Receptor-Receptor Interactions as a Widespread Phenomenon: Novel Targets for Drug Development?

open5The discovery of receptor-receptor interactions (RRI) has expanded our understanding of the role that G protein-coupled receptors (GPCRs) play in intercellular communication. The finding that GPCRs can operate as receptor complexes, and not only as monomers, suggests that several different incoming signals could already be integrated at the plasma membrane level via direct allosteric interactions between the protomers that form the complex. Most research in this field has focused on neuronal populations and has led to the identification of a large number of RRI. However, RRI have been seen to occur not only in neurons but also in astrocytes and, outside the central nervous system, in cells of the cardiovascular and endocrine systems and in cancer cells. Furthermore, RRI involving the formation of macromolecular complexes are not limited to GPCRs, being also observed in other families of receptors. Thus, RRI appear as a widespread phenomenon and oligomerization as a common mechanism for receptor function and regulation. The discovery of these macromolecular assemblies may well have a major impact on pharmacology. Indeed, the formation of receptor complexes significantly broadens the spectrum of mechanisms available to receptors for recognition and signaling, which may be implemented through modulation of the binding sites of the adjacent protomers and of their signal transduction features. In this context, the possible appearance of novel allosteric sites in the receptor complex structure may be of particular relevance. Thus, the existence of RRI offers the possibility of new therapeutic approaches, and novel pharmacological strategies for disease treatment have already been proposed. Several challenges, however, remain. These include the accurate characterization of the role that the receptor complexes identified so far play in pathological conditions and the development of ligands specific to given receptor complexes, in order to efficiently exploit the pharmacological properties of these complexes.openGuidolin, Diego; Marcoli, Manuela; Tortorella, Cinzia; Maura, Guido; Agnati, Luigi FGuidolin, Diego; Marcoli, Manuela; Tortorella, Cinzia; Maura, Guido; Agnati, Luigi

On the G-protein-coupled receptor heteromers and their allosteric receptor-receptor interactions in the central nervous system: focus on their role in pain modulation

The modulatory role of allosteric receptor-receptor interactions in the pain pathways of the Central Nervous System and the peripheral nociceptors has become of increasing interest. As integrators of nociceptive and antinociceptive wiring and volume transmission signals, with a major role for the opioid receptor heteromers, they likely have an important role in the pain circuits and may be involved in acupuncture. The delta opioid receptor (DOR) exerts an antagonistic allosteric influence on the mu opioid receptor (MOR) function in a MOR-DOR heteromer. This heteromer contributes to morphine-induced tolerance and dependence, since it becomes abundant and develops a reduced G-protein-coupling with reduced signaling mainly operating via beta-arrestin 2 upon chronic morphine treatment. A DOR antagonist causes a return of the Gi/o binding and coupling to the heteromer and the biological actions of morphine. The gender- and ovarian steroid-dependent recruitment of spinal cord MOR/kappa opioid receptor (KOR) heterodimers enhances antinociceptive functions and if impaired could contribute to chronic pain states in women. MOR1D heterodimerizes with gastrin-releasing peptide receptor (GRPR) in the spinal cord, mediating morphine induced itch. Other mechanism for the antinociceptive actions of acupuncture along meridians may be that it enhances the cross-desensitization of the TRPA1 (chemical nociceptor)-TRPV1 (capsaicin receptor) heteromeric channel complexes within the nociceptor terminals located along these meridians. Selective ionotropic cannabinoids may also produce cross-desensitization of the TRPA1-TRPV1 heteromeric nociceptor channels by being negative allosteric modulators of these channels leading to antinociception and antihyperalgesia

La culpa latior di Celso, la culpa lata dei Glossatori e il dolus praesumptus di Bartolo da Sassoferrato

