Rab1 Interaction with a GM130 Effector Complex Regulates COPII Vesicle cis ‐Golgi Tethering

174

156

The mechanism(s) of cystic fibrosis transmembrane conductance regulator (CFTR) trafficking from the endoplasmic reticulum (ER) through the Golgi apparatus, the step impaired in individuals afflicted with the prevalent CFTR-⌬F508 mutation leading to cystic fibrosis, is largely unknown. Recent morphological observations suggested that CFTR is largely absent from the Golgi in situ (Bannykh, S. I., Bannykh, G. I., Fish, K. N., Moyer, B. D., Riordan, J. R., and Balch, W. E. (2000) Traffic 1, 852-870), raising the possibility of a novel trafficking pathway through the early secretory pathway. We now report that export of CFTR from the ER is regulated by the conventional coat protein complex II (COPII) in all cell types tested. Remarkably, in a cell type-specific manner, processing of CFTR from the core-glycosylated (band B) ER form to the complex-glycosylated (band C) isoform followed a non-conventional pathway that was insensitive to dominant negative Arf1, Rab1a/Rab2 GTPases, or the SNAp REceptor (SNARE) component syntaxin 5, all of which block the conventional trafficking pathway from the ER to the Golgi. Moreover, CFTR transport through the non-conventional pathway was potently blocked by overexpression of the late endosomal target-SNARE syntaxin 13, suggesting that recycling through a late Golgi/endosomal system was a prerequisite for CFTR maturation. We conclude that CFTR transport in the early secretory pathway can involve a novel pathway between the ER and late Golgi/endosomal compartments that may influence developmental expression of CFTR on the cell surface in polarized epithelial cells.

Section: Fig 1 Cftr Processing Is Blocked By Dominant Negative Sar1mentioning

confidence: 99%

“…CFTR Maturation Is Independent of Syn5 Function-Rab GTPases control the assembly of the targeting/fusion machinery involved in ER to Golgi transport (37,48,49). This machinery includes members of the syntaxin family of SNARE proteins (50,51).…”

Section: Fig 1 Cftr Processing Is Blocked By Dominant Negative Sar1mentioning

confidence: 99%

Non-conventional Trafficking of the Cystic Fibrosis Transmembrane Conductance Regulator through the Early Secretory Pathway

Yoo¹,

Moyer²,

Bannykh³

et al. 2002

174

156

“…During mitosis, phosphorylation of GM130 is crucial for proper disassembly of the Golgi (19). GM130 also binds to the vesicle docking protein, p115, and to Rab1, a GTPase required for endoplasmic reticulum-to-Golgi transport (20,21). In addition, giantin binds p115 suggesting the presence of a complex that tethers Golgi cisternae containing GM130 to giantin on vesicles via p115 (22).…”

mentioning

confidence: 99%

The NH2-terminal Domain of Golgin-160 Contains Both Golgi and Nuclear Targeting Information

Hicks

Machamer

2002

Golgin-160 is a member of the golgin family of Golgilocalized membrane proteins. The COOH-terminal twothirds of golgin-160 is predicted to form a coiled-coil, with an NH 2 -terminal "head" domain. To identify the Golgi targeting information in golgin-160, full-length and deletion constructs tagged with green fluorescent protein were generated. The head domain alone was targeted to the Golgi complex in the absence of assembly with endogenous golgin-160. Further truncations from both ends of the head domain narrowed the Golgi targeting information to 85 amino acids between residues 172 and 257. Surprisingly, certain truncations of the head domain also specifically accumulated in the nucleus. Both a nuclear localization signal (masked in the full-length protein) and information for nuclear retention contributed to the nuclear localization of these truncations. Because the golgin-160 head is cleaved by caspases during apoptosis, we examined the localization of epitope-tagged proteins corresponding to all potential caspase cleavage fragments. Our data suggest that three of six fragments could be targeted to the nucleus, provided that they are released from Golgi membranes after cleavage. The finding that both Golgi and nuclear targeting information is present in the same region of golgin-160 suggests that this protein may have more than one function.

“…A resolution for these discrepancies might be related to the function of Rab1, which also acts during ER to Golgi and intra-Golgi transport and binds directly to p115 and golgin tethering proteins (41)(42)(43). Rab family GTPases function throughout the exocytic pathway and several family members are implicated in tethering (4,6,7,44).…”

mentioning

confidence: 99%

A Cryptic Rab1-binding Site in the p115 TetheringProtein

Beard

Satoh

Shorter

et al. 2005

103

Small GTPases and coiled-coil proteins of the golgin family help to tether COPI vesicles to Golgi membranes. At the cis-side of the Golgi, the Rab1 GTPase binds directly to each of three coiled-coil proteins: p115, GM130, and as now shown, Giantin. Rab1 binds to a coiled-coil region within the tail domain of p115 and this binding is inhibited by the C-terminal, acidic domain of p115. Furthermore, GM130 and Giantin bind to the acidic domain of p115 and stimulate p115 binding to Rab1, suggesting that p115 binding to Rab1 is regulated. Regulation of this interaction by proteins such as GM130 and Giantin may control the membrane recruitment of p115 by Rab1.