Conditional up-regulation of IL-2 production by p38 MAPK inactivation is mediated by increased Erk1/2 activity

The p38 mitogen-activated protein kinase regulates many cellular processes in almost all eukaryotic cell types. In T cells, p38 was shown to regulate thymic development and cytokine production. Here, the role of p38 on interleukin-2 (IL-2) production by human peripheral blood CD4+ T cells was examined. When T cells were stimulated under weak stimulation conditions, pharmaceutical and molecular p38 inhibitors induced a dramatic increase of IL-2 production. In contrast, IL-2 levels were not affected significantly when strong stimulation was provided to T cells. The increase in IL-2 production, following p38 inhibition, was associated with a strong up-regulation of extracellular signal-regulated kinase (Erk)1/2 activity. Furthermore the Erk inhibitor U0126 was able to counteract the effect of p38 inhibition on IL-2 production, supporting the conclusion that p38 mediates its effect through Erk. These results suggest that the p38 kinase, through its ability to control Erk activation levels, acts as a gatekeeper, which prevents inappropriate IL-2 production. Also, the finding that p38 acts in a strength-of-stimulation-dependent way provides an explanation for previously reported, contradictory results regarding the role of this kinase in IL-2 expression.