title: Avicin D, a plant triterpenoid, induces cell apoptosis by recruitment of Fas and downstream signaling molecules into lipid rafts.
abstract: Avicins, a family of triterpene electrophiles originally identified as potent inhibitors of tumor cell growth, have been shown to be pleiotropic compounds that also possess antioxidant, anti-mutagenic, and anti-inflammatory activities. We previously showed that Jurkat cells, which express a high level of Fas, are very sensitive to treatment with avicins. Thus, we hypothesized that avicins may induce cell apoptosis by activation of the Fas pathway. By using a series of cell lines deficient in cell death receptors, we demonstrated that upon avicin D treatment, Fas translocates to the cholesterol- and sphingolipid-enriched membrane microdomains known as lipid rafts. In the lipid rafts, Fas interacts with Fas-associated death domain (FADD) and Caspase-8 to form death-inducing signaling complex (DISC) and thus mediates cell apoptosis. Interfering with lipid raft organization by using a cholesterol-depleting compound, methyl-beta-cyclodextrin, not only prevents the clustering of Fas and its DISC complex but also reduces the sensitivity of the cells to avicin D. Avicin D activates Fas pathways independent of the association between extracellular Fas ligands and Fas receptors. A deficiency in Fas and its downstream signaling molecules leads to the resistance of the cells to avicin D treatment. Taken together, our results demonstrate that avicin D triggers the redistribution of Fas in the membrane lipid rafts, where Fas activates receptor-mediated cell death.
authors.affiliation: Department of Systems Biology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA. zhi-xiang.xu@ccc.uab.edu
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Xu
authors.forename: Tian
authors.initials: T
authors.lastname: Ding
authors.forename: Valsala
authors.initials: V
authors.lastname: Haridas
authors.forename: Fiona
authors.initials: F
authors.lastname: Connolly
authors.forename: Jordan U
authors.initials: JU
authors.lastname: Gutterman
mesh_terms: D000045:Acacia / Q000737:chemistry*; D017209:Apoptosis / Q000187:drug effects*; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004354:Drug Screening Assays, Antitumor; D004789:Enzyme Activation / Q000187:drug effects; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D012503:Saponins / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects*; D014315:Triterpenes / Q000494:pharmacology*; D019014:fas Receptor / Q000378:metabolism*
chemical_list: C491901:FAS protein, human; D012503:Saponins; D014315:Triterpenes; D019014:fas Receptor; C478445:avicin D; D053181:Caspase 8