Laboratory of Physiological Chemistry, Hiroshima International University, 5-1-1 Hirokoshingai, Kure, Hiroshima, 737-0112, Japan.
Laboratory of Clinicopathological Therapeutics, Hiroshima International University, Kure, Japan.
Int J Hematol. 2011 Jul;94(1):54-62. doi: 10.1007/s12185-011-0880-1. Epub 2011 Jun 10.
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.
Shwachman-Diamond 综合征（SDS）是一种常染色体隐性遗传疾病，其特征为外分泌胰腺功能不全和骨髓衰竭。大多数 SDS 患者的 SBDS 基因突变。最近的研究表明，SBDS 参与核糖体生物发生，并定位于核仁。SBDS 的细胞定位意义尚不清楚，特别是因为 SBDS 不表现出典型的核定位信号。在这项研究中，我们构建了 SBDS 基因关键结构域的野生型缺失突变体和与疾病相关的突变体。这些构建体在 HeLa 细胞中表达，以探索正常和突变蛋白的亚细胞分布。野生型 SBDS 检测到在核内。然而，缺失 N 端结构域 I 的构建体和两种与疾病相关的突变体（C31W 和 N34I）未能将 SBDS 定位到核内。此外，突变 SBDS 蛋白的量减少。当 N 端结构域 I 在 HeLa 细胞中过表达时，内源性 SBDS 蛋白的定位从核转移到胞质部分。这些数据表明，N 端结构域 I 负责核定位。此外，一些与疾病相关的突变体中 SBDS 的低表达可能与 SDS 的发病机制有关。
