EVIDENCE OF 2 MECHANISMS FOR THE ACTIVATION OF THE GLUCOSE-TRANSPORTER GLUT1 BY ANISOMYCIN - P38(MAP KINASE) ACTIVATION AND PROTEIN-SYNTHESIS INHIBITION IN MAMMALIAN-CELLS

1. Inhibitors of protein synthesis stimulate sugar transport in mammal ian cells through activation of plasma membrane GLUT1, the housekeepin g isoform of the glucose transporter. However, it has been reported th at some of these compounds, in addition to their effect on protein syn thesis, also activate protein kinases. 2. In the present study we have explored the role of these two effects on GLUT1 activation. In 3T3-L1 adipocytes and Clone 9 cells, stimulation of sugar transport by purom ycin, a translational inhibitor that does not activate kinases, was no t detectable until 90 min after exposure. In contrast, stimulation by anisomycin, a potent Jun-NH2-terminal kinase (JNK) agonist, exhibited no lag phase. An intermediate response was observed to emetine and cyc loheximide, weak activators of JNK. 3. The potency of anisomycin to st imulate transport acutely (30 min of exposure) was 5- to 10-fold great er than for its chronic stimulation of transport, measured after 4 h o f exposure. The stimulation of transport by a low concentration of ani somycin (0.3 mu M) was transient, peaked at 30-60 min and it was inhib ited (IC50 < 1 mu M) by SB203580, which indicates that its mediator is not JNK, but the homologous p38(MAP kinase) (p38(MAPK)). In contrast, the responses to 4 h exposure to 300 mu M anisomycin or puromycin wer e refractory to SB203580. 4. Exposure to anisomycin resulted in rapid activation of p38(MAPK). Activation of both p38(MAPK) and GLUT1 by 0.3 mu M anisomycin was cancelled by puromycin. 5. We conclude that the a ctivation of GLUT1 in response to anisomycin includes two components: a delayed component involving translational inhibition and a fast, pur omycin-inhibitable component that is secondary to activation of p38(MA PK).