ORIGINAL ARTICLE

Cell Research (2007): 772-782
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Glut-4 is translocated to both caveolae and non-caveolar lipid rafts, but is partially internalized through caveolae in insulin-stimulated adipocytes

Taichang Yuan^1,2, Shangyu Hong^1,2, Yao Yao^1,2 and Kan Liao^1,2

Correspondence: Kan Liao Tel: +86-21-54921113; Fax: +86-21-54921011 E-mail: kliao@sibs.ac.cn

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Caveolae and non-caveolar lipid rafts are two types of membrane lipid microdomains that play important roles in insulin-stimulated glucose uptake in adipocytes. In order to ascertain their specific functions in this process, caveolae were ablated by caveolin-1 RNA interference. In Cav-1 RNAi adipocytes, neither insulin-stimulated glucose uptake nor Glut-4 (glucose transporter 4) translocation to membrane lipid microdomains was affected by the ablation of caveolae. With a modified sucrose density gradient, caveolae and non-caveolar lipid rafts could be separated. In the wild-type 3T3-L1 adipocytes, Glut-4 was found to be translocated into both caveolae and non-caveolar lipid rafts. However, in Cav-1 RNAi adipocytes, Glut-4 was localized predominantly in non-caveolar lipid rafts. After the removal of insulin, caveolae-localized Glut-4 was internalized faster than non-caveolar lipid raft-associated Glut-4. The internalization of Glut-4 from plasma membrane was significantly decreased in Cav-1 RNAi adipocytes. These results suggest that insulin-stimulated Glut-4 translocation and glucose uptake are caveolae-independent events. Caveolae play a role in the internalization of Glut-4 from plasma membrane after the removal of insulin.

Cell Research (2007) 17:772–782. doi: 10.1038/cr.2007.73; published online 11 September 2007

Keywords: Glut-4 translocation, Glut-4 internalization, lipid rafts, caveolae, sucrose density gradient flotation