title: Functional monoclonal antibody acts as a biased agonist by inducing internalization of metabotropic glutamate receptor 7.
abstract: OBJECTIVE
  The mGlu(7) receptors are strategically located at the site of vesicle fusion where they modulate the release of the main excitatory and inhibitory neurotransmitters. Consequently, they are implicated in the underlying pathophysiology of CNS diseases such as epilepsy and stress-related psychiatric disorders. Here, we characterized a selective, potent and functional anti-mGlu(7) monoclonal antibody, MAB1/28, that triggers receptor internalization.
  
  
  METHODS
  MAB1/28's activity was investigated using Western blot and direct immunofluorescence on live cells, in vitro pharmacology by functional cAMP and [(35) S]-GTPγ binding assays, the kinetics of IgG-induced internalization by image analysis, and the activation of the ERK1/2 by elisa.
  
  
  RESULTS
  mGlu(7) /mGlu(6) chimeric studies located the MAB1/28 binding site at the extracellular amino-terminus of mGlu(7) . MAB1/28 potently antagonized both orthosteric and allosteric agonist-induced inhibition of cAMP accumulation. The potency of the antagonistic actions was similar to the potency in triggering receptor internalization. The internalization mechanism occurred via a pertussis toxin-insensitive pathway and did not require Gα(i) protein activation. MAB1/28 activated ERK1/2 with potency similar to that for receptor internalization. The requirement of a bivalent receptor binding mode for receptor internalizations suggests that MAB1/28 modulates mGlu(7) dimers.
  
  
  CONCLUSIONS
  We obtained evidence for an allosteric-biased agonist activity triggered by MAB1/28, which activates a novel IgG-mediated GPCR internalization pathway that is not utilized by small molecule, orthosteric or allosteric agonists. Thus, MAB1/28 provides an invaluable biological tool for probing mGlu(7) function and selective activation of its intracellular trafficking.
authors: DTA CV and Metabolism, Discovery Research CV & Metabolic Diseases, F. Hoffmann-La Roche AG, pRED, Pharma Research & Early Development, Basel, Switzerland. christoph.ullmer@roche.com
authors: C
authors: C
authors: Ullmer
authors: S
authors: S
authors: Zoffmann
authors: B
authors: B
authors: Bohrmann
authors: H
authors: H
authors: Matile
authors: L
authors: L
authors: Lindemann
authors: Pj
authors: P
authors: Flor
authors: P
authors: P
authors: Malherbe
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001921:Brain / Q000378:metabolism*; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D018094:Receptors, Metabotropic Glutamate; C102719:metabotropic glutamate receptor 7; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases