Mesa Rosana, Magadán Javier, Barbieri Alejandro, López Cecilia, Stahl Philip D, Mayorga Luis S
Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología (IHEM-CONICET), Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina.
Exp Cell Res. 2005 Apr 1;304(2):339-53. doi: 10.1016/j.yexcr.2004.11.017. Epub 2004 Dec 16.
The transport and sorting of soluble and membrane-associated macromolecules arriving at endosomal compartments require a complex set of Rab proteins. Rab22a has been localized to the endocytic compartment; however, very little is known about the function of Rab22a and inconsistent results have been reported in studies performed in different cell lines. To characterize the function of Rab22a in endocytic transport, the wild-type protein (Rab22a WT), a hydrolysis-deficient mutant (Rab22a Q64L), and a mutant with reduced affinity for GTP (Rab22a S19N) were expressed in CHO cells. None of the three Rab22a constructs affected the transport of rhodamine-dextran to lysosomes, the digestion of internalized proteins, or the lysosomal localization of cathepsin D. In contrast with the mild effect of Rab22a on the endosome-lysosome route, cells expressing Rab22a WT and Rab22a Q64L presented a strong delay in the retrograde transport of cholera toxin from endosomes to the Golgi apparatus. Moreover, these cells accumulated the cation independent mannose 6-phosphate receptor in endosomes. These observations indicate that Rab22a can affect the trafficking from endosomes to the Golgi apparatus probably by promoting fusion among endosomes and impairing the proper segregation of membrane domains required for targeting to the trans-Golgi network (TGN).
到达内体区室的可溶性和膜相关大分子的运输和分选需要一组复杂的Rab蛋白。Rab22a已被定位到内吞区室；然而，关于Rab22a的功能知之甚少，并且在不同细胞系中进行的研究报告了不一致的结果。为了表征Rab22a在内吞运输中的功能，在CHO细胞中表达了野生型蛋白（Rab22a WT）、水解缺陷型突变体（Rab22a Q64L）和对GTP亲和力降低的突变体（Rab22a S19N）。这三种Rab22a构建体均未影响罗丹明-葡聚糖向溶酶体的运输、内化蛋白的消化或组织蛋白酶D的溶酶体定位。与Rab22a对内体-溶酶体途径的轻微影响相反，表达Rab22a WT和Rab22a Q64L的细胞在霍乱毒素从内体向高尔基体的逆行运输中出现了强烈延迟。此外，这些细胞在内体中积累了阳离子非依赖性甘露糖6-磷酸受体。这些观察结果表明，Rab22a可能通过促进内体之间的融合并损害靶向反式高尔基体网络（TGN）所需的膜结构域的正确分离来影响从内体到高尔基体的运输。
