Induction of IL-8 expression by Cordyceps militaris grown on germinated soybeans through lipid rafts formation and signaling pathways via ERK and JNK in A549 cells

Abstract

Aim of the study: In order to elucidate immunoregulatory mechanisms of Cordyceps militaris, a methanol extract of Cordyceps militaris grown on germinated soybeans was prepared and its immunoregulatory effect in the human lung epithelial cells was investigated by examining its ability to induce IL-8 expression.

Materials and methods: Cordyceps militaris grown on germinated soybeans was extracted with 80% methanol (GSC4M) and used for stimulation of a human lung epithelial cell-line, A549. An enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction were performed to examine the production of IL-8 protein and its mRNA, respectively. For the analysis of transcription factors regulating IL-8 transcriptional activation, the nuclear fraction was extracted from GSC4M-treated A549 cells and subjected to electrophoretic mobility shift assay.

Results: GSC4M induced IL-8 protein secretion and its mRNA expression from A549 cells in a dose- and time-dependent manner. GSC4M-induced IL-8 expression was inhibited by an inhibitor for lipid rafts formation but not by that for clathrin-coated pits. In addition, signaling pathways for GSC4M-induced IL-8 expression were mediated through ERK and JNK but hardly through p38 kinase. Furthermore, GSC4M augmented the DNA-binding activity of the transcription factors AP-1, NF-IL6, and NF-kappaB, all of which are involved in the transcriptional activation of the IL-8 gene.

Conclusion: Cordyceps militaris grown on germinated soybeans stimulates lung epithelial cells to produce IL-8 through lipid rafts formation and signaling pathways via ERK and JNK.