Direct Regulation of Myelin Protein Zero Expression by the Egr2 Transactivator

University of Wisconsin–Madison, Madison, Wisconsin, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2006; 281(9):5453-60. DOI: 10.1074/jbc.M512159200
Source: PubMed


During myelination of the peripheral nervous system, the myelin protein zero (Mpz) gene is induced to produce the most abundant protein component (P(0)) of mature myelin. Although the basal embryonic expression of Mpz in Schwann cells has been attributed to regulation by Sox10, the molecular mechanism for the profound up-regulation of this gene during myelination has not been established. In this study, we have identified a highly conserved element within the first intron of the Mpz gene, which contains binding sites for the early growth response 2 (Egr2/Krox20) transcription factor, a critical regulator of peripheral nerve myelination. Egr2 can transactivate the intron element, and the induction is blocked by two known repressors of Egr2 activity. Using chromatin immunoprecipitation assays, we find that Egr2 binds in vivo to the intron element, but not to the Mpz promoter. Known inducers of Mpz expression such as forskolin and insulin-like growth factor-1 also activate the element in an Egr2-dependent manner. In addition, we found that Egr2 can act synergistically with Sox10 to activate this intron element, suggesting a model in which cooperative interactions between Egr2 and Sox10 mediate a large increase in Mpz expression to the high levels found in myelinating Schwann cells.

