Numb isoforms containing a short PTB domain promote neurotrophic factor-induced differentiation and neurotrophic factor withdrawal-induced death of PC12 Cells

Authors

  • Ward A. Pedersen,

    1. Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, Baltimore, Maryland, USA
    2. Johns Hopkins Bayview Medical Center, Baltimore, Maryland, USA
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    • 1

      These authors contributed equally to this work.

  • Sic L. Chan,

    1. Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, Baltimore, Maryland, USA
    2. Johns Hopkins Bayview Medical Center, Baltimore, Maryland, USA
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    • 1

      These authors contributed equally to this work.

  • Haiyan Zhu,

    1. Sanders-Brown Research Center on Aging, University of Kentucky, Lexington, Kentucky, USA
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  • Lilanie A. Abdur-Rahman,

    1. Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, Baltimore, Maryland, USA
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  • Joseph M. Verdi,

    1. Robarts Research Institute, London, Ontario, Canada
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  • Mark P. Mattson

    1. Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, Baltimore, Maryland, USA
    2. Sanders-Brown Research Center on Aging, University of Kentucky, Lexington, Kentucky, USA
    3. Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Address correspondence and reprint requests to Mark P. Mattson, Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center 4F02, 5600 Nathan Shock Drive, Baltimore, Maryland 21224, USA. E-mail: mattsonm@grc.nia.nih.gov

Abstract

The development of the nervous system is regulated by trophic signals that control cell proliferation, differentiation, and survival. Numb is an evolutionarily conserved protein identified by its ability to control cell fate in the nervous system of Drosophila. Mammals express four isoforms of Numb that differ in the length of a phosphotyrosine-binding (PTB) domain and a proline-rich region (PRR). Using PC12 cells stably expressing each of the human isoforms, we show that Numb regulates sensitivity of the cells to neurotrophic factor-induced differentiation and neurotrophic factor withdrawal-induced death in an isoform-specific manner. Numb isoforms containing a short PTB domain enhance the differentiation response to NGF and enhance apoptosis upon NGF withdrawal; Numb isoforms containing a long PTB domain exhibit the same sensitivity to NGF as vector-transfected cells. These effects of Numb were found to be independent of the length of the PRR. In undifferentiated conditions, the levels of full-length TrkA and of phosphorylated p44/p42 mitogen-activated protein kinase (MAPK) are increased in cells expressing Numb isoforms with a short PTB domain, indicating an up-regulation of NGF signaling pathways. Furthermore, we provide evidence that the mechanism whereby short PTB domain Numb isoforms sensitize cells to trophic factor deprivation-induced apoptosis involves elevations in intracellular calcium concentrations. Our results suggest that Numb sensitizes cells to neurotrophin responses in an isoform-specific manner, an effect that may play an important role in the development and plasticity of the nervous system.

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