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Metastasis, the process by which cancer cells colonize distant organs, relies on the ability of these cells to migrate and invade the surrounding tissues. The ezrin, radixin, and moesin family (ERM) of proteins are critical regulators of cell morphology transformations required for cancer cell movement and invasion. Yet, how ERMs are activated during metastasis remains poorly understood. Here, we identified the thromboxane A2 receptor (TBXA2R), a G protein-coupled receptor, as a critical activator of ERMs that promotes motility, invasion, and metastasis of triple-negative breast cancer (TNBC) cells. We found that ERM activation downstream of TBXA2R signaling depends on the Gαq/11and Gα12/13subfamilies, the small GTPase RhoA, and its Ser/Thr kinase effector SLK. We also showed that TBXA2R signaling increases TNBC cell motility and invasionin vitroand metastasisin vivo,depending on ERMs. These findings unveil a novel mechanism by which a member of the largest class of receptors activates key metastatic determinants to promote TNBC metastasis, which could have important implications for developing novel therapeutic strategies.

Activation of the G protein-coupled receptors by agonists may result in the activation of one or more G proteins, and in the recruitment of arrestins. The balance of activation of different pathways can be influenced by the ligand. Using BRET-based biosensors, we showed that the vasopressin V2 receptor activates or at least engages many different G proteins across all G protein subfamilies in response to its native agonist arginine vasopressin (AVP). This includes members of the Gi/o and G12/13 families that have not been previously reported. These signalling pathways are also activated by the synthetic peptide desmopressin and natural homologs of AVP, namely oxytocin and the non-mammalian hormone vasotocin. They demonstrated varying degrees of functional selectivity relative to AVP, as quantified using the operational model for quantifying ligand bias. Additionally, we modelled G protein activation as a Michaelis-Menten reaction. This approach provided a complementary way to quantify signalling bias, with an added benefit of clear separation of the effects of ligand affinity from the intrinsic activity of the receptor. These results showed that V2 receptor is not only promiscuous in its ability to engage several G proteins, but also that its signalling profile could be easily biased by small structural changes in the ligand.

Cannabinoid CB1 and CB2 receptors are members of the G protein-coupled receptor family, which is the largest class of membrane proteins in the human genome. As part of the endocannabinoid system, they have many regulatory functions in the human body. Their malfunction therefore triggers a diverse set of undesired conditions, such as pain, neuropathy, nephropathy, pruritus, osteoporosis, cachexia and Alzheimer’s disease. Although drugs targeting the system exist, the molecular and functional mechanisms involved are still poorly understood, preventing the development of better therapeutics with fewer undesired effects. One path toward the development of better and safer medicines targeting cannabinoid receptors relies on the ability of some compounds to activate a subset of pathways engaged by the receptor while sparing or even inhibiting the others, a phenomenon known as biased signaling. To take advantage of this phenomenon for drug development, a better profiling of the pathways engaged by the receptors is required. Using a BRET-based signaling detection platform, we systematically analyzed the primary signaling cascades activated by CB1 and CB2 receptors, including 9 G protein and 2 β-arrestin subtypes. Given that biased signaling is driven by ligand-specific distinct active conformations of the receptor, establishing a link between the signaling profiles elicited by different drugs and their chemotypes may help designing compounds that selectively activate beneficial pathways while avoiding those leading to undesired effects. We screened a selection of 35 structurally diverse ligands, including endocannabinoids, phytocannabinoids and synthetic compounds structurally similar or significantly different from natural cannabinoids. Our data show that biased signaling is a prominent feature of the cannabinoid receptor system and that, as predicted, ligands with different chemotypes have distinct signaling profiles. The study therefore allows for better understanding of cannabinoid receptors signaling and provides the information about tool compounds that can now be used to link signaling pathways to biological outcomes, aiding the design of improved therapeutics.

SUMMARYEzrin, Radixin and Moesin compose the family of ERM proteins. They link actin and microtubule filaments to the plasma membrane to control signaling and cell morphogenesis. Importantly, their activity promotes invasive properties of metastatic cells from different cancer origins. Therefore, a precise understanding of how these proteins are regulated is important for the understanding of the mechanism controlling cell shape as well as providing new opportunities for the development of innovative cancer therapies. ERMs are believed to exist in two main conformational states: a close-inactive conformation in the cytoplasm that is recruited at the plasma membrane to convert into an open-active conformation. Here, we developed and characterized novel BRET-based conformational biosensors, compatible with high throughput screening, that monitor Ezrin, Radixin or Moesin individual activation in living cells. We showed that these biosensors faithfully monitor ERM activation and can be used to quantify the impact of small molecules, mutation of regulatory amino acids or depletion of upstream regulators on their activity. The use of these biosensors allowed us to uncover a novel aspect of ERM activation process involving a pool of closed-inactive ERMs stably associated with the plasma membrane. Upon stimulation, this pool serves as a cortical reserve that is rapidly activated before the recruitment of cytoplasmic ERMs.

