title: Compound K, a metabolite of ginseng saponin, induces apoptosis via caspase-8-dependent pathway in HL-60 human leukemia cells.
abstract: BACKGROUND
  Compound K [20-O-beta-(D-glucopyranosyl)-20(S)-protopanaxadiol], a metabolite of the protopanaxadiol-type saponins of Panax ginseng C.A. Meyer, has been reported to possess anti-tumor properties to inhibit angiogenesis and to induce tumor apoptosis. In the present study, we investigated the effect of Compound K on apoptosis and explored the underlying mechanisms involved in HL-60 human leukemia cells.
  
  
  METHODS
  We examined the effect of Compound K on the viabilities of various cancer cell lines using MTT assays. DAPI assay, Annexin V and PI double staining, Western blot assay and immunoprecipitation were used to determine the effect of Compound K on the induction of apoptosis.
  
  
  RESULTS
  Compound K was found to inhibit the viability of HL-60 cells in a dose- and time-dependent manner with an IC50 of 14 muM. Moreover, this cell death had typical features of apoptosis, that is, DNA fragmentation, DNA ladder formation, and the externalization of Annexin V targeted phosphatidylserine residues in HL-60 cells. In addition, compound-K induced a series of intracellular events associated with both the mitochondrial- and death receptor-dependent apoptotic pathways, namely, (1) the activation of caspases-3, -8, and -9; (2) the loss of mitochondrial membrane potential; (3) the release of cytochrome c and Smac/DIABLO to the cytosol; (4) the translocation of Bid and Bax to mitochondria; and (5) the downregulations of Bcl-2 and Bcl-xL. Furthermore, a caspase-8 inhibitor completely abolished caspase-3 activation, Bid cleavage, and subsequent DNA fragmentation by Compound K. Interestingly, the activation of caspase-3 and -8 and DNA fragmentation were significantly prevented in the presence of cycloheximide, suggesting that Compound K-induced apoptosis is dependent on de novo protein synthesis.
  
  
  CONCLUSIONS
  The results indicate that caspase-8 plays a key role in Compound K-stimulated apoptosis via the activation of caspase-3 directly or indirectly through Bid cleavage, cytochrome c release, and caspase-9 activation.
authors.affiliation: Department of Pharmaceutical Biochemistry, College of Pharmacy, Kyung-Hee University, Seoul 130-701, South Korea.
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Cho
authors.forename: Kyung-Sook
authors.initials: KS
authors.lastname: Chung
authors.forename: Jung-Hye
authors.initials: JH
authors.lastname: Choi
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Kim
authors.forename: Kyung-Tae
authors.initials: KT
authors.lastname: Lee
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D053181:Caspase 8 / Q000378:metabolism / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D036145:Ginsenosides / Q000494:pharmacology*; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007938:Leukemia / Q000473:pathology*; D008564:Membrane Potentials / Q000187:drug effects; D024101:Mitochondrial Proteins / Q000378:metabolism; D008954:Models, Biological; D005894:Panax / Q000737:chemistry / Q000378:metabolism; D012503:Saponins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured; D020298:U937 Cells
chemical_list: D051017:Apoptosis Regulatory Proteins; D053181:Caspase 8; D045304:Cytochromes c; D036145:Ginsenosides; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D012503:Saponins; C412403:DIABLO protein, human; C112772:ginsenoside compound K; C505530:CASP8 protein, human