title: Tubocapsenolide A, a novel withanolide, inhibits proliferation and induces apoptosis in MDA-MB-231 cells by thiol oxidation of heat shock proteins.
abstract: Tubocapsenolide A (TA), a novel withanolide-type steroid, exhibits potent cytotoxicity against several human cancer cell lines. In the present study, we observed that treatment of human breast cancer MDA-MB-231 cells with TA led to cell cycle arrest at G(1) phase and apoptosis. The actions of TA were correlated with proteasome-dependent degradation of Cdk4, cyclin D1, Raf-1, Akt, and mutant p53, which are heat shock protein 90 (Hsp90) client proteins. TA treatment induced a transient increase in reactive oxygen species and a decrease in the intracellular glutathione contents. Nonreducing SDS-PAGE revealed that TA rapidly and selectively induced thiol oxidation and aggregation of Hsp90 and Hsp70, both in intact cells and in cell-free systems using purified recombinant proteins. Furthermore, TA inhibited the chaperone activity of Hsp90-Hsp70 complex in the luciferase refolding assay. N-Acetylcysteine, a thiol antioxidant, prevented all of the TA-induced effects, including oxidation of heat shock proteins, degradation of Hsp90 client proteins, and apoptosis. In contrast, non-thiol antioxidants (trolox and vitamin C) were ineffective to prevent Hsp90 inhibition and cell death. Taken together, our results demonstrate that the TA inhibits the activity of Hsp90-Hsp70 chaperone complex, at least in part, by a direct thiol oxidation, which in turn leads to the destabilization and depletion of Hsp90 client proteins and thus causes cell cycle arrest and apoptosis in MDA-MB-231 cells. Therefore, TA can be considered as a new type of inhibitor of Hsp90-Hsp70 chaperone complex, which has the potential to be developed as a novel strategy for cancer treatment.
authors.affiliation: Graduate Institute of Natural Products, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan.
authors.forename: Wen-Ying
authors.initials: WY
authors.lastname: Chen
authors.forename: Fang-Rong
authors.initials: FR
authors.lastname: Chang
authors.forename: Zih-You
authors.initials: ZY
authors.lastname: Huang
authors.forename: Jyun-Hong
authors.initials: JH
authors.lastname: Chen
authors.forename: Yang-Chang
authors.initials: YC
authors.lastname: Wu
authors.forename: Chin-Chung
authors.initials: CC
authors.lastname: Wu
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry; D017209:Apoptosis; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D004875:Ergosterol / Q000031:analogs & derivatives* / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D010100:Oxygen / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D054358:Withanolides
chemical_list: C433551:3-rhamnopyranosyl(1-4)-glucopyranosyl-12-diacetoxy-20-hydroxywitha-5,24-dienolide; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D013438:Sulfhydryl Compounds; D054358:Withanolides; C522061:tubocapsanolide A; D010100:Oxygen; D000111:Acetylcysteine; D004875:Ergosterol