Tumor necrosis factor-alpha initiated signal transduction in 3T3-L1 adipocytes.

Examination of the ability of tumor necrosis factor-alpha (TNF) to activate both the p44/42 and p38 MAP kinase cascades in fully differentiated 3T3-L1 adipocytes indicated a rapid MEK1/2-dependent activation of p44/42 MAP kinase. Use of the MEK1/2 inhibitor PD98059 indicated that this pathway at least in part was responsible for nuclear localization of the transcription factor NF-kappaB. The stress/cytokine-activated p38 MAP kinase was observed to be constitutively active, and its phosphorylation (activation) status was not altered with TNF treatment. However, TNF treatment did result in activation of the transcription factor, ATF-2, a primary downstream target of p38 MAP kinase. Use of the p38 MAP kinase inhibitors SB202190 and SB203580 did not interfere with the ability of TNF to activate ATF-2, suggesting that either the gamma isoform of p38 MAP kinase or a p38-independent pathway was utilized by TNF to increase the phosphorylated fraction of ATF-2. In previous studies we had demonstrated the ability of TNF to suppress the transcription of the GLUT4 gene. Prevention of activation of either the p44/42 MAP kinase pathway (PD98059) or the p38 MAP kinase pathway (SB202190 and SB202580) indicated that these pathways did not control GLUT4 transcription.