Cormont M, Mari M, Galmiche A, Hofman P, Le Marchand-Brustel Y
Institut National de la Santé et de la Recherche Médicale (INSERM) E9911, 06107 Nice Cedex 02, France.
Proc Natl Acad Sci U S A. 2001 Feb 13;98(4):1637-42. doi: 10.1073/pnas.98.4.1637. Epub 2001 Jan 30.
The small GTPase Rab4 is implicated in endocytosis in all cell types, but also plays a specific role in some regulated processes. To better understand the role of Rab4 in regulation of vesicular trafficking, we searched for an effector(s) that specifically recognizes its GTP-bound form. We cloned a ubiquitous 69-kDa protein, Rabip4, that behaves as a Rab4 effector in the yeast two-hybrid system and in the mammalian cell. Rabip4 contains two coiled-coil domains and a FYVE-finger domain. When expressed in CHO cells, Rabip4 is present in early endosomes, because it is colocated with endogenous Early Endosome Antigen 1, although it is absent from Rab11-positive recycling endosomes and Rab-7 positive late endosomes. The coexpression of Rabip4 with active Rab4, but not with inactive Rab4, leads to an enlargement of early endosomes. It strongly increases the degree of colocalization of markers of sorting (Rab5) and recycling (Rab11) endosomes with Rab4. Furthermore, the expression of Rabip4 leads to the intracellular retention of a recycling molecule, the glucose transporter Glut 1. We propose that Rabip4, an effector of Rab4, controls early endosomal traffic possibly by activating a backward transport step from recycling to sorting endosomes.
小GTP酶Rab4在所有细胞类型的内吞作用中都有涉及，而且在一些调节过程中发挥特定作用。为了更好地理解Rab4在囊泡运输调节中的作用，我们寻找了能特异性识别其GTP结合形式的效应蛋白。我们克隆了一种广泛存在的69 kDa蛋白Rabip4，它在酵母双杂交系统和哺乳动物细胞中表现为Rab4的效应蛋白。Rabip4包含两个卷曲螺旋结构域和一个FYVE结构域。当在CHO细胞中表达时，Rabip4存在于早期内体中，因为它与内源性早期内体抗原1共定位，尽管在Rab11阳性的再循环内体和Rab - 7阳性的晚期内体中不存在。Rabip4与活性Rab4共表达，但不与非活性Rab4共表达，会导致早期内体增大。它强烈增加了分选（Rab5）和再循环（Rab11）内体标记物与Rab4的共定位程度。此外，Rabip4的表达导致再循环分子葡萄糖转运蛋白Glut 1在细胞内滞留。我们提出，Rabip4作为Rab4的效应蛋白，可能通过激活从再循环内体到分选内体的逆向运输步骤来控制早期内体运输过程。
