Adra C N, Manor D, Ko J L, Zhu S, Horiuchi T, Van Aelst L, Cerione R A, Lim B
Harvard Institutes of Medicine, HIM955, Beth Israel Hospital, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Proc Natl Acad Sci U S A. 1997 Apr 29;94(9):4279-84. doi: 10.1073/pnas.94.9.4279.
GDP-dissociation inhibitors (GDIs) play a primary role in modulating the activation of GTPases and may also be critical for the cellular compartmentalization of GTPases. RhoGDI and GDI/D4 are two currently known GDIs for the Rho-subfamily of GTPases. Using their cDNAs to screen a human brain cDNA library under low stringency, we have cloned a homologous cDNA preferentially expressed at high levels in brain and pancreas. The predicted protein, named RhoGDIgamma, is approximately 50% identical to GDI/D4 and RhoGDI. It binds to CDC42 and RhoA with less affinity compared with RhoGDI and does not bind with Rac1, Rac2, or Ras. RhoGDIgamma functions as a GDI for CDC42 but with approximately 20 times less efficiency than RhoGDI. Immunohistochemical studies showed a diffuse punctate distribution of the protein in the cytoplasm with concentration around the nucleus in cytoplasmic vesicles. Overexpression of the protein in baby hamster kidney cells caused the cells to round up with loss of stress fibers. A distinct hydrophobic amino terminus in RhoGDIgamma, not seen in the other two RhoGDIs, could provide a mechanism for localization of the GDI to specific membranous compartment thus determining function distinct from RhoGDI or GDI/D4. Our results provide evidence that there is a family of GDIs for the Rho-related GTPases and that they differ in binding affinity, target specificity, and tissue expression. We propose that RhoGDI be renamed RhoGDIalpha and GDID4 be renamed RhoGDIbeta. The new GDI should widen the scope of investigation of this important class of regulatory protein.
GDP解离抑制剂（GDI）在调节GTP酶的激活过程中起主要作用，并且可能对GTP酶在细胞内的区室化也至关重要。RhoGDI和GDI/D4是目前已知的Rho亚家族GTP酶的两种GDI。利用它们的cDNA在低严谨度条件下筛选人脑cDNA文库，我们克隆了一个在脑和胰腺中高水平优先表达的同源cDNA。预测的蛋白质命名为RhoGDIγ，与GDI/D4和RhoGDI约有50%的同源性。与RhoGDI相比，它与CDC42和RhoA的结合亲和力较低，并且不与Rac1、Rac2或Ras结合。RhoGDIγ作为CDC42的GDI发挥作用，但其效率比RhoGDI低约20倍。免疫组织化学研究显示该蛋白在细胞质中呈弥漫性点状分布，在细胞核周围的细胞质小泡中浓度较高。该蛋白在幼仓鼠肾细胞中的过表达导致细胞变圆且应力纤维消失。RhoGDIγ中一个在其他两种RhoGDI中未见的独特疏水氨基末端，可能为GDI定位于特定膜区室提供一种机制，从而决定其与RhoGDI或GDI/D4不同的功能。我们的结果提供了证据，表明存在一个Rho相关GTP酶的GDI家族，它们在结合亲和力、靶标特异性和组织表达方面存在差异。我们建议将RhoGDI重新命名为RhoGDIα，将GDID4重新命名为RhoGDIβ。这种新的GDI应拓宽对这一重要调节蛋白类别的研究范围。
