Knockout of STriatal enriched protein tyrosine phosphatase in mice results in increased ERK1/2 phosphorylation

Child Study Center, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Synapse (Impact Factor: 2.13). 01/2009; 63(1):69-81. DOI: 10.1002/syn.20608
Source: PubMed


STriatal Enriched protein tyrosine Phosphatase (STEP) is a brain-specific protein that is thought to play a role in synaptic plasticity. This hypothesis is based on previous findings demonstrating a role for STEP in the regulation of the extracellular signal-regulated kinase1/2 (ERK1/2). We have now generated a STEP knockout mouse and investigated the effect of knocking out STEP in the regulation of ERK1/2 activity. Here, we show that the STEP knockout mice are viable and fertile and have no detectable cytoarchitectural abnormalities in the brain. The homozygous knockout mice lack the expression of all STEP isoforms, whereas the heterozygous mice have reduced STEP protein levels when compared with the wild-type mice. The STEP knockout mice show enhanced phosphorylation of ERK1/2 in the striatum, CA2 region of the hippocampus, as well as central and lateral nuclei of the amygdala. In addition, the cultured neurons from KO mice showed significantly higher levels of pERK1/2 following synaptic stimulation when compared with wild-type controls. These data demonstrate more conclusively the role of STEP in the regulation of ERK1/2 activity.

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    • "Male and female STEP KO (STEP −/− ) [43], heterozygous (STEP +/− ) and wild-type (STEP +/+ ) mice (C57BL/6J background), and male Sprague Dawley rats (200-250 g) were housed in cages lined with sawdust under a standard 12/12 h light/dark cycle (lights on at 08:00 am) with food and water available ad libitum. Every effort was made to minimize animal suffering and to use the minimum number of animals per group and experiment. "
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    ABSTRACT: The information from nociceptors is processed in the dorsal horn of the spinal cord by complex circuits involving excitatory and inhibitory interneurons. It is well documented that GluN2B and ERK1/2 phosphorylation contribute to central sensitization. STriatal-Enriched protein tyrosine Phosphatase (STEP) dephosphorylates GluN2B and ERK1/2, promoting internalization of GluN2B and inactivation of ERK1/2. STEP activity was modulated by genetic (STEP knockout mice) and pharmacological (recently synthesized STEP inhibitor, TC-21539) approaches. STEP61 protein levels in the lumbar spinal cord were determined in male and female mice of different ages. Inflammatory pain was induced by complete Freund's adjuvant injection. Behavioral tests, immunoblotting and electrophysiology were used to analyze the effect of STEP on nociception. Our results show that both genetic deletion and pharmacological inhibition of STEP induced thermal hyperalgesia and mechanical allodynia, which were accompanied by increased pGluN2B and pERK1/2 levels in the lumbar spinal cord. Interestingly, STEP heterozygous and knockout mice presented a similar phenotype. Furthermore, electrophysiological experiments showed that TC-2153 increased C fiber-evoked spinal field potentials. Interestingly, we found that STEP61 protein levels in the lumbar spinal cord inversely correlated with the increased thermal hyperalgesia associated with age and female gender in mice. Consistently, STEP knockout mice failed to show age-related thermal hyperalgesia, while gender-related differences were preserved. Moreover, in a model of inflammatory pain, hyperalgesia was associated with increased phosphorylation-mediated STEP61 inactivation and increased pGluN2B and pERK1/2 levels in the lumbar spinal cord. Collectively, present results underscore an important role of spinal STEP activity in the modulation of nociception.
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    • "This seemingly surprising coincidence can be reconciled by the fact that the inactivation of CaMKII signaling inactivates striatal enriched tyrosine phosphatase (STEP) by dephosphorylating NMDA receptors and reducing calcineurin (Paul et al., 2003). Under normal conditions, ERK1/2 activity remains suppressed by activated STEP (Paul et al., 2003; Venkitaramani et al., 2009). Thus, the inactivation of STEP—due to inactivation of CaMKII signaling—disinhibits ERK1/2 signaling. "
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    ABSTRACT: The pedunculopontine tegmentum nucleus (PPT) is critically involved in the regulation of wakefulness (W) and rapid eye movement (REM) sleep, but our understanding of the mechanisms of this regulation remains incomplete. The present study was designed to determine the role of PPT intracellular calcium/calmodulin kinase (CaMKII) signaling in the regulation of W and sleep. To achieve this aim, three different concentrations (0.5, 1.0, and 2.0 nmol) of the CaMKII activation inhibitor, KN-93, were microinjected bilaterally (100 nl/site) into the PPT of freely moving rats, and the effects on W, slow-wave sleep (SWS), REM sleep, and levels of phosphorylated CaMKII (pCaMKII) expression in the PPT were quantified. These effects, which were concentration-dependent and affected wake-sleep variables for 3 h, resulted in decreased W, due to reductions in the number and duration of W episodes; increased SWS and REM sleep, due to increases in episode duration; and decreased levels of pCaMKII expression in the PPT. Regression analyses revealed that PPT levels of pCaMKII were positively related with the total percentage of time spent in W (R(2) = 0.864; n = 28 rats; p < 0.001) and negatively related with the total percentage of time spent in sleep (R(2) = 0.863; p < 0.001). These data provide the first direct evidence that activation of intracellular CaMKII signaling in the PPT promotes W and suppresses sleep. These findings are relevant for designing a drug that could treat excessive sleepiness by promoting alertness.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 11/2011; 31(47):17007-16. DOI:10.1523/JNEUROSCI.3981-11.2011 · 6.34 Impact Factor
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    • "ERK1/2 phosphorylation is significantly elevated in the striatum, hippocampus, and central/lateral amygdala of STEP KO mice compared with WT littermates (Venkitaramani et al., 2009, 2011), providing additional support for the regulation of ERK1/2 by STEP. DHPG normally enhances phosphorylation and activation of ERK1/2 (Kim et al., 2008a), and this is more pronounced in STEP KOs relative to WT, suggesting that STEP limits the activation of ERK1/2 after mGluR stimulation (Venkitaramani et al., 2009). Downstream of ERK1/2 activation, the transcription factors CREB and Elk1 are also hyperphosphorylated in STEP KOs compared with WT mice (Venkitaramani et al., 2011). "
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    ABSTRACT: Striatal-enriched protein tyrosine phosphatase (STEP) is a brain-specific phosphatase that modulates key signaling molecules involved in synaptic plasticity and neuronal function. Targets include extracellular-regulated kinase 1 and 2 (ERK1/2), stress-activated protein kinase p38 (p38), the Src family tyrosine kinase Fyn, N-methyl-D-aspartate receptors (NMDARs), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). STEP-mediated dephosphorylation of ERK1/2, p38, and Fyn leads to inactivation of these enzymes, whereas STEP-mediated dephosphorylation of surface NMDARs and AMPARs promotes their endocytosis. Accordingly, the current model of STEP function posits that it opposes long-term potentiation and promotes long-term depression. Phosphorylation, cleavage, dimerization, ubiquitination, and local translation all converge to maintain an appropriate balance of STEP in the central nervous system. Accumulating evidence over the past decade indicates that STEP dysregulation contributes to the pathophysiology of several neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, fragile X syndrome, epileptogenesis, alcohol-induced memory loss, Huntington's disease, drug abuse, stroke/ischemia, and inflammatory pain. This comprehensive review discusses STEP expression and regulation and highlights how disrupted STEP function contributes to the pathophysiology of diverse neuropsychiatric disorders.
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