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SummaryThe chemokine receptor CCR7 is essential for lymphocyte and dendritic cell homing to secondary lymphoid organs. Owing to the ability to induce directional migration, CCR7 and its ligands CCL19 and CCL21 are pivotal for the regulation of the immune system. Here, we identify a novel function for receptor ubiquitylation in the regulation of the trafficking process of this G-protein-coupled seven transmembrane receptor. We discovered that CCR7 is ubiquitylated in a constitutive, ligand-independent manner and that receptor ubiquitylation regulates the basal trafficking of CCR7 in the absence of chemokine. Upon CCL19 binding, we show that internalized CCR7 recycles back to the plasma membrane via the trans-Golgi network. An ubiquitylation-deficient CCR7 mutant internalized normally after ligand binding, but inefficiently recycled in immune cells and was transiently retarded in the trans-Golgi network compartment of HEK293 transfectants. Finally, we demonstrate that the lack of CCR7 ubiquitylation profoundly impairs immune cell migration. Our results provide evidence for a novel function of receptor ubiquitylation in the regulation of CCR7 recycling and immune cell migration.

Due to their interesting physicochemical properties, gold nanoparticles (Au-NPs) are the focus of increasing attention in the field of biomedicine and are under consideration for use in drug delivery and bioimaging, or as radiosensitizers and nano-based vaccines. Thorough evaluation of the genotoxic potential of Au-NPs is required, since damage to the genome can remain undetected in standard hazard assessments. Available genotoxicity data is either limited or contradictory. Here, we examined the influence of three surface modified 3-4 nm Au-NPs on human A549 cells, according to the reactive oxygen species (ROS) paradigm. After 24 h of Au-NP treatment, nanoparticles were taken up by cells as agglomerates; however, no influence on cell viability or inflammation was detected. No increase in ROS production was observed by H2-DCF assay; however, intracellular glutathione levels reduced over time, indicating oxidative stress. All three types of Au-NPs induced DNA damage, as detected by alkaline comet assay. The strongest genotoxic effect was observed for positively charged Au-NP I. Further analysis of Au-NP I by neutral comet assay, fluorimetric detection of alkaline DNA unwinding assay, and γH2AX staining, revealed that the induced DNA lesions were predominantly alkali-labile sites. As highly controlled repair mechanisms have evolved to remove a wide range of DNA lesions with great efficiency, it is important to focus on both acute cyto- and genotoxicity, alongside post-treatment effects and DNA repair. We demonstrate that Au-NP-induced DNA damage is largely repaired over time, indicating that the observed damage is of transient nature.

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