Insulin-independent GLUT4 accumulation at cell surface in AP-1 knockdown 3T3-L1 adipocytes

Abstract

Background and aims: Stimulation by insulin results in a rapid and reversible translocation of GLUT4 from storage vesicels to the plasma membrane in muscle and adipose tissue. A N-terminal phenylalanine-containing amino acid motif (F5QQI) is required for the endocytosis and subsequent sorting of GLUT4 into the vesicles. The F5A-mutant of GLUT4 accumulates at the cell-surface in an insulin-independent manner. In previous experiments, we identified the FQQI-motif as binding partner for the heterotetrameric adapter protein complexes AP-1 and AP-2. Our data suggested that the F5-motif is involved in endocytosis of the transporter via an AP-2-mediated-pathway. Analysis of the F5A-GLUT4 recycling kinetics indicated a role of the phenylalanine motif and AP-1 in a post-endosomal sorting step. In order to prove an involvement of AP-1 in GLUT4 recycling, we analyzed GLUT4 targeting in cells lacking either AP-1 or AP-2 respectively.