title: p27 degradation by an ellipticinium series of compound via ubiquitin-proteasome pathway.
abstract: The ellipticinium and its derivatives have been studied as anti-cancer agents with preferentially cyto-toxicity to the brain tumor cell lines. During the course of our study to determine whether an ellipticine derivative, API59-Cl would sensitize radio-resistant U87 glioblastoma cells to radiation, we found that it reduced the level of p27, a cyclin-dependent kinase inhibitor. API59-Cl induced a dose and time dependent p27 reduction in U87 cells. The compound-induced p27 reduction was also seen in three additional glioblastoma lines, T98G, U251 and U118 as well as in mouse embryonic fibroblasts. Mechanistic study of API59-Cl mediated p27 reduction revealed that it was not due to an altered p27 transcription, rather due to a shortened protein half-life as a result of enhanced p27 degradation. Indeed, API59-Cl induced p27 degradation was dependent on ubiquitin-proteasome pathway, particularly E3 ubiquitin ligase component, Skp2, but not Cullin-4A/4B, and can be largely blocked by proteasome inhibitors MG132 or PS341. Finally, we demonstrated that API59-Cl inhibited U87 cell growth with an IC50 of 1.7 muM, which is independent of its p27 degrading activity. This is the first report, to our knowledge, that the ellipticinium class of small molecule compounds promotes p27 degradation via ubiquitin-proteasome pathway. The finding could provide a new tool to further understand the mechanism of p27 degradation.
authors.affiliation: Division of Cancer Biology, Department of Radiation Oncology, University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan 48109-0936, USA.
authors.forename: Deepika
authors.initials: D
authors.lastname: Pamarthy
authors.forename: Mingjia
authors.initials: M
authors.lastname: Tan
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Jianyong
authors.initials: J
authors.lastname: Chen
authors.forename: Dajun
authors.initials: D
authors.lastname: Yang
authors.forename: Shaomeng
authors.initials: S
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D001932:Brain Neoplasms / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004611:Ellipticines / Q000494:pharmacology*; D005909:Glioblastoma / Q000378:metabolism*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D001897:Boronic Acids; D015853:Cysteine Proteinase Inhibitors; D004611:Ellipticines; D007976:Leupeptins; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011838:Radiation-Sensitizing Agents; D044786:S-Phase Kinase-Associated Proteins; D025801:Ubiquitin; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000069286:Bortezomib; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde