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Spatial and Functional Aspects of ER-Golgi Rabs and Tethers.

Saraste J - Front Cell Dev Biol (2016)

Bottom Line: Rab1 and Rab2 have numerous effectors or partners that function in membrane tethering, but also have other roles.However, there is considerable evidence for their specific association with the IC, including its recently identified pericentrosomal domain (pcIC), where many of the effectors turn out to be present, thus being able to exert their functions at the pre-Golgi level.The IC localization of these proteins is of particular interest based on the imaging of Rab1 dynamics, indicating that the IC is a stable organelle that bidirectionally communicates with the ER and Golgi, and is functionally linked to the endosomal system via the pcIC.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedicine and Molecular Imaging Center, University of Bergen Bergen, Norway.

ABSTRACT
Two conserved Rab GTPases, Rab1 and Rab2, play important roles in biosynthetic-secretory trafficking between the endoplasmic reticulum (ER) and the Golgi apparatus in mammalian cells. Both are expressed as two isoforms that regulate anterograde transport via the intermediate compartment (IC) to the Golgi, but are also required for transport in the retrograde direction. Moreover, Rab1 has been implicated in the formation of autophagosomes. Rab1 and Rab2 have numerous effectors or partners that function in membrane tethering, but also have other roles. These include the coiled-coil proteins p115, GM130, giantin, golgin-84, and GMAP-210, as well as the multisubunit COG (conserved oligomeric Golgi) and TRAPP (transport protein particle) tethering complexes. TRAPP also acts as the GTP exchange factor (GEF) in the activation of Rab1. According to the traditional view of the IC elements as motile, transient structures, the functions of the Rabs could take place at the two ends of the ER-Golgi itinerary, i.e., at ER exit sites (ERES) and/or cis-Golgi. However, there is considerable evidence for their specific association with the IC, including its recently identified pericentrosomal domain (pcIC), where many of the effectors turn out to be present, thus being able to exert their functions at the pre-Golgi level. The IC localization of these proteins is of particular interest based on the imaging of Rab1 dynamics, indicating that the IC is a stable organelle that bidirectionally communicates with the ER and Golgi, and is functionally linked to the endosomal system via the pcIC.

No MeSH data available.


Confocal microscopic localization of the two Rab1 isoforms and the effectors of Rab1 (p115, GM130) and Rab2 (GM130, GMAP210) that have been suggested to function in membrane tethering in the early secretory pathway. Normal rat kidney (NRK) cells stably expressing GFP-Rab1A (Marie et al., 2009) were stained with antibodies against Rab1B, p115, GM130, or GMAP210. The images show cells in which the pcIC, an extensive tubular network under the nucleus (large arrowheads), has separated from the Golgi ribbon concomitantly with the movement of the centrosome to the cell center. Rab1A and B display similar localizations; that is, in addition to the Golgi ribbon they both associate with the pcIC, as well as with peripheral IC elements in the vicinity of ERES (small arrowheads). It should be noted that Rab1A and the tethering factors display variable overlap in the pcIC, suggesting their association with its different subdomains. Bars: 10 μm.
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Figure 1: Confocal microscopic localization of the two Rab1 isoforms and the effectors of Rab1 (p115, GM130) and Rab2 (GM130, GMAP210) that have been suggested to function in membrane tethering in the early secretory pathway. Normal rat kidney (NRK) cells stably expressing GFP-Rab1A (Marie et al., 2009) were stained with antibodies against Rab1B, p115, GM130, or GMAP210. The images show cells in which the pcIC, an extensive tubular network under the nucleus (large arrowheads), has separated from the Golgi ribbon concomitantly with the movement of the centrosome to the cell center. Rab1A and B display similar localizations; that is, in addition to the Golgi ribbon they both associate with the pcIC, as well as with peripheral IC elements in the vicinity of ERES (small arrowheads). It should be noted that Rab1A and the tethering factors display variable overlap in the pcIC, suggesting their association with its different subdomains. Bars: 10 μm.

Mentions: Fortunately, while the pcIC during interphase is concealed by the Golgi ribbon, it separates from the latter when cells start to move or enter mitosis—i.e., events that involve centrosome motility, resulting in Golgi repositioning or complete disassembly (Bisel et al., 2008; Marie et al., 2012). This separation (see Figure 1) allowed the demonstration of its function as the primary target for the pleiomorphic cargo carriers that originate at peripheral ERES and move to the cell center along MTs (Marie et al., 2009). In addition, the separated pcIC maintains two-way communication with the Golgi apparatus via tubular and vesicular carriers, and operates as a way station in BFA-stimulated tubular transport of Golgi enzymes to the ER (Marie et al., 2009). Thus, bidirectional trafficking via the pcIC may involve both COPI-dependent and -independent mechanisms.


