@phdthesis{Nemec2023,
  author    = {Nemec, Katarina},
  title     = {Modulation of parathyroid hormone 1 receptor (PTH1R) signaling by receptor activity-modifying proteins (RAMPs)},
  doi       = {10.25972/OPUS-28858},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-288588},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {The receptor activity-modifying proteins (RAMPs) are ubiquitously expressed membrane proteins that interact with several G protein-coupled receptors (GPCRs), the largest and pharmacologically most important family of cell surface receptors. RAMPs can regulate GPCR function in terms of ligand-binding, G-protein coupling, downstream signaling, trafficking, and recycling. The integrity of their interactions translates to many physiological functions or pathological conditions. Regardless of numerous reports on its essential importance for cell biology and pivotal role in (patho-)physiology, the molecular mechanism of how RAMPs modulate GPCR activation remained largely elusive. This work presents new insights that add to the common understanding of the allosteric regulation of receptor activation and will help interpret how accessory proteins - RAMPs - modulate activation dynamics and how this affects the fundamental aspects of cellular signaling. Using a prototypical class B GPCR, the parathyroid hormone 1 receptor (PTH1R) in the form of advanced genetically encoded optical biosensors, I examined RAMP's impact on the PTH1R activation and signaling in intact cells. A panel of single-cell FRET and confocal microscopy experiments as well canonical and non-canonical functional assays were performed to get a holistic picture of the signaling initiation and transduction of that clinically and therapeutically relevant GPCR. Finally, structural modeling was performed to add molecular mechanistic details to that novel art of modulation. I describe here that RAMP2 acts as a specific allosteric modulator of PTH1R, shifting PTH1R to a unique pre-activated state that permits faster activation in a ligand-specific manner. Moreover, RAMP2 modulates PTH1R downstream signaling in an agonist-dependent manner, most notably increasing the PTH-mediated Gi3 signaling sensitivity and kinetics of cAMP accumulation. Additionally, RAMP2 increases PTH- and PTHrP-triggered β-arrestin2 recruitment to PTH1R and modulates cytosolic ERK1/2 phosphorylation. Structural homology modeling shows that structural motifs governing GPCR-RAMP interaction originate in allosteric hotspots and rationalize functional modulation. Moreover, to interpret the broader role of RAMP's modulation in GPCRs pharmacology, different fluorescent tools to investigate RAMP's spatial organization were developed, and novel conformational biosensors for class B GPCRs were engineered. Lastly, a high throughput assay is proposed and prototyped to expand the repertoire of RAMPs or other membrane protein interactors. These data uncover the critical role of RAMPs in GPCR activation and signaling and set up a novel platform for studying GPCR modulation. Furthermore, these insights may provide a new venue for precise modulation of GPCR function and advanced drug design.},
  subject      = {G-Protein gekoppelter Rezeptor},
  language  = {en}
}
@phdthesis{İşbilir2022,
  author    = {İ{\c{s}}bilir, Ali},
  title     = {Localization and Trafficking of CXCR4 and CXCR7},
  doi       = {10.25972/OPUS-24937},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-249378},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {G protein-coupled receptors (GPCRs) constitute the largest class of membrane proteins, and are the master components that translate extracellular stimulus into intracellular signaling, which in turn modulates key physiological and pathophysiological processes. Research within the last three decades suggests that many GPCRs can form complexes with each other via mechanisms that are yet unexplored. Despite a number of functional evidence in favor of GPCR dimers and oligomers, the existence of such complexes remains controversial, as different methods suggest diverse quaternary organizations for individual receptors. Among various methods, high resolution fluorescence microscopy and imagebased fluorescence spectroscopy are state-of-the-art tools to quantify membrane protein oligomerization with high precision. This thesis work describes the use of single molecule fluorescence microscopy and implementation of two confocal microscopy based fluorescence fluctuation spectroscopy based methods for characterizing the quaternary organization of two class A GPCRs that are important clinical targets: the C-X-C type chemokine receptor 4 (CXCR4) and 7 (CXCR7), or recently named as the atypical chemokine receptor 3 (ACKR3). The first part of the results describe that CXCR4 protomers are mainly organized as monomeric entities that can form transient dimers at very low expression levels allowing single molecule resolution. The second part describes the establishment and use of spatial and temporal brightness methods that are based on fluorescence fluctuation spectroscopy. Results