Distinct Sets of Rab6 Effectors Contribute to ZW10‐ and COG‐Dependent Golgi Homeostasis

Abstract

The organization of the Golgi apparatus is determined in part by the interaction of Rab proteins and their diverse array of effectors. Here, we used multiple approaches to identify and characterize a small subset of effectors that mimicked the effects of Rab6 on Golgi ribbon organization. In a visual-based, candidate-protein screen, we found that the individual depletion of any of three Rab6 effectors, myosin IIA (MyoIIA), Kif20A, and Bicaudal D (BicD), was sufficient to suppress Golgi ribbon fragmentation/dispersal coupled to retrograde tether proteins in a manner paralleling Rab6. MyoIIA and Kif20A depletion were pathway selective and suppressed ZW10-dependent Golgi ribbon fragmentation/dispersal only while BicD depletion, like Rab6, suppressed both ZW10- and COG-dependent Golgi ribbon fragmentation. The MyoIIA effects could be produced in short term assays by the reversible myosin inhibitor, blebbistatin. At the electron microscope level, the effects of BicD-depletion mimicked many of those of Rab6-depletion: longer and more continuous Golgi cisternae and a pronounced accumulation of coated vesicles. Functionally, BicD-depleted cells were inhibited in transport of newly synthesized VSV-G protein to the cell surface. In sum, our results indicate small, partially overlapping subsets of Rab6 effectors are differentially important to two tether-dependent pathways essential to Golgi organization and function.

Cohen Syndrome-associated Protein COH1 Physically and Functionally Interacts with the Small GTPase RAB6 at the Golgi Complex and Directs Neurite Outgrowth

“…These Golgi-associated protein complexes comprise molecules required for docking and/or fusion of transport carriers, protein sorting, and luminal pH homeostasis (33). One such example is the COG complex (34), which is critically important for retrograde vesicle transport within the Golgi and for Golgi homeostasis downstream of RAB6 (35,36). RAB6 preferentially interacts with the COG6 subunit and mutations in COG6 leads to a glycosylation disorder due to altered retrograde membrane transport (37,38).…”

ER trapping reveals Golgi enzymes continually revisit the ER through a recycling pathway that controls Golgi organization

“…This pathway is COPI and Arf1 GTPase-dependent (46). A second pathway is Arf1/COPI-independent and relies on Rab6 GTPase, uses tubules rather than vesicles, and carries Shiga and Shiga-like toxins (29,30,47,48). Our results suggest this pathway is used by Golgi enzymes to return to the ER: Not only were tubule intermediates seen carrying Golgi enzymes into the ER during rapamycin-induced ER trapping but no Golgi enzyme trapping occurred in the presence of a dominant-negative rab6a mutant.…”

Myosin-IIA heavy chain phosphorylation on S1943 regulates tumor metastasis

“…Thus, the increased MMP9 secretion observed in S1943E NMHC-IIA cells suggests a more direct role for S1943 phosphorylation in the transport and/or delivery of MMP vesicles to invadopodia. Myosin-IIA has been identified as a Rab6 effector [52,53], and has been reported to mediate vesicle transport as well as vesicle shedding, including MMP-containing vesicles [54–56]. While myosin-IIA filaments are generally considered the functional cellular form of myosin-IIA, the identification of activated myosin-IIA monomers in cells (i.e.…”