Activation of Mitogen-Activated Protein Kinase Pathways by <i>Mycoplasma fermentans</i> Membrane Lipoproteins in Murine Macrophages: Involvement in Cytokine Synthesis

Abstract

Stimulation of monocytes and resident macrophages by mycoplasmas induces production of numerous cytokines. We have previously reported that membrane lipoproteins derived from Mycoplasma fermentans are responsible for the induction of proinflammatory cytokines by monocytic cells and that triggering protein tyrosine kinase activation is an essential requirement for this biologic effect. In the present study, we have investigated the effect of M. fermentans-derived membrane lipoproteins (LAMPf) on mitogen-activated protein kinase (MAPK) cascades in the murine macrophage cell line RAW 264.7 and have analyzed the contribution of these pathways to the cytokine induction mediated by this agent. Treatment of murine macrophages with LAMPf resulted in significant activation of MAPK family members extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-Jun NH2-terminal kinase (JNK), and p38. Unlike LPS, these effects were demonstrated to be independent of the presence of serum. The activation of MAPKs paralleled the tyrosine kinase activation and peaked at 30 min after stimulation. The specific p38 inhibitor SB203580 abrogated the mycoplasma-induced IL-6, IL-1beta, and TNF-alpha synthesis. The selective MAPK/extracellular signal-regulated kinase 1 (MEK-1) inhibitor PD-98059 blocked both IL-1beta and TNF-alpha but not IL-6 production by RAW 264.7 cells in response to LAMPf. Additionally, transfection of murine macrophages with a JNK dominant negative mutant significantly reduced only IL-6 production. These data underscore the role of MAPKs as signal transduction molecules controlling the expression of cytokines upon mycoplasma stimulation.