Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2012 Sep 25;109(39):15787-92. doi: 10.1073/pnas.1204540109. Epub 2012 Sep 10.
Rab4A is a master regulator of receptor recycling from endocytic compartments to the plasma membrane. The protein TBC1D16 is up-regulated in melanoma, and TBC1D16-overexpressing melanoma cells are dependent on TBC1D16. We show here that TBC1D16 enhances the intrinsic rate of GTP hydrolysis by Rab4A. TBC1D16 is both cytosolic and membrane associated; the membrane-associated pool colocalizes with transferrin and EGF receptors (EGFRs) and early endosome antigen 1, but not with LAMP1 protein. Expression of two TBC1D16 isoforms, but not the inactive R494A mutant, reduces transferrin receptor recycling but has no effect on transferrin receptor internalization. Expression of TBC1D16 alters GFP-Rab4A membrane localization. In HeLa cells, overexpression of TBC1D16 enhances EGF-stimulated EGFR degradation, concomitant with decreased EGFR levels and signaling. Thus, TBC1D16 is a GTPase activating protein for Rab4A that regulates transferrin receptor recycling and EGFR trafficking and signaling.
Rab4A 是调节受体从内吞小泡循环到质膜的主控因子。TBC1D16 在黑色素瘤中上调，过表达 TBC1D16 的黑色素瘤细胞依赖 TBC1D16。我们发现 TBC1D16 增强 Rab4A 的固有 GTP 水解速率。TBC1D16 既有胞质部分也有膜结合部分；膜结合部分与转铁蛋白和表皮生长因子受体（EGFR）及早期内体抗原 1 共定位，但与溶酶体相关膜蛋白 1（LAMP1）蛋白不共定位。两种 TBC1D16 异构体的表达（而非无活性的 R494A 突变体），会减少转铁蛋白受体的循环，但对转铁蛋白受体的内化没有影响。TBC1D16 的表达改变 GFP-Rab4A 的膜定位。在 HeLa 细胞中，TBC1D16 的过表达增强了 EGF 刺激的 EGFR 降解，同时 EGFR 水平和信号降低。因此，TBC1D16 是 Rab4A 的 GTP 酶激活蛋白，调节转铁蛋白受体循环和 EGFR 运输及信号。
