G protein-coupled receptor kinases promote phosphorylation and beta-arrestin-mediated internalization of CCR5 homo- and hetero-oligomers

Expression 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-DeltaNT 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-DeltaNT 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 (125)I-CCL5. Co-expression of C5aR, but not of AT(1a)R, 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.     

Associative thoughts in women in different phases of the menstrual cycle

In this study female students in different phases of the menstrual cycle made a test of word association. The results were represented and compared in a pathfinder-network. This special network is a model of knowledge representation in which words are portrayed as nodes, and links between nodes represent associations. This method (pathfinder), developed by Schvaneveldt (1990), generates associative networks from individual's ratings of similarity of word pairs. 51 women had to judge 45 words of the three categories sexual, romantic and neutral in similarity. These networks were compared regarding probability of contraception, partnership and level of testosterone. The number and weights of links differed between women with high and low probability of contraception. The level of testosterone had a large influence on the density of associations, especially in sexual contents.     

CD25-expressing CD8+ T cells are potent memory cells in old age

We have recently described an IL-2/IL-4-producing CD8+CD25+ non-regulatory memory T cell population that occurs in a subgroup of healthy elderly persons who characteristically still have a good humoral response after vaccination. The present study addresses this specific T cell subset and investigates its origin, clonal composition, Ag specificity, and replicative history. We demonstrate that CD8+CD25+ memory T cells frequently exhibit a CD4+CD8+ double-positive phenotype. The expression of the CD8 alphabeta molecule and the occurrence of signal-joint TCR rearrangement excision circles suggest a thymic origin of these cells. They also have longer telomeres than their CD8+CD25- memory counterparts, thus indicating a shorter replicative history. CD8+CD25+ memory T cells display a polyclonal TCR repertoire and respond to IL-2 as well as to a panel of different Ags, whereas the CD8+CD25- memory T cell population has a more restricted TCR diversity, responds to fewer Ags, and does not proliferate in response to stimulation with IL-2. Molecular tracking of specific clones with clonotypic primers reveals that the same clones occur in CD8+CD25+ and CD8+CD25- memory T cell populations, demonstrating a lineage relationship between CD25+ and CD25- memory CD8+ T cells. Our results suggest that CD25-expressing memory T cells represent an early stage in the differentiation of CD8+ cells. Accumulation of these cells in elderly persons appears to be a prerequisite of intact immune responsiveness in the absence of naive T cells in old age.     

How chronic inflammation can affect the brain and support the development of Alzheimer's disease in old age: the role of microglia and astrocytes

A huge amount of evidence has implicated amyloid beta (A beta) peptides and other derivatives of the amyloid precursor protein (beta APP) as central to the pathogenesis of Alzheimer's disease (AD). It is also widely recognized that age is the most important risk factor for AD and that the innate immune system plays a role in the development of neurodegeneration. Little is known, however, about the molecular mechanisms that underlie age-related changes of innate immunity and how they affect brain pathology. Aging is characteristically accompanied by a shift within innate immunity towards a pro-inflammatory status. Pro-inflammatory mediators such as tumour necrosis factor-alpha or interleukin-1 beta can then in combination with interferon-gamma be toxic on neurons and affect the metabolism of beta APP such that increased concentrations of amyloidogenic peptides are produced by neuronal cells as well as by astrocytes. A disturbed balance between the production and the degradation of A beta can trigger chronic inflammatory processes in microglial cells and astrocytes and thus initiate a vicious circle. This leads to a perpetuation of the disease.     

Regulatory RNAs and beyond

The dynamic regulation of biological processes by RNA has emerged as a key field in recent years, and was the topic of the 62nd Mosbacher Colloquium of the German Society for Biochemistry and Molecular Biology (GBM). The 2011 Colloquium, held in April in the romantic Neckar-river region, was also a celebration of the tenth anniversary of the RNA Biochemistry study group within the GBM, which acts as platform for RNA biologists and chemists within Germany and in other European countries.     

Influence of light on the foraging impact of an introduced predatory cladoceran,Bythotrephes longimanus

相似文献