from this part suggests that ACKR3 forms clusters and surface localized monomers, while CXCR4 forms increasing amount of dimers as a function of receptor density in cells. Moreover, CXCR4 dimerization can be modulated by its ligands as well as receptor conformations in distinct manners. Further results suggest that antagonists of CXCR4 display distinct binding modes, and the binding mode influences the oligomerization and the basal activity of the receptor: While the ligands that bind to a "minor" subpocket suppress both dimerization and constitutive activity, ligands that bind to a distinct, "major" subpocket only act as neutral antagonists on the receptor, and do not modulate neither the quaternary organization nor the basal signaling of CXCR4. Together, these results link CXCR4 dimerization to its density and to its activity, which may represent a new strategy to target CXCR4.},
  subject      = {G-Protein gekoppelter Rezeptor},
  language  = {en}
}
@phdthesis{Jarzina2022,
  author    = {Jarzina, Sebastian Oskar},
  title     = {Assessment of systemic toxicity in vitro using the Adverse Outcome Pathway (AOP) concept: nephrotoxicity due to receptor-mediated endocytosis and lysosomal overload and inhibition of mtDNA polymerase-ɣ as case studies},
  doi       = {10.25972/OPUS-26484},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-264842},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {The US National Research Council (NRC) report "Toxicity Testing in the 21st Century: A Vision and a strategy (Tox21)", published in 2007, calls for a complete paradigm shift in tox-icity testing. A central aspect of the proposed strategy includes the transition from apical end-points in in vivo studies to more mechanistically based in vitro tests. To support and facilitate the transition and paradigm shift in toxicity testing, the Adverse Outcome Pathway (AOP) concept is widely recognized as a pragmatic tool. As case studies, the AOP concept was ap-plied in this work to develop AOPs for proximal tubule injuries initiated by Receptor-mediated endocytosis and lysosomal overload and Inhibition of mtDNA polymerase-. These AOPs were used as a mechanistic basis for the development of in vitro assays for each key event (KE). To experimentally support the developed in vitro assays, proximal tubule cells from rat (NRK-52E) and human (RPTEC/TERT1) were treated with model compounds. To measure the dis-turbance of lysosomal function in the AOP - Receptor-mediated endocytosis and lysosomal overload, polymyxin antibiotics (polymyxin B, colistin, polymyxin B nonapeptide) were used as model compounds. Altered expression of lysosomal associated membrane protein 1/2 (LAMP-1/2) (KE1) and cathepsin D release from lysosomes (KE2) were determined by im-munofluorescence, while cytotoxicity (KE3) was measured using the CellTiter-Glo® cell via-bility assay. Importantly, significant differences in polymyxin uptake and susceptibility be-tween cell lines were observed, underlining the importance of in vitro biokinetics to determine an appropriate in vitro point of departure (PoD) for risk assessment. Compared to the in vivo situation, distinct expression of relevant transporters such as megalin and cubilin on mRNA and protein level in the used cell lines (RPTEC/TERT1 and NRK-52E) could not be con-firmed, making integration of quantitative in vitro to in vivo extrapolations (QIVIVE) neces-sary. Integration of QIVIVE by project partners of the University of Utrecht showed an im-provement in the modelled biokinetic data for polymyxin B. To assess the first key event, (KE1) Depletion of mitochondrial DNA, in the AOP - Inhibition of mtDNA polymerase-, a RT-qPCR method was used to determine the mtDNA copy number in cells treated with mod-el compounds (adefovir, cidofovir, tenofovir, adefovir dipivoxil, tenofovir disoproxil fumarate). Mitochondrial toxicity (KE2) was measured by project partners using the high-content imaging technique and MitoTracker® whereas cytotoxicity (KE3) was determined by CellTiter-Glo® cell viability assay. In contrast to the mechanistic hypothesis underlying the AOP - Inhibition of mtDNA polymerase-, treatment with model compounds for 24 h resulted in an increase rather than a decrease in mtDNA copy number (KE1). Only minor effects on mitochondrial toxicity (KE2) and cytotoxicity (KE3) were observed. Treatment of RPT-EC/TERT1 cells for 14 days showed only a slight decrease in mtDNA copy number after treatment with adefovir dipivoxil and tenofovir disoproxil fumarate, underscoring some of the limitations of short-term in vitro systems. To obtain a first estimation for risk assessment based on in vitro data, potential points of departure (PoD) for each KE were calculated from the obtained in vitro data. The most common PoDs were calculated such as the effect concentra-tion at which 10 \% or 20_\% effect was measured (EC10, EC20), the highest no observed effect concentration (NOEC), the lowest observed effect concentration (LOEC), the benchmark 10 \% (lower / upper) concentrations (BMC10, BMCL10, BMCU10) and a modelled non-toxic con-centration (NtC). These PoDs were then compared with serum and tissue concentrations de-termined from in vivo studies after treatment with therapeutic / supratherapeutic doses of the respective drugs in order to obtain a first estimate of risk based on in vitro data. In addition, AOPs were used to test whether the quantitative key event relationships between key events allow prediction of downstream effects and effects on the adverse outcome (AO) based on measurements of an early key event. Predictions of cytotoxicity from the mathematical rela-tionships showed good concordance with measured cytotoxicity after treatment with colistin and polymyxin b nonapeptide. The work also revealed uncertainties and limitations of the ap-plied strategy, which have a significant impact on the prediction and on a risk assessment based on in vitro results.},
  language  = {en}
}
@phdthesis{BathePeters2022,
  author    = {Bathe-Peters, Marc},
  title     = {Spectroscopic approaches for the localization and dynamics of β\(_1\)- and β\(_2\)-adrenergic receptors in cardiomyocytes},
  doi       = {10.25972/OPUS-25812},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-258126},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {In the heart the β\(_1\)-adrenergic receptor (AR) and the β\(_2\)-AR, two prototypical G protein-coupled receptors (GPCRs), are both activated by the same hormones, namely adrenaline and noradrenaline. Both receptors couple to stimulatory G\(_s\) proteins, mediate an increase in cyclic adenosine monophosphate (cAMP) and influence the contractility and frequency of the heart upon stimulation. However, activation of the β\(_1\)-AR, not the β\(_2\)-AR, lead to other additional effects, such as changes in gene transcription resulting in cardiac hypertrophy, leading to speculations on how distinct effects can arise from receptors coupled to the same downstream signaling pathway. In this thesis the question of whether this distinct behavior may originate from a differential localization of these two receptors in adult cardiomyocytes is addressed. Therefore, fluorescence spectroscopy tools are developed and implemented in order to elucidate the presence and dynamics of these endogenous receptors at the outer plasma membrane as well as on the T-tubular network of intact adult cardiomyocytes. This allows the visualization of confined localization and diffusion of the β\(_2\)-AR to the T-tubular network at endogenous expression. In contrast, the β\(_1\)-AR is found diffusing at both the outer plasma membrane and the T-tubules. Upon overexpression of the β\(_2\)-AR in adult transgenic cardiomyocytes, the receptors experience a loss of this compartmentalization and are also found at the cell surface. These data suggest that distinct signaling and functional effects can be controlled by specific cell surface targeting of the receptor subtypes. The tools at the basis of this thesis work are a fluorescent adrenergic antagonist in combination of fluorescence fluctuation spectroscopy to monitor the localization and dynamics of the lowly expressed adrenergic receptors. Along the way to optimizing these approaches, I worked on combining widefield and confocal imaging in one setup, as well as implementing a stable autofocus mechanism using electrically tunable lenses.},
  subject      = {G-Protein gekoppelte Rezeptoren},
  language  = {en}
}
@phdthesis{Bertelsmann2022,
  author    = {Bertelsmann, Dietmar},
  title     = {Analysis of the Frequency of Kidney Toxicity in Preclinical Safety Studies using the eTOX Database},
  doi       = {10.25972/OPUS-25710},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257104},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {This research aimed to obtain reliable data on the frequency of different types of renal toxicity findings in 28-day oral gavage studies in Wistar rats, their consistency across species and study duration, as well as the correlation between histopathological endpoints and routinely used clinical chemistry parameters indicative of kidney injury. Analysis of renal histopathological findings was carried out through extraction of information from the IMI eTOX database. Spontaneous renal histopathological findings in 28-day oral gavage studies in control Wistar rats and beagle dogs confirmed tubular basophilia and renal dilation as the most frequent incidental findings in controls, whereas necrosis and glomerulosclerosis were not identified at all or only rarely as a background lesion. Histopathological evidence of necrosis and glomerulosclerosis was associated with changes in clinical chemistry parameters in 28-day oral gavage Wistar rat studies. Necrosis was frequently accompanied by a statistically significant rise in serum creatinine and serum urea, whereas serum albumin was frequently found to decrease statistically significantly in treatment groups in which necrosis was recorded. In contrast to necrosis, glomerulosclerosis was not associated with statistically significant changes in serum creatinine and urea in any of the 28-day oral gavage Wistar rat treatment groups, but appears