Emodin inhibits HMGB1-induced tumor angiogenesis in human osteosarcoma by regulating SIRT1

The anti-cancer effects of emodin, including inhibition of proliferation, invasion, metastasis and angiogenesis, were confirmed by various previous studies. However, the specific mechanisms were not clear. In this study, we investigated emodin's anti-angiogenesis effect and focused on the mechanisms in human osteosarcoma (OS). OS cells were implanted to nude mice to form OS xenografts. Immunofluorescence assay was used to assess vWF expression in tumor tissue. MTT assay was employed to screen proper emodin concentrations unrelated with proliferation inhibition. siRNA technique was utilized to silence SIRT1 expression in OS cells. Expression levels of SIRT1 and VEGF were investigated by real-time PCR and western blotting. H4-k16Ac expression which indicated the deacetylation activity of SIRT1 was also detected by western blotting. As in results, HMGB1 treatment exacerbated OS angiogenesis both in vivo and in vitro. Emodin administration attenuated angiogenesis in both OS and HMGB1 treated OS in vivo and in vitro. After emodin treatment, the expression level and deacetylation activity of SIRT1 were dramatically enhanced. HMGB1-induced angiogenesis was more striking in SIRT1 silenced OS cells. SIRT1 silencing also impaired the anti-angiogenesis effect of emodin in OS cells. SIRT expression and deacetylation activity elevation are involved in emodin's anti-angiogenesis effect in human OS.