Bitopic Ligands Support the Presence of a Metastable Binding Site at the ß2 Adrenergic Receptor.

Metastable binding sites (MBS) have been observed in a multitude of molecular dynamics simulations and can be considered low affinity allosteric binding sites (ABS) that function as stepping stones as the ligand moves toward the orthosteric binding site (OBS). Herein, we show that MBS can be utilized as ABS in ligand design, resulting in ligands with improved binding kinetics. Four homobivalent bitopic ligands (1-4) were designed by molecular docking of (S)-alprenolol ((S)-ALP) in the cocrystal structure of the ß2 adrenergic receptor (ß2AR) bound to the antagonist ALP. Ligand 4 displayed a potency and affinity similar to (S)-ALP, but with a >4-fold increase in residence time. The proposed binding mode was confirmed by X-ray crystallography of ligand 4 in complex with the ß2AR. This ligand design principle can find applications beyond the ß2AR and G protein-coupled receptors (GPCRs) as a general approach for improving the pharmacological profile of orthosteric ligands by targeting the OBS and an MBS simultaneously.

Structure optimization of Cmpd-15 as negative allosteric modulators for the ß2-adrenergic receptor.

19 derivatives of 1-benzyl-3-arylpyrazole-5-carboxamides (H1-H19) and 5 derivatives of 1-benzyl-5-arylpyrazole-3-carboxamides (J1-J5) have been designed and synthesized as potential negative allosteric modulators (NAMs) for the ß2-adrenergic receptor (ß2AR). The new pyrazole derivatives were screened on the classic G-protein dependent signaling pathway at ß2AR. The majority of 1-benzyl-3-aryl-pyrazole-5-carboxamide derivatives show more potent allosteric antagonistic activity against ß2AR than Cmpd-15, the first reported ß2AR NAM. However, the 1-benzyl-5-arylpyrazole-3-carboxamide derivatives exhibit very poor or even no allosteric antagonistic activity for ß2AR. Furthermore, the active pyrazole derivatives have relative better drug-like profiles than Cmpd-15. Taken together, we discovered a series of derivatives of 1-benzyl-3-arylpyrazole-5-carboxamides as a novel scaffold of ß2AR NAM.

G protein-coupled receptor endocytosis generates spatiotemporal bias in ß-arrestin signaling.

The stabilization of different active conformations of G protein-coupled receptors is thought to underlie the varying efficacies of biased and balanced agonists. Here, profiling the activation of signal transducers by angiotensin II type 1 receptor (AT1R) agonists revealed that the extent and kinetics of ß-arrestin binding exhibited substantial ligand-dependent differences, which were lost when receptor internalization was inhibited. When AT1R endocytosis was prevented, even weak partial agonists of the ß-arrestin pathway acted as full or near-full agonists, suggesting that receptor conformation did not exclusively determine ß-arrestin recruitment. The ligand-dependent variance in ß-arrestin translocation was much larger at endosomes than at the plasma membrane, showing that ligand efficacy in the ß-arrestin pathway was spatiotemporally determined. Experimental investigations and mathematical modeling demonstrated how multiple factors concurrently shaped the effects of agonists on endosomal receptor-ß-arrestin binding and thus determined the extent of functional selectivity. Ligand dissociation rate and G protein activity had particularly strong, internalization-dependent effects on the receptor-ß-arrestin interaction. We also showed that endocytosis regulated the agonist efficacies of two other receptors with sustained ß-arrestin binding: the V2 vasopressin receptor and a mutant ß2-adrenergic receptor. In the absence of endocytosis, the agonist-dependent variance in ß-arrestin2 binding was markedly diminished. Our results suggest that endocytosis determines the spatiotemporal bias in GPCR signaling and can aid in the development of more efficacious, functionally selective compounds.

Improved Highly Mobile Membrane Mimetic Model for Investigating Protein-Cholesterol Interactions.

