Cellular Function Of The ADP-ribosylation Factor 6 (Arf6

Arf 6 GTdR调节质膜（PM）和内体区室之间的膜运输，并影响皮质肌动蛋白细胞骨架的动力学。在许多细胞中，该途径是PM蛋白遵循的途径，PM蛋白缺乏网格蛋白定位序列，因此不依赖于网格蛋白被内吞入细胞。通过这种网格蛋白非依赖性途径被内吞的PM蛋白可以再循环回到PM或路由到与“经典”早期内体途径会聚并在溶酶体中降解。在通过这种非网格蛋白途径进入细胞的PM蛋白中，是主要组织相容性复合物I类（MHCI）。将MHCI再循环回PM的管状内体膜与含有Eps 15同源结构域的蛋白质EHD 1相关联，EHD 1在过表达时增强MHCI再循环。组成型活性Arf 6突变体Arf 6 Q67 L的表达将非网格蛋白货物隔离在富含PIP 2的液泡中，并阻断它们向Rab 5/EEA 1内体的运输和降解，但不影响网格蛋白衍生货物的运输。这些观察结果表明，Arf 6的失活、PIP 2的周转和PI 3 P的获得是Arf 6途径产生的内体与Rab 5/EEA 1早期内体系统融合所必需的。我们已经发现，一些脂筏相关蛋白，那些锚定到膜的糖基磷脂酰肌醇（GPI）部分，也进入细胞通过这种网格蛋白的独立机制，并与Rab 5早期内体或MHCI回收回PM收敛。正在开发测定法以在体外重建这些膜运输事件。

The Arf6 GTPase regulates membrane traffic between the plasma membrane (PM) and an endosomal compartment and influences the dynamics of the cortical actin cytoskeleton. In many cells this pathway is the route followed by PM proteins that lack clathrin localization sequences and hence are endocytosed into cells independently of clathrin. PM proteins that are endocytosed via this clathrin-independent pathway can either be recycled back to the PM or routed to convergence with the "classical" early endosomal pathway and on to degradation in lysosomes. Among the PM proteins that enter cells through this non-clathrin pathway is major histocompatibility complex class I (MHCI). The tubular endosomal membranes that recycle MHCI back to the PM have associated with them the Eps15 homology domain-containing protein, EHD1, which enhances MHCI recycling when overexpressed. Expression of constitutively active Arf6 mutant, Arf6Q67L, sequesters non-clathrin cargo in vacuoles that are enriched in PIP2 and blocks their trafficking to Rab5/EEA1 endosomes and degradation but does not affect trafficking of clathrin-derived cargo. These observations suggest that inactivation of Arf6, PIP2 turnover and acquisition of PI3P are required for fusion of endosomes arising from the Arf6 pathway with the Rab5/EEA1 early endosome system. We have found that some lipid raft-associated proteins, those anchored to the membrane by a glycosylphosphatidyl inositol (GPI) moiety, also enter cells via this clathrin-independent mechanism and converge with the Rab5 early endosome or recycle back to the PM with MHCI. Assays are being developed to reconstitute in vitro these membrane trafficking events.