p38 Mitogen-Activated Protein Kinase Mediates Tumor Necrosis Factor-α-Induced Apoptosis in Rat Fetal Brown Adipocytes*

Abstract

Abstract Tumor necrosis factor-α (TNFα) induces apoptosis and cell growth inhibition in primary rat fetal brown adipocytes. Here, we examine the role played by some members of the mitogen-activated protein kinase (MAPK) superfamily. TNFα activates extracellular regulated kinase-1/2 (ERK1/2) and p38MAPK. Inhibition of p38MAPK by either SB203580 or SB202190 highly reduces apoptosis induced by TNFα, whereas ERK inhibition potentiates it. Moreover, cotransfection of an active MKK3 mutant and p38MAPK induces apoptosis. p38MAPK inhibition also prevents TNFα-induced cell cycle arrest, whereas MEK1 inhibition enhances this effect, which correlates with changes in proliferating cell nuclear antigen expression, but not in cyclin D1. c-Jun and activating transcription factor-1 are potential downstream effectors of p38MAPK and ERKs upon TNFα treatment. Thus, TNFα-induced c-Jun messenger RNA expression requires ERKs activation, whereas p38MAPK inhibition enhances its expression. In addition, TNFα-induced activating transcription factor-1 phosphorylation is extensively decreased by SB203580. However, TNFα- induced NF-κB DNA-binding activity is independent of p38MAPK and ERK activation. On the other hand, C/EBP homology protein does not appear to mediate the actions of TNFα, because its expression is almost undetectable and even reduced by TNFα. Finally, although TNFα induces c-Jun N-terminal kinase (JNK) activation, transfection of a dominant negative of either JNK1 or JNK2 had no effect on TNFα-induced apoptosis. These results suggest that p38MAPK mediates TNFα-induced apoptosis and cell cycle arrest, whereas ERKs do the opposite, and JNKs play no role in this process of apoptosis.