Posttranscriptional regulation of TNFalpha expression via eukaryotic initiation factor 4E (eIF4E) phosphorylation in mouse macrophages.

Resident mouse macrophages secrete Tumor necrosis factor alpha (TNFalpha) upon challenge with LPS. The production of TNFalpha is controlled not only at the transcription of the gene, but also by strong posttranscriptional regulation. When macrophages are stimulated with LPS different signal transduction pathways become activated. Here we show that the combination of the 2 kinases p38 and MEK and presumably ERK1/2 regulate translation of TNFalpha, through the downstream kinase Mnk1. TNFalpha production is inhibited in a concentration-dependent manner by CGP57380 (Mnk1 inhibitor). The corresponding mRNA results show that the inhibition targets posttranscriptional regulation and is paralleled by inhibition of the phosphorylation of eukaryotic initiation factor 4E (eIF4E). Unexpectedly, the activation/inhibition of MAPKAP kinase-2 (MK2) does not parallel TNFalpha production, arguing against a direct/immediate role for this kinase. On the basis of the present and previous results we propose that ARE-containing TNFalpha mRNA requires phosphorylation of eIF4E for initiation of translation.