Electron Tomography Reveals Rab6 Is Essential to the Trafficking of trans-Golgi Clathrin and COPI-Coated Vesicles and the Maintenance of Golgi Cisternal Number

摘要

We have shown previously that Rab6, a small, trans-Golgi-localized GTPase, acts upstream of the COG and ZW10/RINT1 retrograde tether complexes to maintain Golgi homeostasis. Here, we present evidence from the unbiased and high-resolution approach of electron microscopy and electron tomography that Rab6 is essential to the trans-Golgi trafficking of two morphological classes of coated vesicles; the larger corresponds to clathrin-coated vesicles and the smaller to COPI-coated vesicles. Based on the site of coated vesicle accumulation, cisternal dilation, and the normal kinetics of cargo transport from the ER to Golgi followed by delayed Golgi to cell surface transport, we suggest that Golgi function in cargo transport is preferentially inhibited at the trans-Golgi/TGN. The >50% increase in Golgi cisternae number in Rab6-depleted HeLa cells that we observed may well be coupled to the trans-Golgi accumulation of COPI-coated vesicles; depletion of the individual Rab6 effector, myosin IIA, produced an accumulation of uncoated vesicles with if anything a decrease in cisternal number. These results are the first evidence for a Rab6-dependent protein machine affecting Golgi-proximal, coated vesicle accumulation and likely transport at the trans-Golgi and the first example of concomitant cisternal proliferation and increased Golgi stack organization under inhibited transport conditions.