L’hápax culpa latior, contenuto nel frammento del giurista Celso (D. 16.3.32), apre ampi spazi alla rielaborazione successiva, della quale il contributo analizza due differenti sviluppi. Il primo mostra la normalizzazione progressiva dell’hápax: la culpa latior diviene culpa lata, la specifica responsabilità del depositario viene inglobata nella responsabilità del debitore in generale, la diligentia quam in suis rebus confluisce e si stempera nella diligenza media per cui dalla diligenza in concreto si passa alla diligenza misurata secondo un parametro astratto. In sostanza l’hápax, che riguarda in primis la locuzione, ma che coinvolge anche in parte il contenuto, viene quindi progressivamente normalizzato e standardizzato e la Glossa di Accursio riveste in questo processo evolutivo un ruolo centrale, come mostra l'evoluzione considerata attraverso i testi di Azone e di Vivano Toschi. Il secondo percorso posto in rilievo riguarda, al contrario, la valorizzazione del medesimo hápax. Bartolo si applica in questa direzione, dando rilievo e centralità alla culpa latior, sebbene nominata soltanto una volta nelle fonti romane. A partire dunque da una base potenzialmente fragile e limitata, egli identifica un criterio di responsabilità che funge da gradino intermedio tra colpa e dolo in una costruzione complessa e dettagliata, che il giurista di Sassoferrato espone in una celebre repetitio. L’eredità romana, anche in questo caso, viene manipolata, esaltando la peculiarità al di là di quanto presente nella fonte

Brain Receptor Mosaics and Their Intramembrane Receptor-Receptor Interactions: Molecular Integration in Transmission and Novel Targets for Drug Development

Abstract The concept of intramembrane receptor-receptor interactions and evidence for their existence was introduced by Agnati and Fuxe in 1980/81 suggesting the existence of heteromerization of receptors. In 1982, they proposed the existence of aggregates of multiple receptors in the plasma membrane and coined the term receptor mosaics (RM). In this way, cell signaling becomes a branched process beginning at the level of receptor recognition at the plasma membrane where receptors can directly modify the ligand recognition and signaling capacity of the receptors within a RM. Receptor-receptor interactions in RM are classified as operating either with classical cooperativity, when consisting of homomers or heteromers of similar receptor subtypes having the same transmitter, or non-classical cooperativity, when consisting of heteromers. It has been shown that information processing within a RM depends not only on its receptor composition, but also on the topology and the order of receptor activation determined by the concentrations of the ligands and the receptor properties. The general function of RM has also been demonstrated to depend on allosteric regulators (e.g., homocysteine) of the receptor subtypes present. RM as integrative nodes for receptor-receptor interactions in conjunction with membrane associated proteins may form horizontal molecular networks in the plasma membrane coordinating the activity of multiple effector systems modulating the excitability and gene expression of the cells. The key role of electrostatic epitope-epitope interactions will be discussed for the formation of the RM. These interactions probably represent a general molecular mechanism for receptor-receptor interactions and, without a doubt, indicate a role for phosphorylation-dephosphorylation events in these interactions. The novel therapeutic aspects given by the RMs will be discussed in the frame of molecular neurology and psychiatry and combined drug therapy appears as the future way to go

In vitro effects of cocaine on tunneling nanotube formation and extracellular vesicle release in glioblastoma cell cultures

The effects of cocaine (150 nM, 300 nM, and 150 μM) on human glioblastoma cell cultures were studied on tunneling nanotube formation (1-h cocaine treatment) and extracellular vesicle release (1-, 3-, and 8-h cocaine treatment). Cocaine significantly increased the number of tunneling nanotubes only at the lowest concentration used. The release of extracellular vesicles (mainly exosomes) into the medium was stimulated by cocaine at each concentration used with a maximum effect at the highest concentration tested (150 μM). Moreover, cocaine (150 nM) significantly increased the number of vesicles with 61-80 nm diameter while at concentrations of 300 nM and 150 μM, and the smaller vesicles (30-40 nm diameter) were significantly increased with a reduction of the larger vesicles (41-60 nm diameter). A time dependence in the release of extracellular vesicles was observed. In view of the proposed role of these novel intercellular communication modes in the glial-neuronal plasticity, it seems possible that they can participate in the processes leading to cocaine addiction. The molecular target/s involved in these cocaine effects could be specific molecular components of plasma membrane lipid rafts and/or cocaine-induced modifications in cytoplasmic lipid composition

On the expanding terminology in the GPCR field: The meaning of receptor mosaics and receptor heteromers

