FUNCTIONAL ANALYSIS OF SMALL GTP-BINDING PROTEIN, RAB6, BY GENE TRANSFER

点击翻译按钮获取中文摘要

9. SUMMARY OF RESEARCH RESULTSThe Golgi complex is an exceptionally dynamic organelle whose structure is maintained by a balance of vesicles entering and exiting the organelle as well as a balance between anterograde and retrograde membrane traffic within the organelle. A small GTP-binding protein, rab6p, appeared to be involved in the intra-Golgi vesicular transport. We have examined the potential roles of rab6p in maintaining the structural integrity of the Golgi complex. Wild-type rab6, rab6 Q72L (a GTPase-deficient mutant), and rab6 N126I (a mutant with low affinity for both GTP and GDP) were expressed in NRK cells by transfection-mediated gene transfer, and the effects of these proteins on the structural integrity of the Golgi complex were monitored by confocal laser scanning microscopy using mannosidase II (Man II) as a Golgi marker. Expression of wild-type rab6 N126I did not bring about remarkable change of Man II immunostaining pattern, while expression of rab6 Q72L was found to induce disassembly of the Golgi complex into the fragmented elements. Electron microscopy revealed that expression of rab6 Q72L not only promoted swelling or vacuolation of the Golgi cisternae but also caused dilation of the rough endoplasmic reticulum, suggesting that the normal function of rab6p in control of vesicular traffic is essential for maintaining the normal structure of both the Golgi cisternae and the rough endoplasmic reticulum. We also provided morphological evidence that swelling of the Golgi cisternae predominantly occurred at the trans pole of the organelle, which might trigger vacuolation of the Golgi cisternae and subsequent collapse of the organelle. Our findings suggest that rab6 Q72L might disturb the anterograde vesicular traffic from the medial to the trans Golgi cisternae that is regulated by endogenous rab6p, by which the normal morphology of the Golgi complex is disrupted.