Mechanism of autophagy induction and role of autophagy in antagonizing mitomycin C-induced cell apoptosis in silibinin treated human melanoma A375-S2 cells

The aim of this study was to elucidate the molecular mechanisms mediating silibinin-induced autophagy in A375-S2 cells. In the present study it was found that silibinin-induced autophagy through increasing the conversion of LC3 I to LC3 II and up-regulating Beclin-1 expression, which was concomitant with p53 suppression and NF-kappa B activation. P53 inhibitor, pifithrin-alpha (PFT-alpha), increased autophagy and enhanced the expression of NF-kappa B. Moreover, inducing p53 accumulation with MG132 reduced autophagic ratio, and repressed the expression and activation of NF-kappa B expression. NF-kappa B inhibitor, pyrrolidine dithiocarbamate (PDTC) suppressed autophagy. Autophagic specific inhibitor 3-methyladenine (3-MA) treatment reversed silibinin-induced p53 suppression as well as NF-kappa B activation, suggesting that there was a positive feedback loop between p53 inhibition-mediated NF-kappa B activation and autophagy. In addition, we also found that 3-MA efficiently abrogated silibinin's cyto-protective effect against mitomycin C-induced cell death, and reversed the suppressive efficacy of silibinin on p53 expression, suggesting that autophagy contributed to silibinin's cyto-protective effect against mitomycin C-induced cell death in A375-S2 cells. (C) 2011 Elsevier B.V. All rights reserved.