Activators of AMP-activated protein kinase enhance GLUT4 translocation and its glucose transport activity in 3T3-L1 adipocytes

1 Third Department of Internal Medicine and 2 Department of Biochemistry, Kyorin University, Mitaka, Tokyo, Japan Submitted 27 October 2004 ; accepted in final form 5 May 2005 To determine whether the increase in glucose uptake following AMP-activated protein kinase (AMPK) activation in adipocytes is mediated by accelerated GLUT4 translocation into plasma membrane, we constructed a chimera between GLUT4 and enhanced green fluorescent protein (GLUT4-eGFP) and transferred its cDNA into the nucleus of 3T3-L1 adipocytes. Then, the dynamics of GLUT4-eGFP translocation were visualized in living cells by means of laser scanning confocal microscopy. It was revealed that the stimulation with 5-aminoimidazole-4-carboxamide-1- - D -ribofuranoside (AICAR) and 2,4-dinitrophenol (DNP), known activators of AMPK, promptly accelerates its translocation within 4 min, as was found in the case of insulin stimulation. The insulin-induced GLUT4 translocation was markedly inhibited after addition of wortmannin ( P < 0.01). However, the GLUT4 translocation through AMPK activators AICAR and DNP was not affected by wortmannin. Insulin- and AMPK-activated translocation of GLUT4 was not inhibited by SB-203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). Glucose uptake was significantly increased after addition of AMPK activators AICAR and DNP ( P < 0.05). AMPK- and insulin-stimulated glucose uptake were similarly suppressed by wortmannin ( P < 0.05–0.01). In addition, SB-203580 also significantly prevented the enhancement of glucose uptake induced by AMPK and insulin ( P < 0.05). These results suggest that AMPK-activated GLUT4 translocation in 3T3-L1 adipocytes is mediated through the insulin-signaling pathway distal to the site of activated phosphatidylinositol 3-kinase or through a signaling system distinct from that activated by insulin. On the other hand, the increase of glucose uptake dependent on AMPK activators AICAR and DNP would be additionally due to enhancement of the intrinsic activity in translocated GLUT4 protein, possibly through a p38 MAPK-dependent mechanism. glucose transporter 4; mitogen-activated protein kinase; phosphatidylinositol 3-kinase; enhanced green fluorescent protein Address for reprint requests and other correspondence: H. Ishida, Kyorin Univ. School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan (e-mail: ishida{at}kyorin-u.ac.jp )