Osteosarcoma is a most common highly malignant bone
tumor in children and adolescents.
Polyphyllin I (PPI) is an
ethanol extraction from Paris polyphylla Smith var.yunnanensis (Franch.) Hand.-Mazz, which belongs to
antipyretic-detoxicate family and has been used as a natural medicine in the treatment of
infectious disease and
cancer in China for centuries. The
proteasome activity inhibitory and anti-
osteosarcoma effects of PPI have not been known. Here we found PPI exhibited a selective inhibitory effect on proteasomal
chymotrypsin (CT)-like activity, both in purified human
proteasome and in cultured
osteosarcoma cellular
proteasome, and caused an accumulation of
ubiquitinated proteins. PPI also inhibited viability, proliferation, migration, and invasion of MG-63, Saos-2, and U-2 OS
osteosarcoma cells and resulted in S phase arrest and apoptosis. Furthermore, we explored the molecular targets involved. Exposure of
osteosarcoma cells to PPI caused an inactivation of the intrinsic nuclear factor κB (NF-κB) and activation of unfolded protein response (UPR)/endoplasmic reticulum (ER) stress signaling cascade in
osteosarcoma cells, followed by down-regulation of
anti-apoptotic proteins, with up-regulation of
pro-apoptotic proteins. We also demonstrated down-regulation of c-Myc,
Cyclin B1,
Cyclin D1, and CDK1, which are involved in the cell cycle and growth. Finally, we identified down-regulation of
Vimentin, Snail, Slug, and up-regulation of
E-cadherin, which are integral
proteins involved in epithelial-mesenchymal transition (EMT). Taken together, our data provide insights into the mechanism underlying the anticancer activity of PPI in human
osteosarcoma cells.