Styers Melanie L, O'Connor Amber K, Grabski Robert, Cormet-Boyaka Estelle, Sztul Elizabeth
Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USa.
Am J Physiol Cell Physiol. 2008 Jun;294(6):C1485-98. doi: 10.1152/ajpcell.00010.2008. Epub 2008 Apr 2.
We have utilized small interfering RNA (siRNA)-mediated depletion of the beta-COP subunit of COP-I to explore COP-I function in organellar compartmentalization and protein traffic. Reduction in beta-COP levels causes the colocalization of markers for the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC), Golgi, trans-Golgi network (TGN), and recycling endosomes in large, globular compartments. The lack of spatial differentiation of these compartments is not due to a general collapse of all cellular organelles since markers for the early endosomes and lysosomes do not redistribute to the common structures. Anterograde trafficking of the transmembrane cargo vesicular stomatitis virus membrane glycoprotein and of a subset of soluble cargoes is arrested within the common globular compartments. Similarly, recycling traffic of transferrin through the common compartment is perturbed. Furthermore, the trafficking of caveolin-1 (Cav1), a structural protein of caveolae, is arrested within the globular structures. Importantly, Cav1 coprecipitates with the gamma-subunit of COP-I, suggesting that Cav1 is a COP-I cargo. Our findings suggest that COP-I is required for the compartmentalization of the ERGIC, Golgi, TGN, and recycling endosomes and that COP-I plays a novel role in the biosynthetic transport of Cav1.
我们利用小干扰RNA（siRNA）介导的COP-I的β-COP亚基缺失来探究COP-I在细胞器区室化和蛋白质运输中的功能。β-COP水平的降低导致内质网（ER）-高尔基体中间区室（ERGIC）、高尔基体、反式高尔基体网络（TGN）和再循环内体的标志物在大的球状区室中共定位。这些区室缺乏空间分化并非由于所有细胞器的普遍崩溃，因为早期内体和溶酶体的标志物不会重新分布到共同结构中。跨膜货物水泡性口炎病毒膜糖蛋白和一部分可溶性货物的顺向运输在共同的球状区室中停滞。同样，转铁蛋白通过共同区室的再循环运输也受到干扰。此外，小窝蛋白-1（Cav1），一种小窝的结构蛋白，其运输在球状结构中停滞。重要的是，Cav1与COP-I的γ-亚基共沉淀，表明Cav1是COP-I的货物。我们的研究结果表明，COP-I是ERGIC、高尔基体、TGN和再循环内体区室化所必需的，并且COP-I在Cav1的生物合成运输中发挥新的作用。
