title: Clozapine-induced ERK1 and ERK2 signaling in prefrontal cortex is mediated by the EGF receptor.
abstract: The atypical antipsychotic drug clozapine is effective in treatment-refractory schizophrenia. The intracellular signaling pathways that mediate clozapine action remain unknown. A potential candidate is the mitogen-activated protein kinase extracellular signal-regulated kinase (MAPK-ERK) cascade that links G-protein-coupled receptor and ErbB growth factor signaling systems, thereby regulating synaptic plasticity and connectivity, processes impaired in schizophrenia. Here, we examined how clozapine differentially modulated phosphorylation of the MAPK isoforms, ERK1/ERK2 in primary murine prefrontal cortical neurons compared to the typical antipsychotic drug haloperidol. While clozapine and haloperidol acutely decreased cortical pERK1 activation, only clozapine but not haloperidol stimulated pERK1 and pERK2 with continued drug exposure. This delayed ERK increase however, did not occur via the canonical dopamine D(2)-Gi/o-PKA or serotonin 5HT(2A)-Gq-phospholipase-C-linked signaling pathways. Rather, epidermal growth factor (EGF) receptor signaling mediated clozapine-induced ERK activation, given dose-dependent reduction of pERK1 and pERK2 stimulation with the EGF receptor inhibitor, AG1478. Immunocytochemical studies indicated that clozapine treatment increased EGF receptor (Tyr1068) phosphorylation. In vivo mouse treatment studies supported the in vitro findings with initial blockade, subsequent activation, and normalization of the cortical ERK response over 24 h. Furthermore, in vivo clozapine-induced ERK activation was significantly reduced by AG1478. This is the first report that clozapine action on prefrontal cortical neurons involves the EGF signaling system. Since EGF receptor signaling has not been previously linked to antipsychotic drug action, our findings may implicate the EGF system as a molecular substrate in treatment-resistant schizophrenia.
authors.affiliation: Department of Molecular Psychopharmacology, Mental Health Research Institute of Victoria, 155 Oak Street, Parkville, 3052, Victoria, Australia, a.pereira@mhri.edu.au.
authors.forename: Avril
authors.initials: A
authors.lastname: Pereira
authors.forename: George
authors.initials: G
authors.lastname: Fink
authors.forename: Suresh
authors.initials: S
authors.lastname: Sundram
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D018678:Cholinergic Agents / Q000494:pharmacology; D003024:Clozapine / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D006220:Haloperidol / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017397:Prefrontal Cortex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D020891:Raclopride / Q000494:pharmacology; D018490:Serotonin Agents / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D014150:Antipsychotic Agents; D018678:Cholinergic Agents; D004791:Enzyme Inhibitors; D018490:Serotonin Agents; D020891:Raclopride; D066246:ErbB Receptors; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D010738:Type C Phospholipases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D003024:Clozapine; D006220:Haloperidol