title: Mislocalization or low expression of mutated Shwachman-Bodian-Diamond syndrome protein.
abstract: Shwachman-Diamond syndrome (SDS) is an autosomal-recessive disorder characterized by exocrine pancreatic insufficiency and bone marrow failure. Mutations in the SBDS gene are identified in most patients with SDS. Recent studies have shown that SBDS is involved in ribosome biogenesis and is localized to the nucleolus. The significance of cellular localization in SBDS is unknown, particularly as SBDS does not exhibit canonical nuclear localization signals. In this study, we have constructed wild-type deletion mutants of the critical domains and disease-associated mutants of the SBDS gene. These constructs were expressed in HeLa cells to explore the subcellular distribution of normal and mutant proteins. Wild-type SBDS was detected in the nucleus. However, constructs lacking N-terminal Domain I and two disease-associated mutants (C31W and N34I) failed to localize SBDS to the nucleus. Moreover, the amount of mutated SBDS protein was decreased. When N-terminal Domain I was overexpressed in HeLa cells, the localization of endogenous SBDS protein was changed from nuclei to cytosolic fraction. These data indicate that the N-terminal Domain I is responsible for nuclear localization. Furthermore, low expression of SBDS, as exhibited in some of the disease-associated mutants, may be associated with the pathogenesis of SDS.
authors.affiliation: Laboratory of Physiological Chemistry, Hiroshima International University, 5-1-1 Hirokoshingai, Kure, Hiroshima, 737-0112, Japan. m-yamagu@ps.hirokoku-u.ac.jp.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Laboratory of Clinicopathological Therapeutics, Hiroshima International University, Kure, Japan.
authors.forename: Kingo
authors.initials: K
authors.lastname: Fujimura
authors.affiliation: Department of Pediatrics, Graduate School of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kanegane
authors.affiliation: Laboratory of Physiological Chemistry, Hiroshima International University, 5-1-1 Hirokoshingai, Kure, Hiroshima, 737-0112, Japan.
authors.forename: Hanae
authors.initials: H
authors.lastname: Toga-Yamaguchi
authors.affiliation: Celgene Corporation, Summit, NJ, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Chopra
authors.affiliation: Laboratory of Physiological Chemistry, Hiroshima International University, 5-1-1 Hirokoshingai, Kure, Hiroshima, 737-0112, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Okamura
mesh_terms: D021581:Active Transport, Cell Nucleus; D001855:Bone Marrow Diseases / Q000209:etiology* / Q000235:genetics; D010188:Exocrine Pancreatic Insufficiency / Q000209:etiology* / Q000235:genetics; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D008068:Lipomatosis / Q000209:etiology* / Q000235:genetics; D050505:Mutant Proteins / Q000378:metabolism*; D009687:Nuclear Proteins; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D000081003:Shwachman-Diamond Syndrome
chemical_list: D050505:Mutant Proteins; D009687:Nuclear Proteins; D011506:Proteins; C470521:SBDS protein, human