Rab6 Coordinates a Novel Golgi to ER Retrograde Transport Pathway in Live Cells

Abstract

We visualized a fluorescent-protein (FP) fusion to Rab6, a Golgi-associated GTPase, in conjunction with fluorescent secretory pathway markers. FP-Rab6 defined highly dynamic transport carriers (TCs) translocating from the Golgi to the cell periphery. FP-Rab6 TCs specifically accumulated a retrograde cargo, the wild-type Shiga toxin B-fragment (STB), during STB transport from the Golgi to the endoplasmic reticulum (ER). FP-Rab6 TCs associated intimately with the ER, and STB entered the ER via specialized peripheral regions that accumulated FP-Rab6. Microinjection of antibodies that block coatomer protein I (COPI) function inhibited trafficking of a KDEL-receptor FP-fusion, but not FP-Rab6. Additionally, markers of COPI-dependent recycling were excluded from FP-Rab6/STB TCs. Overexpression of Rab6:GDP (T27N mutant) using T7 vaccinia inhibited toxicity of Shiga holotoxin, but did not alter STB transport to the Golgi or Golgi morphology. Taken together, our results indicate Rab6 regulates a novel Golgi to ER transport pathway.

Regulation of anterograde transport of adrenergic and angiotensin II receptors by Rab2 and Rab6 GTPases

“…1C). These data are consistent with the localization and function of Rab2 and Rab6 GTPases in modulating protein transport [36][37][38][39][40][41][42][43], suggesting that the GFP and FLAG epitop tagging did not influence the subcellular localization of Rab2 and Rab6 GTPases.…”

“…Whereas Rab1 GTPase mediates anterograde transport of newly synthesized proteins from the ER to the Golgi, Rab2 and Rab6 GTPases modulate retrograde Golgi-to-ER transport, which is essential for retrieval of ER or Golgi resident proteins to maintain the organelle homeostasis as well as recycling of the components of the transport machinery required for anterograde transport [36][37][38][39][40][41][42][43]. We recently demonstrated that Rab1 GTPase differentially regulates the cell-surface targeting of distinct GPCRs [33][34][35].…”

“…In contrast to Rab2 function in coordinating the ERGIC-to-ER transport, Rab6 may be involved in transport from the late to the early Golgi cisternae or from the Golgi to the ER of proteins such as β-1, 4-galactosyltransferase and protein toxins [41][42][43]. It has also been demonstrated that manipulation of Rab6 function through expressing its GTP-bound, GDP-bound or guanidine nucleotide deficient mutants inhibits transport of the plasma membrane proteins hemagglutinin protein and CFTR in mammalian cells and rhodopsin in Drosophila [42,45,46].…”

“…In contrast, Rab6B is only expressed in neuronal cells. Rab6 is mainly localized to the Golgi and the TGN and are involved in the retrograde transport between Golgi cisternae or from the Golgi to the ER [41][42][43]. In this work, we have determined the role of Rab2 and Rab6 GTPases in the cell-surface targeting and signaling of α 2B -AR, β 2 -AR and AT1R, three representative GPCRs, which couple to different G proteins and initiate distinct signaling pathways.…”

Bacterial protein toxins and lipids: role in toxin targeting and activity

“…In addition, phospholipid composition in the surrounding membrane and interaction of Gb3-bound toxin with surface proteins are probably involved in the location of ST into membrane microdomains and subsequent sorting of endocytosis trafficking (Arab and Lingwood, 1996;Arab et al, 1998;Shimizu et al, 2003). Then, ST retrograde transport from the Golgi to ER uses a COP-Iindependent and Rab6-dependent pathway, the signalling molecules of which remain to be defined White et al, 1999). Interestingly, ricin, a plant toxin related to ST, which binds to glycosphingolipids and glycoproteins containing a terminal galactose, uses a cholesterol-dependent and glycosphingolipid-independent retrograde transport.…”