Cholesterol (CHL) plays an integral role in modulating the function and activity of various mammalian membrane proteins. Due to the slow dynamics of lipids, conventional computational studies of protein-CHL interactions rely on either long-time scale atomistic simulations or coarse-grained approximations to sample the process. A highly mobile membrane mimetic (HMMM) has been developed to enhance lipid diffusion and thus used to facilitate the investigation of lipid interactions with peripheral membrane proteins and, with customized in silico solvents to replace phospholipid tails, with integral membrane proteins. Here, we report an updated HMMM model that is able to include CHL, a nonphospholipid component of the membrane, henceforth called HMMM-CHL. To this end, we had to optimize the effect of the customized solvents on CHL behavior in the membrane. Furthermore, the new solvent is compatible with simulations using force-based switching protocols. In the HMMM-CHL, both improved CHL dynamics and accelerated lipid diffusion are integrated. To test the updated model, we have applied it to the characterization of protein-CHL interactions in two membrane protein systems, the human ß2-adrenergic receptor (ß2AR) and the mitochondrial voltage-dependent anion channel 1 (VDAC-1). Our HMMM-CHL simulations successfully identified CHL binding sites and captured detailed CHL interactions in excellent consistency with experimental data as well as other simulation results, indicating the utility of the improved model in applications where an enhanced sampling of protein-CHL interactions is desired.

Identification of adrenergic presynaptic and postsynaptic protein locations at neuromuscular junctions, their decrease during aging, and recovery by nicotinamide mononucleotide administration.

Neuromuscular junctions are innervated by motor and sympathetic nerves. The sympathetic modulation of motor innervation shows functional decline during aging, but the cellular and molecular mechanism of this change is not fully known. This study aimed to evaluate the effect of aging on sympathetic nerves and synaptic proteins at mouse neuromuscular junctions. Sympathetic nerves, presynaptic, and postsynaptic proteins of sympathetic nerves at neuromuscular junctions were visualized using immunohistochemistry, and aging-related changes were compared between adult-, aged-, and nicotinamide mononucleotide (NMN) administered aged mice. Sympathetic nerves were detected by anti-tyrosine hydroxylase antibody, and presynaptic protein vesicular monoamine transporter 2 colocalized with the sympathetic nerves. These two signals surrounded motor nerve terminals and acetylcholine receptor clusters. Postsynaptic neurotransmitter receptor ß2-adrenergic receptors colocalized with motor nerve terminals and resided in reduced density at extrasynaptic sarcolemma. The signal intensity of the sympathetic nerve marker did not show a significant difference at neuromuscular junctions between 8.5-month-old adult mice and 25-month-old aged mice. However, the signal intensity of vesicular monoamine transporter 2 and ß2-adrenergic receptors showed age-related decline at neuromuscular junctions. Interestingly, both age-related declines reverted to the adult level after 1 month of oral administration of NMN by drinking water. In contrast, NMN administration did not alter the expression level of sympathetic marker tyrosine hydroxylase at neuromuscular junctions. The results suggest a functional decline of sympathetic nerves at aged neuromuscular junctions due to decreases in presynaptic and postsynaptic proteins, which can be reverted to the adult level by NMN administration.

A Study on the Robustness and Stability of Explainable Deep Learning in an Imbalanced Setting: The Exploration of the Conformational Space of G Protein-Coupled Receptors.

G-protein coupled receptors (GPCRs) are transmembrane proteins that transmit signals from the extracellular environment to the inside of the cells. Their ability to adopt various conformational states, which influence their function, makes them crucial in pharmacoproteomic studies. While many drugs target specific GPCR states to exert their effects-thereby regulating the protein's activity-unraveling the activation pathway remains challenging due to the multitude of intermediate transformations occurring throughout this process, and intrinsically influencing the dynamics of the receptors. In this context, computational modeling, particularly molecular dynamics (MD) simulations, may offer valuable insights into the dynamics and energetics of GPCR transformations, especially when combined with machine learning (ML) methods and techniques for achieving model interpretability for knowledge generation. The current study builds upon previous work in which the layer relevance propagation (LRP) technique was employed to interpret the predictions in a multi-class classification problem concerning the conformational states of the ß2-adrenergic (ß2AR) receptor from MD simulations. Here, we address the challenges posed by class imbalance and extend previous analyses by evaluating the robustness and stability of deep learning (DL)-based predictions under different imbalance mitigation techniques. By meticulously evaluating explainability and imbalance strategies, we aim to produce reliable and robust insights.

Screening for promising multi-target bioactive components from Cortex Mori Radicis for the treatment of chronic cor pulmonale based on immobilized beta1-adrenergic receptor and beta2-adrenergic receptor chromatography.

