Recycling of the insulin-sensitive glucose transporter GLUT4 - Access of surface internalized GLUT4 molecules to the perinuclear storage compartment is mediated by the Phe(5)-Gln(6)-Gln(7)-Ile(8) MOTIF

The insulin-sensitive glucose transporter GLUT4 is translocated to the plas ma membrane in response to insulin and recycled back to the intracellular s tore(s) after removal of the hormone. We have used clonal 3T3-L1 fibroblast s and adipocyte-like cells stably expressing wild-type GLUT4 to characteriz e (a) the intracellular compartment where the bulk of GLUT4 is intracellula rly stored and (b) the mechanisms involved in the recycling of endocytosed GLUT4 to the store compartment. Surface internalized GLUT4 is targeted to a large, flat, fenestrated saccular structure resistant to brefeldin A that localized to the vicinity of the Golgi complex is sealed to endocytosed tra nsferrin (GLUT4 storage compartment). Recycling of endocytosed GLUT4 was st udied by comparing the cellular distributions of anti-body/biotin tagged GL UT4 and GLUT4(Ser(5)), a mutant with the Phe(5)-Gln(6)-Gln(7)-Ile(8) inacti vated by the substitution of Ser for Phe(5). Ablation of the Phe(5)-Gln(6)- Gln(7)-Ile(8) inhibits the recycling of endocytosed GLUT4 to the GLUT4 stor e compartment and results in its transport to late endosomes/lysosomes wher e it is rapidly degraded.