Guanine nucleotide dissociation inhibitor is essential for Rab1 function in budding from the endoplasmic reticulum and transport through the Golgi stack.

Feng

et al. 1998

MBoC

352

293

The rab11 GTPase has been localized to both the Golgi and recycling endosomes; however, its Golgi-associated function has remained obscure. In this study, rab11 function in exocytic transport was analyzed by using two independent means to perturb its activity. First, expression of the dominant interfering rab11S25N mutant protein led to a significant inhibition of the cell surface transport of vesicular stomatitis virus (VSV) G protein and caused VSV G protein to accumulate in the Golgi. On the other hand, the expression of wild-type rab11 or the activating rab11Q70L mutant had no adverse effect on VSV G transport. Next, the membrane association of rab11, which is crucial for its function, was perturbed by modest increases in GDP dissociation inhibitor (GDI) levels. This led to selective inhibition of the trans-Golgi network to cell surface delivery, whereas endoplasmic reticulum–to–Golgi and intra-Golgi transport were largely unaffected. The transport inhibition was reversed specifically by coexpression of wild-type rab11 with GDI. Under the same conditions two other exocytic rab proteins, rab2 and rab8, remained membrane bound, and the transport steps regulated by these rab proteins were unaffected. Neither mutant rab11S25N nor GDI overexpression had any impact on the cell surface delivery of influenza hemagglutinin. These data show that functional rab11 is critical for the export of a basolateral marker but not an apical marker from the trans-Golgi network and pinpoint rab11 as a sensitive target for inhibition by excess GDI.

Section: Rab11 As a Select Target Of Gdi In Vivocontrasting

confidence: 36%

Section: Rab11 Is Selectively Released From Membranes By Overexpressementioning

confidence: 99%

Rab11 Is Required for Trans-Golgi Network–to–Plasma Membrane Transport and a Preferential Target for GDP Dissociation Inhibitor

Feng

et al. 1998

MBoC

352

293

Journal of Biological Chemistry

“…Previous studies have established that the Rab1 GTPase functions as a molecular switch in the ER 3 Golgi transport pathway (89,90). Introduction of the amino acid substitution, N121I, into Rab1B drastically reduces its affinity for GTP and renders the protein a dominant suppressor of protein trafficking between the ER and Golgi compartments (58,91).…”

Section: Retention Of C99 In the Er Affects The Biogenesis Of Both A␤mentioning

confidence: 99%

Retention of the Alzheimer's Amyloid Precursor Fragment C99 in the Endoplasmic Reticulum Prevents Formation of Amyloid β-Peptide

Maltese

Wilson

Tan³

et al. 2001

␥-Secretase is a membrane-associated endoprotease that catalyzes the final step in the processing of Alzheimer's ␤-amyloid precursor protein (APP), resulting in the release of amyloid ␤-peptide (A␤). The molecular identity of ␥-secretase remains in question, although recent studies have implicated the presenilins, which are membrane-spanning proteins localized predominantly in the endoplasmic reticulum (ER). Based on these observations, we have tested the hypothesis that ␥-secretase cleavage of the membrane-anchored C-terminal stump of APP (i.e. C99) occurs in the ER compartment. When recombinant C99 was expressed in 293 cells, it was localized mainly in the Golgi apparatus and gave rise to abundant amounts of A␤. Co-expression of C99 with mutant forms of presenilin-1 (PS1) found in familial Alzheimer's disease resulted in a characteristic elevation of the A␤ 42 /A␤ 40 ratio, indicating that the N-terminal exodomain of APP is not required for mutant PS1 to influence the site of ␥-secretase cleavage. Biogenesis of both A␤ 40 and A␤ 42 was almost completely eliminated when C99 was prevented from leaving the ER by addition of a di-lysine retention motif (KKQN) or by co-expression with a dominant-negative mutant of the Rab1B GTPase. These findings indicate that the ER is not a major intracellular site for ␥-secretase cleavage of C99. Thus, by inference, PS1 localized in this compartment does not appear to be active as ␥-secretase. The results suggest that presenilins may acquire the characteristics of ␥-secretase after leaving the ER, possibly by assembling with other proteins in peripheral membranes.Amyloid ␤-peptide (A␤) 1 is the major molecular component of the cerebral amyloid plaques associated with Alzheimer's disease. The cellular pathways involved in the biogenesis of A␤ have been the subject of intense investigation since the discovery that A␤ originates from intracellular endoproteolytic processing of a type I membrane-spanning glycoprotein termed amyloid precursor protein (APP) (1-4). Extensive studies have established that APP can be processed via two alternative routes, one of which yields the 4-kDa A␤, whereas the other yields a truncated non-amyloidogenic peptide (p3) (5, 6). In most cells the non-amyloidogenic pathway predominates. The first step involves the cleavage of APP within the A␤ domain by a protease termed ␣-secretase (7-9). After release of the Nterminal exodomain, the residual 83-amino acid membranespanning C-terminal fragment is further processed by another protease termed ␥-secretase to remove the cytoplasmic tail and generate p3 (6, 10). Because the latter cleavage occurs within the predicted membrane spanning region of APP (11-13), ␥-secretase is generally thought to be an intramembrane protease. In the alternative amyloidogenic pathway, APP is initially cleaved proximal to the A␤ sequence by ␤-secretase, leaving a 99-amino acid C-terminal fragment (C99) that contains the intact A␤ sequence and the cytoplasmic tail (1,14,15). Thus, when ␥-secretase cuts the latter substrate, A␤ is rel...

“…These results are in agreement with the previous in vitro transport assays. These studies have shown that membrane transport between the ER and Golgi [32] and intra-Golgi transport [33] are inhibited with NEM.…”

Section: Reconstitution Of P62 Cleavage In Slo-permeabilized Cellsmentioning

confidence: 99%

“…Since Rab-GDI binds to and inactivates several di¡erent Rabs, it acts as a general regulator [31]. Rab-GDI has been reported to inhibit intracellular vesicle tra¤cking in several systems, for instance between the ER and Golgi [32], inter-cisternal Golgi transport [33], and basolateral transport of MDCK cells [34]. In our reconstituted system, the addition of 5 WM recombinant Rab-GDI with the cytosol to SLO-permeabilized cells caused 50% reduction in the cleavage of p62 (Fig.…”

Section: Reconstitution Of P62 Cleavage In Slo-permeabilized Cellsmentioning

confidence: 99%

Inhibition of the membrane fusion machinery prevents exit from the TGN and proteolytic processing by furin

Band¹,

Määttä²,

Kääriäinen³

et al. 2001

FEBS Letters