Malaria causes millions of deaths worldwide and is considered a huge public health problem for underdeveloped countries. The most severe cases of malaria present complications of the host circulatory system, which may cause clogging and rupture of blood vessels, leading to death or important sequelae. Because of the previously suggested role of thrombin and platelet aggregation in Plasmodium falciparum biology, we hypothesized that one of the GPCR-like proteins identified in the genome of the parasite, P. falciparum serpentine receptor 12 (PfSR12), could be a thrombin-activated GPCR. To test this hypothesis we used a series of Bioluminescence and Bioluminescence Resonance Energy Transfer (BRET)-based biosensors to investigate the signaling activity of PfSR12. Using an Obelin based biosensor, thrombin promoted a PfSR12-dependent cytosolic Ca2+ rise in HEK293 cells. This Ca2+ mobilization was accompanied by DAG formation and PKC activation as detected using DAG and PKC BRET-based biosensors indicating a Gq/PLC/IP3 signaling pathway. The role of Gq was confirm using Gq/11 knockout HEK293 cells as well as the Gq-selective inhibitor, YM254890. Further investigation revealed that PfSR12 is not itself a thrombin receptor but rather promotes the increase of cell surface expression of an endogenous thrombin receptor. This chaperone-like effect was not selective for thrombin receptors as PfSR12 expression also promoted an increased muscarinic type 3 receptor (M3R)-promoted DAG and PKC responses. This increase response was accompanied by an increase in surface expression of M3R. Our data indicate that PfSR12 acts as a chaperone and increases the expression of several GPCRs resulting in increased responsiveness to various hormones of mammalian cells that could contribute to the deleterious effects of Plasmodium falciparum infection.

G protein-coupled receptors (GPCRs) drive an array of important physiological functions and are the targets of nearly one-third of all FDA approved drugs. Large scale genomic initiatives are mapping the genetic diversity in GPCRs, however, a map of which GPCR genetic variants are associated with phenotypic variation and disease is lacking. Furthermore, the mechanistic basis of how the individual GPCR genetic variants regulate molecular function is also largely unknown. We performed a phenome-wide association analysis for 269 common protein-altering variants in 156 GPCRs and 275 phenotypes using data from 337,205 unrelated white British UK Biobank participants and identified 138 associations at a false discovery rate of 5%. We found a novel association between rs12295710 in MRGPRE , a member of the Mas-related receptor family involved in nociception, and migraine risk. We also identified an association between rs3732378, a missense mutation in the binding pocket of CX3CR1, and hypothyroidism. Five orphan GPCRs had eight genetic associations, highlighting novel biology for these receptors of unknown function. We found several associations between GPCR variants and food intake phenotypes, including an association between the variants in TAS2R38 known to affect the ability to taste phenylthiocarbamide and tea intake as well as a non-additive associations between variants in TAS2R19 and TAS2R31 and coffee and tea intake. Finally, we tested whether genetic variants in ADRB2 associated with immune cell amounts and pulmonary function affect downstream signaling pathways and found that two ADRB2 haplotypes are associated with differential signaling relative to the most common haplotype. Overall, this study provides a map of genetic associations for GPCR coding variants across a wide variety of phenotypes that can inform future drug discovery efforts targeting GPCRs.

Interaction of β-arrestins (βarrs) upon agonist-stimulation is a hallmark of G protein-coupled receptors (GPCRs) resulting in receptor desensitization, endocytosis and signaling. Although overall functional roles of βarrs are typically believed to be conserved across different receptors, emerging data now clearly unveils receptor-specific functional contribution of βarrs. The underlying mechanism however remains mostly speculative and represents a key missing link in our current understanding of GPCR signaling and regulatory paradigms. Here, we develop synthetic intrabody-based conformational sensors that help us visualize the assembly and trafficking of GPCR-βarr1 complexes in cellular context for a broad set of receptors with spatio-temporal resolution. Surprisingly, these conformational sensors reveal a previously unappreciated level of diversity in GPCR-βarr complexes that extends beyond the current framework of affinity-based classification and phosphorylation-code-based interaction patterns. More importantly, this conformational diversity arising from spatial signature of phosphorylation sites manifests directly in the form of distinct functional outcomes, including even opposite contribution of βarrs in signal-transduction for different receptors. Taken together, these findings uncover that despite an overall similar interaction and trafficking patterns; critical structural and functional differences exist in βarr complexes for different GPCRs that define and fine-tune receptor-specific downstream responses.

Transport of mRNA is an efficient mechanism to target proteins to specific regions of a cell. Although it is well documented that mRNAs are transported in ribonucleoprotein (RNP) complexes, several of the mechanisms involved in complex formation and localization are poorly understood. Staufen (Stau) 1, a double-stranded RNA-binding protein, is a well accepted marker of mRNA transport complexes. In this manuscript, we provide evidence that Stau1 self-associates in live cells using immunoprecipitation and bioluminescence resonance energy transfer (BRET) assays. The double-stranded RNA-binding domains dsRBD3 and dsRBD4 contributed about half of the signal, suggesting that Stau1 RNA-binding activity is involved in Stau1 self-association. Protein–protein interaction also occurred, via dsRBD5 and dsRBD2, as shown by in vitro pull-down, yeast two-hybrid, and BRET assays in live cells. Interestingly, Stau1 self-association contributes to the formation of oligomeric complexes as evidenced by the coexpression of split Renilla luciferase halves covalently linked to Stau1 in a protein complementation assay (PCA) combined with a BRET assay with Stau1-YFP. Moreover, we showed that these higher-order Stau1-containing complexes carry RNAs when the RNA stain SYTO 14 was used as the energy acceptor in the PCA/BRET assay. The oligomeric composition of Stau1-containing complexes and the presence of specific mRNAs have been confirmed by biochemical approaches involving two successive immunoprecipitations of Stau1-tagged molecules followed by qRT-PCR amplification. Altogether, these results indicate that Stau1 self-associates in mRNPs via its multiple functional domains that can select mRNAs to be transported and establish protein–protein interaction.