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Accumulation of caveolin in the endoplasmic reticulum redirects the protein to lipid storage droplets.

Ostermeyer AG, Paci JM, Zeng Y, Lublin DM, Munro S, Brown DA - J. Cell Biol. (2001)

Bottom Line: We found three treatments that redirected the protein to lipid storage droplets, identified by staining with the lipophilic dye Nile red and the marker protein ADRP.Experimental reduction of cellular cholesteryl ester by 80% did not prevent targeting of Cav-KKSL to the droplets.Cav-KKSL expression did not grossly alter cellular triacylglyceride or cholesteryl levels, although droplet morphology was affected in some cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Cell Biology, State University of New York at Stony Brook, Stony Brook, New York 11794, USA.

ABSTRACT
Caveolin-1 is normally localized in plasma membrane caveolae and the Golgi apparatus in mammalian cells. We found three treatments that redirected the protein to lipid storage droplets, identified by staining with the lipophilic dye Nile red and the marker protein ADRP. Caveolin-1 was targeted to the droplets when linked to the ER-retrieval sequence, KKSL, generating Cav-KKSL. Cav-DeltaN2, an internal deletion mutant, also accumulated in the droplets, as well as in a Golgi-like structure. Third, incubation of cells with brefeldin A caused caveolin-1 to accumulate in the droplets. This localization persisted after drug washout, showing that caveolin-1 was transported out of the droplets slowly or not at all. Some overexpressed caveolin-2 was also present in lipid droplets. Experimental reduction of cellular cholesteryl ester by 80% did not prevent targeting of Cav-KKSL to the droplets. Cav-KKSL expression did not grossly alter cellular triacylglyceride or cholesteryl levels, although droplet morphology was affected in some cells. These data suggest that accumulation of caveolin-1 to unusually high levels in the ER causes targeting to lipid droplets, and that mechanisms must exist to ensure the rapid exit of newly synthesized caveolin-1 from the ER to avoid this fate.

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Localization of Cav–KKSL. Cav–KKSL in transiently transfected FRT (A and B) or COS (C and D) cells was visualized by IF.
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Figure 1: Localization of Cav–KKSL. Cav–KKSL in transiently transfected FRT (A and B) or COS (C and D) cells was visualized by IF.

Mentions: Cav–KKSL was expressed transiently in FRT cells, which lack endogenous caveolin-1 and caveolae (Lipardi et al. 1998), or in COS cells, which express caveolin-1 endogenously (Fig. 1). Cav–KKSL was not detected in the plasma membrane, suggesting that direct transport from the ER to the plasma membrane (Uittenbogaard et al. 1998) is at most a minor pathway. In some cells, Cav–KKSL was detectable in the ER (Fig. 1 C). In most cells, however, the protein accumulated predominantly on the surface of spherical structures that varied in size and were often, but not always, clustered together. Cav–KKSL was also seen in these structures when expressed in HEK-293 and CHO cells, although ER staining was more prominent than in the other two lines (not shown).


Accumulation of caveolin in the endoplasmic reticulum redirects the protein to lipid storage droplets.

Ostermeyer AG, Paci JM, Zeng Y, Lublin DM, Munro S, Brown DA - J. Cell Biol. (2001)

Localization of Cav–KKSL. Cav–KKSL in transiently transfected FRT (A and B) or COS (C and D) cells was visualized by IF.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2198801&req=5

Figure 1: Localization of Cav–KKSL. Cav–KKSL in transiently transfected FRT (A and B) or COS (C and D) cells was visualized by IF.
Mentions: Cav–KKSL was expressed transiently in FRT cells, which lack endogenous caveolin-1 and caveolae (Lipardi et al. 1998), or in COS cells, which express caveolin-1 endogenously (Fig. 1). Cav–KKSL was not detected in the plasma membrane, suggesting that direct transport from the ER to the plasma membrane (Uittenbogaard et al. 1998) is at most a minor pathway. In some cells, Cav–KKSL was detectable in the ER (Fig. 1 C). In most cells, however, the protein accumulated predominantly on the surface of spherical structures that varied in size and were often, but not always, clustered together. Cav–KKSL was also seen in these structures when expressed in HEK-293 and CHO cells, although ER staining was more prominent than in the other two lines (not shown).

Bottom Line: We found three treatments that redirected the protein to lipid storage droplets, identified by staining with the lipophilic dye Nile red and the marker protein ADRP.Experimental reduction of cellular cholesteryl ester by 80% did not prevent targeting of Cav-KKSL to the droplets.Cav-KKSL expression did not grossly alter cellular triacylglyceride or cholesteryl levels, although droplet morphology was affected in some cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Cell Biology, State University of New York at Stony Brook, Stony Brook, New York 11794, USA.

ABSTRACT
Caveolin-1 is normally localized in plasma membrane caveolae and the Golgi apparatus in mammalian cells. We found three treatments that redirected the protein to lipid storage droplets, identified by staining with the lipophilic dye Nile red and the marker protein ADRP. Caveolin-1 was targeted to the droplets when linked to the ER-retrieval sequence, KKSL, generating Cav-KKSL. Cav-DeltaN2, an internal deletion mutant, also accumulated in the droplets, as well as in a Golgi-like structure. Third, incubation of cells with brefeldin A caused caveolin-1 to accumulate in the droplets. This localization persisted after drug washout, showing that caveolin-1 was transported out of the droplets slowly or not at all. Some overexpressed caveolin-2 was also present in lipid droplets. Experimental reduction of cellular cholesteryl ester by 80% did not prevent targeting of Cav-KKSL to the droplets. Cav-KKSL expression did not grossly alter cellular triacylglyceride or cholesteryl levels, although droplet morphology was affected in some cells. These data suggest that accumulation of caveolin-1 to unusually high levels in the ER causes targeting to lipid droplets, and that mechanisms must exist to ensure the rapid exit of newly synthesized caveolin-1 from the ER to avoid this fate.

Show MeSH