to be best reflected by a pattern of statistically significantly lowered serum albumin and serum protein together with a statistically significant increase in serum cholesterol. As might have been expected based on the high background incidences of tubular basophilia and dilation, no consistent changes in any of the clinical chemistry parameters were evident in animals in which renal lesions were con� fined to renal tubular basophilia or dilation. In summary, the routinely provided clinical chemistry parameters are rather insensitive - novel kidney biomarkers such as Cystatin C, β-trace protein and Kidney injury molecule 1 should further be evaluated and integrated into routine preclinical and clinical practice. However, evaluation of clinical chemistry data was limited by the lack of individual animal data. Even though an extensive amount of preclinical studies is accessible through the eTOX database, comparison of consistency across time was limited by the limited number of shorter- and longer term studies conducted with the compounds identified as causing renal histopathological changes within a 28- day study in rats. A high consistency across time for both treatment-related tubular basophilia and treatment-related dilation cannot be confirmed for either of the two effects as these two findings were both induced only rarely in studies over a different treatment-duration other than 28 days after administration of the compounds which provoked the respective effect in a 28-day study. For the finding of necrosis consistency across time was low with the exception of "AZ_GGA_200002321", in which renal papillary necrosis was identified consist� ently throughout different treatment durations (2, 4, 26, 104 weeks). No shorter and longer-term studies were available for the compounds identified as causing glomerulosclerosis within a 28-day study in rats. No consistent findings of the selected histopathological endpoints were identified in any of the corresponding 28-day oral gavage beagle dog studies after treatment with the identical compounds, which caused the respective ef� fect after 28-day treatment in rats. However, in the overwhelming majority of cases, beagle dogs were administered lower doses in these studies in compar� ison to the corresponding 28-day Wistar rat studies. Searching the eTOX database yielded no 28-day oral gavage studies in Wistar and Wistar Han rats in which accumulation of hyaline droplets, tubular atrophy or hyperplasia was recorded. Only one 28-day oral gavage Wistar rat study was identified with the histopathological result of neutrophilic inflammation. Consequently, evaluation of these four renal findings in relation to clinical chemistry parameters and consistency across time and species cannot be made. In summary, this work contributes knowledge through mining and evaluating the eTOX database on a variety of specific renal endpoints that frequently occur after administration of trial substances in 28-day oral gavage studies in Wistar rats in the field of preclinical toxicity with specific focus on their frequency relation to background findings, as well as consistency across time and species. Targeted statistical evaluation of in vivo data within joint research ventures such as the eTOX project, presents an enormous opportunity for an innovative future way of aiding preclinical research towards a more efficient research in the preclinical stage of drug development. This could be achieved through the aug� mentation of methodological strategies and possibly novel software tools in order to predict in vivo toxicology of new molecular entities by means of information that is already available before early stages of the drug development pipeline begin.},
  language  = {en}
}
@phdthesis{Anton2021,
  author    = {Anton, Selma},
  title     = {Characterization of cAMP nanodomains surrounding the human Glucagon-like peptide 1 receptor using FRET-based reporters},
  doi       = {10.25972/OPUS-19069},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-190695},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Cyclic adenosine monophosphate (cAMP), the ubiquitous second messenger produced upon stimulation of GPCRs which couple to the stimulatory GS protein, orchestrates an array of physiological processes including cardiac function, neuronal plasticity, immune responses, cellular proliferation and apoptosis. By interacting with various effector proteins, among others protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac), it triggers signaling cascades for the cellular response. Although the functional outcomes of GSPCR-activation are very diverse depending on the extracellular stimulus, they are all mediated exclusively by this single second messenger. Thus, the question arises how specificity in such responses may be attained. A hypothesis to explain signaling specificity is that cellular signaling architecture, and thus precise operation of cAMP in space and time would appear to be essential to achieve signaling specificity. Compartments with elevated cAMP levels would allow specific signal relay