title: Functional selectivity induced by mGlu₄ receptor positive allosteric modulation and concomitant activation of Gq coupled receptors.
abstract: Metabotropic glutamate receptors (mGlus) are a group of Family C Seven Transmembrane Spanning Receptors (7TMRs) that play important roles in modulating signaling transduction, particularly within the central nervous system. mGlu(4) belongs to a subfamily of mGlus that is predominantly coupled to G(i/o) G proteins. We now report that the ubiquitous autacoid and neuromodulator, histamine, induces substantial glutamate-activated calcium mobilization in mGlu(4)-expressing cells, an effect which is observed in the absence of co-expressed chimeric G proteins. This strong induction of calcium signaling downstream of glutamate activation of mGlu(4) depends upon the presence of H(1) histamine receptors. Interestingly, the potentiating effect of histamine activation does not extend to other mGlu(4)-mediated signaling events downstream of G(i/o) G proteins, such as cAMP inhibition, suggesting that the presence of G(q) coupled receptors such as H(1) may bias normal mGlu(4)-mediated G(i/o) signaling events. When the activity induced by small molecule positive allosteric modulators of mGlu(4) is assessed, the potentiated signaling of mGlu(4) is further biased by histamine toward calcium-dependent pathways. These results suggest that G(i/o)-coupled mGlus may induce substantial, and potentially unexpected, calcium-mediated signaling events if stimulation occurs concomitantly with activation of G(q) receptors. Additionally, our results suggest that signaling induced by small molecule positive allosteric modulators may be substantially biased when G(q) receptors are co-activated. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.
authors.affiliation: Vanderbilt Center for Neuroscience Drug Discovery, Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors.forename: Shen
authors.initials: S
authors.lastname: Yin
authors.forename: Rocio
authors.initials: R
authors.lastname: Zamorano
authors.forename: P Jeffrey
authors.initials: PJ
authors.lastname: Conn
authors.forename: Colleen M
authors.initials: CM
authors.lastname: Niswender
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000494:Allosteric Regulation / Q000502:physiology*; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000502:physiology*; D018698:Glutamic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011969:Receptors, Histamine H1 / Q000502:physiology; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001578:Benzopyrans; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; C442478:N-phenyl-7-(hydroxyimino)cyclopropa(b)chromen-1a-carboxamide; D010716:Phosphatidylinositols; D011969:Receptors, Histamine H1; D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid; D006632:Histamine; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D000262:Adenylyl Cyclases; D002118:Calcium; C108823:metabotropic glutamate receptor 4