The oligomerization of G protein-coupled receptors (GPCRs) is a fact that deserves further attention as increases both the complexity and diversity of the receptor-mediated signal transduction, thus enriching the cell signaling. Consequently, in the present review we tackle among others the problems concerning the terminology used to describe aspects surrounding the GPCRs oligomerization phenomenon. Therefore, the theoretical implications of the GPCR oligomerization will be briefly discussed together with possible implications of this phenomenon especially for new strategies in drug development

The G protein-coupled receptor heterodimer network (GPCR-HetNet) and its hub components

G protein-coupled receptors (GPCRs) oligomerization has emerged as a vital characteristic of receptor structure. Substantial experimental evidence supports the existence of GPCR-GPCR interactions in a coordinated and cooperative manner. However, despite the current development of experimental techniques for large-scale detection of GPCR heteromers, in order to understand their connectivity it is necessary to develop novel tools to study the global heteroreceptor networks. To provide insight into the overall topology of the GPCR heteromers and identify key players, a collective interaction network was constructed. Experimental interaction data for each of the individual human GPCR protomers was obtained manually from the STRING and SCOPUS databases. The interaction data were used to build and analyze the network using Cytoscape software. The network was treated as undirected throughout the study. It is comprised of 156 nodes, 260 edges and has a scale-free topology. Connectivity analysis reveals a significant dominance of intrafamily versus interfamily connections. Most of the receptors within the network are linked to each other by a small number of edges. DRD2, OPRM, ADRB2, AA2AR, AA1R, OPRK, OPRD and GHSR are identified as hubs. In a network representation 10 modules/clusters also appear as a highly interconnected group of nodes. Information on this GPCR network can improve our understanding of molecular integration. GPCR-HetNet has been implemented in Java and is freely available at http://www.iiia.csic.es/similar to ismel/GPCR-Nets/index.html

Bioinformatics and mathematical modelling in the study of receptor-receptor interactions and receptor oligomerization: focus on adenosine receptors.

none8sìThe concept of intra-membrane receptor-receptor interactions (RRIs) between different types of G protein-coupled receptors (GPCRs) and evidence for their existence was introduced by Agnati and Fuxe in 1980/81 through the biochemical analysis of the effects of neuropeptides on the binding characteristics of monoamine receptors in membrane preparations from discrete brain regions and functional studies of the interactions between neuropeptides and monoamines in the control of specific functions such as motor control and arterial blood pressure control in animal models. Whether GPCRs can form high-order structures is still a topic of an intense debate. Increasing evidence, however, suggests that the hypothesis of the existence of high-order receptor oligomers is correct. A fundamental consequence of the view describing GPCRs as interacting structures, with the likely formation at the plasma membrane of receptor aggregates of multiple receptors (Receptor Mosaics) is that it is no longer possible to describe signal transduction simply as the result of the binding of the chemical signal to its receptor, but rather as the result of a filtering/integration of chemical signals by the Receptor Mosaics (RMs) and membrane-associated proteins. Thus, in parallel with experimental research, significant efforts were spent in bioinformatics and mathematical modelling. We review here the main approaches that have been used to assess the interaction interfaces allowing the assembly of GPCRs and to shed some light on the integrative functions emerging from the complex behaviour of these RMs. Particular attention was paid to the RMs generated by adenosine A(2A), dopamine D-2, cannabinoid CB1, and metabotropic glutamate mGlu(5) receptors (A(2A). D-2, CB1, and mGlu(5), respectively), and a possible approach to model the interplay between the D-2-A(2A)-CB1 and D-2-A(2A)-mGlu(5) trimers is proposed. This article is part of a Special Issue entitled: "Adenosine Receptors". (C) 2010 Elsevier B.V. All rights reserved.openD. GUIDOLIN; F. CIRUELA; S. GENEDANI; M. GUESCINI; C. TORTORELLA; G. ALBERTIN; K. FUXE; L.F. AGNATID., Guidolin; F., Ciruela; S., Genedani; Guescini, Michele; C., Tortorella; G., Albertin; K., Fuxe; L. F., Agnat