@phdthesis{PerpinaViciano2020, author = {Perpi{\~n}{\´a} Viciano, Cristina}, title = {Study of the activation mechanisms of the CXC chemokine receptor 4 (CXCR4) and the atypical chemokine receptor 3 (ACKR3)}, doi = {10.25972/OPUS-19237}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-192371}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {The CXC chemokine receptor 4 (CXCR4) and the atypical chemokine receptor 3 (ACKR3) are seven transmembrane receptors that are involved in numerous pathologies, including several types of cancers. Both receptors bind the same chemokine, CXCL12, leading to significantly different outcomes. While CXCR4 activation generally leads to canonical GPCR signaling, involving Gi proteins and β-arrestins, ACKR3, which is predominantly found in intracellular vesicles, has been shown to signal via β-arrestin-dependent signaling pathways. Understanding the dynamics and kinetics of their activation in response to their ligands is of importance to understand how signaling proceeds via these two receptors. In this thesis, different F{\"o}rster resonance energy transfer (FRET)-based approaches have been combined to individually investigate the early events of their signaling cascades. In order to investigate receptor activation, intramolecular FRET sensors for CXCR4 and ACKR3 were developed by using the pair of fluorophores cyan fluorescence protein and fluorescence arsenical hairpin binder. The sensors, which exhibited similar functional properties to their wild-type counterparts, allowed to monitor their ligand-induced conformational changes and represent the first RET-based receptor sensors in the field of chemokine receptors. Additional FRET-based settings were also established to investigate the coupling of receptors with G proteins, rearrangements within dimers, as well as G protein activation. On one hand, CXCR4 showed a complex activation mechanism in response to CXCL12 that involved rearrangements in the transmembrane domain of the receptor followed by rearrangements between the receptor and the G protein as well as rearrangements between CXCR4 protomers, suggesting a role of homodimers in the activation course of this receptor. This was followed by a prolonged activation of Gi proteins, but not Gq activation, via the axis CXCL12/CXCR4. In contrast, the structural rearrangements at each step of the signaling cascade in response to macrophage migration inhibitory factor (MIF) were dynamically and kinetically different and no Gi protein activation via this axis was detected. These findings suggest distinct mechanisms of action of CXCL12 and MIF on CXCR4 and provide evidence for a new type of sequential signaling events of a GPCR. Importantly, evidence in this work revealed that CXCR4 exhibits some degree of constitutive activity, a potentially important feature for drug development. On the other hand, by cotransfecting the ACKR3 sensor with K44A dynamin, it was possible to increase its presence in the plasma membrane and measure the ligand-induced activation of this receptor. Different kinetics of ACKR3 activation were observed in response to CXCL12 and three other agonists by means of using the receptor sensor developed in this thesis, showing that it is a valuable tool to study the activation of this atypical receptor and pharmacologically characterize ligands. No CXCL12-induced G protein activation via ACKR3 was observed even when the receptor was re-localized to the plasma membrane by means of using the mutant dynamin. Altogether, this thesis work provides the temporal resolution of signaling patterns of two chemokine receptors for the first time as well as valuable tools that can be applied to characterize their activation in response to pharmacologically relevant ligands.}, subject = {G protein-coupled receptors}, language = {en} } @article{vanUnenStumpfSchmidetal.2016, author = {van Unen, Jakobus and Stumpf, Anette D. and Schmid, Benedikt and Reinhard, Nathalie R. and Hordijk, Peter L. and Hoffmann, Carsten and Gadella, Theodorus W. J. and Goedhart, Joachim}, title = {A New Generation of FRET Sensors for Robust Measurement of Gα\(_{i1}\), Gα\(_{i2}\) and Gα\(_{i3}\) Activation Kinetics in Single Cells}, series = {PLoS ONE}, volume = {11}, journal = {PLoS ONE}, number = {1}, doi = {10.1371/journal.pone.0146789}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167387}, pages = {e0146789}, year = {2016}, abstract = {G-protein coupled receptors (GPCRs) can activate a heterotrimeric G-protein complex with subsecond kinetics. Genetically encoded biosensors based on F{\"o}rster resonance energy transfer (FRET) are ideally suited for the study of such fast signaling events in single living cells. Here we report on the construction and characterization of three FRET biosensors for the measurement of Gα\(_{i1}\), Gα\(_{i2}\) and Gα\(_{i3}\) activation. To enable quantitative long-term imaging of FRET biosensors with high dynamic range, fluorescent proteins with enhanced photophysical properties are required. Therefore, we use the currently brightest and most photostable CFP variant, mTurquoise2, as donor fused to Gα\(_{i}\) subunit, and cp173Venus fused to the Gγ\(_{2}\) subunit as acceptor. The Gα\(_{i}\) FRET biosensors constructs are expressed together with Gβ\(_{1}\) from a single plasmid, providing preferred relative expression levels with reduced variation in mammalian cells. The Gα\(_{i}\) FRET sensors showed a robust response to activation of endogenous or over-expressed alpha-2A-adrenergic receptors, which was inhibited by pertussis toxin. Moreover, we observed activation of the Gα\(_{i}\) FRET sensor in single cells upon stimulation of several GPCRs, including the LPA\(_{2}\), M\(_{3}\) and BK\(_{2}\) receptor. Furthermore, we show that the sensors are well suited to extract kinetic parameters from fast measurements in the millisecond time range. This new generation of FRET biosensors for Gα\(_{i1}\), Gα\(_{i2}\) and Gα\(_{i3}\) activation will be valuable for live-cell measurements that probe Gα\(_{i}\) activation.}, language = {en} }