CRM1 Is a Cellular Target of Curcumin: New Insights for the Myriad of Biological Effects of an Ancient Spice

Curcumin is the major constituent of turmeric plant, an ancient spice widely used in Indian cuisine and traditional herbal medicine. Recently, the potential medical use of curcumin as anti-cancer and anti-inflammatory agent has set off an upsurge in research into the mechanism for its broad biological effects. We showed that CRM1e, an important nuclear exportin, is a cellular target of curcumin by serious experimental and theoretical investigation. Using a nuclear export functional assay, we observed a clear and rapid shift of cargo proteins from a cytoplasmic localization to the nucleus when treated with curcumin or its structural analogue dibenzylideneacetone (DBAe). We demonstrated that curcumin could specifically target the conserved Cys(528) of CRM1e through mass spectrometric analysis and in vivo experiments. Furthermore, computational modeling has revealed that curcumin could be correctly docked into the hydrophobic pocket of CRM1e judged from shape complementarity and putative molecular interactions. The Michael acceptor moiety on curcumin is within the appropriate distance to enable Michael reaction with Cys residue of CRM1e. More importantly, we showed that nuclear retention of FOXO1e could be observed in the presence of Leptomycin B (LMBe) or curcumin whereas in cells expressing the CRM1e-Cys(528) mutant, only a cytoplasmic localization was observed. The inhibition of nuclear traffic by curcumin may account for its myriad of biological effects, particularly for its therapeutic properties in cancer and inflammatory diseases. Our findings may have important implications for further clinical investigation of curcumin.