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The Super-Conserved Receptors Expressed in the Brain (SREBs) form a subfamily of orphan G protein-coupled receptors, highly conserved in evolution and characterized by a predominant expression in the brain. The signaling pathways activated by these receptors (if any) are presently unclear. Given the strong conservation of their intracellular loops, we used a BioID2 proximity-labeling assay to identify protein partners of SREBs that would interact with these conserved domains. Using streptavidin pull-down followed by mass spectrometry analysis, we identified the amino acid transporter SLC3A2, the AKAP protein LRBA, and the 4.1 protein EPB41L2 as potential interactors of these GPCRs. Using co-immunoprecipitation experiments, we confirmed the physical association of these proteins with the receptors. We then studied the functional relevance of the interaction between EPB41L2 and SREB1. Immunofluorescence microscopy revealed that SREB1 and EPB41L2 co-localize at the plasma membrane and that SREB1 is enriched in the β-catenin-positive cell membranes. siRNA knockdown experiments revealed that EPB41L2 promotes the localization of SREB1 at the plasma membrane and increases the solubilization of SREB1 when using detergents, suggesting a modification of its membrane microenvironment. Altogether, these data suggest that EPB41L2 could regulate the subcellular compartmentalization of SREBs and, as proposed for other GPCRs, could affect their stability or activation. [ABSTRACT FROM AUTHOR]

Background: Chemerin is an extracellular protein with chemotactic activities and its expression is increased in various diseases such as metabolic syndrome and inflammatory conditions. Its role in lung pathology has not yet been extensively studied but both known pro- and anti-inflammatory properties have been observed. The aim of our study was to evaluate the involvement of the chemerin/ChemR23 system in the physiopathology of COVID-19 with a particular focus on its prognostic value. Methods: Blood samples from confirmed COVID-19 patients were collected at day 1, 5 and 14 from admission to Erasme Hospital (Brussels - Belgium). Chemerin concentrations and inflammatory biomarkers were analyzed in the plasma. Blood cells subtypes and their expression of ChemR23 were determined by flow cytometry. The expression of chemerin and ChemR23 was evaluated on lung tissue from autopsied COVID-19 patients by immunohistochemistry (IHC). Results: 21 healthy controls (HC) and 88 COVID-19 patients, including 40 in intensive care unit (ICU) were included. Plasma chemerin concentration were significantly higher in ICU patients than in HC at all time-points analyzed (p<0.0001). Moreover, they were higher in deceased patients compared to survivors (p<0.05). Logistic univariate regression and multivariate analysis demonstrated that chemerin level at day 14 of admission was an independent risk factor for death. Accordingly, chemerin levels correlated with inflammatory biomarkers such as C-reactive protein and tumor necrosis factor α. Finally, IHC analysis revealed a strong expression of ChemR23 on smooth muscle cells and chemerin on myofibroblasts in advanced acute respiratory distress syndrome (ARDS). Discussion: Increased plasma chemerin levels are a marker of severity and may predict death of COVID-19 patients. However, multicentric studies are needed, before chemerin can be considered as a biomarker of severity and death used in daily clinical practice. Further studies are also necessary to identify the precise mechanisms of the chemerin/ChemR23 system in ARDS secondary to viral pneumonia. [ABSTRACT FROM AUTHOR]

Acute pancreatitis (AP) is an inflammatory disease involving the production of different cytokines and chemokines and is characterized by leukocyte infiltration. Because the chemokine receptor CCR5 and its ligands [the CC chemokines CCL3/MIP-1[alpha], CCL4/MIP-1[beta], and CCL5/regulated upon activation, normal T cell expressed and secreted (RANTES)] regulate leukocyte chemotaxis and activation, we investigated the expression of CCR5 ligands and the role of CCR5 and its ligands in experimental AP in mice. AP was induced by hourly intraperitoneal injections of cerulein in CCR5-deficient ([CCR5.sup.-/-]) or wild-type (WT) mice. Induction of AP by cerulein resulted in an early increase of pancreatic CCL2, CCL3, and CCL4 mRNA expression, whereas CCL5 mRNA expression occurred later. [CCR5.sup.-/-] mice developed a more severe pancreatic injury than WT mice during cerulein-induced AP, as assessed by a more pronounced increase in serum amylase and lipase levels and by more severe pancreatic edema, inflammatory infiltrates (mainly neutrophils), and necrosis. [CCR5.sup.-/-] mice also exhibited increased production of CCL2/MCP-1, CCL3/MIP-1[alpha], and CCL4/MIP-1[beta] during the course of cerulein-induced AP. In vivo simultaneous neutralization of CC chemokines with monoclonal antibodies in [CCR5.sup.-/-] mice reduced the severity of cerulein-induced AP, indicating a role of CC chemokines in exacerbating the course of AP in the absence of CCR5. Moreover, simultaneous neutralization of CCR5 ligands in WT mice also reduced the severity of cerulein-induced AP. In conclusion, lack of the chemokine receptor CCR5 exacerbates experimental cerulein-induced AP and leads to increased levels of CC chemokines and a more pronounced pancreatic inflammatory infiltrate, suggesting that CCR5 expression can modulate severity of AP.

