Rab1 Defines a Novel Pathway Connecting the Pre-Golgi Intermediate Compartment with the Cell Periphery

Abstract

The function of the pre-Golgi intermediate compartment (IC) and its relationship with the endoplasmic reticulum (ER) and Golgi remain only partially understood. Here, we report striking segregation of IC domains in polarized PC12 cells that develop neurite-like processes. Differentiation involves expansion of the IC and movement of Rab1-containing tubules to the growth cones of the neurites, whereas p58- and COPI-positive IC elements, like rough ER and Golgi, remain in the cell body. Exclusion of Rab1 effectors p115 and GM130 from the neurites further indicated that the centrifugal, Rab1-mediated pathway has functions that are not directly related to ER-to-Golgi trafficking. Disassembly of COPI coats did not affect this pathway but resulted in missorting of p58 to the neurites. Live cell imaging showed that green fluorescent protein (GFP)-Rab1A-containing IC elements move bidirectionally both within the neurites and cell bodies, interconnecting different ER exit sites and the cis-Golgi region. Moreover, in nonpolarized cells GFP-Rab1A-positive tubules moved centrifugally towards the cell cortex. Hydroxymethylglutaryl-CoA reductase, the key enzyme of cholesterol biosynthesis, colocalized with slowly sedimenting, Rab1-enriched membranes when the IC subdomains were separated by velocity sedimentation. These results reveal a novel pathway directly connecting the IC with the cell periphery and suggest that this Rab1-mediated pathway is linked to the dynamics of smooth ER.

Endocytosis of Secreted Carboxyl Ester Lipase in a Syndrome of Diabetes and Pancreatic Exocrine Dysfunction

“…Monoclonal antibody detecting ERGIC-53/p58 (clone G1/93) was from Enzo Life Sciences, and monoclonal antibody directed against GM130 (610822) was from BD Transduction Laboratories. Rabbit antiserum against Rab1A was affinitypurified as described earlier (28). MG132 was obtained from Biomol.…”

“…This pool of CEL-MUT could correspond to the smallest vacuolar structures (VAC3; Fig. 2C), which resemble pleomorphic IC elements in their morphology and sedimentation behavior (28,33). The immature, low molecular weight forms of both CEL variants co-distributed with a minor pool of p58 in the fast-sedimenting ER factions (fractions 6 -9).…”

Targeting of the 5-HT1ASerotonin Receptor to Neuronal Dendrites Is Mediated by Yif1B

“…Such an idea is supported by differences in IC protein composition observed between soma and neurites of differentiated PC12 cells. Indeed, Rab1, P58, and COPI IC proteins mainly colocalize in the ER exit sites (ERESs) at the soma, whereas only Rab1 is present in dynamic vesicular-tubular structures at the neurites, suggesting the existence of neurite-specific ERESs (Sannerud et al, 2006).…”

The Role of Glycans in Apical Sorting of Proteins in Polarized Epithelial Cells

“…In mammalian cells, the intermediate compartment (IC), consisting of vacuolar and tubular membrane domains and functionally positioned between the ER and the Golgi apparatus, is also stably localized in a perinuclear position at the cell center, close to the Golgi cisternae. Although the trans region of the Golgi apparatus has been regarded as the primary sorting area for proteins and lipids in the secretory pathway, the IC has been suggested as a protein and lipid sorting station operating prior to entry into the Golgi apparatus (47)(48)(49). In fact, lateral segregation of proteins in the secretory pathway can occur already in the ER (50-53, 3, 18).…”