Caveolin-2 is targeted to lipid droplets, a new "membrane domain" in the cell.
Caveolin-1 and -2 constitute a framework of caveolae in nonmuscle cells. In the present study, we showed that caveolin-2, especially its beta isoform, is targeted to the surface of lipid droplets (LD) by immunofluorescence and immunoelectron microscopy, and by subcellular fractionation. Brefeldin A treatment induced further accumulation of caveolin-2 along with caveolin-1 in LD. Analysis of mouse caveolin-2 deletion mutants revealed that the central hydrophobic domain (residues 87-119) and the NH(2)-terminal (residues 70-86) and COOH-terminal (residues 120-150) hydrophilic domains are all necessary for the localization in LD. The NH(2)- and COOH-terminal domains appeared to be related to membrane binding and exit from ER, respectively, implying that caveolin-2 is synthesized and transported to LD as a membrane protein. In conjunction with recent findings that LD contain unesterified cholesterol and raft proteins, the result implies that the LD surface may function as a membrane domain. It also suggests that LD is related to trafficking of lipid molecules mediated by caveolins.
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan. tfujimot@med.nagoya-u.ac.jp
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Fujimoto
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Kogo
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Ishiguro
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Tauchi
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Nomura
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D020126:Brefeldin A / Q000494:pharmacology; D051242:Caveolin 1; D051243:Caveolin 2; D022461:Caveolins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005347:Fibroblasts; D005455:Fluorescent Antibody Technique; D006801:Humans; D050356:Lipid Metabolism; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D016253:Microscopy, Immunoelectron; D015388:Organelles / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017384:Sequence Deletion / Q000235:genetics
C495540:CAV1 protein, human; C495541:Cav1 protein, mouse; C495537:Cav1 protein, rat; D051242:Caveolin 1; D051243:Caveolin 2; D022461:Caveolins; D020033:Protein Isoforms; D021382:Protein Sorting Signals; D020126:Brefeldin A