title: Zn2+-dependent Activation of the Trk Signaling Pathway Induces Phosphorylation of the Brain-enriched Tyrosine Phosphatase STEP: MOLECULAR BASIS FOR ZN2+-INDUCED ERK MAPK ACTIVATION.
abstract: Excessive release of Zn(2+) in the brain is implicated in the progression of acute brain injuries. Although several signaling cascades have been reported to be involved in Zn(2+)-induced neurotoxicity, a potential contribution of tyrosine phosphatases in this process has not been well explored. Here we show that exposure to high concentrations of Zn(2+) led to a progressive increase in phosphorylation of the striatal-enriched phosphatase (STEP), a component of the excitotoxic-signaling pathway that plays a role in neuroprotection. Zn(2+)-mediated phosphorylation of STEP61 at multiple sites (hyperphosphorylation) was induced by the up-regulation of brain-derived neurotropic factor (BDNF), tropomyosin receptor kinase (Trk) signaling, and activation of cAMP-dependent PKA (protein kinase A). Mutational studies further show that differential phosphorylation of STEP61 at the PKA sites, Ser-160 and Ser-221 regulates the affinity of STEP61 toward its substrates. Consistent with these findings we also show that BDNF/Trk/PKA mediated signaling is required for Zn(2+)-induced phosphorylation of extracellular regulated kinase 2 (ERK2), a substrate of STEP that is involved in Zn(2+)-dependent neurotoxicity. The strong correlation between the temporal profile of STEP61 hyperphosphorylation and ERK2 phosphorylation indicates that loss of function of STEP61 through phosphorylation is necessary for maintaining sustained ERK2 phosphorylation. This interpretation is further supported by the findings that deletion of the STEP gene led to a rapid and sustained increase in ERK2 phosphorylation within minutes of exposure to Zn(2+). The study provides further insight into the mechanisms of regulation of STEP61 and also offers a molecular basis for the Zn(2+)-induced sustained activation of ERK2.
authors.affiliation: From the Departments of Neurology and.
authors.forename: Ranjana
authors.initials: R
authors.lastname: Poddar
authors.affiliation: From the Departments of Neurology and.
authors.forename: Sathyanarayanan
authors.initials: S
authors.lastname: Rajagopal
authors.affiliation: Neurosciences University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131.
authors.forename: C William
authors.initials: CW
authors.lastname: Shuttleworth
authors.affiliation: From the Departments of Neurology and Neurosciences University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131 spaul@salud.unm.edu.
authors.forename: Surojit
authors.initials: S
authors.lastname: Paul
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D020813:Receptor, trkB / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D015032:Zinc / Q000494:pharmacology*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D010768:Phosphoserine; D020813:Receptor, trkB; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C082101:Ptpn5 protein, mouse; D015032:Zinc; D002118:Calcium
keywords: STEP; brain-derived neurotrophic factor (BDNF); extracellular-signal-regulated kinase (ERK); protein phosphorylation; tropomyosin receptor kinase; tyrosine-protein phosphatase (tyrosine phosphatase); zinc