Tumour necrosis factor-alpha regulates expression of the CCAAT-enhancer binding proteins (C/EBPs)alpha and beta and determines the occupation of the C/EBP site in the promoter of the insulin-responsive glucose-transporter gene in 3T3-L1 adipocytes

We have demonstrated previously that treatment of 3T3-L1 adipocytes with tu mour necrosis factor-a (TNF) results in a rapid (4h) and significant (75-80 %) reduction in the rate of transcription of the GLUT4 gene. Control of GLU T4 gene transcription has been suggested at least in part to reside with th e CCAAT-enhancer-binding protein (C/EBP) family (alpha, beta and delta isof orms) of transcription factors. Using electrophoretic mobility shift assays , we have examined the ability of TNF to alter the occupation of the C/EBP site in the GLUT4 promoter. The data suggest that in fully differentiated a dipocytes the C/EBP site is a ligand for predominantly alpha/alpha homodime rs; however, after exposure to TNF, a shift in occupancy of the site occurs and the ligands become alpha/beta heterodimers and beta/beta homodimers. P artner selection in dimer formation appears to be controlled by selective t ranslocation of the beta-isoform from the cytosol to the nucleus after expo sure of the cells to TNF.