from receptors to effectors within a micro- or nanometer range, setting the molecular basis for signaling specificity. Although the paradigm of signaling compartmentation gains continuous recognition and is thoroughly being investigated, the molecular composition of such compartments and how they are maintained remains to be elucidated. In addition, such compartments would require very restricted diffusion of cAMP, but all direct measurements have indicated that it can diffuse in cells almost freely. In this work, we present the identification and characterize of a cAMP signaling compartment at a GSPCR. We created a F{\"o}rster resonance energy transfer (FRET)-based receptor-sensor conjugate, allowing us to study cAMP dynamics in direct vicinity of the human glucagone-like peptide 1 receptor (hGLP1R). Additional targeting of analogous sensors to the plasma membrane and the cytosol enables assessment of cAMP dynamics in different subcellular regions. We compare both basal and stimulated cAMP levels and study cAMP crosstalk of different receptors. With the design of novel receptor nanorulers up to 60nm in length, which allow mapping cAMP levels in nanometer distance from the hGLP1R, we identify a cAMP nanodomain surrounding it. Further, we show that phosphodiesterases (PDEs), the only enzymes known to degrade cAMP, are decisive in constraining cAMP diffusion into the cytosol thereby maintaining a cAMP gradient. Following the discovery of this nanodomain, we sought to investigate whether downstream effectors such as PKA are present and active within the domain, additionally studying the role of A-kinase anchoring proteins (AKAPs) in targeting PKA to the receptor compartment. We demonstrate that GLP1-produced cAMP signals translate into local nanodomain-restricted PKA phosphorylation and determine that AKAP-tethering is essential for nanodomain PKA. Taken together, our results provide evidence for the existence of a dynamic, receptor associated cAMP nanodomain and give prospect for which key proteins are likely to be involved in its formation. These conditions would allow cAMP to exert its function in a spatially and temporally restricted manner, setting the basis for a cell to achieve signaling specificity. Understanding the molecular mechanism of cAMP signaling would allow modulation and thus regulation of GPCR signaling, taking advantage of it for pharmacological treatment.},
  language  = {en}
}
@phdthesis{Kodandaraman2021,
  author    = {Kodandaraman, Geema},
  title     = {Influence of insulin-induced oxidative stress in genotoxicity and disease},
  doi       = {10.25972/OPUS-24200},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-242005},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Hormones are essential components in the body and their imbalance leads to pathological consequences. T2DM, insulin resistance and obesity are the most commonly occurring lifestyle diseases in the past decade. Also, an increased cancer incidence has been strongly associated with obese and T2DM patients. Therefore, our aim was to study the influence of high insulin levels in accumulating DNA damage in in vitro models and patients, through the induction of oxidative stress. The primary goal of this study was to analyze the genotoxicity induced by the combined action of two endogenous hormones (insulin and adrenaline) with in vitro models, through the induction of micronuclei and to see if they cause an additive increase in genomic damage. This is important for multifactorial diseases having high levels of more than one hormone, such as metabolic syndrome and conditions with multiple pathologies (e.g., T2DM along with high stress levels). Furthermore, the combination of insulin and the pharmacological inhibition of the tumor suppressor gene: PTEN, was to be tested in in vitro models for their genotoxic effect and oxidative stress inducing potential. As the tumor suppressor gene: PTEN is downregulated in PTEN associated syndromes and when presented along with T2DM and insulin resistance, this may increase the potential to accumulate genomic damage. The consequences of insulin action were to be further elucidated by following GFP-expressing cells in live cell-imaging to observe the ability of insulin, to induce micronuclei and replicative stress. Finally, the detrimental potential of high insulin levels in obese patients with hyperinsulinemia and pre-diabetes was to be studied by analyzing markers of oxidative stress and genomic damage. In summary, the intention of this work was to understand the effects of high insulin levels in in vitro and in patients to understand its relevance for the development of genomic instability and thus an elevated cancer risk.},
  subject      = {Insulin},
  language  = {en}
}
@phdthesis{Classen2021,
  author    = {Claßen, Alexandra},
  title     = {The ERK-cascade in the pathophysiology of cardiac hypertrophy},