Cortex Morin Radicis (CMR) is the dried root bark of Morus alba. L. It has a variety of effects such as antibacterial, anti-tumour, treatment of cardiovascular diseases or upper respiratory tract disease and so on. The pursuit for drugs selected from Cortex Mori Radicis having improved therapeutic efficacy necessitates increasing research on new assays for screening bioactive compounds with multi-targets. In this work, we applied immobilized ß1-AR and ß2-AR as the stationary phase in chromatographic column to screen bioactive compounds from Cortex Morin Radicis. Specific ligands of the two receptors (e.g. esmolol, metoprolol, atenolol, salbutamol, methoxyphenamine, tulobuterol and clorprenaline) were utilized to characterize the specificity and bioactivity of the columns. We used high performance affinity chromatography coupled with ESI-MS to screen targeted compounds of Cortex Morin Radicis. By zonal elution, we identified morin as a bioactive compound simultaneously binding to ß1-AR and ß2-AR. The compound exhibited the association constants of 3.10 × 104 and 2.60 × 104 M-1 on the ß1-AR and ß2-AR column. On these sites, the dissociation rate constants were calculated to be 0.131 and 0.097 s-1. Molecular docking indicated that the binding of morin to the two receptors occurred on Asp200, Asp121, and Val122 of ß1-AR, Asn312, Thr110, Asp113, Tyr316, Gly90, Phe193, Ile309, and Trp109 of ß2-AR. Likewise, mulberroside C was identified as the bioactive compound binding to ß2-AR. The association constants and dissociation rate constants were calculated to be 1.08 × 104 M-1 and 0.900 s-1. Molecular docking also indicated that mulberroside C could bind to ß2-AR receptor on its agonist site. Taking together, we demonstrated that the chromatographic strategy to identify bioactive natural products based on the ß1-AR and ß2-AR immobilization, has potential for screening bioactive compounds with multi-targets from complex matrices including traditional Chinese medicines.

Role of Phenylethanolamine-N-methyltransferase on Nicotine-Induced Vasodilation in Rat Cerebral Arteries.

OBJECTIVE: The sympathetic-parasympathetic (or axo-axonal) interaction mechanism mediated that neurogenic relaxation, which was dependent on norepinephrine (NE) releases from sympathetic nerve terminal and acts on ß2-adrenoceptor of parasympathetic nerve terminal, has been reported. As NE is a weak ß2-adrenoceptor agonist, there is a possibility that synaptic NE is converted to epinephrine by phenylethanolamine-N-methyltransferase (PNMT) and then acts on the ß2-adrenoceptors to induce neurogenic vasodilation. METHODS: Blood vessel myography technique was used to measure relaxation and contraction responses of isolated basilar arterial rings of rats. RESULTS: Nicotine-induced relaxation was sensitive to propranolol, guanethidine (an adrenergic neuronal blocker), and Nω-nitro-l-arginine. Nicotine- and exogenous NE-induced vasorelaxation was partially inhibited by LY-78335 (a PNMT inhibitor), and transmural nerve stimulation depolarized the nitrergic nerve terminal directly and was not inhibited by LY-78335; it then induced the release of nitric oxide (NO). Epinephrine-induced vasorelaxation was not affected by LY-78335. However, these vasorelaxations were completely inhibited by atenolol (a ß1-adrenoceptor antagonist) combined with ICI-118,551 (a ß2-adrenoceptor antagonist). CONCLUSIONS: These results suggest that NE may be methylated by PNMT to form epinephrine and cause the release of NO and vasodilation. These results provide further evidence supporting the physiological significance of the axo-axonal interaction mechanism in regulating brainstem vascular tone.

Optical control of nanobody-mediated protein activity modulation with a photocleavable fluorescent protein.

