Sc65 Is a Novel Endoplasmic Reticulum Protein That Regulates Bone Mass Homeostasis

Authors

  • Katrin Gruenwald,

    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Patrizio Castagnola,

    1. IRCCS AOU San Martino–IST, Genova, Italy
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  • Roberta Besio,

    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Milena Dimori,

    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Yuqing Chen,

    1. Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
    2. Howard Hughes Medical Institute, Houston, TX, USA
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  • Nisreen S Akel,

    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Frances L Swain,

    1. Department of Orthopedic Surgery, Center for Orthopaedic Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Robert A Skinner,

    1. Department of Orthopedic Surgery, Center for Orthopaedic Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • David R Eyre,

    1. Department of Orthopedics and Sports Medicine, University of Washington, Seattle, WA, USA
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  • Dana Gaddy,

    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
    2. Department of Orthopedic Surgery, Center for Orthopaedic Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Larry J Suva,

    1. Department of Orthopedic Surgery, Center for Orthopaedic Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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  • Roy Morello

    Corresponding author
    1. Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
    2. Division of Genetics, University of Arkansas for Medical Sciences, Little Rock, AR, USA
    • Address correspondence to: Roy Morello, PhD, Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, 4301 West Markham Street, #505, Little Rock, AR 72205-7199, USA. E-mail: rmorello@uams.edu

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ABSTRACT

Members of the Leprecan family of proteins include enzymes, prolyl 3-hydroxylase 1 (P3h1), P3h2, and P3h3, and nonenzymatic proteins, Crtap and Sc65. Mutations in CRTAP and LEPRE1 (encoding P3H1) have been associated with human disease such as recessive osteogenesis imperfecta; however, the function of Sc65, which is closely related and highly homologous to Crtap, is unknown. Sc65 has been described as a synaptonemal complex protein, a nucleolar protein, and a cytoplasmic adapter protein. In light of its high sequence similarity with Crtap, an endoplasmic reticulum (ER)-associated protein, and the importance of post-translational modifications such as collagen prolyl 3-hydroxylation in bone metabolism, we hypothesized that Sc65 was an ER-resident protein that would have an important role in bone homeostasis. In this study, we demonstrate that Sc65 is a previously unrecognized ER protein and that it does not localize in the nucleus of somatic cells. Moreover, Sc65 is expressed and functional during skeletal development because loss of Sc65 results in a progressive osteopenia that affects both trabecular and cortical bone. Bone loss is the result of increased bone resorption mediated by a non-cell–autonomous effect on osteoclasts. Therefore, Sc65, like its related family member Crtap, is an important modulator of bone homeostasis, acting as a negative regulator of osteoclastogenesis. © 2014 American Society for Bone and Mineral Research

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