25,452 research outputs found
Chemokine receptor CCR5: insights into structure, function, and regulation
No full textCC chemokine receptor 5 (CCR5) is a seven-transmembrane, G protein-coupled receptor (GPCR) which regulates trafficking and effector functions of memory/effector T-lymphocytes, macrophages, and immature dendritic cells. It also serves as the main coreceptor for the entry of R5 strains of human immunodeficiency virus (HIV-1, HIV-2). Chemokine binding to CCR5 leads to cellular activation through pertussis toxin-sensitive heterotrimeric G proteins as well as G protein-independent signalling pathways, Like many other GPCR, CCR5 is regulated by agonist-dependent processes which involve G protein coupled receptor kinase (GRK)-dependent phosphorylation, P-arrestin-mediated desensitization and internalization. This review discusses recent advances in the elucidation of the structure and function of CCR5, as well as the complex mechanisms that regulate CCR5 signalling and cell surface expression. (C) 2004 Elsevier Inc. All rights reserved
Phosphorylation-state specific monoclonal antihodies reveal phosphorylation of distinct serine residues on chemokine receptor CCR5 by G protein-coupled receptor kinases (GRK) versus protein kinase C (PKC)
No full textPhosphorylation-state specific monoclonal antihodies reveal phosphorylation of distinct serine residues on chemokine receptor CCR5 by G protein-coupled receptor kinases (GRK) versus protein kinase C (PKC)
No full textDestination Threshold Potential and the Law of Repeat Visitation
No full textThis article addresses the issue of how repeat visitation ratios can be used as a management tool in determining a destination’s position on the destination life-cycle curve. Following a review of the literature on repeat visitation, it presents the concepts of destination threshold potential (TP) and cumulative travel experience (CTE). It then relates how the number of first-time and repeat visitors is inextricably linked to the CTE and TP, as well as to the tourist arrivals in any given year. From those elaborations, several axioms on the law of repeat visitation are developed that provide desti-nation and product managers with the necessary measuring tools to determine their destinations ’ current position. The tourism literature is ripe with market segmentation studies that use a wide range of approaches (e.g., Andereck and Caldwell 1994; Mo, Havitz, and Howard 1994; Shoe-maker 1994) and that deal with destination development, specifically Butler’s (1980) destination life cycle (e.g., Doug-las 1997; Tooman 1997). However, few examine outbound tourism (e.g., Oppermann and Chon 1995) or lifelong travel patterns or travel careers of individuals (e.g., Becker 1992; Oppermann 1995; Pearce 1993). One can note that research-ers have given little recognition to the interactions between tourists and destination in the form of studies on destination choice. Having said that, several destination choice models have been proposed (e.g., Chon 1990; Crompton 1992
Analysis of Chemokine Receptor Trafficking by Site-Specific Biotinylation.
No full textChemokine receptors undergo internalization and desensitization in response to ligand activation. Internalized receptors are either preferentially directed towards recycling pathways (e.g. CCR5) or sorted for proteasomal degradation (e.g. CXCR4). Here we describe a method for the analysis of receptor internalization and recycling based on specific Bir A-mediated biotinylation of an acceptor peptide coupled to the receptor, which allows a more detailed analysis of receptor trafficking compared to classical antibody-based detection methods. Studies on constitutive internalization of the chemokine receptors CXCR4 (12.1% ± 0.99% receptor internalization/h) and CCR5 (13.7% ± 0.68%/h) reveals modulation of these processes by inverse (TAK779; 10.9% ± 0.95%/h) or partial agonists (Met-CCL5; 15.6% ± 0.5%/h). These results suggest an actively driven internalization process. We also demonstrate the advantages of specific biotinylation compared to classical antibody detection during agonist-induced receptor internalization, which may be used for immunofluorescence analysis as well. Site-specific biotinylation may be applicable to studies on trafficking of transmembrane proteins, in general
G protein-coupled receptor kinases promote phosphorylation and beta-arrestin-mediated internalization of CCR5 homo- and hetero-oligomers
No full textExpression levels of the chemokine receptor, CC chemokine receptor 5 (CCR5), at the cell surface determine cell susceptibility to HIV entry and infection. Cellular activation by CCR5 itself, but also by unrelated receptors leads to cross-phosphorylation and cross-internalization of CCR5. This study addresses the underlying molecular mechanisms of homologous and heterologous CCR5 regulation. As shown by bioluminescence resonance energy transfer experiments, CCR5 formed constitutive homo- as well as heterooligomeric complexes together with C5aR but not with the unrelated AT(1a)R in living cells. Stimulation with CCL5 of RBL cells, which co-expressed CCR5 together with an N-terminally truncated CCR5-Delta NT mutant, resulted in both protein kinase C(PKC)- and G protein-coupled receptor (GPCR) kinase (GRK)-mediated cross-phosphorylation of the mutant unligated receptor, as determined by phosphosite-specific monoclonal antibody. Similarly, both PKC and GRK cross-phosphorylated CCR5 in a heterologous manner after C5a stimulation of RBL-CCR5/ C5aR cells, whereas AT(1a)R stimulation resulted only in classical PKC-mediated CCR5 phosphorylation. Co-expression of CCR5-Delta NT together with a phosphorylation-deficient CCR5 mutant that neither binds beta-arrestin nor undergoes internalization partially restored the CCL5-induced association of beta-arrestin with the homo- oligomeric receptor complex and augmented cellular uptake of I-125-CCL5. Co-expression of C5aR, but not of AT1aR, promoted CCR5 co-internalization upon agonist stimulation by a mechanism independent of CCR5 phosphorylation. Co-internalization of phosphorylated CCR5 was also observed in C5a-stimulated macrophages. Finally, co-expression of a constitutively internalized C5aR-US28(CT) mutant led to intracellular accumulation of CCR5 in the absence of ligand stimulation. These results show that GRKs and beta-arrestin are involved in heterologous receptor regulation by cross-phosphorylating and co-internalizing unligated receptors within homo- or hetero-oligomeric protein complexes
Targetting CCL25/CCR9: A succesful therapeutic strategy during early chronic murine ileitis
No full textKinetic analysis of PKC- and GRK-mediated phosphorylation of chemokine receptor CCR5 by phosphosite-specific antibodies
No full text- …