Antibodies are crucial in various biological applications due to their specific binding to target molecules, altering protein function and structure. The advent of single-chain antibodies such as nanobodies has paved the way for broader applicability in both research and therapies due to their small size and efficient tissue penetration. Recently, several approaches have been reported to optically control the antigen-binding affinity of nanobodies. Here, we show an alternative strategy for creating photo-activatable nanobodies. By fusing the photocleavable protein PhoCl with the N-terminus of the nanobody (named optoNb60), we successfully demonstrated light-dependent restoration of the antigen-binding ability and the following modulation of the activity of a target protein, the beta-2 adrenergic receptor. Moreover, the activation of optoNb60 was monitored by the fluorescence changes upon photoconversion. The compatibility of the uncaging design with the previously reported optogenetic molecules using nanobodies will contribute to the further optimization of the response capabilities of existing optogenetic tools, thereby expanding their applicability.

Internalized ß2-Adrenergic Receptors Oppose PLC-Dependent Hypertrophic Signaling.

BACKGROUND: Chronically elevated neurohumoral drive, and particularly elevated adrenergic tone leading to ß-adrenergic receptor (ß-AR) overstimulation in cardiac myocytes, is a key mechanism involved in the progression of heart failure. ß1-AR (ß1-adrenergic receptor) and ß2-ARs (ß2-adrenergic receptor) are the 2 major subtypes of ß-ARs present in the human heart; however, they elicit different or even opposite effects on cardiac function and hypertrophy. For example, chronic activation of ß1-ARs drives detrimental cardiac remodeling while ß2-AR signaling is protective. The underlying molecular mechanisms for cardiac protection through ß2-ARs remain unclear. METHODS: ß2-AR signaling mechanisms were studied in isolated neonatal rat ventricular myocytes and adult mouse ventricular myocytes using live cell imaging and Western blotting methods. Isolated myocytes and mice were used to examine the roles of ß2-AR signaling mechanisms in the regulation of cardiac hypertrophy. RESULTS: Here, we show that ß2-AR activation protects against hypertrophy through inhibition of phospholipaseCε signaling at the Golgi apparatus. The mechanism for ß2-AR-mediated phospholipase C inhibition requires internalization of ß2-AR, activation of Gi and Gßγ subunit signaling at endosome and ERK (extracellular regulated kinase) activation. This pathway inhibits both angiotensin II and Golgi-ß1-AR-mediated stimulation of phosphoinositide hydrolysis at the Golgi apparatus ultimately resulting in decreased PKD (protein kinase D) and histone deacetylase 5 phosphorylation and protection against cardiac hypertrophy. CONCLUSIONS: This reveals a mechanism for ß2-AR antagonism of the phospholipase Cε pathway that may contribute to the known protective effects of ß2-AR signaling on the development of heart failure.

Role of the ß2-adrenergic receptor in podocyte injury and recovery.

BACKGROUND: Podocytes have a remarkable ability to recover from injury; however, little is known about the recovery mechanisms involved in this process. We recently showed that formoterol, a long-acting ß2-adrenergic receptor (ß2-AR) agonist, induced mitochondrial biogenesis (MB) in podocytes and led to renoprotection in mice. However, it is not clear whether this effect was mediated by formoterol acting through the ß2-AR or if it occurred through "off-target" effects. METHODS: We genetically deleted the ß2-AR specifically in murine podocytes and used these mice to determine whether formoterol acting through the podocyte ß2-AR alone is sufficient for recovery of renal filtration function following injury. The podocyte-specific ß2-AR knockout mice (ß2-ARfl/fl/PodCre) were generated by crossing ß2-AR floxed mice with podocin Cre (B6.Cg-Tg(NPHS2-cre)295Lbh/J) mice. These mice were then subjected to both acute and chronic glomerular injury using nephrotoxic serum (NTS) and adriamycin (ADR), respectively. The extent of injury was evaluated by measuring albuminuria and histological and immunostaining analysis of the murine kidney sections. RESULTS: A similar level of injury was observed in ß2-AR knockout and control mice; however, the ß2-ARfl/fl/PodCre mice failed to recover in response to formoterol. Functional evaluation of the ß2-ARfl/fl/PodCre mice following injury plus formoterol showed similar albuminuria and glomerular injury to control mice that were not treated with formoterol. CONCLUSIONS: These results indicate that the podocyte ß2-AR is a critical component of the recovery mechanism and may serve as a novel therapeutic target for treating podocytopathies.

Exercise-induced ß2-adrenergic Receptor Activation Enhances the Antileukemic Activity of Expanded γδ T-Cells via DNAM-1 Upregulation and PVR/Nectin-2 Recognition.

