Role of triptolide in cell proliferation, cell cycle arrest, apoptosis and histone methylation in multiple myeloma U266 cells.

Multiple myeloma is an incurable hematological malignancy. Different studies demonstrated the occurrence of genetic and epigenetic alterations in multiple myeloma. Histone lysine methylation has emerged as a central epigenetic change in the organization of eukaryotic chromatin with far-reaching implications for the regulation of cell proliferation, cell-type differentiation, gene expression, genome stability, overall development, and genesis of cancer. Triptolide is the principal active ingredient in extracts from the Chinese herb Tripterygium wilfordii Hook.F (TwHF), and numerous studies have elucidated its antitumor property. Our experiments discovered that triptolide inhibited the proliferation of multiple myeloma cell line U266 in a time- and dose-dependent manner, induced G2/M cell cycle arrest and caspase-dependent apoptosis. Triptolide could decrease the expression of histone H3K4, H3K27 and H3K36 trimethylation in parallel with histone methyltransferases SMYD3, EZH2 and NSD1 respectively, which possibly was the anti-myeloma mechanism of triptolide.