title: Lithium enhances CRTC oligomer formation and the interaction between the CREB coactivators CRTC and CBP--implications for CREB-dependent gene transcription.
abstract: Lithium salts are important drugs to treat bipolar disorder. Previous work showed that lithium by enforcing the interaction between the transcription factor CREB and its coactivator CRTC1 enhanced cAMP-stimulated CREB-dependent gene transcription. Both CREB and CRTC have been implicated in neuronal adaptation, which might underlie lithium's therapeutic action. In the present study the mechanisms of lithium action on cAMP-induced CREB-dependent gene transcription were further elucidated. Transient transfection assays revealed that all three CRTC isoforms conferred lithium responsiveness to CREB whereas their intrinsic transcriptional activities remained unchanged by lithium, suggesting a conformational change of CREB or CRTC by lithium. In in vitro protein-protein interaction assays lithium enhanced the interaction between CREB and both coactivators CRTC and CBP. Furthermore, lithium enforced the oligomerization of CRTC, a prerequisite for CREB interaction. For further evaluation it was investigated whether lithium competes with magnesium, which coordinates the conformation of the CREB basic region leucine zipper (bZip). Mutational analysis of the magnesium coordinating lysine-290 within the bZip, in vitro and intracellular interaction assays and luciferase reporter-gene assays revealed that the effect of lithium on the CREB-CRTC interaction or on the transcriptional activity, respectively, was not affected by the mutation, thus excluding a magnesium-lithium competition. However, the CREB-CRTC interaction was strongly increased in lysine-290-mutants thereby extending the CRTC-CREB interaction domain. Taken together the results exclude a competition between lithium and magnesium at the bZip, but suggest that lithium by enforcing the CRTC-oligomer formation and the interaction of CREB-CBP-CRTC enhances cAMP-induced CREB-dependent gene transcription.
authors.affiliation: Department of Pharmacology, Georg-August-University Goettingen, Robert-Koch-Str. 40, 37075 Goettingen, Germany. Electronic address: annette.heinrich@uniklinik-freiburg.de.
authors.forename: Annette
authors.initials: A
authors.lastname: Heinrich
authors.forename: Anne Sophie
authors.initials: AS
authors.lastname: von der Heyde
authors.forename: Ulrike
authors.initials: U
authors.lastname: Böer
authors.forename: Do Thanh
authors.initials: do T
authors.lastname: Phu
authors.forename: Mladen
authors.initials: M
authors.lastname: Tzvetkov
authors.forename: Elke
authors.initials: E
authors.lastname: Oetjen
mesh_terms: D000818:Animals; D050882:CREB-Binding Protein / Q000378:metabolism*; D045744:Cell Line, Tumor; D006224:Cricetinae; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology*; D015636:Magnesium Chloride / Q000494:pharmacology; D009154:Mutation; D025941:Protein Interaction Mapping; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000187:drug effects*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: C500984:CRTC1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D020033:Protein Isoforms; D014157:Transcription Factors; D015636:Magnesium Chloride; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D018021:Lithium Chloride