Exercise mobilizes cytotoxic lymphocytes to blood which may allow superior cell products to be harvested and manufactured for cancer therapy. Gamma-Delta (γδ) T-cells have shown promise for treating solid tumors, but there is a need to increase their potency against hematologic malignancies. Here, we show that human γδ T-cells mobilized to blood in response to just 20 minutes of graded exercise have surface phenotypes and transcriptomic profiles associated with cytotoxicity, adhesion, migration, and cytokine signaling. Following 14 days ex vivo expansion with zoledronic acid and IL2, exercise mobilized γδ T-cells had surface phenotypes and transcriptomic profiles associated with enhanced effector functions and demonstrated superior cytotoxic activity against multiple hematologic tumors in vitro and in vivo in leukemia-bearing xenogeneic mice. Infusing humans with the ß1+ß2-agonist isoproterenol and administering ß1 or ß1+ß2 antagonists prior to exercise revealed these effects to be ß2-adrenergic receptor (AR) dependent. Antibody blocking of DNAM-1 on expanded γδ T-cells, as well as the DNAM-1 ligands PVR and Nectin-2 on leukemic targets, abolished the enhanced antileukemic effects of exercise. These findings provide a mechanistic link between exercise, ß2-AR activation, and the manufacture of superior γδ T-cell products for adoptive cell therapy against hematologic malignancies. SIGNIFICANCE: Exercise mobilizes effector γδ T-cells to blood via ß2-adrenergic signaling which allows for generation of a potent expanded γδ T-cell product that is highly cytotoxic against hematologic malignancies.

Single-chain fluorescent integrators for mapping G-protein-coupled receptor agonists.

G protein-coupled receptors (GPCRs) transduce the effects of many neuromodulators including dopamine, serotonin, epinephrine, acetylcholine, and opioids. The localization of synthetic or endogenous GPCR agonists impacts their action on specific neuronal pathways. In this paper, we show a series of single-protein chain integrator sensors that are highly modular and could potentially be used to determine GPCR agonist localization across the brain. We previously engineered integrator sensors for the mu- and kappa-opioid receptor agonists called M- and K-Single-chain Protein-based Opioid Transmission Indicator Tool (SPOTIT), respectively. Here, we engineered red versions of the SPOTIT sensors for multiplexed imaging of GPCR agonists. We also modified SPOTIT to create an integrator sensor design platform called SPOTIT for all GPCRs (SPOTall). We used the SPOTall platform to engineer sensors for the beta 2-adrenergic receptor (B2AR), the dopamine receptor D1, and the cholinergic receptor muscarinic 2 agonists. Finally, we demonstrated the application of M-SPOTIT and B2AR-SPOTall in detecting exogenously administered morphine, isoproterenol, and epinephrine in the mouse brain via locally injected viruses. The SPOTIT and SPOTall sensor design platform has the potential for unbiased agonist detection of many synthetic and endogenous neuromodulators across the brain.

Can the heptapeptide ASSIVSF of the ß2-adrenoceptor recognize ephedrine and pseudoephedrine epimers in a complex system?

Epimer separation is crucial in the field of analytical chemistry, separation science, and the pharmaceutical industry. No reported methods could separate simultaneously epimers or even isomers and remove other unwanted, co-existing, interfering substances from complex systems like herbal extracts. Herein, we prepared a heptapeptide-modified stationary phase for the separation of 1R,2S-(-)-ephedrine [(-)-Ephe] and 1S,2S-(+)-pseudoephedrine [(+)-Pse] epimers from Ephedra sinica Stapf extract and blood samples. The heptapeptide stationary phase was comprehensively characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The separation efficiency of the heptapeptide column was compared with an affinity column packed with full-length ß2-AR functionalized silica gel (ß2-AR column). The binding affinity of the heptapeptide with (+)-Pse was 3-fold greater than that with (-)-Ephe. Their binding mechanisms were extensively characterized by chromatographic analysis, ultraviolet spectra, circular dichroism analysis, isothermal titration calorimetry, and molecule docking. An enhanced hydrogen bonding was clearly observed in the heptapeptide-(+)-Pse complex. Such results demonstrated that the heptapeptide can recognize (+)-Pse and (-)-Ephe epimers in a complex system. This work, we believe, was the first report to simultaneously separate epimers and remove non-specific interfering substances from complex samples. The method was potentially applicable to more challenging sample separation, such as chiral separation from complex systems.

