Analysis of GPCR Dimerization Using Acceptor Photobleaching Resonance Energy Transfer Techniques

Co-Stimulation of Oxytocin and Arginine-Vasopressin Receptors Affect Hypothalamic Neurospheroid Size

Oxytocin (OXT) is a neuropeptide involved in a plethora of behavioral and physiological processes. However, there is a prominent lack of 3D cell culture models that investigate the effects of OXT on a cellular/molecular level. In this study, we established a hypothalamic neuronal spheroid model to investigate the cellular response in a more realistic 3D setting. Our data indicate that the formation of spheroids itself does not alter the basic characteristics of the cell line and that markers of cellular morphology and connectivity are stably expressed. We found that both OXT and arginine vasopressin (AVP) treatment increase spheroid size (surface area and volume), as well as individual nucleus size, which serves as an indicator for cellular proliferation. The cellular response to both OXT and AVP seems mainly to be mediated by the AVP receptor 1a (V1aR); however, the OXT receptor (OXTR) contributes significantly to the observed proliferative effect. When we blocked the OXTR pharmacologically or knocked down the OXTR by siRNA, the OXT- or AVP-induced cellular proliferation decreased. In summary, we established a 3D cell culture model of the neuronal response to OXT and AVP and found that spheroids react to the treatment via their respective receptors but also via cross-talk between the two receptor types.

What Role Might Non-Mating Receptors Play in Schizophyllum commune?

The B mating-type locus of the tetrapolar basidiomycete Schizophyllum commune encodes pheromones and pheromone receptors in multiple allelic specificities. This work adds substantial new evidence into the organization of the B mating-type loci of distantly related S. commune strains showing a high level of synteny in gene order and neighboring genes. Four pheromone receptor-like genes were found in the genome of S. commune with brl1, brl2 and brl3 located at the B mating-type locus, whereas brl4 is located separately. Expression analysis of brl genes in different developmental stages indicates a function in filamentous growth and mating. Based on the extensive sequence analysis and functional characterization of brl-overexpression mutants, a function of Brl1 in mating is proposed, while Brl3, Brl4 and Brl2 (to a lower extent) have a role in vegetative growth, possible determination of growth direction. The brl3 and brl4 overexpression mutants had a dikaryon-like, irregular and feathery phenotype, and they avoided the formation of same-clone colonies on solid medium, which points towards enhanced detection of self-signals. These data are supported by localization of Brl fusion proteins in tips, at septa and in not-yet-fused clamps of a dikaryon, confirming their importance for growth and development in S. commune.

Heterodimerization of Mu Opioid Receptor Protomer with Dopamine D2 Receptor Modulates Agonist-Induced Internalization of Mu Opioid Receptor

The interplay between the dopamine (DA) and opioid systems in the brain is known to modulate the additive effects of substances of abuse. On one hand, opioids serve mankind by their analgesic properties, which are mediated via the mu opioid receptor (MOR), a Class A G protein-coupled receptor (GPCR), but on the other hand, they pose a potential threat by causing undesired side effects such as tolerance and dependence, for which the exact molecular mechanism is still unknown. Using human embryonic kidney 293T (HEK 293T) and HeLa cells transfected with MOR and the dopamine D₂ receptor (D₂R), we demonstrate that these receptors heterodimerize, using an array of biochemical and biophysical techniques such as coimmunoprecipitation (co-IP), bioluminescence resonance energy transfer (BRET¹), Fӧrster resonance energy transfer (FRET), and functional complementation of a split luciferase. Furthermore, live cell imaging revealed that D_2LR, when coexpressed with MOR, slowed down internalization of MOR, following activation with the MOR agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO).

SETBP1 induces transcription of a network of development genes by acting as an epigenetic hub

SETBP1 variants occur as somatic mutations in several hematological malignancies such as atypical chronic myeloid leukemia and as de novo germline mutations in the Schinzel–Giedion syndrome. Here we show that SETBP1 binds to gDNA in AT-rich promoter regions, causing activation of gene expression through recruitment of a HCF1/KMT2A/PHF8 epigenetic complex. Deletion of two AT-hooks abrogates the binding of SETBP1 to gDNA and impairs target gene upregulation. Genes controlled by SETBP1 such as MECOM are significantly upregulated in leukemias containing SETBP1 mutations. Gene ontology analysis of deregulated SETBP1 target genes indicates that they are also key controllers of visceral organ development and brain morphogenesis. In line with these findings, in utero brain electroporation of mutated SETBP1 causes impairment of mouse neurogenesis with a profound delay in neuronal migration. In summary, this work unveils a SETBP1 function that directly affects gene transcription and clarifies the mechanism operating in myeloid malignancies and in the Schinzel–Giedion syndrome caused by SETBP1 mutations.

SETBP1 variants occur as somatic mutations in several malignancies and as de novo germline mutations in developmental disorders. Here the authors provide evidence that SETBP1 binds to gDNA in AT-rich promoter regions to promote target gene upregulation, indicating SETBP1 functions directly to regulate transcription.

