title: Neurotrophic effect of citrus 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone: promotion of neurite outgrowth via cAMP/PKA/CREB pathway in PC12 cells.
abstract: 5-Hydroxy-3,6,7,8,3',4'-hexamethoxyflavone (5-OH-HxMF), a hydroxylated polymethoxyflavone, is found exclusively in the Citrus genus, particularly in the peels of sweet orange. In this research, we report the first investigation of the neurotrophic effects and mechanism of 5-OH-HxMF in PC12 pheochromocytoma cells. We found that 5-OH-HxMF can effectively induce PC12 neurite outgrowth accompanied with the expression of neuronal differentiation marker protein growth-associated protein-43(GAP-43). 5-OH-HxMF caused the enhancement of cyclic AMP response element binding protein (CREB) phosphorylation, c-fos gene expression and CRE-mediated transcription, which was inhibited by 2-naphthol AS-E phosphate (KG-501), a specific antagonist for the CREB-CBP complex formation. Moreover, 5-OH-HxMF-induced both CRE transcription activity and neurite outgrowth were inhibited by adenylate cyclase and protein kinase A (PKA) inhibitor, but not MEK1/2, protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3K) or calcium/calmodulin-dependent protein kinase (CaMK) inhibitor. Consistently, 5-OH-HxMF treatment increased the intracellular cAMP level and downstream component, PKA activity. We also found that addition of K252a, a TrKA antagonist, significantly inhibited NGF- but not 5-OH-HxMF-induced neurite outgrowth. These results reveal for the first time that 5-OH-HxMF is an effective neurotrophic agent and its effect is mainly through a cAMP/PKA-dependent, but TrKA-independent, signaling pathway coupling with CRE-mediated gene transcription. A PKC-dependent and CREB-independent pathway was also involved in its neurotrophic action.
authors.affiliation: Department of Molecular Biology and Human Genetics, Tzu Chi University, Hualien, Taiwan.
authors.forename: Hui-Chi
authors.initials: HC
authors.lastname: Lai
authors.forename: Ming-Jiuan
authors.initials: MJ
authors.lastname: Wu
authors.forename: Pei-Yi
authors.initials: PY
authors.lastname: Chen
authors.forename: Ting-Ting
authors.initials: TT
authors.lastname: Sheu
authors.forename: Szu-Ping
authors.initials: SP
authors.lastname: Chiu
authors.forename: Meng-Han
authors.initials: MH
authors.lastname: Lin
authors.forename: Chi-Tang
authors.initials: CT
authors.lastname: Ho
authors.forename: Jui-Hung
authors.initials: JH
authors.lastname: Yen
mesh_terms: D000818:Animals; D048430:Cell Shape / Q000187:drug effects; D002957:Citrus / Q000737:chemistry*; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D047309:Flavones / Q000737:chemistry / Q000494:pharmacology*; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D008954:Models, Biological; D009284:Naphthols / Q000494:pharmacology; D009414:Nerve Growth Factors / Q000737:chemistry / Q000494:pharmacology*; D016501:Neurites / Q000187:drug effects / Q000378:metabolism*; D010755:Organophosphates / Q000494:pharmacology; D016716:PC12 Cells; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020917:Receptor, trkA / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D047309:Flavones; D019922:GAP-43 Protein; D009284:Naphthols; D009414:Nerve Growth Factors; D010755:Organophosphates; D012333:RNA, Messenger; C495860:naphthol AS-E phosphate; C521815:5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone; C008661:nobiletin; D000242:Cyclic AMP; D020917:Receptor, trkA; D017868:Cyclic AMP-Dependent Protein Kinases