Computational Modeling and Characterization of Peptides Derived from Nanobody Complementary-Determining Region 2 (CDR2) Targeting Active-State Conformation of the ß2-Adrenergic Receptor (ß2AR).

This study assessed the suitability of the complementarity-determining region 2 (CDR2) of the nanobody (Nb) as a template for the derivation of nanobody-derived peptides (NDPs) targeting active-state ß2-adrenergic receptor (ß2AR) conformation. Sequences of conformationally selective Nbs favoring the agonist-occupied ß2AR were initially analyzed by the informational spectrum method (ISM). The derived NDPs in complex with ß2AR were subjected to protein-peptide docking, molecular dynamics (MD) simulations, and metadynamics-based free-energy binding calculations. Computational analyses identified a 25-amino-acid-long CDR2-NDP of Nb71, designated P4, which exhibited the following binding free-energy for the formation of the ß2AR:P4 complex (ΔG = -6.8 ± 0.8 kcal/mol or a Ki = 16.5 µM at 310 K) and mapped the ß2AR:P4 amino acid interaction network. In vitro characterization showed that P4 (i) can cross the plasma membrane, (ii) reduces the maximum isoproterenol-induced cAMP level by approximately 40% and the isoproterenol potency by up to 20-fold at micromolar concentration, (iii) has a very low affinity to interact with unstimulated ß2AR in the cAMP assay, and (iv) cannot reduce the efficacy and potency of the isoproterenol-mediated ß2AR/ß-arrestin-2 interaction in the BRET2-based recruitment assay. In summary, the CDR2-NDP, P4, binds preferentially to agonist-activated ß2AR and disrupts Gαs-mediated signaling.

Expression of ß1- and ß2-adrenergic receptors in oral squamous cell carcinoma and their association with psychological and clinical factors.

BACKGROUND: Psychological stressors have been related to tumor progression through the activation of beta-adrenergic receptors (ß-AR) in several types of cancer. PURPOSE: This study aimed to investigate the expressions of ß1- and ß2-AR and their association with psychological and clinicopathological variables in patients with oral squamous cell carcinoma. METHODS: Tumor samples from 99 patients diagnosed with OSCC were subjected to immunohistochemical reaction to detect the expression of ß1-AR and ß2-AR. Anxiety and depression symptoms were assessed using the Beck Anxiety Inventory and Beck Depression Inventory (BDI), respectively. The Brunel Mood Scale was used for measuring affective mood states. RESULTS: Univariate analyzes revealed that higher expression of ß1-AR was associated with increased alcohol consumption (p = 0.032), higher education (p = 0.042), worse sleep quality (p = 0.044) and increased levels of pain related to the primary tumor (p < 0.001). Higher expression of ß2-AR was related with regional metastasis (p = 0.014), increased levels of pain related to the primary tumor (p = 0.044), anxiety (p < 0.001) and depressive (p = 0.010) symptoms and higher mood scores of angry (p = 0.010) and fatigue (p = 0.010). Multivariate analysis identified that patients with advanced clinical stage had lower ß1-AR expression (OR=0.145, 95% CI=0.025-0.828, p = 0.003). Higher anxiety symptoms and higher mood fatigue are independent factors for increased ß2-AR expression (OR=4256, 95% CI=1439-12606, p = 0.009; OR=3816, 95% CI=1258-11,573, p = 0.018, respectively). CONCLUSION: This study reveal that anxiety, fatigue symptoms, and clinical staging are associated with tumor expression of beta-adrenergic receptors in patients with oral cancer.

The ß2-adrenergic receptor associates with CXCR4 multimers in human cancer cells.

