Induction of apoptotic cell death by mycelium extracts of Phellinus linteus in human neuroblastoma cells

Phellinus linteus is a well-known Oriental medicinal fungus that has various biological activities, including immunomodulatory and anti-tumor activities, the mechanisms of which are poorly understood. In the present study, we investigated the effects of mycelium extracts of P. linteus (MEPL) on the growth of human neuroblastoma SK-N-MC cells. Upon treatment with MEPL, a concentration-dependent inhibition of cell proliferation was observed and cells developed many of the hallmark features of apoptosis, including condensation of chromatin and an increase in the sub-G1 population. The anti-proliferative and apoptotic effects of MEPL were associated with a marked induction of the Bax and cyclin-dependent kinase inhibitor p21. Western blotting and in vitro caspase-3 activity assay demonstrated that the processing/ activation of caspases accompanies the generation of MEPL-mediating apoptotic cell death. In addition, the proteolytic cleavage of specific target proteins such as poly (ADP-ribo se) polymerase and 6-catenin were observed. Taken together, the present results suggest that apoptotic signals evoked by MEPL in human neuroblastoma SK-N-MC cells may converge caspase-3 activation through an up-regulation of Bax rather than a down-regulation of Bcl-2.