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    • "During development, immature Schwann cells differentiate into myelinating cells when associated with an axon of >1-lm diameter (Nave and Salzer 2006), thereby activating the expression of genes encoding myelin-related transcription factors and structural proteins (Jessen et al., 2015; Monk et al., 2015; Stolt and Wegner, 2010; Svaren and Meijer, 2008). For example, the transcription factors SOX10 (Peirano et al. 2000) and KROX20 (also termed EGR2) (LeBlanc et al., 2006) activate the gene encoding myelin protein zero (P0; also termed MPZ), the most abundant protein of peripheral myelin (Lemke and Axel, 1985), in which it constitutes 21% of the total protein (Patzig et al., 2011). P0, an immunoglobulin-like cell-adhesion molecule (Ig-CAM), mediates the compaction of the extracellular surfaces of adjacent myelin layers (D'Urso et al., 1990; Filbin et al., 1990; Giese et al., 1992; Martini and Schachner, 1997). "
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    ABSTRACT: Protein zero (P0) is the major structural component of peripheral myelin. Lack of this adhesion protein from Schwann cells causes a severe dysmyelinating neuropathy with secondary axonal degeneration in humans with the neuropathy Dejerine-Sottas syndrome (DSS) and in the corresponding mouse model (P0(null) -mice). In the mammalian CNS, the tetraspan-membrane protein PLP is the major structural myelin constituent and required for the long-term preservation of myelinated axons, which fails in hereditary spastic paraplegia (SPG type-2) and the relevant mouse model (Plp(null) -mice). The Plp-gene is also expressed in Schwann cells but PLP is of very low abundance in normal peripheral myelin; its function has thus remained enigmatic. Here we show that the abundance of PLP but not of other tetraspan myelin proteins is strongly increased in compact peripheral myelin of P0(null) -mice. To determine the functional relevance of PLP expression in the absence of P0, we generated P0(null) *Plp(null) -double-mutant mice. Compared with either single-mutant, P0(null) *Plp(null) -mice display impaired nerve conduction, reduced motor functions, and premature death. At the morphological level, axonal segments were frequently non-myelinated but in a one-to-one relationship with a hypertrophic Schwann cell. Importantly, axonal numbers were reduced in the vital phrenic nerve of P0(null) *Plp(null) -mice. In the absence of P0, thus, PLP also contributes to myelination by Schwann cells and to the preservation of peripheral axons. These data provide a link between the Schwann cell-dependent support of peripheral axons and the oligodendrocyte-dependent support of central axons. GLIA 2015.
    Glia 09/2015; DOI:10.1002/glia.22922 · 6.03 Impact Factor
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    • "SOX10 first activates the POU homeo-domain transcription factor, OCT6 [6] which then cooperates with SOX10 to activate expression of the zinc finger transcriptional regulator, KROX20 [7]. In the next step, pro-myelinating Schwann cells transition to myelinating cells as SOX10 and KROX20 synergistically activate high levels of MPZ and the expression of genes encoding other components of myelin [8,9]. "
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    ABSTRACT: SOX10 is a Sry-related high mobility (HMG)-box transcriptional regulator that promotes differentiation of neural crest precursors into Schwann cells, oligodendrocytes, and melanocytes. Myelin, formed by Schwann cells in the peripheral nervous system, is essential for propagation of nerve impulses. SWI/SNF complexes are ATP dependent chromatin remodeling enzymes that are critical for cellular differentiation. It was recently demonstrated that the BRG1 subunit of SWI/SNF complexes activates SOX10 expression and also interacts with SOX10 to activate expression of OCT6 and KROX20, two transcriptional regulators of Schwann cell differentiation. To determine the requirement for SWI/SNF enzymes in the regulation of genes that encode components of myelin, which are downstream of these transcriptional regulators, we introduced SOX10 into fibroblasts that inducibly express dominant negative versions of the SWI/SNF ATPases, BRM or BRG1. Dominant negative BRM and BRG1 have mutations in the ATP binding site and inhibit gene activation events that require SWI/SNF function. Ectopic expression of SOX10 in cells derived from NIH 3T3 fibroblasts led to the activation of the endogenous Schwann cell specific gene, myelin protein zero (MPZ) and the gene that encodes myelin basic protein (MBP). Thus, SOX10 reprogrammed these cells into myelin gene expressing cells. Ectopic expression of KROX20 was not sufficient for activation of these myelin genes. However, KROX20 together with SOX10 synergistically activated MPZ and MBP expression. Dominant negative BRM and BRG1 abrogated SOX10 mediated activation of MPZ and MBP and synergistic activation of these genes by SOX10 and KROX20. SOX10 was required to recruit BRG1 to the MPZ locus. Similarly, in immortalized Schwann cells, BRG1 recruitment to SOX10 binding sites at the MPZ locus was dependent on SOX10 and expression of dominant negative BRG1 inhibited expression of MPZ and MBP in these cells. Thus, SWI/SNF enzymes cooperate with SOX10 to directly activate genes that encode components of peripheral myelin.
    PLoS ONE 07/2013; 8(7):e69037. DOI:10.1371/journal.pone.0069037 · 3.23 Impact Factor
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    • "Mutations of Krox-20 are linked to Charcot-Marie Tooth disease and Dejerine-Sottas syndrome (Bellone et al., 1999; Timmerman et al., 1999). Krox-20 regulates myelin proteins expression directly (LeBlanc et al., 2006; Nagarajan et al., 2001) or together with Sox10, a high-mobility-group transcription factor (Jones et al., 2007). SCIP, expressed in response to increased cAMP (Monuki et al., 1989), induces Krox-20 expression together with Brn2 and Sox10 (Ghislain and Charnay, 2006). "
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    ABSTRACT: We previously reported that addition of extracellular matrix (ECM) extracts to rat Schwann cell-dorsal root ganglion neuron (DRGN) co-cultures activated mitogen-activated protein kinase (MAPK) p38, whereas inhibition blocked myelination. Here, we used p38 pharmacological inhibitors and gene silencing to assess their effects on downstream kinases and key transcription factors. We show that p38α regulates expression of the master transcription factor, Krox-20, required for the onset of myelination in Schwann cell-DRGNs, as assessed by immunocytochemistry and qRT-PCR. p38 activity is also required for the expression of the cell cycle inhibitor p27(kip1) , associated with Schwann cell differentiation. Three potential effectors of p38 were explored: MAPK-activated protein kinase-2 (MK2), mitogen and stress-activated protein kinase-1 (MSK-1), and the transcription factor cAMP response element-binding protein (CREB). Inhibition of MK2 with CMPD1 or gene knockdown with siRNAs reduced numbers of Krox-20-positive Schwann cells and expression of myelin proteins MBP and MAG. ECM activated CREB and increased Krox-20 expression, whereas CREB1 gene silencing reduced Krox-20. Furthermore, two nonselective inhibitors of MSK-1 (H89 and R0-318820) decreased ECM-induced CREB phosphorylation and, similar to anti-MSK-1 siRNAs, reduced Krox-20-positive cells. In addition, p38 modulated the expression of two transcription factors involved in the regulation of Krox-20 [suppressed cAMP-inducible protein (SCIP) and Sox10], but not Sox2, an antagonist of Krox-20. Collectively, our results show that p38 primarily directs Schwann cell differentiation and peripheral myelination by regulating Krox-20 expression through its downstream effectors, MK2 and MSK-1/CREB, and transcription factors SCIP and Sox10.
    Glia 07/2012; 60(7):1130-44. DOI:10.1002/glia.22340 · 6.03 Impact Factor
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