Cellular Function Of The ADP-ribosylation Factor 6

ADP-核糖基化因子 6 的细胞功能

• 批准号: 6966863
• 负责人: Julie G Donaldson
• 金额: --
• 依托单位: NATIONAL HEART, LUNG, AND BLOOD INSTITUTE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6966863
• 关键词: ADP ribosylation; actins; binding proteins; cell morphology; cell motility; clathrin; cytoskeleton; endocytosis; glycosylphosphatidylinositols; guanine nucleotide binding protein; guanosinetriphosphatases; intracellular transport; membrane activity; membrane fusion; protein degradation; protein structure function; protein transport; tissue /cell culture; transfection

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 endocytic pathway is the route followed by PM proteins that lack clathrin localization sequences (such as MHCI, the major histocompatibility complex class I) and hence are endocytosed into cells independently of clathrin. After internalization, these membrane vesicles fuse with early endosomes containing clathrin-dependent cargo proteins. From here, proteins such as MHCI can either be trafficked on to late endosomes and lysosomes for degradation or recycled back to the PM along tubular endosomes that lack clathrin cargo. 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 follow a pathway, either to degradation or recycling, similar to MHCI. We found that endocytosis of these GPI anchored proteins and MHCI is stimulated by active Arf6-GTP, is dependent upon PM cholesterol but is not dependent upon dynamin, a GTPase required for clathrin-dependent endocytosis. During our studies on recycling of MHCI back to the PM, we have uncovered an intricate coordination of Rab GTP-binding proteins in this process. Recycling of transferrin receptor, a typical clathrin-dependent cargo protein that is also recycled, requires the function of Rab11. The recycling of MHCI along distinct tubular structures requires the function of Rab11 and Rab22a. Rab22a is specifically required for the re-segregation of clathrin-independent cargo into these distinct tubular endosomes whereas Rab11 may function at a later step prior to PM fusion. The ability of cells to regulate separately the internalization and recycling of clathrin-dependent vs. clathrin-independent cargo proteins enables cells to differentially regulate these processes. Since this clathrin-independent endosomal system carries important membrane proteins that influence immune function and cell adhesion, such as MHCI and integrins, understanding how this pathway is regulated may be critical in disease states such as pathogen invasion and tumor cell metastasis.

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，这种内吞途径是PM蛋白遵循的途径，所述PM蛋白缺乏网格蛋白定位序列（例如MHCI，主要组织相容性复合物I类），因此不依赖于网格蛋白而被内吞到细胞中。在内化后，这些膜囊泡与含有网格蛋白依赖性货物蛋白的早期内体融合。从这里，蛋白质如MHCI可以被运输到晚期内体和溶酶体上进行降解，或者沿着沿着缺乏网格蛋白货物的管状内体再循环回到PM。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，并遵循一个途径，无论是降解或回收，类似于MHCI。我们发现这些GPI锚定蛋白和MHCI的内吞作用由活性Arf 6-GTP刺激，依赖于PM胆固醇，但不依赖于发动蛋白，发动蛋白是网格蛋白依赖性内吞作用所需的一种GTP酶。在我们对MHCI再循环回PM的研究中，我们发现了Rab GTP结合蛋白在此过程中的复杂协调。转铁蛋白受体是一种典型的网格蛋白依赖性货物蛋白，也是一种再循环蛋白，其再循环需要Rab 11的功能。MHCI沿着不同的管状结构再循环需要Rab 11和Rab 22 a的功能。Rab 22 a是将不依赖网格蛋白的货物重新分离到这些不同的管状内体中所特别需要的，而Rab 11可能在PM融合之前的稍后步骤中起作用。细胞分别调节网格蛋白依赖性与网格蛋白非依赖性货物蛋白的内化和再循环的能力使细胞能够差异地调节这些过程。由于这种不依赖网格蛋白的内体系统携带影响免疫功能和细胞粘附的重要膜蛋白，如MHCI和整合素，因此了解该途径如何调节可能对疾病状态如病原体入侵和肿瘤细胞转移至关重要。