While the existence and functional role of class C G-protein-coupled receptors (GPCR) dimers is well established, there is still a lack of consensus regarding class A and B GPCR multimerization. This lack of consensus is largely due to the inherent challenges of demonstrating the presence of multimeric receptor complexes in a physiologically relevant cellular context. The C-X-C motif chemokine receptor 4 (CXCR4) is a class A GPCR that is a promising target of anticancer therapy. Here, we investigated the potential of CXCR4 to form multimeric complexes with other GPCRs and characterized the relative size of the complexes in a live-cell environment. Using a bimolecular fluorescence complementation (BiFC) assay, we identified the ß2 adrenergic receptor (ß2AR) as an interaction partner. To investigate the molecular scale details of CXCR4-ß2AR interactions, we used a time-resolved fluorescence spectroscopy method called pulsed-interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). PIE-FCCS can resolve membrane protein density, diffusion, and multimerization state in live cells at physiological expression levels. We probed CXCR4 and ß2AR homo- and heteromultimerization in model cell lines and found that CXCR4 assembles into multimeric complexes larger than dimers in MDA-MB-231 human breast cancer cells and in HCC4006 human lung cancer cells. We also found that ß2AR associates with CXCR4 multimers in MDA-MB-231 and HCC4006 cells to a higher degree than in COS-7 and CHO cells and in a ligand-dependent manner. These results suggest that CXCR4-ß2AR heteromers are present in human cancer cells and that GPCR multimerization is significantly affected by the plasma membrane environment.

Time-resolved cryo-EM of G-protein activation by a GPCR.

G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by stimulating guanine nucleotide exchange in the Gα subunit1. To visualize this mechanism, we developed a time-resolved cryo-EM approach that examines the progression of ensembles of pre-steady-state intermediates of a GPCR-G-protein complex. By monitoring the transitions of the stimulatory Gs protein in complex with the ß2-adrenergic receptor at short sequential time points after GTP addition, we identified the conformational trajectory underlying G-protein activation and functional dissociation from the receptor. Twenty structures generated from sequential overlapping particle subsets along this trajectory, compared to control structures, provide a high-resolution description of the order of main events driving G-protein activation in response to GTP binding. Structural changes propagate from the nucleotide-binding pocket and extend through the GTPase domain, enacting alterations to Gα switch regions and the α5 helix that weaken the G-protein-receptor interface. Molecular dynamics simulations with late structures in the cryo-EM trajectory support that enhanced ordering of GTP on closure of the α-helical domain against the nucleotide-bound Ras-homology domain correlates with α5 helix destabilization and eventual dissociation of the G protein from the GPCR. These findings also highlight the potential of time-resolved cryo-EM as a tool for mechanistic dissection of GPCR signalling events.

Synergistic anti-tumor effects of lenalidomide and gefitinib by upregulating ADRB2 and inactivating the mTOR/PI3K/AKT signaling pathway in lung adenocarcinoma.

Gefitinib is commonly used to be the first-line therapy for advanced non-small cell lung cancer (NSCLC). Therapeutic effect of gefitinib is reduced due to acquired resistance, and combined treatment is recommended. In this research, we planned to explore the impacts of combined treatment of lenalidomide and gefitinib on gefitinib-sensitive or -resistant NSCLC cells. The co-treatment results demonstrated that enhanced antitumor impact on NSCLC cell growth, migration, invasion, cell cycle process and apoptosis. The tumor-bearing mouse models were established using PC9/GR cells. In vivo assays also showed that lenalidomide and gefitinib synergistically inhibited mouse tumor growth along increased the survival of mice. ADRB2 was identified as a lowly expressed gene in PC9/GR cells and LUAD tumor tissues. LUAD patients with high ADRB2 expression were indicated with favorable survival outcomes. Moreover, ADRB2 was upregulated in lenalidomide and/or gefitinib-treated PC9/GR cells. ADRB2 deficiency partially offsets the suppressive impacts of lenalidomide and gefitinib co-treatment on the viability and proliferation of PC9/GR cells. Additionally, lenalidomide and gefitinib cotreatment significantly inactivated the mTOR/PI3K/AKT signaling pathway compared with each treatment alone. Rescue assays were performed to explore whether lenalidomide and gefitinib synergistically inhibited the growth of PC9/GR cells via the PI3K/AKT pathway. PI3K activator SC79 significantly restored reduced cell proliferation, migration and invasion along with elevated cell cycle arrest and apoptosis caused by lenalidomide and gefitinib cotreatment. In conclusion, lenalidomide and gefitinib synergistically suppressed LUAD progression and attenuated gefitinib resistance by upregulating ADRB2 and inactivating the mTOR/PI3K/AKT signaling pathway in lung adenocarcinoma.