title: Cholinergic differentiation triggered by blocking cell proliferation and treatment with all-trans-retinoic acid.
abstract: This study determined whether the effect of all-trans-retinoic acid (t-RA) on markers of cholinergic differentiation in a murine septal cell line, SN56.B5.G4, differed depending upon the cell's proliferative status. To develop a model of non-proliferating cells, aphidicolin, a DNA alpha-polymerase inhibitor, was used. Cessation of proliferation by aphidicolin increased intracellular choline and acetylcholine (ACh) levels in the absence of change to choline acetyltransferase (ChAT) activity and mRNA and vesicular ACh transporter (VAChT) mRNA. Importantly, the response to t-RA differed depending upon proliferative status. Consistent with previous reports, t-RA increased ChAT and VAChT mRNA, ChAT activity and intracellular ACh levels in proliferating SN56 cells with no effect on intracellular choline levels. When cells were treated with t-RA while undergoing proliferative arrest, an additive effect of combined treatment was observed on ACh levels; nevertheless, this was only accompanied by an increase in choline levels, VAChT and ChAT mRNAs, but not ChAT activity. Indeed, aphidicolin treatment completely suppressed the t-RA-induced increase in ChAT activity observed in proliferating cells. To explore the response to t-RA in post-mitotic cells, a sequential treatment of aphidicolin and t-RA was employed. t-RA treatment was ineffective in increasing ACh and choline levels, over and above that observed with the aphidicolin treatment alone. Comparable to the combined treatment, sequential treatment lead to an increase in ChAT mRNA without any increase in ChAT activity. In conclusion, both the magnitude and the mechanism(s) of action whereby t-RA enhances the cholinergic phenotype of SN56 cells is dependent upon the cell's proliferative status.
authors.affiliation: Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, FitzGerald Building, 150 College Street, Toronto, M5S 3E2, Ontario, Canada.
authors.forename: M A
authors.initials: MA
authors.lastname: Malik
authors.forename: C E
authors.initials: CE
authors.lastname: Greenwood
authors.forename: J K
authors.initials: JK
authors.lastname: Blusztajn
authors.forename: B
authors.initials: B
authors.lastname: Berse
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002794:Choline / Q000378:metabolism*; D002795:Choline O-Acetyltransferase / Q000235:genetics / Q000378:metabolism*; D004258:DNA Polymerase III / Q000037:antagonists & inhibitors; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D026901:Membrane Transport Proteins; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C493460:Slc18a3 protein, mouse; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins; D016590:Aphidicolin; D014212:Tretinoin; D002795:Choline O-Acetyltransferase; C065639:DNA polymerase A; D004258:DNA Polymerase III; D002794:Choline; D000109:Acetylcholine