Nokes Rita L, Fields Ian C, Collins Ruth N, Fölsch Heike
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208, USA.
J Cell Biol. 2008 Sep 8;182(5):845-53. doi: 10.1083/jcb.200802176.
To maintain polarity, epithelial cells continuously sort transmembrane proteins to the apical or basolateral membrane domains during biosynthetic delivery or after internalization. During biosynthetic delivery, some cargo proteins move from the trans-Golgi network (TGN) into recycling endosomes (RE) before being delivered to the plasma membrane. However, proteins that regulate this transport step remained elusive. In this study, we show that Rab13 partially colocalizes with TGN38 at the TGN and transferrin receptors in RE. Knockdown of Rab13 with short hairpin RNA in human bronchial epithelial cells or overexpression of dominant-active or dominant-negative alleles of Rab13 in Madin-Darby canine kidney cells disrupts TGN38/46 localization at the TGN. Moreover, overexpression of Rab13 mutant alleles inhibits surface arrival of proteins that move through RE during biosynthetic delivery (vesicular stomatitis virus glycoprotein [VSVG], A-VSVG, and LDLR-CT27). Importantly, proteins using a direct route from the TGN to the plasma membrane are not affected. Thus, Rab13 appears to regulate membrane trafficking between TGN and RE.
为维持极性，上皮细胞在生物合成运输过程中或内化后，持续将跨膜蛋白分选至顶端或基底外侧膜结构域。在生物合成运输过程中，一些货物蛋白在被运送至质膜之前，会从反式高尔基体网络（TGN）进入再循环内体（RE）。然而，调控这一运输步骤的蛋白质仍不清楚。在本研究中，我们发现Rab13在TGN处与TGN38部分共定位，并在RE中与转铁蛋白受体共定位。在人支气管上皮细胞中用短发夹RNA敲低Rab13，或在Madin-Darby犬肾细胞中过表达Rab13的显性活性或显性阴性等位基因，会破坏TGN38/46在TGN处的定位。此外，Rab13突变等位基因的过表达会抑制在生物合成运输过程中通过RE的蛋白质到达细胞表面（水泡性口炎病毒糖蛋白[VSVG]、A-VSVG和LDLR-CT27）。重要的是，从TGN直接运输至质膜的蛋白质不受影响。因此，Rab13似乎调控TGN和RE之间的膜运输。