  doi       = {10.25972/OPUS-22966},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229664},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {ERK1/2 are known key players in the pathophysiology of heart failure, but the members of the ERK cascade, in particular Raf1, can also protect the heart from cell death and ischemic injury. An additional autophosphorylation (ERK1 at Thr208, ERK2 at Thr188) empowers ERK1/2 translocation to the nucleus and phosphorylation of nuclear targets which take part in the development of cardiac hypertrophy. Thereby, targeting this additional phosphorylation is a promising pharmacological approach. In this thesis, an in silico model of ERK cascade in the cardiomyocyte is introduced. The model is a semi-quantitive model and its behavior was tested with different softwares (SQUAD and CellNetAnalyzer). Different phosphorylation states of ERK1/2 as well as different stimuli can be reproduced. The different types of stimuli include hypertrophic as well as non-hypertrophic stimuli. With the introduced in-silico model time courses and synergistic as well as antagonistic receptor stimuli combinations can be predicted. The simulated time courses were experimentally validated. SQUAD was mainly used to make predictions about time courses and thresholds, whereas CNA was used to analyze steady states and feedback loops. Furthermore, new targets of ERK1/2 which partially contribute, also in the formation of cardiac hypertrophy, were identified and the most promising of them were illuminated. Important further targets are Caspase 8, GAB2, Mxi-2, SMAD2, FHL2 and SPIN90. Cardiomyocyte gene expression data sets were analyzed to verify involved components and to find further significantly altered genes after induced hypertrophy with TAC (transverse aortic constriction). Changes in the ultrastructure of the cardiomyocyte are the final result of induced hypertrophy.},
  subject      = {Herzhypertrophie},
  language  = {en}
}
@phdthesis{Schihada2021,
  author    = {Schihada, Hannes},
  title     = {Novel optical methods to monitor G-protein-coupled receptor activation in microtiter plates},
  doi       = {10.25972/OPUS-17541},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-175415},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {G-protein-coupled receptors (GPCRs) regulate diverse physiological processes in the human body and represent prime targets in modern drug discovery. Engagement of different ligands to these membrane-embedded proteins evokes distinct receptor conformational rearrangements that facilitate subsequent receptor-mediated signalling and, ultimately, enable cellular adaptation to altered environmental conditions. Since the early 2000s, the technology of resonance energy transfer (RET) has been exploited to assess these conformational receptor dynamics in living cells and real time. However, to date, these conformational GPCR studies are restricted to single-cell microscopic setups, slowing down the discovery of novel GPCR-directed therapeutics. In this work, we present the development of a novel generalizable high-throughput compatible assay for the direct measurement of GPCR activation and deactivation. By screening a variety of energy partners for fluorescence (FRET) and bioluminescence resonance energy transfer (BRET), we identified a highly sensitive design for an α2A-adrenergic receptor conformational biosensor. This biosensor reports the receptor's conformational change upon ligand binding in a 96-well plate reader format with the highest signal amplitude obtained so far. We demonstrate the capacity of this sensor prototype to faithfully quantify efficacy and potency of GPCR ligands in intact cells and real time. Furthermore, we confirm its universal applicability by cloning and validating five further equivalent GPCR biosensors. To prove the suitability of this new GPCR assay for screening purposes, we measured the well-accepted Z-factor as a parameter for the assay quality. All tested biosensors show excellent Z-factors indicating outstanding assay quality. Furthermore, we demonstrate that this assay provides excellent throughput and presents low rates of erroneous hit identification (false positives and false negatives). Following this phase of assay development, we utilized these biosensors to understand the mechanism and consequences of the postulated modulation of parathyroid hormone receptor 1 (PTHR1) through receptor activity-modifying protein 2 (RAMP2). We found that RAMP2 desensitizes PTHR1, but not the β2-adrenergic receptor (β2AR), for agonist-induced structural changes. This generalizable sensor design offers the first possibility to upscale conformational GPCR studies, which represents the most direct and unbiased approach to monitor receptor activation and deactivation. Therefore, this novel technology provides substantial advantages over currently established methods for GPCR ligand screening. We feel confident that this technology will aid the discovery of novel types of GPCR ligands, help to identify the endogenous ligands of so-called orphan GPCRs and deepen our understanding of the physiological regulation of GPCR function.},
  subject      = {G-Protein gekoppelte Rezeptoren},
  language  = {en}
}
@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}
}