GTPase activating protein activity for Rab4 is enriched in the plasma membrane of 3T3-L1 adipocytes. Possible involvement in the regulation of Rab4 subcellular localization

被引:16
作者
Bortoluzzi, MN [1 ]
Cormont, M [1 ]
Gautier, N [1 ]
VanObberghen, E [1 ]
LeMarchandBrustel, Y [1 ]
机构
[1] FAC MED NICE,INSERM,U145,NICE,FRANCE
关键词
insulin; small GTPases; GLUT4; translocation; adipocytes;
D O I
10.1007/BF00403908
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
The small guanosine 5'-triphosphate (GTP)ase Rab4 has been suggested to play a role in insulin-induced GLUT4 translocation. Under insulin stimulation, GLUT4 translocates to the plasma membranes, while Rab4 leaves the GLUT4-containing vesicles and becomes cytosolic. Rab proteins cycle between a GTP-bound active form and a guanosine 5'-diphosphate (GDP)-bound inactive form. The intrinsic GTPase activity of Rab proteins is low and the interconversion between the two forms is dependent on accessory factors. In the present work: we searched for a GTPase activating protein (GAP) for Rab4 in 3T3-L1 adipocytes. We used a glutathione-transferase (GST)-Rab4 protein which possesses the properties of a small GTPase (ability to bind GDP and GTP and to hydrolyse GTP) and can be isolated in a rapid and efficient way. This GAP activity was observed in 3T3-L1 adipocyte lysates, and was able to accelerate the hydrolysis of the [alpha-P-32]GTP bound to GST-Rab4 into [alpha-P-32]GDP. This activity, tentatively called Rab4-GAP, was also present in 3T3-L1 fibroblasts. The Rab4-GAP activity was present in total membrane fractions and nearly undetectable in cytosol. Following subcellular fractionation, Rab4-GAP was found to be enriched in plasma membranes when compared to internal microsomes. Insulin treatment of the cells had no effect on the total Rab4-GAP activity or on its subcellular localization. Taking our results together with the accepted model of Rab cycling in intracellular traffic, we propose that Rab4-GAP activity plays a role in the cycling between the GTP- and GDP-bound forms of Rab4, and thus possibly in the traffic of GLUT4-containing vesicles.
引用
收藏
页码:899 / 906
页数:8
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