title: Inositol synthesis regulates the activation of GSK-3α in neuronal cells.
abstract: The synthesis of inositol provides precursors of inositol lipids and inositol phosphates that are pivotal for cell signaling. Mood stabilizers lithium and valproic acid, used for treating bipolar disorder, cause cellular inositol depletion, which has been proposed as a therapeutic mechanism of action of both drugs. Despite the importance of inositol, the requirement for inositol synthesis in neuronal cells is not well understood. Here, we examined inositol effects on proliferation of SK-N-SH neuroblastoma cells. The essential role of inositol synthesis in proliferation is underscored by the findings that exogenous inositol was dispensable for proliferation, and inhibition of inositol synthesis decreased proliferation. Interestingly, the inhibition of inositol synthesis by knocking down INO1, which encodes inositol-3-phosphate synthase, the rate-limiting enzyme of inositol synthesis, led to the inactivation of GSK-3α by increasing the inhibitory phosphorylation of this kinase. Similarly, the mood stabilizer valproic acid effected transient decreases in intracellular inositol, leading to inactivation of GSK-3α. As GSK-3 inhibition has been proposed as a likely therapeutic mechanism of action, the finding that inhibition of inositol synthesis results in the inactivation of GSK-3α suggests a unifying hypothesis for mechanism of mood-stabilizing drugs. Inositol is an essential metabolite that serves as a precursor for inositol lipids and inositol phosphates. We report that inhibition of the rate-limiting enzyme of inositol synthesis leads to the inactivation of glycogen synthase kinase (GSK) 3α by increasing inhibitory phosphorylation of this kinase. These findings have implications for the therapeutic mechanisms of mood stabilizers and suggest that inositol synthesis and GSK 3α activity are intrinsically related.
authors.affiliation: Department of Biological Sciences, Wayne State University, Detroit, Michigan, USA.
authors.forename: Cunqi
authors.initials: C
authors.lastname: Ye
authors.forename: Miriam L
authors.initials: ML
authors.lastname: Greenberg
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D051246:Glucose Transport Proteins, Facilitative / Q000235:genetics / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007294:Inositol / Q000378:metabolism* / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D019753:Intramolecular Lyases / Q000235:genetics / Q000378:metabolism; D009447:Neuroblastoma / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism; D027981:Symporters / Q000235:genetics / Q000378:metabolism; D014635:Valproic Acid / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D051246:Glucose Transport Proteins, Facilitative; D006360:Heat-Shock Proteins; D012333:RNA, Messenger; C437315:SLC2A13 protein, human; D027981:Symporters; C073884:SLC5A3 protein, human; D007294:Inositol; D014635:Valproic Acid; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha; D019753:Intramolecular Lyases; C105497:D-myo-inositol-3-phosphate synthase
keywords: Inositol; bipolar disorder; glycogen synthesis kinase; inositol depletion; myo-inositol-3-phosphate synthase; valproic acid