title: Striatal-enriched protein tyrosine phosphatase expression and activity in Huntington's disease: a STEP in the resistance to excitotoxicity.
abstract: Striatal-enriched protein tyrosine phosphatase (STEP) is highly expressed in striatal projection neurons, the neuronal population most affected in Huntington's disease. Here, we examined STEP expression and phosphorylation, which regulates its activity, in N-terminal exon-1 and full-length mutant huntingtin mouse models. R6/1 mice displayed reduced STEP protein levels in the striatum and cortex, whereas its phosphorylation was increased in the striatum, cortex, and hippocampus. The early increase in striatal STEP phosphorylation levels correlated with a deregulation of the protein kinase A pathway, and decreased calcineurin activity at later stages further contributes to an enhancement of STEP phosphorylation and inactivation. Accordingly, we detected an accumulation of phosphorylated ERK2 and p38, two targets of STEP, in R6/1 mice striatum at advanced stages of the disease. Activation of STEP participates in excitotoxic-induced cell death. Because Huntington's disease mouse models develop resistance to excitotoxicity, we analyzed whether decreased STEP activity was involved in this process. After intrastriatal quinolinic acid (QUIN) injection, we detected higher phosphorylated STEP levels in R6/1 than in wild-type mice, suggesting that STEP inactivation could mediate neuroprotection in R6/1 striatum. In agreement, intrastriatal injection of TAT-STEP increased QUIN-induced cell death. R6/2, Tet/HD94, and Hdh(Q7/Q111) mice striatum also displayed decreased STEP protein and increased phosphorylation levels. In Tet/HD94 mice striatum, mutant huntingtin transgene shutdown reestablished STEP expression. In conclusion, the STEP pathway is severely downregulated in the presence of mutant huntingtin and may participate in compensatory mechanisms activated by striatal neurons that lead to resistance to excitotoxicity.
authors.affiliation: Departament de Biologia Cellular, Facultat de Medicina, Universitat de Barcelona, Institut d'Investigacions Biomèdiques August Pi-Sunyer, 08036 Barcelona, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Saavedra
authors.forename: Albert
authors.initials: A
authors.lastname: Giralt
authors.forename: Laura
authors.initials: L
authors.lastname: Rué
authors.forename: Xavier
authors.initials: X
authors.lastname: Xifró
authors.forename: Jian
authors.initials: J
authors.lastname: Xu
authors.forename: Zaira
authors.initials: Z
authors.lastname: Ortega
authors.forename: José J
authors.initials: JJ
authors.lastname: Lucas
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Lombroso
authors.forename: Jordi
authors.initials: J
authors.lastname: Alberch
authors.forename: Esther
authors.initials: E
authors.lastname: Pérez-Navarro
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D019703:Calcineurin / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects*; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D015696:Gene Products, tat / Q000235:genetics; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008818:Mice, Neurologic Mutants; D008822:Mice, Transgenic; D008845:Microinjections; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000096:biosynthesis / Q000378:metabolism*; D017378:Quinolinic Acid / Q000008:administration & dosage / Q000494:pharmacology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D015696:Gene Products, tat; C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D019703:Calcineurin; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C082101:Ptpn5 protein, mouse; D017378:Quinolinic Acid