Expression and compartmentalization of caveolin in adipose cells: coordinate regulation with and structural segregation from GLUT4.

Kandror, Konstantin V.; Stephens, Jacqueline M.; Pilch, Paul F.

doi:10.1083/jcb.129.4.999

Cited by 93 publications

(68 citation statements)

References 57 publications

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“…Biochemical isolation and immunogold electron microscopy of plasma membranes revealed the transient localization of Glut4 immunoreactivity in lipid rafts after insulin stimulation of 3T3L1 adipocytes (Scherer et al, 1994;Gustavsson et al, 1996;Karlsson et al, 2002), although others found no evidence for Glut4 in lipid rafts (Voldstedlund et al, 1993;Kandror et al, 1995). Although this discrepancy might be the result of different methodologies, it seems possible that Glut4 initially docks and fuses at lipid rafts, due to the assembly of the exocyst in this microdomain, and then transits into nonraft domains.…”

Section: Discussionmentioning

confidence: 69%

Compartmentalization of the Exocyst Complex in Lipid Rafts Controls Glut4 Vesicle Tethering

Inoue

Chiang

Chang

et al. 2006

MBoC

108

135

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Lipid raft microdomains act as organizing centers for signal transduction. We report here that the exocyst complex, consisting of Exo70, Sec6, and Sec8, regulates the compartmentalization of Glut4-containing vesicles at lipid raft domains in adipocytes. Exo70 is recruited by the G protein TC10 after activation by insulin and brings with it Sec6 and Sec8. Knockdowns of these proteins block insulin-stimulated glucose uptake. Moreover, their targeting to lipid rafts is required for glucose uptake and Glut4 docking at the plasma membrane. The assembly of this complex also requires the PDZ domain protein SAP97, a member of the MAGUKs family, which binds to Sec8 upon its translocation to the lipid raft. Exocyst assembly at lipid rafts sets up targeting sites for Glut4 vesicles, which transiently associate with these microdomains upon stimulation of cells with insulin. These results suggest that the TC10/exocyst complex/SAP97 axis plays an important role in the tethering of Glut4 vesicles to the plasma membrane in adipocytes. INTRODUCTIONInsulin stimulates glucose transport in fat and muscle cells through a process of regulated vesicle recycling in which the facilitative glucose transporter Glut4 is translocated from intracellular sites to the plasma membrane (Saltiel and Kahn, 2001;Bryant et al., 2002). In unstimulated cells, Glut4 undergoes endocytosis into endosomes and subsequently sorts into specialized storage vesicles that traffic to the plasma membrane after activation of the insulin receptor. The vesicles then dock and fuse at specific sites at the membrane, resulting in extracellular exposure of the transporter. The precise signals from the insulin receptor that control these events involve the tyrosine phosphorylation of a number of intracellular substrates. These phosphorylations lead to activation of the PI3-kinase pathway (Saltiel and Kahn, 2001) and also to activation of the G protein TC10 Maffucci et al., 2003), which in turn binds to numerous effectors, including the exocyst protein Exo70 (Inoue et al., 2003). Exo70 exists in a multiprotein complex with the proteins Sec6 and Sec8. A dominant-negative mutant of Exo70 blocked insulin-stimulated glucose uptake, but was without effect on translocation of Glut4 to the plasma membrane. However, this Exo70 mutant prevented the appearance of Glut4 at the cell surface, leading us to propose that the exocyst complex may play a critical role in tethering Glut4 vesicles to the plasma membrane for subsequent docking and fusion (Inoue et al., 2003).Lipid rafts are specialized compartments of the plasma membrane enriched in cholesterol and glycosphingolipids. Numerous signaling and cytoskeletal proteins are found in these subdomains, suggesting that they may act as organizing centers for signal transduction, particularly for insulin (Anderson, 1998;Schlegel et al., 1998;Bickel, 2002; Pessin, 2002, 2003). Both the insulin receptor and TC10 reside in lipid rafts (Yamamoto et al., 1998;Gustavsson et al., 1999;Nystrom et al., 1999;Kimura et al., 2002;Vainio et al., 2002)...

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Section: Discussionmentioning

confidence: 69%

Compartmentalization of the Exocyst Complex in Lipid Rafts Controls Glut4 Vesicle Tethering

Inoue

Chiang

Chang

et al. 2006

MBoC

108

135

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“…This was performed on differentiated 3T3-L1 adipocytes (Kandror et al, 1995) essentially as described for rat adipocytes (Simpson et al, 1983). Cells were treated with insulin (100 nM) or carrier for 15 min at 37°C.…”

Section: Subcellular Fractionation Of Adipocytesmentioning

confidence: 99%

p115 Interacts with the GLUT4 Vesicle Protein, IRAP, and Plays a Critical Role in Insulin-stimulated GLUT4 Translocation

