Mitogen activated protein kinases are prime signalling enzymes in nitric oxide production induced by soluble β-glucan from Sparassis crispa

Sparassis crispa (SC) is an edible mushroom that harbours β-glucans reported to possess immunostimulatory and anticancer properties. The role of SC in regulating the functional activation of macrophages is yet to be fully elucidated. The objective of this study was to investigate the molecular mechanism underlying the immune-stimulatory function of Sparassis crispa soluble β-glucan (Sc-SG) on macrophages. According to this study, Sc-SG was able to stimulate nitric oxide (NO) production as well as enhance the expression of inducible NO synthase (iNOS) from macrophage-like RAW264.7 cells. NO production was strongly suppressed by mitogen-activated protein kinase (MAPK) inhibitors such as U0126, extracellular signal-regulated kinase, SB203580, a p38 inhibitor, and SP600125, a c-Jun N-terminal kinase inhibitor. Thus, indicating that Sc-SG-induced NO release is possibly mediated by MAPK. Sc-SG induced phosphorylation of extracellular signal-regulated kinase, p38, and JNK in a time-dependent manner. Moreover, Sc-SG triggered the phosphorylation and translocation of c-Jun and c-Fos, components of the transcription factor AP-1, activated by MAPK. The results of this study suggest that MAPK may be a major signaling enzyme that regulates the Sc-SG-mediated NO production in macrophages.