title: Cannabinoid CB1 receptors transactivate multiple receptor tyrosine kinases and regulate serine/threonine kinases to activate ERK in neuronal cells.
abstract: OBJECTIVE
  Signalling networks that regulate the progression of cannabinoid CB(1)  receptor-mediated extracellular signal-regulated kinase (ERK) activation in neurons are poorly understood. We investigated the cellular mechanisms involved in CB(1)  receptor-stimulated ERK phosphorylation in a neuronal cell model.
  
  
  METHODS
  Murine N18TG2 neuronal cells were used to analyse the effect of specific protein kinase and phosphatase inhibitors on CB(1)  receptor-stimulated ERK phosphorylation. The LI-COR In Cell Western assay and immunoblotting were used to measure ERK phosphorylation.
  
  
  RESULTS
  The time-course of CB(1)  receptor-stimulated ERK activation occurs in three phases that are regulated by distinct cellular mechanisms in N18TG2 cells. Phase I (0-5 min) maximal ERK phosphorylation is mediated by CB(1)  receptor-stimulated ligand-independent transactivation of multiple receptor tyrosine kinases (RTKs). Phase I requires G(i/o) βγ subunit-stimulated phosphatidylinositol 3-kinase activation and Src kinase activation and is modulated by inhibition of cAMP-activated protein kinase A (PKA) levels. Src kinase activation is regulated by the protein tyrosine phosphatases 1B and Shp1. The Phase II (5-10 min) rapid decline in ERK phosphorylation involves PKA inhibition and serine/threonine phosphatase PP1/PP2A activation. The Phase III (>10 min) plateau in ERK phosphorylation is mediated by CB(1)  receptor-stimulated, ligand-independent, transactivation of multiple RTKs.
  
  
  CONCLUSIONS
  The complex expression of CB(1)  receptor-stimulated ERK activation provides cellular selectivity, modulation of sensitivity to agonists, and coincidence detection with RTK signalling. RTK and PKA pathways may provide routes to novel CB(1) -based therapeutic interventions in the treatment of addictive disorders or neurodegenerative diseases. LINKED ARTICLES This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.
authors.affiliation: Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
authors.forename: George D
authors.initials: GD
authors.lastname: Dalton
authors.forename: Allyn C
authors.initials: AC
authors.lastname: Howlett
mesh_terms: D000818:Animals; D048588:Benzoxazines / Q000494:pharmacology; D002186:Cannabinoids / Q000494:pharmacology; D045744:Cell Line, Tumor; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D048588:Benzoxazines; D002186:Cannabinoids; D009025:Morpholines; D009281:Naphthalenes; D043884:Receptor, Cannabinoid, CB1; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D011494:Protein Kinases