ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASE PATHWAYS BY MYCOPLASMA-FERMENTANS MEMBRANE LIPOPROTEINS IN MURINE MACROPHAGES - INVOLVEMENT IN CYTOKINE SYNTHESIS

Stimulation of monocytes and resident macrophages by mycoplasmas induc es production of numerous cytokines. We have previously reported that membrane lipoproteins derived from Mycoplasma fermentans are responsib le far the induction of proinflammatory cytokines by monocytic cells a nd that triggering protein tyrosine kinase activation is an essential requirement for this biologic effect, In the present study, we have in vestigated the effect of M. fermentans-derived membrane lipoproteins ( LAMPf) on mitogen-activated protein kinase (MAPK) cascades in the muri ne macrophage cell line RAW 264.7 and hale analyzed the contribution o f these pathways to the cytokine induction mediated by this agent, Tre atment of murine macrophages with LAMPf resulted in significant activa tion of MAPK family members extracellular signal regulated kinase 1 an d 2 (ERK1/2), c-Jun NH2-terminal kinase (JNK), and p38, Unlike LPS, th ese effects were demonstrated to he independent of the presence of ser um. The activation of MAPKs paralleled the tyrosine kinase activation and peaked at 30 min after stimulation, The specific p38 inhibitor SB2 03580 abrogated the mycoplasma-induced IL-6, IL-1 beta, and TNF-alpha synthesis. The selective MAPK/extracellular signal-regulated kinase 1 (MEK-1) inhibitor PD-98059 blocked both IL-1 beta and TNF-alpha but no t IL-6 production by RAW 264.7 cells in response to LAMPf. Additionall y, transfection of murine macrophages with a JNK dominant negative mut ant significantly reduced only IL-6 production, These data underscore the role of MAPKs as signal transduction molecules controlling the exp ression of cytokines upon mycoplasma stimulation.