Spatial and Functional Aspects of ER-Golgi Rabs and Tethers.

Saraste J - Front Cell Dev Biol (2016)

Confocal microscopic localization of the two Rab1 isoforms and the effectors of Rab1 (p115, GM130) and Rab2 (GM130, GMAP210) that have been suggested to function in membrane tethering in the early secretory pathway. Normal rat kidney (NRK) cells stably expressing GFP-Rab1A (Marie et al., 2009) were stained with antibodies against Rab1B, p115, GM130, or GMAP210. The images show cells in which the pcIC, an extensive tubular network under the nucleus (large arrowheads), has separated from the Golgi ribbon concomitantly with the movement of the centrosome to the cell center. Rab1A and B display similar localizations; that is, in addition to the Golgi ribbon they both associate with the pcIC, as well as with peripheral IC elements in the vicinity of ERES (small arrowheads). It should be noted that Rab1A and the tethering factors display variable overlap in the pcIC, suggesting their association with its different subdomains. Bars: 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834429&req=5

Figure 1: Confocal microscopic localization of the two Rab1 isoforms and the effectors of Rab1 (p115, GM130) and Rab2 (GM130, GMAP210) that have been suggested to function in membrane tethering in the early secretory pathway. Normal rat kidney (NRK) cells stably expressing GFP-Rab1A (Marie et al., 2009) were stained with antibodies against Rab1B, p115, GM130, or GMAP210. The images show cells in which the pcIC, an extensive tubular network under the nucleus (large arrowheads), has separated from the Golgi ribbon concomitantly with the movement of the centrosome to the cell center. Rab1A and B display similar localizations; that is, in addition to the Golgi ribbon they both associate with the pcIC, as well as with peripheral IC elements in the vicinity of ERES (small arrowheads). It should be noted that Rab1A and the tethering factors display variable overlap in the pcIC, suggesting their association with its different subdomains. Bars: 10 μm.
Mentions: Fortunately, while the pcIC during interphase is concealed by the Golgi ribbon, it separates from the latter when cells start to move or enter mitosis—i.e., events that involve centrosome motility, resulting in Golgi repositioning or complete disassembly (Bisel et al., 2008; Marie et al., 2012). This separation (see Figure 1) allowed the demonstration of its function as the primary target for the pleiomorphic cargo carriers that originate at peripheral ERES and move to the cell center along MTs (Marie et al., 2009). In addition, the separated pcIC maintains two-way communication with the Golgi apparatus via tubular and vesicular carriers, and operates as a way station in BFA-stimulated tubular transport of Golgi enzymes to the ER (Marie et al., 2009). Thus, bidirectional trafficking via the pcIC may involve both COPI-dependent and -independent mechanisms.

Bottom Line: Rab1 and Rab2 have numerous effectors or partners that function in membrane tethering, but also have other roles.However, there is considerable evidence for their specific association with the IC, including its recently identified pericentrosomal domain (pcIC), where many of the effectors turn out to be present, thus being able to exert their functions at the pre-Golgi level.The IC localization of these proteins is of particular interest based on the imaging of Rab1 dynamics, indicating that the IC is a stable organelle that bidirectionally communicates with the ER and Golgi, and is functionally linked to the endosomal system via the pcIC.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedicine and Molecular Imaging Center, University of Bergen Bergen, Norway.

ABSTRACT
Two conserved Rab GTPases, Rab1 and Rab2, play important roles in biosynthetic-secretory trafficking between the endoplasmic reticulum (ER) and the Golgi apparatus in mammalian cells. Both are expressed as two isoforms that regulate anterograde transport via the intermediate compartment (IC) to the Golgi, but are also required for transport in the retrograde direction. Moreover, Rab1 has been implicated in the formation of autophagosomes. Rab1 and Rab2 have numerous effectors or partners that function in membrane tethering, but also have other roles. These include the coiled-coil proteins p115, GM130, giantin, golgin-84, and GMAP-210, as well as the multisubunit COG (conserved oligomeric Golgi) and TRAPP (transport protein particle) tethering complexes. TRAPP also acts as the GTP exchange factor (GEF) in the activation of Rab1. According to the traditional view of the IC elements as motile, transient structures, the functions of the Rabs could take place at the two ends of the ER-Golgi itinerary, i.e., at ER exit sites (ERES) and/or cis-Golgi. However, there is considerable evidence for their specific association with the IC, including its recently identified pericentrosomal domain (pcIC), where many of the effectors turn out to be present, thus being able to exert their functions at the pre-Golgi level. The IC localization of these proteins is of particular interest based on the imaging of Rab1 dynamics, indicating that the IC is a stable organelle that bidirectionally communicates with the ER and Golgi, and is functionally linked to the endosomal system via the pcIC.

No MeSH data available.