Valproic acid enhances protein L-isoaspartyl methyltransferase expression by stimulating extracellular signal-regulated kinase signaling pathway.
Proteins are susceptible to various non-enzymatic post-translational modifications occurring during aging and in certain pathological states. The protein L-isoaspartyl methyltransferase (PIMT) is an enzyme that recognizes and repairs the abnormal L-isoaspartyl residues in proteins. Recently, we reported that PIMT expression was stimulated by the anti-epileptic drug valproic acid and that this was mediated through the glycogen synthase kinase-3 (GSK-3)/beta-catenin pathway. In this study, to gain further insights into which of the signaling pathways activated by valproic acid regulate PIMT abundance, astrocytoma U-87 MG and neuroblastoma SH-SY5Y cells were treated with this drug to investigate the possible involvement of the extracellular-regulated kinase (ERK) pathway in PIMT induction. Valproic acid increased ERK1/2 phosphorylation on Thr202/Tyr204 and Thr185/Tyr187, respectively. Pharmacological inhibitors against the kinases Src, c-Raf, MEK1/2 and ERK1/2 abolished the ERK1/2 phosphorylation stimulated by valproic acid, thus preventing PIMT induction by the drug. Furthermore, MEK1/2 inhibition with U0126 blocked the higher phosphorylation of RSK-1 on Thr359/Ser363 and of GSK-3beta on Ser9 as well as the increased expression of RSK-1, beta-catenin and PIMT upon treatment with valproic acid. RSK-1 knockdown by interfering RNA abrogated the increased expression of RSK-1, beta-catenin and PIMT as well as the induced phosphorylation of RSK-1 and GSK-3beta due to valproic acid. Thus, our findings demonstrated that PIMT up-regulation by valproic acid required the activation of the ERK signaling pathway including RSK-1 the latter being responsible for inactivating GSK-3 and subsequently leading to beta-catenin stabilization.
Cournoyer
Philippe
P
Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3P8.
Desrosiers
Richard R
RR
D000927:Anticonvulsants / Q000494:pharmacology*; D018692:Antimanic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D010766:Phosphorylation; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase / Q000096:biosynthesis*; D034741:RNA, Small Interfering / Q000235:genetics; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction; D015854:Up-Regulation; D014635:Valproic Acid / Q000494:pharmacology*; D051176:beta Catenin / Q000378:metabolism
D000927:Anticonvulsants; D018692:Antimanic Agents; D034741:RNA, Small Interfering; D051176:beta Catenin; D014635:Valproic Acid; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C069329:RPS6KA1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D048049:Extracellular Signal-Regulated MAP Kinases; D038362:Glycogen Synthase Kinase 3