Hosaka

Brooks

Presman

et al. 2005

MBoC

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Insulin-regulated aminopeptidase (IRAP) is an abundant cargo protein of Glut4 storage vesicles (GSVs) that traffics to and from the plasma membrane in response to insulin. We used the amino terminus cytoplasmic domain of IRAP, residues 1-109, as an affinity reagent to identify cytosolic proteins that might be involved in GSV trafficking. In this way, we identified p115, a peripheral membrane protein known to be involved in membrane trafficking. In murine adipocytes, we determined that p115 was localized to the perinuclear region by immunofluorescence and throughout the cell by fractionation. By immunofluorescence, p115 partially colocalizes with GLUT4 and IRAP in the perinuclear region of cultured fat cells. The amino terminus of p115 binds to IRAP and overexpression of a N-terminal construct results in its colocalization with GLUT4 throughout the cell. Insulin-stimulated GLUT4 translocation is completely inhibited under these conditions. Overexpression of p115 C-terminus has no significant effect on GLUT4 distribution and translocation. Finally, expression of the p115 N-terminus construct has no effect on the distribution and trafficking of GLUT1. These data suggest that p115 has an important and specific role in insulin-stimulated Glut4 translocation, probably by way of tethering insulin-sensitive Glut4 vesicles at an as yet unknown intracellular site. INTRODUCTIONInsulin normalizes blood glucose levels by mobilizing the muscle and adipocyte glucose transporter isoform, GLUT4, from intracellular storage vesicles and moving it to the plasma membrane (Simpson et al., 2001;Bryant et al., 2002). Various models of GLUT4 trafficking suggest that GLUT4 must exist in more than one intracellular compartment and the major insulin sensitive pool is localized to a compartment that is distinct from endosomal markers and is commonly referred to as glucose transporter storage vesicles (GSVs), or insulin responsive vesicle (IRVs). Despite the critical function of glucose transport in glucose homeostasis, many of the details by which adipocytes and muscle form a pathway of insulin-sensitive GLUT4 trafficking remain unknown. However, it is virtually certain that the major cargo proteins of GSVs must interact with a number of cytosolic and membrane proteins, such as adaptors and tethers, in order to be properly sorted and regulated by insulin.Insulin-responsive aminopeptidase (IRAP) was identified as an abundant cargo protein associated with GLUT4 vesicles that translocates in response to insulin in a manner seemingly identical to GLUT4 Mastick et al., 1994;Keller et al., 1995;Malide et al., 1997;Martin et al., 1997;Ross et al., 1997). In fact, it is more abundantly expressed in vesicles than the transporter (Kupriyanova et al., 2002). When the cytoplasmic N-terminus of IRAP was microinjected into 3T3-L1 adipocytes, GLUT4 was localized on the plasma membrane even in the basal state (Waters et al., 1997), suggesting IRAP can play a role in GSV movement/targeting. A chimeric protein containing the intracellular domain of IRAP and ...

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“…Fat cells contain a distinct population of vesicles that translocate the glucose transporter GLUT4 to the surface upon stimulation with insulin [11,12]. These vesicles are distinguished from caveolae by the absence of caveolin [13], and furthermore GLUT4 is not associated with caveolae in the plasma membrane [14].…”

Section: Introductionmentioning

confidence: 99%

“…It has been proposed that caveolae may play a role in the translocation of GLUT4-containing vesicles to the plasma membrane, either by physically mediating the vesicular contact with the plasma membrane by generating areas rich in cholesterol [13] or by regulation of exocytosis via interaction with the molecular machinery of exocytosis [2]. In line with these theories, caveolae have been shown to be associated with the following docking/fusion proteins: vesicle-associated membrane protein (VAMP), N-ethylmaleimide sensitive factor (NSF), and soluble NSF attachment protein (SNAP) [15].…”

Section: Introductionmentioning

confidence: 99%

Human neutrophils are devoid of the integral membrane protein caveolin

Sengeløv

Voldstedlund

Vinten

et al. 1998

Journal of Leukocyte Biology

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The secretory vesicles of human neutrophils are rapidly mobilizable vesicles that contain several GPI-linked proteins, a characteristic feature of caveolae in other cells. To investigate whether secretory vesicles are structurally related to caveolae, we examined human neutrophils for the presence of caveolin, a major constituent of caveolae, by immunoblotting using monoclonal and polyclonal antibodies. Caveolin was not detected in lysates of human neutrophils nor in isolated plasma membrane/light membrane fractions in which secretory vesicles localize. In contrast, caveolin was readily detected in isolated membranes of adipose cells. We conclude that human neutrophils are devoid of caveolin and that secretory vesicles are not related to caveolae nor dependent on caveolae for mobilization.

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Expression and compartmentalization of caveolin in adipose cells: coordinate regulation with and structural segregation from GLUT4.

Cited by 93 publications

References 57 publications

Compartmentalization of the Exocyst Complex in Lipid Rafts Controls Glut4 Vesicle Tethering

Compartmentalization of the Exocyst Complex in Lipid Rafts Controls Glut4 Vesicle Tethering

p115 Interacts with the GLUT4 Vesicle Protein, IRAP, and Plays a Critical Role in Insulin-stimulated GLUT4 Translocation

Human neutrophils are devoid of the integral membrane protein caveolin

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