereby Gβγ signaling was indispensable. In contrast, Gβγ signaling did not contribute to cell migration induced by other CCR8 ligands (vCCL1, ZK756326, AZ6). Although all tested CCR8 agonists were full agonists for calcium mobilization, a significant contribution for Gβγ signaling herein was only apparent for human and viral CCL1. Despite both Gα_i- and Gα_q-signaling regulate intracellular Ca²⁺-release, cellular impedance experiments showed that CCR8 agonists predominantly induce Gα_i-dependent signaling. Finally, small molecule agonists displayed higher efficacy in β-arrestin 1 recruitment, which occurred independently of Gα_i signaling. Also in this latter assay, only hCCL1-induced activity was dependent on Gβγ-signaling. Our study provides insight into CCR8 signaling and function and demonstrates differential CCR8 activation by different classes of ligands. This reflects the ability of CCR8 small molecules to evoke different subsets of the receptor's signaling repertoire, which categorizes them as biased agonists.

Emerging regulators of vascular smooth muscle cell migration

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the blood vessel wall and normally adopt a quiescent, contractile phenotype. VSMC migration is tightly controlled, however, disease associated changes in the soluble and insoluble environment promote VSMC migration. Classically, studies investigating VSMC migration have described the influence of soluble factors. Emerging data has highlighted the importance of insoluble factors, including extracellular matrix stiffness and porosity. In this review, we will recap on the important signalling pathways that regulate VSMC migration and reflect on the potential importance of emerging regulators of VSMC function.

MicroRNA-144 mediates chronic inflammation and tumorigenesis in colorectal cancer progression via regulating C-X-C motif chemokine ligand 11

Colorectal cancer (CRC) is one of the most common malignancies worldwide. The aim of the present study was to investigate the expression of microRNA-144 (miR-144) and C-X-C motif chemokine ligand 11 (CXCL11) in CRC and their association. Data from Gene Expression Omnibus (GEO) DataSets were analyzed to obtain the expression profile of CXCL11 in CRC. Subsequently, serum samples were collected from 65 subjects, including 39 patients with CRC and 26 controls; CRC and adjacent normal tissues were collected from all 39 CRC patients and the expression of CXCL11 was measured in these specimens. After searching for the potential regulator of CXCL11 through bioinformatics analysis, the levels of miR-144 in the clinical specimens were also detected. Finally, the regulatory association between miR-144 and CXCL11 was certified via the dual-luciferase reporter assay. Microarray data and bioinformatics analysis demonstrated that CXCL11 was significantly upregulated in CRC tissues and miR-144 was a potential regulator of CXCL11. In line with this finding, the expression of CXCL11 was significantly increased in the serum and tumor samples of patients with CRC, while that of miR-144 was downregulated. Dual-luciferase reporter assay revealed that miR-144 directly targets the 3′-untranslated region of CXCL11 mRNA to regulate its expression. These results demonstrated that enhanced CXCL11 expression in patients with CRC was associated with reduced miR-144 expression. The results of the present study may indicate a novel regulatory role of miR-144 in CRC through CXCL11 downregulation.

Activation of Adenosine 2A receptor inhibits neutrophil apoptosis in an autophagy-dependent manner in mice with systemic inflammatory response syndrome

Systemic inflammatory response syndrome (SIRS) is an overwhelming whole body inflammation caused by infectious diseases or sterile insults. Neutrophils are the dominant participants during inflammation, and their survival and death determine the initiation as well as resolution of SIRS. Apoptosis and autophagy are two fundamental cellular processes that modulating cell fate, but their correlation and regulators in neutrophils under SIRS condition have not been elucidated. In this study, we demonstrated that high dose of LPS induced both apoptosis and autophagy of neutrophils in a mouse SIRS model and LPS-stimulated neutrophils in vitro. Moreover, we found that the adenosine 2A receptor (A2AR), a known anti-inflammatory G protein-coupled receptor (GPCR), could inhibit LPS-induced neutrophil apoptosis by suppressing the LPS-induced autophagy. Activation of A2AR suppressed LPS-induced autophagy by inhibiting the ROS-JNK pathway as well as promoting GPCR βϒ subunit–AKT signaling. The A2AR-inhibited autophagy suppressed apoptosis of neutrophils by blocking caspase8, caspase3 and PARP signaling. These findings not only increase our understandings of neutrophils’ fate and function in response to systemic inflammation, but also identify a novel anti-inflammatory role of A2AR in modulating neutrophils’ survival during inflammation.

The impact of RGS and other G-protein regulatory proteins on Gαi-mediated signaling in immunity

Leukocyte chemoattractant receptors are members of the G-protein coupled receptor (GPCR) family. Signaling downstream of these receptors directs the localization, positioning and homeostatic trafficking of leukocytes; as well as their recruitment to, and their retention at, inflammatory sites. Ligand induced changes in the molecular conformation of chemoattractant receptors results in the engagement of heterotrimeric G-proteins, which promotes α subunits to undergo GTP/GDP exchange. This results in the functional release of βγ subunits from the heterotrimers, thereby activating downstream effector molecules, which initiate leukocyte polarization, gradient sensing, and directional migration. Pertussis toxin ADP ribosylates Gαi subunits and prevents chemoattractant receptors from triggering Gαi nucleotide exchange. The use of pertussis toxin revealed the essential importance of Gαi subunit nucleotide exchange for chemoattractant receptor signaling. More recent studies have identified a range of regulatory mechanisms that target these receptors and their associated heterotrimeric G-proteins, thereby helping to control the magnitude, kinetics, and duration of signaling. A failure in these regulatory pathways can lead to impaired receptor signaling and immunopathology. The analysis of mice with targeted deletions of Gαi isoforms as well as some of these G-protein regulatory proteins is providing insights into their roles in chemoattractant receptor signaling.

Inhibition of G-protein βγ signaling enhances T cell receptor-stimulated interleukin 2 transcription in CD4+ T helper cells

G-protein-coupled receptor (GPCR) signaling modulates the expression of cytokines that are drug targets for immune disorders. However, although GPCRs are common targets for other diseases, there are few GPCR-based pharmaceuticals for inflammation. The purpose of this study was to determine whether targeting G-protein βγ (Gβγ) complexes could provide a useful new approach for modulating interleukin 2 (IL-2) levels in CD4⁺ T helper cells. Gallein, a small molecule inhibitor of Gβγ, increased levels of T cell receptor (TCR)-stimulated IL-2 mRNA in primary human naïve and memory CD4⁺ T helper cells and in Jurkat human CD4⁺ leukemia T cells. Gβ₁ and Gβ₂ mRNA accounted for >99% of Gβ mRNA, and small interfering RNA (siRNA)-mediated silencing of Gβ₁ but not Gβ₂ enhanced TCR-stimulated IL-2 mRNA increases. Blocking Gβγ enhanced TCR-stimulated increases in IL-2 transcription without affecting IL-2 mRNA stability. Blocking Gβγ also enhanced TCR-stimulated increases in nuclear localization of nuclear factor of activated T cells 1 (NFAT1), NFAT transcriptional activity, and levels of intracellular Ca²⁺. Potentiation of IL-2 transcription required continuous Gβγ inhibition during at least two days of TCR stimulation, suggesting that induction or repression of additional signaling proteins during T cell activation and differentiation might be involved. The potentiation of TCR-stimulated IL-2 transcription that results from blocking Gβγ in CD4⁺ T helper cells could have applications for autoimmune diseases.