Rab18 and Rab43 have key roles in ER-Golgi trafficking

Abstract

Rabs and Arfs/Arls are Ras-related small GTPases of particular relevance to membrane trafficking. It is thought that these proteins regulate specific pathways through interactions with coat, motor, tether and SNARE proteins. We screened a comprehensive list of Arf/Arl/Rab proteins, previously identified on purified Golgi membranes by a proteomics approach (37 in total), for Golgi or intra-Golgi localization, dominant-negative and overexpression phenotypes. Further analysis of two of these proteins, Rab18 and Rab43, strongly indicated roles in ER-Golgi trafficking. Rab43-T32N redistributed Golgi elements to ER exit sites without blocking trafficking of the secretory marker VSVG-GFP from ER to cell surface. Wild-type Rab43 redistributes the p150Glued subunit of dynactin, consistent with a specific role in regulating association of pre-Golgi intermediates with microtubules. Overexpression of wild-type GFP-Rab18 or incubation with any of three siRNAs directed against Rab18 severely disrupts the Golgi complex and reduces secretion of VSVG. Rab18 mutants specifically enhance retrograde Golgi-ER transport of the COPI-independent cargo β-1,4-galactosyltransferase (Galtase)-YFP but not the COPI-dependent cargo p58-YFP from the Golgi to ER in a photobleach assay. Rab18-S22N also potentiated brefeldin-A-induced ER-Golgi fusion. This study is the first comprehensive application of large-scale proteomics to the cell biology of small GTPases of the secretory pathway.

Rab18 Facilitates Dengue Virus Infection by Targeting Fatty Acid Synthase to Sites of Viral Replication

“…1C), as previously reported (15,17). Similar to the previous studies (14,18), some colocalization of mCherry-Rab18-WT and -Q67L (but barely for mCherry-Rab18 -S22N) with the ER and Golgi apparatus, but not with mitochondria, was noted (data not shown).…”

“…Besides localizing on LDs, Rab18 also localizes to the Golgi complex, ER, cytosol, and secretory granules of various cell types. Rab18 has other functions, such as inhibition of secretory activity by impairing secretory granule transport (17) and by disrupting ER-Golgi apparatus trafficking (18). Thus, Rab18 is a small GTPase located on cellular organelles known to participate in the DENV life cycle; however, its role in DENV infection has not been illustrated.…”

Membrane Phospholipid Asymmetry Counters the Adverse Effects of Sterol Overloading in the Golgi Membrane of Drosophila

“…Overexpression of constitutively active Rab18 resulted in strong suppression of the Osbp-overexpressing unexpanded wing phenotype (Table 1). Because it has been postulated that Rab18 is involved in ER-Golgi trafficking, and disturbing Rab18 activity affects the secretion of the secretory marker VSVG-GFP from the Golgi apparatus (Dejgaard et al 2008), our results indicate that constitute active Rab18 may suppress the Golgi bursicon secretion defect in Osbp overexpression by modulating trafficking in the Golgi apparatus. In addition, expressing constitutively active versions of six other Rabs (Rab10, Rab11, Rab26, Rab35, Rab40, and RabX2) resulted in weak suppression (Table 1).…”

A high-content screening microscopy approach to dissect the role of Rab proteins in Golgi-to-ER retrograde trafficking

“…These studies have long suggested that the primary function of Rab2 is in COPImediated Golgi-to-ER transport, and our functional experiments now add strong support to this. Other studies have also suggested roles for Rab33b (Starr et al, 2010;Valsdottir et al, 2001), Rab18, Rab43 (Dejgaard et al, 2008) and Rab30 (Kelly et al, 2012) at the ER-Golgi interface. Of these Rab proteins, our screen only confirmed a role for Rab33b in Golgi-to-ER traffic, suggesting that these other candidates play roles outside of this specific trafficking event, for example in anterograde traffic or organelle morphology maintenance (Sandoval and Simmen, 2012).…”