Yang C, Slepnev V I, Goud B
Unité de Génétique Somatique (URA CNRS 361), Institut Pasteur, Paris, France.
J Biol Chem. 1994 Dec 16;269(50):31891-9.
GTPases of the Rab family play a key role in the regulation of vesicular transport in eukaryotic cells. Several accessory proteins that regulate their GDP/GTP cycle as well as their subcellular localization have been identified within the past few years. The best known is Rab3A GDP dissociation inhibitor protein (GDI), originally identified as an inhibitor of GDP dissociation from Rab3A, a Rab protein specifically expressed in neuronal and neuroendocrine cells. Recent studies have pointed out a role of Rab3A GDI as a chaperone of several Rab proteins during their cycling between cytosol and membranes and Rab3A GDI has been considered so far as a general regulator of Rab function. However, cDNAs encoding potential isoforms of this protein, called GDI beta and GDI-2, have been recently isolated. In this study, we have characterized cytosolic Rab protein complexes in various cell types and tissues using Mono Q chromatography. We show that in rat brain and in insulin-secreting RINm5F cells, the majority of Rab proteins are complexed with Rab3A GDI. In contrast, in Chinese hamster ovary cells, they are mainly complexed to a protein that we have identified as GDI beta. In rat liver cytosol, Rab proteins form complexes with both isoforms. We also show that the proportion of Rab proteins complexed with either isoform depends on the relative abundance of Rab3A GDI and GDI beta in the cytosol. These findings suggest that GDI isoforms are either redundant or could be involved in the fine control of Rab function.
Rab家族的GTP酶在真核细胞的囊泡运输调节中起关键作用。在过去几年中，已经鉴定出几种调节其GDP / GTP循环以及亚细胞定位的辅助蛋白。最著名的是Rab3A GDP解离抑制蛋白（GDI），最初被鉴定为Rab3A（一种在神经元和神经内分泌细胞中特异性表达的Rab蛋白）的GDP解离抑制剂。最近的研究指出，Rab3A GDI在几种Rab蛋白在细胞质和膜之间循环过程中作为伴侣蛋白发挥作用，并且迄今为止Rab3A GDI被认为是Rab功能的一般调节剂。然而，最近已经分离出编码该蛋白潜在异构体（称为GDIβ和GDI-2）的cDNA。在本研究中，我们使用Mono Q色谱法对各种细胞类型和组织中的细胞质Rab蛋白复合物进行了表征。我们表明，在大鼠脑和胰岛素分泌型RINm5F细胞中，大多数Rab蛋白与Rab3A GDI复合。相比之下，在中国仓鼠卵巢细胞中，它们主要与我们鉴定为GDIβ的蛋白复合。在大鼠肝脏细胞质中，Rab蛋白与两种异构体都形成复合物。我们还表明，与任一异构体复合的Rab蛋白比例取决于细胞质中Rab3A GDI和GDIβ的相对丰度。这些发现表明，GDI异构体要么是冗余的，要么可能参与Rab功能的精细控制。
