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ABSTRACT: Biallelic mutations in the neurofibromatosis 2 (NF2) gene are linked to schwannoma and meningioma tumorigenesis. Cells with NF2 mutations exhibit elevated levels of phosphorylated extracellular signal-regulated kinase (ERK) and aberrant cell-cell and cell-matrix contacts. The NF2 gene product, merlin, associates with adherens junction protein complexes, suggesting that part of its function as a tumor suppressor involves regulating cell junctions. Here, we find that a novel PDZ protein, called erbin, binds directly to the merlin-binding partner, EBP0, and regulates adherens junction dissociation through a MAP kinase-dependent mechanism. Reducing erbin expression using a targeted siRNA in primary cultures of Schwann cells results in altered cell-cell interactions, disruption of E-cadherin adherens junctions, increased cell proliferation, and elevated levels of phosphorylated ERK, all phenotypes observed in cells that lack merlin. Reduction of erbin expression also results in the dissociation of merlin from adherens junction proteins and an increase in the levels of phosphorylated merlin. These phenotypes can be rescued if cells with reduced levels of erbin are treated with a pharmacological inhibitor of ERK kinase. Collectively, these data indicate that erbin regulates MAP kinase activation in Schwann cells and suggest that erbin links merlin to both adherens junction protein complexes and the MAP kinase signaling pathway.
Journal of Biological Chemistry 04/2005; 280(12):11790-7. · 4.77 Impact Factor
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Dongren Yang,
Jesse Bierman,
Yukie S Tarumi,
Yong-Ping Zhong, Reshma Rangwala,
Thomas M Proctor,
Yuko Miyagoe-Suzuki,
Shin'ichi Takeda,
Jeffrey H Miner,
Larry S Sherman,
Bruce G Gold,
Bruce L Patton
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ABSTRACT: Schwann cells form basal laminae (BLs) containing laminin-2 (Ln-2; heterotrimer alpha2beta1gamma1) and Ln-8 (alpha4beta1gamma1). Loss of Ln-2 in humans and mice carrying alpha2-chain mutations prevents developing Schwann cells from fully defasciculating axons, resulting in partial amyelination. The principal pathogenic mechanism is thought to derive from structural defects in Schwann cell BLs, which Ln-2 scaffolds. However, we found loss of Ln-8 caused partial amyelination in mice without affecting BL structure or Ln-2 levels. Combined Ln-2/Ln-8 deficiency caused nearly complete amyelination, revealing Ln-2 and -8 together have a dominant role in defasciculation, and that Ln-8 promotes myelination without BLs. Transgenic Ln-10 (alpha5beta1gamma1) expression also promoted myelination without BL formation. Rather than BL structure, we found Ln-2 and -8 were specifically required for the increased perinatal Schwann cell proliferation that attends myelination. Purified Ln-2 and -8 directly enhanced in vitro Schwann cell proliferation in collaboration with autocrine factors, suggesting Lns control the onset of myelination by modulating responses to mitogens in vivo.
The Journal of Cell Biology 03/2005; 168(4):655-66. · 10.26 Impact Factor
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10/2004; , ISBN: 9780471675068
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ABSTRACT: The proteasome catalytic beta subunits LMP2, LMP7, and MECL-1 and two proteasome activator proteins, PA28 alpha and beta, are induced following exposure to IFN-gamma in vitro. Induction of these immunosubunits and the PA28 alpha/beta hetero-oligomer alters proteasome catalytic functions and specificity and enhances production of certain MHC class I epitopes. We sought to determine whether and to what extent proteasome subunit composition is regulated in vivo and to elucidate the mechanisms of such regulation. We analyzed basal expression levels of these inducible genes in normal, IFN-gamma-deficient, and Stat-1-deficient mice. Mice of all three genotypes display constitutive expression of the immunosubunits and PA28, demonstrating that basal expression in vivo is independent of endogenous IFN-gamma production. However, basal expression levels are reduced in Stat-1(-/-) mice, demonstrating a role for Stat-1 independent of IFN-gamma signaling. To demonstrate that IFN-gamma can induce these genes in vivo, mice were infected with Histoplasma capsulatum. Elevated expression of these genes followed the same time course as IFN-gamma expression in infected mice. IFN-gamma-deficient mice did not display elevated protein expression following infection, suggesting that other inflammatory cytokines produced in infected mice are unable to influence proteasome expression. Cytokines other than IFN-gamma also failed to influence proteasome gene expression in vitro in cell lines that had no basal expression of LMP2, LMP7, or MECL-1. Thus, both in vitro and in vivo data demonstrate that IFN-gamma is essential for up-regulation, but not constitutive expression, of immunoproteasome subunits in mice.
The Journal of Immunology 10/2002; 169(6):3046-52. · 5.79 Impact Factor
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Glia 05/2002; 38(2):93-102. · 4.82 Impact Factor
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ABSTRACT: Type I receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR) and erbB2, have been implicated in mammary carcinoma growth and metastasis. Recent evidence suggests that type I receptor signaling may be mediated by the CD44 family of transmembrane glycoproteins that also have been implicated in mammary tumor progression. Here, the authors tested whether CD44, EGFR, and erbB2 interacted and colocalized with one another in four mammary carcinoma cell lines (MCF-7, MDA-MB-231, MDA-MB-435, and MDA-MB-436) and in cytology samples obtained from patients with metastatic breast cancer. CD44 constitutively colocalized and coimmunoprecipitated with erbB2 and EGFR in all four mammary carcinoma cell lines. CD44 also colocalized with erbB2 and EGFR in all cytology samples expressing erbB2. CD44 colocalized with EGFR in cells from only 1 of 16 erbB2-negative cytology samples. These data indicate that CD44-EGFR-erbB2 protein complexes occur in a high proportion of metastatic mammary carcinomas and suggest that CD44-type I receptor colocalization may be a novel prognostic marker for aggressive mammary cancers.
Applied immunohistochemistry & molecular morphology: AIMM / official publication of the Society for Applied Immunohistochemistry 04/2002; 10(1):34-9. · 1.63 Impact Factor
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Glia 03/2002; 38(2):93 - 102. · 4.82 Impact Factor
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ABSTRACT: Type I receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR) and erbB2, have been implicated in mammary carcinoma growth and metastasis. Recent evidence suggests that type I receptor signaling may be mediated by the CD44 family of transmembrane glycoproteins that also have been implicated in mammary tumor progression. Here, the authors tested whether CD44, EGFR, and erbB2 interacted and colocalized with one another in four mammary carcinoma cell lines (MCF-7, MDA-MB-231, MDA-MB-435, and MDA-MB-436) and in cytology samples obtained from patients with metastatic breast cancer. CD44 constitutively colocalized and coimmunoprecipitated with erbB2 and EGFR in all four mammary carcinoma cell lines. CD44 also colocalized with erbB2 and EGFR in all cytology samples expressing erbB2. CD44 colocalized with EGFR in cells from only 1 of 16 erbB2-negative cytology samples. These data indicate that CD44-EGFR-erbB2 protein complexes occur in a high proportion of metastatic mammary carcinomas and suggest that CD44-type I receptor colocalization may be a novel prognostic marker for aggressive mammary cancers.
Applied Immunohistochemistry 02/2002; 10(1):34-39. · 1.63 Impact Factor