Atypical chemokine receptors (ACKRs) have emerged as a subfamily of chemokine receptors regulating the local bioavailability of their ligands through scavenging, concentration, or transport. The biological roles of ACKRs in human physiology and diseases are often studied by using transgenic mouse models. However, it is unknown whether mouse and human ACKRs share the same properties. In this study, we compared the properties of the human and mouse atypical chemerin receptor GPR1 and showed that they behave differently regarding their interaction with β-arrestins. Human hGPR1 interacts with β-arrestins as a result of chemerin stimulation, whereas its mouse orthologue mGPR1 displays a strong constitutive interaction with β-arrestins in basal conditions. The constitutive interaction of mGPR1 with β-arrestins is accompanied by a redistribution of the receptor from the plasma membrane to early and recycling endosomes. In addition, β-arrestins appear mandatory for the chemerin-induced internalization of mGPR1, whereas they are dispensable for the trafficking of hGPR1. However, mGPR1 scavenges chemerin and activates MAP kinases ERK1/2 similarly to hGPR1. Finally, we showed that the constitutive interaction of mGPR1 with β-arrestins required different structural constituents, including the receptor C-terminus and arginine 3.50 in the second intracellular loop. Altogether, our results show that sequence variations within cytosolic regions of GPR1 orthologues influence their ability to interact with β-arrestins, with important consequences on GPR1 subcellular distribution and trafficking. [ABSTRACT FROM AUTHOR]

Research has been conducted on MIP-1(beta), a CC-chemokine responsible for inflammation and host defense mechanism. The study of the MIP-1(beta) CCR5 determinants and their role in receptor activation has been carried out via generated MIP-1(beta) variants with mutated residues within N-loop and the results demonstrate that none of the residues is directly involved in receptor activation.

Results show that G protein coupled receptor RANTES exhibits glycosaminoglycans binding speicificity to heparin using side chain residues R44, K45, and R47. Data further reveal that heparin binding site is a 40s loop, which overlaps beta-chemokine receptor 1 and 3 binding and activation domains.

The binding of the chemokine MIP-1beta to heparin and the CCR5 receptor is completely dependent on the integrity of the 40's loop. The quaternary structure of the MIP-1beta dimer is also important, since a truncated form that cannot dimerize does not bind as well.

Research has been conducted on the CC chemokine structures. The use of nuclear magnetic resonance spectroscopy in analyzing the mutants' oligomeric state is described.

The role of the adenosine-receptor subtype A sub 2a was examined in mice. It has been found that mice lacking this receptor, or A sub 2a R knockout mice, seem to exhibit normal behavior and bred normally but were found to have high anxiety levels and increased blood pressure and heart rates. However, their exploratory behavior was reduced. Male knockout mice displayed a greater level of aggression towards intruders. Caffeine, a psychoactive drug which normally stimulates exploratory behavior, was found to have a strong depressant effect on the mice.

The beta-chemokine receptors CCR5 and CCR2b are the cofactors for entry of M-tropic viruses into cells. Previous studies have reported that M-tropic trains are more sensitive to substitutions in the regions of CCR5 than CCR2b. To understand the molecular basis of CCR5 usage in viral tropism, chimeric molecules of both CCR5 and CCR2b were constructed and regions involved in cofactor utilization by HIV-1 strains were mapped. The chimeras showed that the amino terminus and the first extracellular loop of CCR5 contribute to enhancing the entry of HIV-1 cofactors into the cell.

A mutant allele of the CC-chemokine receptor-5, which is common in caucasians is involved in resistance to HIV-1 infection. None of the HIV-1 infected caucasians in a cohort are homozygous for the mutation, while the frequency of heterozygotes is 35% less than that in normal populations. The white blood cells in homozygous individuals with null alleles are highly resistant to the HIV-1 virus, while the lower frequency of heterozygotes implied partial resistance in seropositive Caucasians. The mutation prevents HIV infection by inhibiting membrane fusion.