Gene expression profiling in colon of mice exposed to food additive titanium dioxide (E171)

Dietary factors that may influence the risks of colorectal cancer, including specific supplements, are under investigation. Previous studies showed the capacity of food additive titanium dioxide (E171) to induce DNA damage in vitro and facilitate growth of colorectal tumours in vivo. This study aimed to investigate the molecular mechanisms behind these effects after E171 exposure. BALB/c mice were exposed by gavage to 5 mg/kg_bw/day of E171 for 2, 7, 14, and 21 days. Transcriptome changes were studied by whole genome mRNA microarray analysis on the mice's distal colons. In addition, histopathological changes as well as a proliferation marker were analysed. The results showed significant gene expression changes in the olfactory/GPCR receptor family, oxidative stress, the immune system and of cancer related genes. Transcriptome analysis also identified genes that thus far have not been included in known biological pathways and can induce functional changes by interacting with other genes involved in different biological pathways. Histopathological analysis showed alteration and disruption in the normal structure of crypts inducing a hyperplastic epithelium. At cell proliferation level, no consistent increase over time was observed. These results may offer a mechanistic framework for the enhanced tumour growth after ingestion of E171 in BALB/c mice.

Bradykinin B2 and dopamine D2 receptors form a functional dimer

In recent years a wide range of studies have shown that G protein-coupled receptors modulate a variety of cell functions through the formation of dimers. For instance, there is growing evidence for the dimerization of bradykinin or dopamine receptors, both as homodimers and heterodimers. A discovery of direct interactions of angiotensin II receptors with bradykinin 2 receptor (B2R) or dopamine D2 (D2R) receptor has led to a hypothesis on a potential dimerization between two latter receptors. In this study, we have demonstrated a constitutive colocalization of receptors on the membranes of HEK293 cells transiently transfected with plasmid vectors encoding B2R and D2R, fused with fluorescent proteins. The receptor colocalization was significantly enhanced by specific agonists of B2R or D2R after 5min following the addition, whereas simultaneous stimulation with these agonists did not influence the B2R/D2R colocalization level. In addition, B2R-D2R heterodimerization was confirmed with FLIM-FRET technique. The most characteristic signaling pathways for B2R and D2R, dependent on intracellular Ca²⁺ and cAMP concentration, respectively, were analyzed in cells presenting similar endogenous expression of B2R and D2R. Significant changes in receptors' signaling were observed after simultaneous stimulation with agonists, suggesting transformations in proteins' conformation after dimerization. The evidence of B2R-D2R dimerization may open new perspectives in the modulation of diverse cellular functions which depend on their activation.

Molecular Basis of Oxytocin Receptor Signalling in the Brain: What We Know and What We Need to Know

Oxytocin (OT), a hypothalamic neuropeptide involved in regulating the social behaviour of all vertebrates, has been proposed as a treatment for a number of neuropsychiatric disorders characterised by deficits in the social domain. Over the last few decades, advances focused on understanding the social effects of OT and its role in physiological conditions and brain diseases, but much less has been done to clarify the molecular cascade of events involved in mediating such effects and in particular the cellular and molecular pharmacology of OT and its target receptor (OTR) in neuronal and glial cells.The entity and persistence of OT activity in the brain is closely related to the expression and regulation of the OTR expressed on the cell surface, which transmits the signal intracellularly and permits OT to affect cell function. Understanding the various signalling mechanisms mediating OTR-induced cell responses is crucial to determine the different responses in different cells and brain regions, and the success of OT and OT-derived analogues in the treatment of neurodevelopmental and psychiatric diseases depends on how well we can control such responses. In this review, we will consider the most important aspects of OT/OTR signalling by focusing on the molecular events involved in OT binding and coupling, on the main signalling pathways activated by the OTR in neuronal cells and on intracellular and plasma membrane OTR trafficking, all of which contribute to the quantitative and qualitative features of OT responses in the brain.

Visualizing G protein-coupled receptors in action through confocal microscopy techniques

G protein-coupled receptors constitute one of the most abundant entities in cellular communication. Elucidation of their structure and function as well as of their regulation began 30-40 years ago and the advance has markedly increased during the last 15 years. They participate in a plethora of cell functions such as regulation of metabolic fluxes, contraction, secretion, differentiation, or proliferation, and in essentially all activities of our organism; these receptors are targets of a large proportion of prescribed and illegal drugs. Fluorescence techniques have been used to study receptors for many years. The experimental result was usually a two-dimensional (2D) micrograph. Today, the result can be a spatiotemporal (four-dimensional, 4D) movie. Advances in microscopy, fluorescent protein design, and computer-assisted analysis have been of great importance to increase our knowledge on receptor regulation and function and create opportunities for future research. In this review we briefly depict the state of the art of the G protein-coupled receptor field and the methodologies used to study G protein-coupled receptor location, trafficking, dimerization, and other types of receptor-protein interaction. Fluorescence techniques now permit the capture of receptor images with high resolution and, together with a variety of fluorescent dyes that color organelles (such as the plasma membrane or the nucleus) or the cytoskeleton, allow researchers to obtain a much clearer idea of what is taking place at the cellular level. These developments are changing the way we explore cell communication and signal transduction, permitting deeper understanding of the physiological and pathophysiological processes.