Splicing Factor SF3b as a Target of the Antitumor Natural Product Pladienolide
エーザイ株式会社 創薬第二研究所 評価グループ
Pladienolide is a naturally occuring antitumor macrolide discovered by using a cell-based reporter gene expression assay controlled by the human vascular endothelial growth factor (VEGF) promoter. Despite the unique mechanisms of action and prominent antitumor activities of pladienolides B and D in diverse in vitro and in vivo systems, their target protein has remained unclear. We used 3H-labelled, fluorescence-tagged, and photoaffinity/biotin (PB)-tagged 'chemical probes' to identify a 140-kDa protein in splicing factor SF3b as the binding target of pladienolide.
Immunoblotting of an enhanced green fluorescent protein (GFP) fusion protein of SF3b subunit 3 (SAP130) revealed direct interaction between the PB-probe and SAP130. The binding affinities of pladienolide derivatives to the SF3b complex were highly correlated with their inhibitory activities against reporter gene expression and cell proliferation. Furthermore, pladienolide B impaired in vivo splicing in a dose-dependent manner. Our results demonstrate that the SF3b complex is a pharmacologically-relevant protein target of pladienolide and suggest that this splicing factor is a potential antitumor drug target.